Merge #9306 'vim-patch: integrate xdiff library'

closes #1466
closes #1007
closes #1391

26 files changed, 5019 insertions, 297 deletions

diff --git a/src/nvim/CMakeLists.txt b/src/nvim/CMakeLists.txt
index 29a4e1e163..a2c4e677d4 100644
--- a/src/nvim/CMakeLists.txt
+++ b/src/nvim/CMakeLists.txt
@@ -79,6 +79,8 @@ file(MAKE_DIRECTORY ${LINT_SUPPRESSES_ROOT}/src)
 
 file(GLOB NVIM_SOURCES *.c)
 file(GLOB NVIM_HEADERS *.h)
+file(GLOB XDIFF_SOURCES xdiff/*.c)
+file(GLOB XDIFF_HEADERS xdiff/*.h)
 
 foreach(subdir
         os
@@ -148,12 +150,13 @@ set(CONV_SOURCES
   syntax.c
   tag.c
   window.c)
-
 foreach(sfile ${CONV_SOURCES})
   if(NOT EXISTS "${CMAKE_CURRENT_LIST_DIR}/${sfile}")
     message(FATAL_ERROR "${sfile} doesn't exist (it was added to CONV_SOURCES)")
   endif()
 endforeach()
+# xdiff: inlined external project, we don't maintain it. #9306
+list(APPEND CONV_SOURCES ${XDIFF_SOURCES})
 
 if(NOT MSVC)
   set_source_files_properties(
@@ -404,7 +407,8 @@ if(POLICY CMP0069)
 endif()
 
 add_executable(nvim ${NVIM_GENERATED_FOR_SOURCES} ${NVIM_GENERATED_FOR_HEADERS}
-  ${NVIM_GENERATED_SOURCES} ${NVIM_SOURCES} ${NVIM_HEADERS})
+  ${NVIM_GENERATED_SOURCES} ${NVIM_SOURCES} ${NVIM_HEADERS}
+  ${XDIFF_SOURCES} ${XDIFF_HEADERS})
 target_link_libraries(nvim ${NVIM_EXEC_LINK_LIBRARIES})
 install_helper(TARGETS nvim)
 
@@ -490,6 +494,7 @@ add_library(
   EXCLUDE_FROM_ALL
   ${NVIM_SOURCES} ${NVIM_GENERATED_SOURCES}
   ${NVIM_HEADERS} ${NVIM_GENERATED_FOR_SOURCES} ${NVIM_GENERATED_FOR_HEADERS}
+  ${XDIFF_SOURCES} ${XDIFF_HEADERS}
 )
 set_property(TARGET libnvim APPEND PROPERTY
              INCLUDE_DIRECTORIES ${LUA_PREFERRED_INCLUDE_DIRS})
@@ -514,6 +519,7 @@ else()
     EXCLUDE_FROM_ALL
     ${NVIM_SOURCES} ${NVIM_GENERATED_SOURCES}
     ${NVIM_HEADERS} ${NVIM_GENERATED_FOR_SOURCES} ${NVIM_GENERATED_FOR_HEADERS}
+    ${XDIFF_SOURCES} ${XDIFF_HEADERS}
     ${UNIT_TEST_FIXTURES}
   )
   target_link_libraries(nvim-test ${NVIM_TEST_LINK_LIBRARIES})
diff --git a/src/nvim/auevents.lua b/src/nvim/auevents.lua
index a6290aaac1..ab92e84799 100644
--- a/src/nvim/auevents.lua
+++ b/src/nvim/auevents.lua
@@ -33,6 +33,7 @@ return {
     'CursorHoldI',            -- idem, in Insert mode
     'CursorMoved',            -- cursor was moved
     'CursorMovedI',           -- cursor was moved in Insert mode
+    'DiffUpdated',            -- diffs have been updated
     'DirChanged',             -- directory changed
     'EncodingChanged',        -- after changing the 'encoding' option
     'ExitPre',                -- before exiting
diff --git a/src/nvim/buffer_defs.h b/src/nvim/buffer_defs.h
index e86eaf010f..d270714611 100644
--- a/src/nvim/buffer_defs.h
+++ b/src/nvim/buffer_defs.h
@@ -58,10 +58,10 @@ typedef struct {
  * functions that set or reset the flags.
  *
  * VALID_BOTLINE    VALID_BOTLINE_AP
- *     on		on		w_botline valid
- *     off		on		w_botline approximated
- *     off		off		w_botline not valid
- *     on		off		not possible
+ *     on       on      w_botline valid
+ *     off      on      w_botline approximated
+ *     off      off     w_botline not valid
+ *     on       off     not possible
  */
 #define VALID_WROW      0x01    /* w_wrow (window row) is valid */
 #define VALID_WCOL      0x02    /* w_wcol (window col) is valid */
@@ -159,7 +159,7 @@ typedef struct {
   int wo_arab;
 # define w_p_arab w_onebuf_opt.wo_arab  /* 'arabic' */
   int wo_bri;
-# define w_p_bri w_onebuf_opt.wo_bri	/* 'breakindent' */
+# define w_p_bri w_onebuf_opt.wo_bri    // 'breakindent'
   char_u *wo_briopt;
 # define w_p_briopt w_onebuf_opt.wo_briopt /* 'breakindentopt' */
   int wo_diff;
@@ -412,13 +412,13 @@ typedef struct {
    * syntax state too often.
    * b_sst_array[] is allocated to hold the state for all displayed lines,
    * and states for 1 out of about 20 other lines.
-   * b_sst_array	pointer to an array of synstate_T
-   * b_sst_len	number of entries in b_sst_array[]
-   * b_sst_first	pointer to first used entry in b_sst_array[] or NULL
-   * b_sst_firstfree	pointer to first free entry in b_sst_array[] or NULL
-   * b_sst_freecount	number of free entries in b_sst_array[]
-   * b_sst_check_lnum	entries after this lnum need to be checked for
-   *			validity (MAXLNUM means no check needed)
+   * b_sst_array        pointer to an array of synstate_T
+   * b_sst_len          number of entries in b_sst_array[]
+   * b_sst_first        pointer to first used entry in b_sst_array[] or NULL
+   * b_sst_firstfree    pointer to first free entry in b_sst_array[] or NULL
+   * b_sst_freecount    number of free entries in b_sst_array[]
+   * b_sst_check_lnum   entries after this lnum need to be checked for
+   *                    validity (MAXLNUM means no check needed)
    */
   synstate_T  *b_sst_array;
   int b_sst_len;
@@ -475,15 +475,15 @@ struct file_buffer {
   int b_locked;                 // Buffer is being closed or referenced, don't
                                 // let autocommands wipe it out.
 
-  /*
-   * b_ffname has the full path of the file (NULL for no name).
-   * b_sfname is the name as the user typed it (or NULL).
-   * b_fname is the same as b_sfname, unless ":cd" has been done,
-   *		then it is the same as b_ffname (NULL for no name).
-   */
-  char_u      *b_ffname;        /* full path file name */
-  char_u      *b_sfname;        /* short file name */
-  char_u      *b_fname;         /* current file name */
+  //
+  // b_ffname   has the full path of the file (NULL for no name).
+  // b_sfname   is the name as the user typed it (or NULL).
+  // b_fname    is the same as b_sfname, unless ":cd" has been done,
+  //            then it is the same as b_ffname (NULL for no name).
+  //
+  char_u      *b_ffname;        // full path file name
+  char_u      *b_sfname;        // short file name
+  char_u      *b_fname;         // current file name
 
   bool file_id_valid;
   FileID file_id;
@@ -587,12 +587,12 @@ struct file_buffer {
 
   bool b_scanned;               /* ^N/^P have scanned this buffer */
 
-  /* flags for use of ":lmap" and IM control */
-  long b_p_iminsert;            /* input mode for insert */
-  long b_p_imsearch;            /* input mode for search */
-#define B_IMODE_USE_INSERT -1   /*	Use b_p_iminsert value for search */
-#define B_IMODE_NONE 0          /*	Input via none */
-#define B_IMODE_LMAP 1          /*	Input via langmap */
+  // flags for use of ":lmap" and IM control
+  long b_p_iminsert;            // input mode for insert
+  long b_p_imsearch;            // input mode for search
+#define B_IMODE_USE_INSERT -1   //  Use b_p_iminsert value for search
+#define B_IMODE_NONE 0          //  Input via none
+#define B_IMODE_LMAP 1          //  Input via langmap
 # define B_IMODE_LAST 1
 
   short b_kmap_state;           /* using "lmap" mappings */
@@ -760,7 +760,7 @@ struct file_buffer {
   /* Two special kinds of buffers:
    * help buffer  - used for help files, won't use a swap file.
    * spell buffer - used for spell info, never displayed and doesn't have a
-   *		      file name.
+   *                file name.
    */
   bool b_help;                  /* TRUE for help file buffer (when set b_p_bt
                                    is "help") */
@@ -787,6 +787,8 @@ struct file_buffer {
   // array of channelids which have asked to receive updates for this
   // buffer.
   kvec_t(uint64_t) update_channels;
+
+  int b_diff_failed;    // internal diff failed for this buffer
 };
 
 /*
@@ -840,6 +842,7 @@ struct tabpage_S {
   diff_T          *tp_first_diff;
   buf_T           *(tp_diffbuf[DB_COUNT]);
   int tp_diff_invalid;              ///< list of diffs is outdated
+  int tp_diff_update;               ///< update diffs before redrawing
   frame_T         *(tp_snapshot[SNAP_COUNT]);    ///< window layout snapshots
   ScopeDictDictItem tp_winvar;      ///< Variable for "t:" Dictionary.
   dict_T          *tp_vars;         ///< Internal variables, local to tab page.
@@ -916,9 +919,9 @@ typedef struct {
 /// Same as lpos_T, but with additional field len.
 typedef struct
 {
-    linenr_T    lnum;	///< line number
-    colnr_T     col;	///< column number
-    int         len;	///< length: 0 - to the end of line
+    linenr_T    lnum;   ///< line number
+    colnr_T     col;    ///< column number
+    int         len;    ///< length: 0 - to the end of line
 } llpos_T;
 
 /// posmatch_T provides an array for storing match items for matchaddpos()
@@ -926,10 +929,10 @@ typedef struct
 typedef struct posmatch posmatch_T;
 struct posmatch
 {
-    llpos_T     pos[MAXPOSMATCH];	///< array of positions
-    int         cur;			///< internal position counter 
-    linenr_T    toplnum;		///< top buffer line
-    linenr_T    botlnum;		///< bottom buffer line
+    llpos_T     pos[MAXPOSMATCH];   ///< array of positions
+    int         cur;                ///< internal position counter
+    linenr_T    toplnum;            ///< top buffer line
+    linenr_T    botlnum;            ///< bottom buffer line
 };
 
 /*
@@ -1036,7 +1039,7 @@ struct window_S {
    * Recomputing is minimized by storing the result of computations.
    * Use functions in screen.c to check if they are valid and to update.
    * w_valid is a bitfield of flags, which indicate if specific values are
-   * valid or need to be recomputed.	
+   * valid or need to be recomputed.
    */
   int w_valid;
   pos_T w_valid_cursor;             /* last known position of w_cursor, used
diff --git a/src/nvim/diff.c b/src/nvim/diff.c
index 4bfe67c9d3..2e0b198c13 100644
--- a/src/nvim/diff.c
+++ b/src/nvim/diff.c
@@ -4,11 +4,17 @@
 /// @file diff.c
 ///
 /// Code for diff'ing two, three or four buffers.
+///
+/// There are three ways to diff:
+/// - Shell out to an external diff program, using files.
+/// - Use the compiled-in xdiff library.
+/// - Let 'diffexpr' do the work, using files.
 
 #include <inttypes.h>
 #include <stdbool.h>
 
 #include "nvim/vim.h"
+#include "xdiff/xdiff.h"
 #include "nvim/ascii.h"
 #include "nvim/diff.h"
 #include "nvim/buffer.h"
@@ -36,16 +42,24 @@
 #include "nvim/os/os.h"
 #include "nvim/os/shell.h"
 
-static int diff_busy = FALSE;    // ex_diffgetput() is busy
+static int diff_busy = false;         // using diff structs, don't change them
+static int diff_need_update = false;  // ex_diffupdate needs to be called
 
 // Flags obtained from the 'diffopt' option
-#define DIFF_FILLER     1        // display filler lines
-#define DIFF_ICASE      2        // ignore case
-#define DIFF_IWHITE     4        // ignore change in white space
-#define DIFF_HORIZONTAL 8        // horizontal splits
-#define DIFF_VERTICAL   16       // vertical splits
-#define DIFF_HIDDEN_OFF 32       // diffoff when hidden
-static int diff_flags = DIFF_FILLER;
+#define DIFF_FILLER     0x001   // display filler lines
+#define DIFF_IBLANK     0x002   // ignore empty lines
+#define DIFF_ICASE      0x004   // ignore case
+#define DIFF_IWHITE     0x008   // ignore change in white space
+#define DIFF_IWHITEALL  0x010   // ignore all white space changes
+#define DIFF_IWHITEEOL  0x020   // ignore change in white space at EOL
+#define DIFF_HORIZONTAL 0x040   // horizontal splits
+#define DIFF_VERTICAL   0x080   // vertical splits
+#define DIFF_HIDDEN_OFF 0x100   // diffoff when hidden
+#define DIFF_INTERNAL   0x200   // use internal xdiff algorithm
+#define ALL_WHITE_DIFF (DIFF_IWHITE | DIFF_IWHITEALL | DIFF_IWHITEEOL)
+static int diff_flags = DIFF_INTERNAL | DIFF_FILLER;
+
+static long diff_algorithm = 0;
 
 #define LBUFLEN 50               // length of line in diff file
 
@@ -53,6 +67,25 @@ static int diff_flags = DIFF_FILLER;
 // kNone when not checked yet
 static TriState diff_a_works = kNone;
 
+// used for diff input
+typedef struct {
+    char_u   *din_fname;   // used for external diff
+    mmfile_t  din_mmfile;  // used for internal diff
+} diffin_T;
+
+// used for diff result
+typedef struct {
+    char_u   *dout_fname;  // used for external diff
+    garray_T  dout_ga;     // used for internal diff
+} diffout_T;
+
+// two diff inputs and one result
+typedef struct {
+    diffin_T    dio_orig;      // original file input
+    diffin_T    dio_new;       // new file input
+    diffout_T   dio_diff;      // diff result
+    int         dio_internal;  // using internal diff
+} diffio_T;
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "diff.c.generated.h"
@@ -68,10 +101,10 @@ void diff_buf_delete(buf_T *buf)
 
     if (i != DB_COUNT) {
       tp->tp_diffbuf[i] = NULL;
-      tp->tp_diff_invalid = TRUE;
+      tp->tp_diff_invalid = true;
 
       if (tp == curtab) {
-        diff_redraw(TRUE);
+        diff_redraw(true);
       }
     }
   }
@@ -98,8 +131,8 @@ void diff_buf_adjust(win_T *win)
       int i = diff_buf_idx(win->w_buffer);
       if (i != DB_COUNT) {
         curtab->tp_diffbuf[i] = NULL;
-        curtab->tp_diff_invalid = TRUE;
-        diff_redraw(TRUE);
+        curtab->tp_diff_invalid = true;
+        diff_redraw(true);
       }
     }
   } else {
@@ -127,8 +160,8 @@ void diff_buf_add(buf_T *buf)
   for (i = 0; i < DB_COUNT; ++i) {
     if (curtab->tp_diffbuf[i] == NULL) {
       curtab->tp_diffbuf[i] = buf;
-      curtab->tp_diff_invalid = TRUE;
-      diff_redraw(TRUE);
+      curtab->tp_diff_invalid = true;
+      diff_redraw(true);
       return;
     }
   }
@@ -192,9 +225,9 @@ void diff_invalidate(buf_T *buf)
   FOR_ALL_TABS(tp) {
     int i = diff_buf_idx_tp(buf, tp);
     if (i != DB_COUNT) {
-      tp->tp_diff_invalid = TRUE;
+      tp->tp_diff_invalid = true;
       if (tp == curtab) {
-        diff_redraw(TRUE);
+        diff_redraw(true);
       }
     }
   }
@@ -234,6 +267,15 @@ void diff_mark_adjust(linenr_T line1, linenr_T line2, long amount,
 static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1,
                                 linenr_T line2, long amount, long amount_after)
 {
+  if (diff_internal()) {
+    // Will update diffs before redrawing.  Set _invalid to update the
+    // diffs themselves, set _update to also update folds properly just
+    // before redrawing.
+    // Do update marks here, it is needed for :%diffput.
+    tp->tp_diff_invalid = true;
+    tp->tp_diff_update = true;
+  }
+
   int inserted;
   int deleted;
   if (line2 == MAXLNUM) {
@@ -293,14 +335,14 @@ static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1,
 
     //
     // Check for these situations:
-    //	  1  2	3
-    //	  1  2	3
-    // line1     2	3  4  5
-    //	     2	3  4  5
-    //	     2	3  4  5
-    // line2     2	3  4  5
-    //		3     5  6
-    //		3     5  6
+    //    1  2  3
+    //    1  2  3
+    // line1     2  3  4  5
+    //       2  3  4  5
+    //       2  3  4  5
+    // line2     2  3  4  5
+    //      3     5  6
+    //      3     5  6
 
     // compute last line of this change
     last = dp->df_lnum[idx] + dp->df_count[idx] - 1;
@@ -316,7 +358,7 @@ static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1,
         }
         dp->df_lnum[idx] += amount_after;
       } else {
-        int check_unchanged = FALSE;
+        int check_unchanged = false;
 
         // 2. 3. 4. 5.: inserted/deleted lines touching this diff.
         if (deleted > 0) {
@@ -341,7 +383,7 @@ static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1,
               // 5. delete lines at or just before top of diff
               n = off;
               dp->df_count[idx] -= line2 - dp->df_lnum[idx] + 1;
-              check_unchanged = TRUE;
+              check_unchanged = true;
             }
             dp->df_lnum[idx] = line1;
           } else {
@@ -361,7 +403,7 @@ static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1,
               } else {
                 n = line2 - last;
               }
-              check_unchanged = TRUE;
+              check_unchanged = true;
             } else {
               // 3. delete lines inside the diff
               n = 0;
@@ -380,7 +422,7 @@ static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1,
           if (dp->df_lnum[idx] <= line1) {
             // inserted lines somewhere in this diff
             dp->df_count[idx] += inserted;
-            check_unchanged = TRUE;
+            check_unchanged = true;
           } else {
             // inserted lines somewhere above this diff
             dp->df_lnum[idx] += inserted;
@@ -447,12 +489,12 @@ static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1,
   }
 
   if (tp == curtab) {
-    diff_redraw(TRUE);
+    diff_redraw(true);
 
     // Need to recompute the scroll binding, may remove or add filler
     // lines (e.g., when adding lines above w_topline). But it's slow when
     // making many changes, postpone until redrawing.
-    diff_need_scrollbind = TRUE;
+    diff_need_scrollbind = true;
   }
 }
 
@@ -519,7 +561,7 @@ static void diff_check_unchanged(tabpage_T *tp, diff_T *dp)
       }
       char_u *line_org = vim_strsave(ml_get_buf(tp->tp_diffbuf[i_org],
                                                 dp->df_lnum[i_org] + off_org,
-                                                FALSE));
+                                                false));
 
       int i_new;
       for (i_new = i_org + 1; i_new < DB_COUNT; ++i_new) {
@@ -538,7 +580,7 @@ static void diff_check_unchanged(tabpage_T *tp, diff_T *dp)
 
         if (diff_cmp(line_org, ml_get_buf(tp->tp_diffbuf[i_new],
                                           dp->df_lnum[i_new] + off_new,
-                                          FALSE)) != 0) {
+                                          false)) != 0) {
           break;
         }
       }
@@ -612,42 +654,243 @@ static void diff_redraw(int dofold)
       } else if ((n > 0) && (n > wp->w_topfill)) {
         wp->w_topfill = n;
       }
-      check_topfill(wp, FALSE);
+      check_topfill(wp, false);
+    }
+  }
+}
+
+static void clear_diffin(diffin_T *din)
+{
+  if (din->din_fname == NULL) {
+    xfree(din->din_mmfile.ptr);
+    din->din_mmfile.ptr = NULL;
+  } else {
+    os_remove((char *)din->din_fname);
+  }
+}
+
+static void clear_diffout(diffout_T *dout)
+{
+  if (dout->dout_fname == NULL) {
+    ga_clear_strings(&dout->dout_ga);
+  } else {
+    os_remove((char *)dout->dout_fname);
+  }
+}
+
+/// Write buffer "buf" to a memory buffer.
+///
+/// @param buf
+/// @param din
+///
+/// @return FAIL for failure.
+static int diff_write_buffer(buf_T *buf, diffin_T *din)
+{
+  linenr_T   lnum;
+  char_u    *s;
+  long       len = 0;
+  char_u    *ptr;
+
+  // xdiff requires one big block of memory with all the text.
+  for (lnum = 1; lnum <= buf->b_ml.ml_line_count; lnum++) {
+    len += (long)STRLEN(ml_get_buf(buf, lnum, false)) + 1;
+  }
+  ptr = xmalloc(len);
+  if (ptr == NULL) {
+    // Allocating memory failed.  This can happen, because we try to read
+    // the whole buffer text into memory.  Set the failed flag, the diff
+    // will be retried with external diff.  The flag is never reset.
+    buf->b_diff_failed = true;
+    if (p_verbose > 0) {
+      verbose_enter();
+      smsg(_("Not enough memory to use internal diff for buffer \"%s\""),
+           buf->b_fname);
+      verbose_leave();
+    }
+    return FAIL;
+  }
+  din->din_mmfile.ptr = (char *)ptr;
+  din->din_mmfile.size = len;
+
+  len = 0;
+  for (lnum = 1; lnum <= buf->b_ml.ml_line_count; lnum++) {
+    for (s = ml_get_buf(buf, lnum, false); *s != NUL; ) {
+      if (diff_flags & DIFF_ICASE) {
+        int c;
+
+        // xdiff doesn't support ignoring case, fold-case the text.
+        int     orig_len;
+        char_u  cbuf[MB_MAXBYTES + 1];
+
+        c = PTR2CHAR(s);
+        c = enc_utf8 ? utf_fold(c) : TOLOWER_LOC(c);
+        orig_len = MB_PTR2LEN(s);
+        if (utf_char2bytes(c, cbuf) != orig_len) {
+          // TODO(Bram): handle byte length difference
+          memmove(ptr + len, s, orig_len);
+        } else {
+          memmove(ptr + len, cbuf, orig_len);
+        }
+
+        s += orig_len;
+        len += orig_len;
+      } else {
+        ptr[len++] = *s++;
+      }
     }
+    ptr[len++] = NL;
   }
+  return OK;
 }
 
-/// Write buffer "buf" to file "name".
+/// Write buffer "buf" to file or memory buffer.
 ///
 /// Always use 'fileformat' set to "unix".
 ///
 /// @param buf
-/// @param fname
+/// @param din
 ///
 /// @return FAIL for failure
-static int diff_write(buf_T *buf, char_u *fname)
+static int diff_write(buf_T *buf, diffin_T *din)
 {
+  if (din->din_fname == NULL) {
+    return diff_write_buffer(buf, din);
+  }
+
+  // Always use 'fileformat' set to "unix".
   char_u *save_ff = buf->b_p_ff;
   buf->b_p_ff = vim_strsave((char_u *)FF_UNIX);
-  int r = buf_write(buf, fname, NULL, (linenr_T)1, buf->b_ml.ml_line_count,
-                    NULL, FALSE, FALSE, FALSE, TRUE);
+  int r = buf_write(buf, din->din_fname, NULL,
+                    (linenr_T)1, buf->b_ml.ml_line_count,
+                    NULL, false, false, false, true);
   free_string_option(buf->b_p_ff);
   buf->b_p_ff = save_ff;
   return r;
 }
 
+///
+/// Update the diffs for all buffers involved.
+///
+/// @param dio
+/// @param idx_orig
+/// @param eap   can be NULL
+static void diff_try_update(diffio_T    *dio,
+                            int     idx_orig,
+                            exarg_T     *eap)
+{
+  buf_T *buf;
+  int    idx_new;
+
+  if (dio->dio_internal) {
+    ga_init(&dio->dio_diff.dout_ga, sizeof(char *), 1000);
+  } else {
+    // We need three temp file names.
+    dio->dio_orig.din_fname = vim_tempname();
+    dio->dio_new.din_fname = vim_tempname();
+    dio->dio_diff.dout_fname = vim_tempname();
+    if (dio->dio_orig.din_fname == NULL
+        || dio->dio_new.din_fname == NULL
+        || dio->dio_diff.dout_fname == NULL) {
+      goto theend;
+    }
+  }
+
+  // Check external diff is actually working.
+  if (!dio->dio_internal && check_external_diff(dio) == FAIL) {
+    goto theend;
+  }
+
+  // :diffupdate!
+  if (eap != NULL && eap->forceit) {
+    for (idx_new = idx_orig; idx_new < DB_COUNT; idx_new++) {
+      buf = curtab->tp_diffbuf[idx_new];
+      if (buf_valid(buf)) {
+        buf_check_timestamp(buf, false);
+      }
+    }
+  }
+
+  // Write the first buffer to a tempfile or mmfile_t.
+  buf = curtab->tp_diffbuf[idx_orig];
+  if (diff_write(buf, &dio->dio_orig) == FAIL) {
+    goto theend;
+  }
+
+  // Make a difference between the first buffer and every other.
+  for (idx_new = idx_orig + 1; idx_new < DB_COUNT; idx_new++) {
+    buf = curtab->tp_diffbuf[idx_new];
+    if (buf == NULL || buf->b_ml.ml_mfp == NULL) {
+      continue;  // skip buffer that isn't loaded
+    }
+
+    // Write the other buffer and diff with the first one.
+    if (diff_write(buf, &dio->dio_new) == FAIL) {
+      continue;
+    }
+    if (diff_file(dio) == FAIL) {
+      continue;
+    }
+
+    // Read the diff output and add each entry to the diff list.
+    diff_read(idx_orig, idx_new, &dio->dio_diff);
+
+    clear_diffin(&dio->dio_new);
+    clear_diffout(&dio->dio_diff);
+  }
+  clear_diffin(&dio->dio_orig);
+
+theend:
+  xfree(dio->dio_orig.din_fname);
+  xfree(dio->dio_new.din_fname);
+  xfree(dio->dio_diff.dout_fname);
+}
+
+///
+/// Return true if the options are set to use the internal diff library.
+/// Note that if the internal diff failed for one of the buffers, the external
+/// diff will be used anyway.
+///
+int diff_internal(void)
+{
+  return (diff_flags & DIFF_INTERNAL) != 0 && *p_dex == NUL;
+}
+
+///
+/// Return true if the internal diff failed for one of the diff buffers.
+///
+static int diff_internal_failed(void)
+{
+  int idx;
+
+  // Only need to do something when there is another buffer.
+  for (idx = 0; idx < DB_COUNT; idx++) {
+    if (curtab->tp_diffbuf[idx] != NULL
+        && curtab->tp_diffbuf[idx]->b_diff_failed) {
+      return true;
+    }
+  }
+  return false;
+}
+
 /// Completely update the diffs for the buffers involved.
 ///
-/// This uses the ordinary "diff" command.
-/// The buffers are written to a file, also for unmodified buffers (the file
-/// could have been produced by autocommands, e.g. the netrw plugin).
+/// When using the external "diff" command the buffers are written to a file,
+/// also for unmodified buffers (the file could have been produced by
+/// autocommands, e.g. the netrw plugin).
 ///
 /// @param eap can be NULL
 void ex_diffupdate(exarg_T *eap)
 {
+  if (diff_busy) {
+    diff_need_update = true;
+    return;
+  }
+
+  int had_diffs = curtab->tp_first_diff != NULL;
+
   // Delete all diffblocks.
   diff_clear(curtab);
-  curtab->tp_diff_invalid = FALSE;
+  curtab->tp_diff_invalid = false;
 
   // Use the first buffer as the original text.
   int idx_orig;
@@ -658,7 +901,7 @@ void ex_diffupdate(exarg_T *eap)
   }
 
   if (idx_orig == DB_COUNT) {
-    return;
+    goto theend;
   }
 
   // Only need to do something when there is another buffer.
@@ -670,49 +913,70 @@ void ex_diffupdate(exarg_T *eap)
   }
 
   if (idx_new == DB_COUNT) {
-    return;
+    goto theend;
   }
 
-  // We need three temp file names.
-  char *tmp_orig = (char *) vim_tempname();
-  char *tmp_new = (char *) vim_tempname();
-  char *tmp_diff = (char *) vim_tempname();
+  // Only use the internal method if it did not fail for one of the buffers.
+  diffio_T  diffio;
+  memset(&diffio, 0, sizeof(diffio));
+  diffio.dio_internal = diff_internal() && !diff_internal_failed();
 
-  if ((tmp_orig == NULL) || (tmp_new == NULL) || (tmp_diff == NULL)) {
-    goto theend;
+  diff_try_update(&diffio, idx_orig, eap);
+  if (diffio.dio_internal && diff_internal_failed()) {
+    // Internal diff failed, use external diff instead.
+    memset(&diffio, 0, sizeof(diffio));
+    diff_try_update(&diffio, idx_orig, eap);
+  }
+
+  // force updating cursor position on screen
+  curwin->w_valid_cursor.lnum = 0;
+
+theend:
+  // A redraw is needed if there were diffs and they were cleared, or there
+  // are diffs now, which means they got updated.
+  if (had_diffs || curtab->tp_first_diff != NULL) {
+    diff_redraw(true);
+    apply_autocmds(EVENT_DIFFUPDATED, NULL, NULL, false, curbuf);
   }
+}
 
-  // Do a quick test if "diff" really works.  Otherwise it looks like there
-  // are no differences.  Can't use the return value, it's non-zero when
-  // there are differences.
+///
+/// Do a quick test if "diff" really works.  Otherwise it looks like there
+/// are no differences.  Can't use the return value, it's non-zero when
+/// there are differences.
+///
+static int check_external_diff(diffio_T *diffio)
+{
   // May try twice, first with "-a" and then without.
   int io_error = false;
   TriState ok = kFalse;
   for (;;) {
     ok = kFalse;
-    FILE *fd = mch_fopen(tmp_orig, "w");
+    FILE *fd = mch_fopen((char *)diffio->dio_orig.din_fname, "w");
 
     if (fd == NULL) {
-      io_error = TRUE;
+      io_error = true;
     } else {
       if (fwrite("line1\n", (size_t)6, (size_t)1, fd) != 1) {
-        io_error = TRUE;
+        io_error = true;
       }
       fclose(fd);
-      fd = mch_fopen(tmp_new, "w");
+      fd = mch_fopen((char *)diffio->dio_new.din_fname, "w");
 
       if (fd == NULL) {
-        io_error = TRUE;
+        io_error = true;
       } else {
         if (fwrite("line2\n", (size_t)6, (size_t)1, fd) != 1) {
-          io_error = TRUE;
+          io_error = true;
         }
         fclose(fd);
-        diff_file(tmp_orig, tmp_new, tmp_diff);
-        fd = mch_fopen(tmp_diff, "r");
+        fd = NULL;
+        if (diff_file(diffio) == OK) {
+          fd = mch_fopen((char *)diffio->dio_diff.dout_fname, "r");
+        }
 
         if (fd == NULL) {
-          io_error = TRUE;
+          io_error = true;
         } else {
           char_u linebuf[LBUFLEN];
 
@@ -728,10 +992,10 @@ void ex_diffupdate(exarg_T *eap)
           }
           fclose(fd);
         }
-        os_remove(tmp_diff);
-        os_remove(tmp_new);
+        os_remove((char *)diffio->dio_diff.dout_fname);
+        os_remove((char *)diffio->dio_new.din_fname);
       }
-      os_remove(tmp_orig);
+      os_remove((char *)diffio->dio_orig.din_fname);
     }
 
     // When using 'diffexpr' break here.
@@ -757,83 +1021,92 @@ void ex_diffupdate(exarg_T *eap)
     }
     EMSG(_("E97: Cannot create diffs"));
     diff_a_works = kNone;
-    goto theend;
-  }
-
-  // :diffupdate!
-  if ((eap != NULL) && eap->forceit) {
-    for (idx_new = idx_orig; idx_new < DB_COUNT; ++idx_new) {
-      buf_T *buf = curtab->tp_diffbuf[idx_new];
-      if (buf_valid(buf)) {
-        buf_check_timestamp(buf, FALSE);
-      }
-    }
+    return FAIL;
   }
+  return OK;
+}
 
-  // Write the first buffer to a tempfile.
-  buf_T *buf = curtab->tp_diffbuf[idx_orig];
-  if (diff_write(buf, (char_u *) tmp_orig) == FAIL) {
-    goto theend;
-  }
+///
+/// Invoke the xdiff function.
+///
+static int diff_file_internal(diffio_T *diffio)
+{
+  xpparam_t     param;
+  xdemitconf_t    emit_cfg;
+  xdemitcb_t        emit_cb;
 
-  // Make a difference between the first buffer and every other.
-  for (idx_new = idx_orig + 1; idx_new < DB_COUNT; ++idx_new) {
-    buf_T *buf = curtab->tp_diffbuf[idx_new];
-    if (buf == NULL || buf->b_ml.ml_mfp == NULL) {
-      continue;  // skip buffer that isn't loaded
-    }
+  memset(&param, 0, sizeof(param));
+  memset(&emit_cfg, 0, sizeof(emit_cfg));
+  memset(&emit_cb, 0, sizeof(emit_cb));
 
-    if (diff_write(buf, (char_u *) tmp_new) == FAIL) {
-      continue;
-    }
-    diff_file(tmp_orig, tmp_new, tmp_diff);
+  param.flags = diff_algorithm;
 
-    // Read the diff output and add each entry to the diff list.
-    diff_read(idx_orig, idx_new, (char_u *) tmp_diff);
-    os_remove(tmp_diff);
-    os_remove(tmp_new);
+  if (diff_flags & DIFF_IWHITE) {
+    param.flags |= XDF_IGNORE_WHITESPACE_CHANGE;
+  }
+  if (diff_flags & DIFF_IWHITEALL) {
+    param.flags |= XDF_IGNORE_WHITESPACE;
+  }
+  if (diff_flags & DIFF_IWHITEEOL) {
+    param.flags |= XDF_IGNORE_WHITESPACE_AT_EOL;
+  }
+  if (diff_flags & DIFF_IBLANK) {
+    param.flags |= XDF_IGNORE_BLANK_LINES;
   }
-  os_remove(tmp_orig);
-
-  // force updating cursor position on screen
-  curwin->w_valid_cursor.lnum = 0;
-
-  diff_redraw(TRUE);
 
-theend:
-  xfree(tmp_orig);
-  xfree(tmp_new);
-  xfree(tmp_diff);
+  emit_cfg.ctxlen = 0;  // don't need any diff_context here
+  emit_cb.priv = &diffio->dio_diff;
+  emit_cb.outf = xdiff_out;
+  if (xdl_diff(&diffio->dio_orig.din_mmfile,
+               &diffio->dio_new.din_mmfile,
+               &param, &emit_cfg, &emit_cb) < 0) {
+    EMSG(_("E960: Problem creating the internal diff"));
+    return FAIL;
+  }
+  return OK;
 }
 
 /// Make a diff between files "tmp_orig" and "tmp_new", results in "tmp_diff".
 ///
-/// @param tmp_orig
-/// @param tmp_new
-/// @param tmp_diff
-static void diff_file(const char *const tmp_orig, const char *const tmp_new,
-                      const char *const tmp_diff)
+/// @param dio
+///
+/// @return OK or FAIL
+static int diff_file(diffio_T *dio)
 {
+  char  *tmp_orig = (char *)dio->dio_orig.din_fname;
+  char  *tmp_new = (char *)dio->dio_new.din_fname;
+  char  *tmp_diff = (char *)dio->dio_diff.dout_fname;
   if (*p_dex != NUL) {
     // Use 'diffexpr' to generate the diff file.
     eval_diff(tmp_orig, tmp_new, tmp_diff);
+    return OK;
+  }
+  // Use xdiff for generating the diff.
+  if (dio->dio_internal) {
+    return diff_file_internal(dio);
   } else {
     const size_t len = (strlen(tmp_orig) + strlen(tmp_new) + strlen(tmp_diff)
                         + STRLEN(p_srr) + 27);
     char *const cmd = xmalloc(len);
+    if (cmd == NULL) {
+      return FAIL;
+    }
 
-    /* We don't want $DIFF_OPTIONS to get in the way. */
+    // We don't want $DIFF_OPTIONS to get in the way.
     if (os_getenv("DIFF_OPTIONS")) {
       os_unsetenv("DIFF_OPTIONS");
     }
 
-    /* Build the diff command and execute it.  Always use -a, binary
-     * differences are of no use.  Ignore errors, diff returns
-     * non-zero when differences have been found. */
-    vim_snprintf(cmd, len, "diff %s%s%s%s%s %s",
+    // Build the diff command and execute it.  Always use -a, binary
+    // differences are of no use.  Ignore errors, diff returns
+    // non-zero when differences have been found.
+    vim_snprintf((char *)cmd, len, "diff %s%s%s%s%s%s%s%s %s",
                  diff_a_works == kFalse ? "" : "-a ",
                  "",
                  (diff_flags & DIFF_IWHITE) ? "-b " : "",
+                 (diff_flags & DIFF_IWHITEALL) ? "-w " : "",
+                 (diff_flags & DIFF_IWHITEEOL) ? "-Z " : "",
+                 (diff_flags & DIFF_IBLANK) ? "-B " : "",
                  (diff_flags & DIFF_ICASE) ? "-i " : "",
                  tmp_orig, tmp_new);
     append_redir(cmd, len, (char *) p_srr, tmp_diff);
@@ -843,6 +1116,7 @@ static void diff_file(const char *const tmp_orig, const char *const tmp_new,
                      NULL);
     unblock_autocmds();
     xfree(cmd);
+    return OK;
   }
 }
 
@@ -876,7 +1150,7 @@ void ex_diffpatch(exarg_T *eap)
   // Write the current buffer to "tmp_orig".
   if (buf_write(curbuf, tmp_orig, NULL,
                 (linenr_T)1, curbuf->b_ml.ml_line_count,
-                NULL, FALSE, FALSE, FALSE, TRUE) == FAIL) {
+                NULL, false, false, false, true) == FAIL) {
     goto theend;
   }
 
@@ -907,7 +1181,7 @@ void ex_diffpatch(exarg_T *eap)
       tempdir = "/tmp";
     }
     os_chdir(tempdir);
-    shorten_fnames(TRUE);
+    shorten_fnames(true);
   }
 #endif
 
@@ -934,7 +1208,7 @@ void ex_diffpatch(exarg_T *eap)
     if (os_chdir((char *)dirbuf) != 0) {
       EMSG(_(e_prev_dir));
     }
-    shorten_fnames(TRUE);
+    shorten_fnames(true);
   }
 #endif
 
@@ -971,8 +1245,8 @@ void ex_diffpatch(exarg_T *eap)
       // check that split worked and editing tmp_new
       if ((curwin != old_curwin) && win_valid(old_curwin)) {
         // Set 'diff', 'scrollbind' on and 'wrap' off.
-        diff_win_options(curwin, TRUE);
-        diff_win_options(old_curwin, TRUE);
+        diff_win_options(curwin, true);
+        diff_win_options(old_curwin, true);
 
         if (newname != NULL) {
           // do a ":file filename.new" on the patched buffer
@@ -1025,7 +1299,7 @@ void ex_diffsplit(exarg_T *eap)
   if (win_split(0, (diff_flags & DIFF_VERTICAL) ? WSP_VERT : 0) != FAIL) {
     // Pretend it was a ":split fname" command
     eap->cmdidx = CMD_split;
-    curwin->w_p_diff = TRUE;
+    curwin->w_p_diff = true;
     do_exedit(eap, old_curwin);
 
     // split must have worked
@@ -1052,7 +1326,7 @@ void ex_diffsplit(exarg_T *eap)
 void ex_diffthis(exarg_T *eap)
 {
   // Set 'diff', 'scrollbind' on and 'wrap' off.
-  diff_win_options(curwin, TRUE);
+  diff_win_options(curwin, true);
 }
 
 static void set_diff_option(win_T *wp, int value)
@@ -1085,12 +1359,12 @@ void diff_win_options(win_T *wp, int addbuf)
   if (!wp->w_p_diff) {
     wp->w_p_scb_save = wp->w_p_scb;
   }
-  wp->w_p_scb = TRUE;
+  wp->w_p_scb = true;
 
   if (!wp->w_p_diff) {
     wp->w_p_crb_save = wp->w_p_crb;
   }
-  wp->w_p_crb = TRUE;
+  wp->w_p_crb = true;
 
   if (!wp->w_p_diff) {
     wp->w_p_wrap_save = wp->w_p_wrap;
@@ -1116,7 +1390,7 @@ void diff_win_options(win_T *wp, int addbuf)
     wp->w_p_fdl_save = wp->w_p_fdl;
   }
   wp->w_p_fdc = diff_foldcolumn;
-  wp->w_p_fen = TRUE;
+  wp->w_p_fen = true;
   wp->w_p_fdl = 0;
   foldUpdateAll(wp);
 
@@ -1211,88 +1485,97 @@ void ex_diffoff(exarg_T *eap)
 ///
 /// @param idx_orig idx of original file
 /// @param idx_new idx of new file
-/// @param fname name of diff output file
-static void diff_read(int idx_orig, int idx_new, char_u *fname)
+/// @dout diff output
+static void diff_read(int idx_orig, int idx_new, diffout_T *dout)
 {
-  FILE *fd;
+  FILE *fd = NULL;
+  int line_idx = 0;
   diff_T *dprev = NULL;
   diff_T *dp = curtab->tp_first_diff;
   diff_T *dn, *dpl;
-  long f1, l1, f2, l2;
-  char_u linebuf[LBUFLEN]; // only need to hold the diff line
-  int difftype;
-  char_u *p;
+  char_u linebuf[LBUFLEN];  // only need to hold the diff line
+  char_u *line;
   long off;
   int i;
   linenr_T lnum_orig, lnum_new;
   long count_orig, count_new;
-  int notset = TRUE; // block "*dp" not set yet
-
-  fd = mch_fopen((char *)fname, "r");
-
-  if (fd == NULL) {
-    EMSG(_("E98: Cannot read diff output"));
-    return;
+  int notset = true;  // block "*dp" not set yet
+  enum {
+    DIFF_ED,
+    DIFF_UNIFIED,
+    DIFF_NONE
+  } diffstyle = DIFF_NONE;
+
+  if (dout->dout_fname == NULL) {
+    diffstyle = DIFF_UNIFIED;
+  } else {
+    fd = mch_fopen((char *)dout->dout_fname, "r");
+    if (fd == NULL) {
+      EMSG(_("E98: Cannot read diff output"));
+      return;
+    }
   }
 
   for (;;) {
-    if (vim_fgets(linebuf, LBUFLEN, fd)) {
-      // end of file
-      break;
-    }
-
-    if (!isdigit(*linebuf)) {
-      // not the start of a diff block
-      continue;
-    }
-
-    // This line must be one of three formats:
-    // {first}[,{last}]c{first}[,{last}]
-    // {first}a{first}[,{last}]
-    // {first}[,{last}]d{first}
-    p = linebuf;
-    f1 = getdigits_long(&p);
-
-    if (*p == ',') {
-      ++p;
-      l1 = getdigits_long(&p);
-    } else {
-      l1 = f1;
-    }
-
-    if ((*p != 'a') && (*p != 'c') && (*p != 'd')) {
-      // invalid diff format
-      continue;
-    }
-    difftype = *p++;
-    f2 = getdigits_long(&p);
-
-    if (*p == ',') {
-      ++p;
-      l2 = getdigits_long(&p);
-    } else {
-      l2 = f2;
-    }
-
-    if ((l1 < f1) || (l2 < f2)) {
-      // invalid line range
-      continue;
-    }
-
-    if (difftype == 'a') {
-      lnum_orig = f1 + 1;
-      count_orig = 0;
+    if (fd == NULL) {
+      if (line_idx >= dout->dout_ga.ga_len) {
+        break;      // did last line
+      }
+      line = ((char_u **)dout->dout_ga.ga_data)[line_idx++];
     } else {
-      lnum_orig = f1;
-      count_orig = l1 - f1 + 1;
+      if (vim_fgets(linebuf, LBUFLEN, fd)) {
+        break;      // end of file
+      }
+      line = linebuf;
+    }
+
+    if (diffstyle == DIFF_NONE) {
+      // Determine diff style.
+      // ed like diff looks like this:
+      // {first}[,{last}]c{first}[,{last}]
+      // {first}a{first}[,{last}]
+      // {first}[,{last}]d{first}
+      //
+      // unified diff looks like this:
+      // --- file1       2018-03-20 13:23:35.783153140 +0100
+      // +++ file2       2018-03-20 13:23:41.183156066 +0100
+      // @@ -1,3 +1,5 @@
+      if (isdigit(*line)) {
+        diffstyle = DIFF_ED;
+      } else if ((STRNCMP(line, "@@ ", 3) == 0)) {
+        diffstyle = DIFF_UNIFIED;
+      } else if ((STRNCMP(line, "--- ", 4) == 0)
+                 && (vim_fgets(linebuf, LBUFLEN, fd) == 0)
+                 && (STRNCMP(line, "+++ ", 4) == 0)
+                 && (vim_fgets(linebuf, LBUFLEN, fd) == 0)
+                 && (STRNCMP(line, "@@ ", 3) == 0)) {
+        diffstyle = DIFF_UNIFIED;
+      } else {
+        // Format not recognized yet, skip over this line.  Cygwin diff
+        // may put a warning at the start of the file.
+        continue;
+      }
     }
 
-    if (difftype == 'd') {
-      lnum_new = f2 + 1;
-      count_new = 0;
+    if (diffstyle == DIFF_ED) {
+      if (!isdigit(*line)) {
+        continue;   // not the start of a diff block
+      }
+      if (parse_diff_ed(line, &lnum_orig, &count_orig,
+                        &lnum_new, &count_new) == FAIL) {
+        continue;
+      }
+    } else if (diffstyle == DIFF_UNIFIED) {
+      if (STRNCMP(line, "@@ ", 3)  != 0) {
+        continue;   // not the start of a diff block
+      }
+      if (parse_diff_unified(line, &lnum_orig, &count_orig,
+                             &lnum_new, &count_new) == FAIL) {
+        continue;
+      }
     } else {
-      lnum_new = f2;
-      count_new = l2 - f2 + 1;
+      EMSG(_("E959: Invalid diff format."));
+      break;
     }
 
     // Go over blocks before the change, for which orig and new are equal.
@@ -1304,7 +1587,7 @@ static void diff_read(int idx_orig, int idx_new, char_u *fname)
       }
       dprev = dp;
       dp = dp->df_next;
-      notset = TRUE;
+      notset = true;
     }
 
     if ((dp != NULL)
@@ -1391,7 +1674,7 @@ static void diff_read(int idx_orig, int idx_new, char_u *fname)
         }
       }
     }
-    notset = FALSE; // "*dp" has been set
+    notset = false;  // "*dp" has been set
   }
 
   // for remaining diff blocks orig and new are equal
@@ -1401,10 +1684,12 @@ static void diff_read(int idx_orig, int idx_new, char_u *fname)
     }
     dprev = dp;
     dp = dp->df_next;
-    notset = TRUE;
+    notset = true;
   }
 
-  fclose(fd);
+  if (fd != NULL) {
+    fclose(fd);
+  }
 }
 
 /// Copy an entry at "dp" from "idx_orig" to "idx_new".
@@ -1503,23 +1788,23 @@ int diff_check(win_T *wp, linenr_T lnum)
   }
 
   if (lnum < dp->df_lnum[idx] + dp->df_count[idx]) {
-    int zero = FALSE;
+    int zero = false;
 
     // Changed or inserted line.  If the other buffers have a count of
     // zero, the lines were inserted.  If the other buffers have the same
     // count, check if the lines are identical.
-    cmp = FALSE;
+    cmp = false;
 
     for (i = 0; i < DB_COUNT; ++i) {
       if ((i != idx) && (curtab->tp_diffbuf[i] != NULL)) {
         if (dp->df_count[i] == 0) {
-          zero = TRUE;
+          zero = true;
         } else {
           if (dp->df_count[i] != dp->df_count[idx]) {
             // nr of lines changed.
             return -1;
           }
-          cmp = TRUE;
+          cmp = true;
         }
       }
     }
@@ -1543,7 +1828,7 @@ int diff_check(win_T *wp, linenr_T lnum)
     // the difference.  Can't remove the entry here, we might be halfway
     // through updating the window.  Just report the text as unchanged.
     // Other windows might still show the change though.
-    if (zero == FALSE) {
+    if (zero == false) {
       return 0;
     }
     return -2;
@@ -1635,20 +1920,28 @@ static bool diff_equal_char(const char_u *const p1, const char_u *const p2,
 /// @return on-zero if the two strings are different.
 static int diff_cmp(char_u *s1, char_u *s2)
 {
-  if ((diff_flags & (DIFF_ICASE | DIFF_IWHITE)) == 0) {
+  if ((diff_flags & DIFF_IBLANK)
+      && (*skipwhite(s1) == NUL || *skipwhite(s2) == NUL)) {
+    return 0;
+  }
+
+  if ((diff_flags & (DIFF_ICASE | ALL_WHITE_DIFF)) == 0) {
     return STRCMP(s1, s2);
   }
 
-  if ((diff_flags & DIFF_ICASE) && !(diff_flags & DIFF_IWHITE)) {
+  if ((diff_flags & DIFF_ICASE) && !(diff_flags & ALL_WHITE_DIFF)) {
     return mb_stricmp((const char *)s1, (const char *)s2);
   }
 
-  // Ignore white space changes and possibly ignore case.
   char_u *p1 = s1;
   char_u *p2 = s2;
 
+  // Ignore white space changes and possibly ignore case.
   while (*p1 != NUL && *p2 != NUL) {
-    if (ascii_iswhite(*p1) && ascii_iswhite(*p2)) {
+    if (((diff_flags & DIFF_IWHITE)
+         && ascii_iswhite(*p1) && ascii_iswhite(*p2))
+        || ((diff_flags & DIFF_IWHITEALL)
+            && (ascii_iswhite(*p1) || ascii_iswhite(*p2)))) {
       p1 = skipwhite(p1);
       p2 = skipwhite(p2);
     } else {
@@ -1815,6 +2108,8 @@ int diffopt_changed(void)
   int diff_context_new = 6;
   int diff_flags_new = 0;
   int diff_foldcolumn_new = 2;
+  long diff_algorithm_new = 0;
+  long diff_indent_heuristic = 0;
 
   char_u *p = p_dip;
   while (*p != NUL) {
@@ -1824,9 +2119,18 @@ int diffopt_changed(void)
     } else if ((STRNCMP(p, "context:", 8) == 0) && ascii_isdigit(p[8])) {
       p += 8;
       diff_context_new = getdigits_int(&p);
+    } else if (STRNCMP(p, "iblank", 6) == 0) {
+      p += 6;
+      diff_flags_new |= DIFF_IBLANK;
     } else if (STRNCMP(p, "icase", 5) == 0) {
       p += 5;
       diff_flags_new |= DIFF_ICASE;
+    } else if (STRNCMP(p, "iwhiteall", 9) == 0) {
+      p += 9;
+      diff_flags_new |= DIFF_IWHITEALL;
+    } else if (STRNCMP(p, "iwhiteeol", 9) == 0) {
+      p += 9;
+      diff_flags_new |= DIFF_IWHITEEOL;
     } else if (STRNCMP(p, "iwhite", 6) == 0) {
       p += 6;
       diff_flags_new |= DIFF_IWHITE;
@@ -1842,6 +2146,29 @@ int diffopt_changed(void)
     } else if (STRNCMP(p, "hiddenoff", 9) == 0) {
       p += 9;
       diff_flags_new |= DIFF_HIDDEN_OFF;
+    } else if (STRNCMP(p, "indent-heuristic", 16) == 0) {
+      p += 16;
+      diff_indent_heuristic = XDF_INDENT_HEURISTIC;
+    } else if (STRNCMP(p, "internal", 8) == 0) {
+      p += 8;
+      diff_flags_new |= DIFF_INTERNAL;
+    } else if (STRNCMP(p, "algorithm:", 10) == 0) {
+      p += 10;
+      if (STRNCMP(p, "myers", 5) == 0) {
+        p += 5;
+        diff_algorithm_new = 0;
+      } else if (STRNCMP(p, "minimal", 7) == 0) {
+        p += 7;
+        diff_algorithm_new = XDF_NEED_MINIMAL;
+      } else if (STRNCMP(p, "patience", 8) == 0) {
+        p += 8;
+        diff_algorithm_new = XDF_PATIENCE_DIFF;
+      } else if (STRNCMP(p, "histogram", 9) == 0) {
+        p += 9;
+        diff_algorithm_new = XDF_HISTOGRAM_DIFF;
+      } else {
+        return FAIL;
+      }
     }
 
     if ((*p != ',') && (*p != NUL)) {
@@ -1853,23 +2180,27 @@ int diffopt_changed(void)
     }
   }
 
+  diff_algorithm_new |= diff_indent_heuristic;
+
   // Can't have both "horizontal" and "vertical".
   if ((diff_flags_new & DIFF_HORIZONTAL) && (diff_flags_new & DIFF_VERTICAL)) {
     return FAIL;
   }
 
-  // If "icase" or "iwhite" was added or removed, need to update the diff.
-  if (diff_flags != diff_flags_new) {
+  // If flags were added or removed, or the algorithm was changed, need to
+  // update the diff.
+  if (diff_flags != diff_flags_new || diff_algorithm != diff_algorithm_new) {
     FOR_ALL_TABS(tp) {
-      tp->tp_diff_invalid = TRUE;
+      tp->tp_diff_invalid = true;
     }
   }
 
   diff_flags = diff_flags_new;
   diff_context = diff_context_new;
   diff_foldcolumn = diff_foldcolumn_new;
+  diff_algorithm = diff_algorithm_new;
 
-  diff_redraw(TRUE);
+  diff_redraw(true);
 
   // recompute the scroll binding with the new option value, may
   // remove or add filler lines
@@ -1910,7 +2241,7 @@ bool diff_find_change(win_T *wp, linenr_T lnum, int *startp, int *endp)
   int l;
 
   // Make a copy of the line, the next ml_get() will invalidate it.
-  char_u *line_org = vim_strsave(ml_get_buf(wp->w_buffer, lnum, FALSE));
+  char_u *line_org = vim_strsave(ml_get_buf(wp->w_buffer, lnum, false));
 
   int idx = diff_buf_idx(wp->w_buffer);
   if (idx == DB_COUNT) {
@@ -1942,15 +2273,18 @@ bool diff_find_change(win_T *wp, linenr_T lnum, int *startp, int *endp)
       }
       added = false;
       line_new = ml_get_buf(curtab->tp_diffbuf[i],
-                            dp->df_lnum[i] + off, FALSE);
+                            dp->df_lnum[i] + off, false);
 
       // Search for start of difference
       si_org = si_new = 0;
 
       while (line_org[si_org] != NUL) {
-        if ((diff_flags & DIFF_IWHITE)
-            && ascii_iswhite(line_org[si_org])
-            && ascii_iswhite(line_new[si_new])) {
+        if (((diff_flags & DIFF_IWHITE)
+             && ascii_iswhite(line_org[si_org])
+             && ascii_iswhite(line_new[si_new]))
+            || ((diff_flags & DIFF_IWHITEALL)
+                && (ascii_iswhite(line_org[si_org])
+                    || ascii_iswhite(line_new[si_new])))) {
           si_org = (int)(skipwhite(line_org + si_org) - line_org);
           si_new = (int)(skipwhite(line_new + si_new) - line_new);
         } else {
@@ -1980,9 +2314,12 @@ bool diff_find_change(win_T *wp, linenr_T lnum, int *startp, int *endp)
                && ei_new >= si_new
                && ei_org >= 0
                && ei_new >= 0) {
-          if ((diff_flags & DIFF_IWHITE)
-              && ascii_iswhite(line_org[ei_org])
-              && ascii_iswhite(line_new[ei_new])) {
+          if (((diff_flags & DIFF_IWHITE)
+               && ascii_iswhite(line_org[ei_org])
+               && ascii_iswhite(line_new[ei_new]))
+              || ((diff_flags & DIFF_IWHITEALL)
+                  && (ascii_iswhite(line_org[ei_org])
+                      || ascii_iswhite(line_new[ei_new])))) {
             while (ei_org >= *startp && ascii_iswhite(line_org[ei_org])) {
               ei_org--;
             }
@@ -2117,7 +2454,7 @@ void ex_diffgetput(exarg_T *eap)
   int start_skip, end_skip;
   int new_count;
   int buf_empty;
-  int found_not_ma = FALSE;
+  int found_not_ma = false;
   int idx_other;
   int idx_from;
   int idx_to;
@@ -2138,7 +2475,7 @@ void ex_diffgetput(exarg_T *eap)
             || MODIFIABLE(curtab->tp_diffbuf[idx_other])) {
           break;
         }
-        found_not_ma = TRUE;
+        found_not_ma = true;
       }
     }
 
@@ -2176,7 +2513,7 @@ void ex_diffgetput(exarg_T *eap)
       // digits only
       i = atol((char *)eap->arg);
     } else {
-      i = buflist_findpat(eap->arg, p, FALSE, TRUE, FALSE);
+      i = buflist_findpat(eap->arg, p, false, true, false);
 
       if (i < 0) {
         // error message already given
@@ -2202,7 +2539,7 @@ void ex_diffgetput(exarg_T *eap)
     }
   }
 
-  diff_busy = TRUE;
+  diff_busy = true;
 
   // When no range given include the line above or below the cursor.
   if (eap->addr_count == 0) {
@@ -2239,7 +2576,7 @@ void ex_diffgetput(exarg_T *eap)
     change_warning(0);
     if (diff_buf_idx(curbuf) != idx_to) {
       EMSG(_("E787: Buffer changed unexpectedly"));
-      return;
+      goto theend;
     }
   }
 
@@ -2308,7 +2645,7 @@ void ex_diffgetput(exarg_T *eap)
       for (i = 0; i < count; ++i) {
         // remember deleting the last line of the buffer
         buf_empty = curbuf->b_ml.ml_line_count == 1;
-        ml_delete(lnum, FALSE);
+        ml_delete(lnum, false);
         added--;
       }
 
@@ -2317,15 +2654,15 @@ void ex_diffgetput(exarg_T *eap)
         if (nr > curtab->tp_diffbuf[idx_from]->b_ml.ml_line_count) {
           break;
         }
-        p = vim_strsave(ml_get_buf(curtab->tp_diffbuf[idx_from], nr, FALSE));
-        ml_append(lnum + i - 1, p, 0, FALSE);
+        p = vim_strsave(ml_get_buf(curtab->tp_diffbuf[idx_from], nr, false));
+        ml_append(lnum + i - 1, p, 0, false);
         xfree(p);
         added++;
         if (buf_empty && (curbuf->b_ml.ml_line_count == 2)) {
           // Added the first line into an empty buffer, need to
           // delete the dummy empty line.
-          buf_empty = FALSE;
-          ml_delete((linenr_T)2, FALSE);
+          buf_empty = false;
+          ml_delete((linenr_T)2, false);
         }
       }
       new_count = dp->df_count[idx_to] + added;
@@ -2399,20 +2736,31 @@ void ex_diffgetput(exarg_T *eap)
     // another buffer.  Sync undo if the command was typed.  This isn't
     // 100% right when ":diffput" is used in a function or mapping.
     if (KeyTyped) {
-      u_sync(FALSE);
+      u_sync(false);
     }
     aucmd_restbuf(&aco);
   }
 
-  diff_busy = FALSE;
+theend:
+  diff_busy = false;
+  if (diff_need_update) {
+    ex_diffupdate(NULL);
+  }
 
-  // Check that the cursor is on a valid character and update it's position.
-  // When there were filler lines the topline has become invalid.
+  // Check that the cursor is on a valid character and update its
+  // position.  When there were filler lines the topline has become
+  // invalid.
   check_cursor();
   changed_line_abv_curs();
 
-  // Also need to redraw the other buffers.
-  diff_redraw(FALSE);
+  if (diff_need_update) {
+    // redraw already done by ex_diffupdate()
+    diff_need_update = false;
+  } else {
+    // Also need to redraw the other buffers.
+    diff_redraw(false);
+    apply_autocmds(EVENT_DIFFUPDATED, NULL, NULL, false, curbuf);
+  }
 }
 
 /// Update folds for all diff buffers for entry "dp".
@@ -2637,3 +2985,145 @@ linenr_T diff_lnum_win(linenr_T lnum, win_T *wp)
   }
   return n;
 }
+
+///
+/// Handle an ED style diff line.
+/// Return FAIL if the line does not contain diff info.
+///
+static int parse_diff_ed(char_u     *line,
+                         linenr_T    *lnum_orig,
+                         long       *count_orig,
+                         linenr_T    *lnum_new,
+                         long       *count_new)
+{
+  char_u *p;
+  long    f1, l1, f2, l2;
+  int       difftype;
+
+  // The line must be one of three formats:
+  // change: {first}[,{last}]c{first}[,{last}]
+  // append: {first}a{first}[,{last}]
+  // delete: {first}[,{last}]d{first}
+  p = line;
+  f1 = getdigits(&p);
+  if (*p == ',') {
+    p++;
+    l1 = getdigits(&p);
+  } else {
+    l1 = f1;
+  }
+  if (*p != 'a' && *p != 'c' && *p != 'd') {
+    return FAIL;        // invalid diff format
+  }
+  difftype = *p++;
+  f2 = getdigits(&p);
+  if (*p == ',') {
+    p++;
+    l2 = getdigits(&p);
+  } else {
+    l2 = f2;
+  }
+  if (l1 < f1 || l2 < f2) {
+    return FAIL;
+  }
+
+  if (difftype == 'a') {
+    *lnum_orig = f1 + 1;
+    *count_orig = 0;
+  } else {
+    *lnum_orig = f1;
+    *count_orig = l1 - f1 + 1;
+  }
+  if (difftype == 'd') {
+    *lnum_new = f2 + 1;
+    *count_new = 0;
+  } else {
+    *lnum_new = f2;
+    *count_new = l2 - f2 + 1;
+  }
+  return OK;
+}
+
+///
+/// Parses unified diff with zero(!) context lines.
+/// Return FAIL if there is no diff information in "line".
+///
+static int parse_diff_unified(char_u        *line,
+                              linenr_T    *lnum_orig,
+                              long      *count_orig,
+                              linenr_T    *lnum_new,
+                              long      *count_new)
+{
+  char_u *p;
+  long    oldline, oldcount, newline, newcount;
+
+  // Parse unified diff hunk header:
+  // @@ -oldline,oldcount +newline,newcount @@
+  p = line;
+  if (*p++ == '@' && *p++ == '@' && *p++ == ' ' && *p++ == '-') {
+    oldline = getdigits(&p);
+    if (*p == ',') {
+      p++;
+      oldcount = getdigits(&p);
+    } else {
+      oldcount = 1;
+    }
+    if (*p++ == ' ' && *p++ == '+') {
+      newline = getdigits(&p);
+      if (*p == ',') {
+        p++;
+        newcount = getdigits(&p);
+      } else {
+        newcount = 1;
+      }
+    } else {
+      return FAIL;  // invalid diff format
+    }
+
+    if (oldcount == 0) {
+      oldline += 1;
+    }
+    if (newcount == 0) {
+      newline += 1;
+    }
+    if (newline == 0) {
+      newline = 1;
+    }
+
+    *lnum_orig = oldline;
+    *count_orig = oldcount;
+    *lnum_new = newline;
+    *count_new = newcount;
+
+    return OK;
+  }
+
+  return FAIL;
+}
+
+///
+/// Callback function for the xdl_diff() function.
+/// Stores the diff output in a grow array.
+///
+static int xdiff_out(void *priv, mmbuffer_t *mb, int nbuf)
+{
+  diffout_T *dout = (diffout_T *)priv;
+  char_u    *p;
+
+  // The header line always comes by itself, text lines in at least two
+  // parts.  We drop the text part.
+  if (nbuf > 1) {
+    return 0;
+  }
+
+  // sanity check
+  if (STRNCMP(mb[0].ptr, "@@ ", 3)  != 0) {
+    return 0;
+  }
+
+  ga_grow(&dout->dout_ga, 1);
+
+  p = vim_strnsave((char_u *)mb[0].ptr, mb[0].size);
+  ((char_u **)dout->dout_ga.ga_data)[dout->dout_ga.ga_len++] = p;
+  return 0;
+}
diff --git a/src/nvim/fileio.c b/src/nvim/fileio.c
index 7e8a7d1a35..8e5455bc67 100644
--- a/src/nvim/fileio.c
+++ b/src/nvim/fileio.c
@@ -1739,13 +1739,13 @@ failed:
     close(0);
 #ifndef WIN32
     // On Unix, use stderr for stdin, makes shell commands work.
-    ignored = dup(2);
+    vim_ignored = dup(2);
 #else
     // On Windows, use the console input handle for stdin.
     HANDLE conin = CreateFile("CONIN$", GENERIC_READ | GENERIC_WRITE,
                               FILE_SHARE_READ, (LPSECURITY_ATTRIBUTES)NULL,
                               OPEN_EXISTING, 0, (HANDLE)NULL);
-    ignored = _open_osfhandle(conin, _O_RDONLY);
+    vim_ignored = _open_osfhandle(conin, _O_RDONLY);
 #endif
   }
 
diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index df74e8b2ff..04ff1320ce 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -1125,8 +1125,7 @@ EXTERN FILE *time_fd INIT(= NULL);  /* where to write startup timing */
  * can't do anything useful with the value.  Assign to this variable to avoid
  * the warning.
  */
-EXTERN int ignored;
-EXTERN char *ignoredp;
+EXTERN int vim_ignored;
 
 // Start a msgpack-rpc channel over stdin/stdout.
 EXTERN bool embedded_mode INIT(= false);
diff --git a/src/nvim/misc1.c b/src/nvim/misc1.c
index d4a406cdba..d77c196a3a 100644
--- a/src/nvim/misc1.c
+++ b/src/nvim/misc1.c
@@ -1953,10 +1953,10 @@ changed_lines(
 {
   changed_lines_buf(curbuf, lnum, lnume, xtra);
 
-  if (xtra == 0 && curwin->w_p_diff) {
-    /* When the number of lines doesn't change then mark_adjust() isn't
-     * called and other diff buffers still need to be marked for
-     * displaying. */
+  if (xtra == 0 && curwin->w_p_diff && !diff_internal()) {
+    // When the number of lines doesn't change then mark_adjust() isn't
+    // called and other diff buffers still need to be marked for
+    // displaying.
     linenr_T wlnum;
 
     FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
@@ -2025,6 +2025,10 @@ static void changed_common(linenr_T lnum, colnr_T col, linenr_T lnume, long xtra
   /* mark the buffer as modified */
   changed();
 
+  if (curwin->w_p_diff && diff_internal()) {
+    curtab->tp_diff_update = true;
+  }
+
   /* set the '. mark */
   if (!cmdmod.keepjumps) {
     RESET_FMARK(&curbuf->b_last_change, ((pos_T) {lnum, col, 0}), 0);
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index f87de52a82..38ee0936aa 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -1325,6 +1325,14 @@ static int normal_check(VimState *state)
     normal_check_cursor_moved(s);
     normal_check_text_changed(s);
 
+    // Updating diffs from changed() does not always work properly,
+    // esp. updating folds.  Do an update just before redrawing if
+    // needed.
+    if (curtab->tp_diff_update || curtab->tp_diff_invalid) {
+      ex_diffupdate(NULL);
+      curtab->tp_diff_update = false;
+    }
+
     // Scroll-binding for diff mode may have been postponed until
     // here.  Avoids doing it for every change.
     if (diff_need_scrollbind) {
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index b0575df7ec..0cc6f58c5f 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -615,7 +615,7 @@ return {
       alloced=true,
       redraw={'current_window'},
       varname='p_dip',
-      defaults={if_true={vi="filler"}}
+      defaults={if_true={vi="internal,filler"}}
     },
     {
       full_name='digraph', abbreviation='dg',
diff --git a/src/nvim/testdir/test_diffmode.vim b/src/nvim/testdir/test_diffmode.vim
index afe289b262..ad3eec3274 100644
--- a/src/nvim/testdir/test_diffmode.vim
+++ b/src/nvim/testdir/test_diffmode.vim
@@ -2,6 +2,9 @@
 
 func Test_diff_fold_sync()
   enew!
+  let g:update_count = 0
+  au DiffUpdated * let g:update_count += 1
+
   let l = range(50)
   call setline(1, l)
   diffthis
@@ -27,12 +30,27 @@ func Test_diff_fold_sync()
   call win_gotoid(winone)
   call assert_equal(23, getcurpos()[1])
 
+  call assert_equal(1, g:update_count)
+  au! DiffUpdated
+
   windo diffoff
   close!
   set nomodified
 endfunc
 
 func Test_vert_split()
+  set diffopt=filler
+  call Common_vert_split()
+  set diffopt&
+endfunc
+
+func Test_vert_split_internal()
+  set diffopt=internal,filler
+  call Common_vert_split()
+  set diffopt&
+endfunc
+
+func Common_vert_split()
   " Disable the title to avoid xterm keeping the wrong one.
   set notitle noicon
   new
@@ -201,6 +219,26 @@ func Test_diffget_diffput()
   %bwipe!
 endfunc
 
+" Test putting two changes from one buffer to another
+func Test_diffput_two()
+  new a
+  let win_a = win_getid()
+  call setline(1, range(1, 10))
+  diffthis
+  new b
+  let win_b = win_getid()
+  call setline(1, range(1, 10))
+  8del
+  5del
+  diffthis
+  call win_gotoid(win_a)
+  %diffput
+  call win_gotoid(win_b)
+  call assert_equal(map(range(1, 10), 'string(v:val)'), getline(1, '$'))
+  bwipe! a
+  bwipe! b
+endfunc
+
 func Test_dp_do_buffer()
   e! one
   let bn1=bufnr('%')
@@ -257,6 +295,28 @@ func Test_dp_do_buffer()
   %bwipe!
 endfunc
 
+func Test_do_lastline()
+  e! one
+  call setline(1, ['1','2','3','4','5','6'])
+  diffthis
+
+  new two
+  call setline(1, ['2','4','5'])
+  diffthis
+
+  1
+  norm dp]c
+  norm dp]c
+  wincmd w
+  call assert_equal(4, line('$'))
+  norm G
+  norm do
+  call assert_equal(3, line('$'))
+
+  windo diffoff
+  %bwipe!
+endfunc
+
 func Test_diffoff()
   enew!
   call setline(1, ['Two', 'Three'])
@@ -275,10 +335,8 @@ func Test_diffoff()
   bwipe!
 endfunc
 
-func Test_diffopt_icase()
-  set diffopt=icase,foldcolumn:0
-
-  e one
+func Common_icase_test()
+  edit one
   call setline(1, ['One', 'Two', 'Three', 'Four', 'Fi#ve'])
   redraw
   let normattr = screenattr(1, 1)
@@ -300,32 +358,54 @@ func Test_diffopt_icase()
 
   diffoff!
   %bwipe!
+endfunc
+
+func Test_diffopt_icase()
+  set diffopt=icase,foldcolumn:0
+  call Common_icase_test()
   set diffopt&
 endfunc
 
-func Test_diffopt_iwhite()
-  set diffopt=iwhite,foldcolumn:0
+func Test_diffopt_icase_internal()
+  set diffopt=icase,foldcolumn:0,internal
+  call Common_icase_test()
+  set diffopt&
+endfunc
 
-  e one
-  " Difference in trailing spaces should be ignored,
+func Common_iwhite_test()
+  edit one
+  " Difference in trailing spaces and amount of spaces should be ignored,
   " but not other space differences.
-  call setline(1, ["One \t", 'Two', 'Three', 'Four'])
+  call setline(1, ["One \t", 'Two', 'Three', 'one two', 'one two', 'Four'])
   redraw
   let normattr = screenattr(1, 1)
   diffthis
 
   botright vert new two
-  call setline(1, ["One\t ", "Two\t ", 'Three', ' Four'])
+  call setline(1, ["One\t ", "Two\t ", 'Three', 'one   two', 'onetwo', ' Four'])
   diffthis
 
   redraw
   call assert_equal(normattr, screenattr(1, 1))
   call assert_equal(normattr, screenattr(2, 1))
   call assert_equal(normattr, screenattr(3, 1))
-  call assert_notequal(normattr, screenattr(4, 1))
+  call assert_equal(normattr, screenattr(4, 1))
+  call assert_notequal(normattr, screenattr(5, 1))
+  call assert_notequal(normattr, screenattr(6, 1))
 
   diffoff!
   %bwipe!
+endfunc
+
+func Test_diffopt_iwhite()
+  set diffopt=iwhite,foldcolumn:0
+  call Common_iwhite_test()
+  set diffopt&
+endfunc
+
+func Test_diffopt_iwhite_internal()
+  set diffopt=internal,iwhite,foldcolumn:0
+  call Common_iwhite_test()
   set diffopt&
 endfunc
 
@@ -339,8 +419,13 @@ func Test_diffopt_context()
 
   set diffopt=context:2
   call assert_equal('+--  2 lines: 1', foldtextresult(1))
+  set diffopt=internal,context:2
+  call assert_equal('+--  2 lines: 1', foldtextresult(1))
+
   set diffopt=context:1
   call assert_equal('+--  3 lines: 1', foldtextresult(1))
+  set diffopt=internal,context:1
+  call assert_equal('+--  3 lines: 1', foldtextresult(1))
 
   diffoff!
   %bwipe!
@@ -348,7 +433,7 @@ func Test_diffopt_context()
 endfunc
 
 func Test_diffopt_horizontal()
-  set diffopt=horizontal
+  set diffopt=internal,horizontal
   diffsplit
 
   call assert_equal(&columns, winwidth(1))
@@ -362,7 +447,7 @@ func Test_diffopt_horizontal()
 endfunc
 
 func Test_diffopt_vertical()
-  set diffopt=vertical
+  set diffopt=internal,vertical
   diffsplit
 
   call assert_equal(&lines - 2, winheight(1))
@@ -376,7 +461,7 @@ func Test_diffopt_vertical()
 endfunc
 
 func Test_diffopt_hiddenoff()
-  set diffopt=filler,foldcolumn:0,hiddenoff
+  set diffopt=internal,filler,foldcolumn:0,hiddenoff
   e! one
   call setline(1, ['Two', 'Three'])
   redraw
@@ -399,7 +484,7 @@ func Test_diffopt_hiddenoff()
 endfunc
 
 func Test_diffoff_hidden()
-  set diffopt=filler,foldcolumn:0
+  set diffopt=internal,filler,foldcolumn:0
   e! one
   call setline(1, ['Two', 'Three'])
   redraw
@@ -480,7 +565,9 @@ func Test_diffexpr()
   endif
 
   func DiffExpr()
-    silent exe '!diff ' . v:fname_in . ' ' . v:fname_new . '>' . v:fname_out
+    " Prepend some text to check diff type detection
+    call writefile(['warning', '  message'], v:fname_out)
+    silent exe '!diff ' . v:fname_in . ' ' . v:fname_new . '>>' . v:fname_out
   endfunc
   set diffexpr=DiffExpr()
   set diffopt=foldcolumn:0
@@ -523,7 +610,7 @@ func Test_diffpatch()
   3
 + 4
 .
-  saveas Xpatch
+  saveas! Xpatch
   bwipe!
   new
   call assert_fails('diffpatch Xpatch', 'E816:')
@@ -569,6 +656,22 @@ func Test_diff_nomodifiable()
   %bwipe!
 endfunc
 
+func Test_diff_filler()
+  new
+  call setline(1, [1, 2, 3, 'x', 4])
+  diffthis
+  vnew
+  call setline(1, [1, 2, 'y', 'y', 3, 4])
+  diffthis
+  redraw
+
+  call assert_equal([0, 0, 0, 0, 0, 0, 0, 1, 0], map(range(-1, 7), 'diff_filler(v:val)'))
+  wincmd w
+  call assert_equal([0, 0, 0, 0, 2, 0, 0, 0], map(range(-1, 6), 'diff_filler(v:val)'))
+
+  %bwipe!
+endfunc
+
 func Test_diff_lastline()
   enew!
   only!
@@ -615,3 +718,23 @@ func Test_diff_with_cursorline()
   call StopVimInTerminal(buf)
   call delete('Xtest_diff_cursorline')
 endfunc
+
+func Test_diff_of_diff()
+  if !CanRunVimInTerminal()
+    return
+  endif
+
+  call writefile([
+	\ 'call setline(1, ["aa","bb","cc","@@ -3,2 +5,7 @@","dd","ee","ff"])',
+	\ 'vnew',
+	\ 'call setline(1, ["aa","bb","cc"])',
+	\ 'windo diffthis',
+	\ ], 'Xtest_diff_diff')
+  let buf = RunVimInTerminal('-S Xtest_diff_diff', {})
+
+  call VerifyScreenDump(buf, 'Test_diff_of_diff_01', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('Xtest_diff_diff')
+endfunc
diff --git a/src/nvim/xdiff/COPYING b/src/nvim/xdiff/COPYING
new file mode 100644
index 0000000000..f3f1b3b65e
--- /dev/null
+++ b/src/nvim/xdiff/COPYING
@@ -0,0 +1,504 @@
+		  GNU LESSER GENERAL PUBLIC LICENSE
+		       Version 2.1, February 1999
+
+ Copyright (C) 1991, 1999 Free Software Foundation, Inc.
+     59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ Everyone is permitted to copy and distribute verbatim copies
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+[This is the first released version of the Lesser GPL.  It also counts
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+and reuse of software generally.
+
+			    NO WARRANTY
+
+  15. BECAUSE THE LIBRARY IS LICENSED FREE OF CHARGE, THERE IS NO
+WARRANTY FOR THE LIBRARY, TO THE EXTENT PERMITTED BY APPLICABLE LAW.
+EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR
+OTHER PARTIES PROVIDE THE LIBRARY "AS IS" WITHOUT WARRANTY OF ANY
+KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE
+LIBRARY IS WITH YOU.  SHOULD THE LIBRARY PROVE DEFECTIVE, YOU ASSUME
+THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
+WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY
+AND/OR REDISTRIBUTE THE LIBRARY AS PERMITTED ABOVE, BE LIABLE TO YOU
+FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
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+LIBRARY (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING
+RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A
+FAILURE OF THE LIBRARY TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF
+SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+DAMAGES.
+
+		     END OF TERMS AND CONDITIONS
+
+           How to Apply These Terms to Your New Libraries
+
+  If you develop a new library, and you want it to be of the greatest
+possible use to the public, we recommend making it free software that
+everyone can redistribute and change.  You can do so by permitting
+redistribution under these terms (or, alternatively, under the terms of the
+ordinary General Public License).
+
+  To apply these terms, attach the following notices to the library.  It is
+safest to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least the
+"copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the library's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This library is free software; you can redistribute it and/or
+    modify it under the terms of the GNU Lesser General Public
+    License as published by the Free Software Foundation; either
+    version 2.1 of the License, or (at your option) any later version.
+
+    This library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+    Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public
+    License along with this library; if not, write to the Free Software
+    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+Also add information on how to contact you by electronic and paper mail.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the library, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the
+  library `Frob' (a library for tweaking knobs) written by James Random Hacker.
+
+  <signature of Ty Coon>, 1 April 1990
+  Ty Coon, President of Vice
+
+That's all there is to it!
+
+
diff --git a/src/nvim/xdiff/README.txt b/src/nvim/xdiff/README.txt
new file mode 100644
index 0000000000..1afe74095b
--- /dev/null
+++ b/src/nvim/xdiff/README.txt
@@ -0,0 +1,16 @@
+The files in this directory come from the xdiff implementation in git.
+You can find it here: https://github.com/git/git/tree/master/xdiff
+The files were last updated 2018 September 10.
+
+This is originally based on libxdiff, which can be found here:
+http://www.xmailserver.org/xdiff-lib.html
+
+The git version was used because it has been maintained and improved.
+And since it's part of git it is expected to be reliable.
+
+The code is distributed under the GNU LGPL license.  It is included in the
+COPYING file.
+
+Changes in these files were made to avoid compiler warnings.
+
+The first work for including xdiff in Vim was done by Christian Brabandt.
diff --git a/src/nvim/xdiff/xdiff.h b/src/nvim/xdiff/xdiff.h
new file mode 100644
index 0000000000..bc26fb64fd
--- /dev/null
+++ b/src/nvim/xdiff/xdiff.h
@@ -0,0 +1,143 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XDIFF_H)
+#define XDIFF_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* #ifdef __cplusplus */
+
+/* xpparm_t.flags */
+#define XDF_NEED_MINIMAL (1 << 0)
+
+#define XDF_IGNORE_WHITESPACE (1 << 1)
+#define XDF_IGNORE_WHITESPACE_CHANGE (1 << 2)
+#define XDF_IGNORE_WHITESPACE_AT_EOL (1 << 3)
+#define XDF_IGNORE_CR_AT_EOL (1 << 4)
+#define XDF_WHITESPACE_FLAGS (XDF_IGNORE_WHITESPACE | \
+			      XDF_IGNORE_WHITESPACE_CHANGE | \
+			      XDF_IGNORE_WHITESPACE_AT_EOL | \
+			      XDF_IGNORE_CR_AT_EOL)
+
+#define XDF_IGNORE_BLANK_LINES (1 << 7)
+
+#define XDF_PATIENCE_DIFF (1 << 14)
+#define XDF_HISTOGRAM_DIFF (1 << 15)
+#define XDF_DIFF_ALGORITHM_MASK (XDF_PATIENCE_DIFF | XDF_HISTOGRAM_DIFF)
+#define XDF_DIFF_ALG(x) ((x) & XDF_DIFF_ALGORITHM_MASK)
+
+#define XDF_INDENT_HEURISTIC (1 << 23)
+
+/* xdemitconf_t.flags */
+#define XDL_EMIT_FUNCNAMES (1 << 0)
+#define XDL_EMIT_FUNCCONTEXT (1 << 2)
+
+/* merge simplification levels */
+#define XDL_MERGE_MINIMAL 0
+#define XDL_MERGE_EAGER 1
+#define XDL_MERGE_ZEALOUS 2
+#define XDL_MERGE_ZEALOUS_ALNUM 3
+
+/* merge favor modes */
+#define XDL_MERGE_FAVOR_OURS 1
+#define XDL_MERGE_FAVOR_THEIRS 2
+#define XDL_MERGE_FAVOR_UNION 3
+
+/* merge output styles */
+#define XDL_MERGE_DIFF3 1
+
+typedef struct s_mmfile {
+	char *ptr;
+	long size;
+} mmfile_t;
+
+typedef struct s_mmbuffer {
+	char *ptr;
+	long size;
+} mmbuffer_t;
+
+typedef struct s_xpparam {
+	unsigned long flags;
+
+	/* See Documentation/diff-options.txt. */
+	char **anchors;
+	size_t anchors_nr;
+} xpparam_t;
+
+typedef struct s_xdemitcb {
+	void *priv;
+	int (*outf)(void *, mmbuffer_t *, int);
+} xdemitcb_t;
+
+typedef long (*find_func_t)(const char *line, long line_len, char *buffer, long buffer_size, void *priv);
+
+typedef int (*xdl_emit_hunk_consume_func_t)(long start_a, long count_a,
+					    long start_b, long count_b,
+					    void *cb_data);
+
+typedef struct s_xdemitconf {
+	long ctxlen;
+	long interhunkctxlen;
+	unsigned long flags;
+	find_func_t find_func;
+	void *find_func_priv;
+	xdl_emit_hunk_consume_func_t hunk_func;
+} xdemitconf_t;
+
+typedef struct s_bdiffparam {
+	long bsize;
+} bdiffparam_t;
+
+#include "../memory.h"
+
+#define xdl_malloc(x) xmalloc((x))
+#define xdl_free(ptr) xfree(ptr)
+#define xdl_realloc(ptr,x) xrealloc((ptr),(x))
+
+void *xdl_mmfile_first(mmfile_t *mmf, long *size);
+long xdl_mmfile_size(mmfile_t *mmf);
+
+int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+	     xdemitconf_t const *xecfg, xdemitcb_t *ecb);
+
+typedef struct s_xmparam {
+	xpparam_t xpp;
+	int marker_size;
+	int level;
+	int favor;
+	int style;
+	const char *ancestor;	/* label for orig */
+	const char *file1;	/* label for mf1 */
+	const char *file2;	/* label for mf2 */
+} xmparam_t;
+
+#define DEFAULT_CONFLICT_MARKER_SIZE 7
+
+int xdl_merge(mmfile_t *orig, mmfile_t *mf1, mmfile_t *mf2,
+		xmparam_t const *xmp, mmbuffer_t *result);
+
+#ifdef __cplusplus
+}
+#endif /* #ifdef __cplusplus */
+
+#endif /* #if !defined(XDIFF_H) */
diff --git a/src/nvim/xdiff/xdiffi.c b/src/nvim/xdiff/xdiffi.c
new file mode 100644
index 0000000000..96d5277027
--- /dev/null
+++ b/src/nvim/xdiff/xdiffi.c
@@ -0,0 +1,1043 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003	Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include "xinclude.h"
+
+#define XDL_MAX_COST_MIN 256
+#define XDL_HEUR_MIN_COST 256
+#define XDL_LINE_MAX (long)((1UL << (CHAR_BIT * sizeof(long) - 1)) - 1)
+#define XDL_SNAKE_CNT 20
+#define XDL_K_HEUR 4
+
+typedef struct s_xdpsplit {
+	long i1, i2;
+	int min_lo, min_hi;
+} xdpsplit_t;
+
+/*
+ * See "An O(ND) Difference Algorithm and its Variations", by Eugene Myers.
+ * Basically considers a "box" (off1, off2, lim1, lim2) and scan from both
+ * the forward diagonal starting from (off1, off2) and the backward diagonal
+ * starting from (lim1, lim2). If the K values on the same diagonal crosses
+ * returns the furthest point of reach. We might end up having to expensive
+ * cases using this algorithm is full, so a little bit of heuristic is needed
+ * to cut the search and to return a suboptimal point.
+ */
+static long xdl_split(unsigned long const *ha1, long off1, long lim1,
+		      unsigned long const *ha2, long off2, long lim2,
+		      long *kvdf, long *kvdb, int need_min, xdpsplit_t *spl,
+		      xdalgoenv_t *xenv) {
+	long dmin = off1 - lim2, dmax = lim1 - off2;
+	long fmid = off1 - off2, bmid = lim1 - lim2;
+	long odd = (fmid - bmid) & 1;
+	long fmin = fmid, fmax = fmid;
+	long bmin = bmid, bmax = bmid;
+	long ec, d, i1, i2, prev1, best, dd, v, k;
+
+	/*
+	 * Set initial diagonal values for both forward and backward path.
+	 */
+	kvdf[fmid] = off1;
+	kvdb[bmid] = lim1;
+
+	for (ec = 1;; ec++) {
+		int got_snake = 0;
+
+		/*
+		 * We need to extent the diagonal "domain" by one. If the next
+		 * values exits the box boundaries we need to change it in the
+		 * opposite direction because (max - min) must be a power of two.
+		 * Also we initialize the external K value to -1 so that we can
+		 * avoid extra conditions check inside the core loop.
+		 */
+		if (fmin > dmin)
+			kvdf[--fmin - 1] = -1;
+		else
+			++fmin;
+		if (fmax < dmax)
+			kvdf[++fmax + 1] = -1;
+		else
+			--fmax;
+
+		for (d = fmax; d >= fmin; d -= 2) {
+			if (kvdf[d - 1] >= kvdf[d + 1])
+				i1 = kvdf[d - 1] + 1;
+			else
+				i1 = kvdf[d + 1];
+			prev1 = i1;
+			i2 = i1 - d;
+			for (; i1 < lim1 && i2 < lim2 && ha1[i1] == ha2[i2]; i1++, i2++);
+			if (i1 - prev1 > xenv->snake_cnt)
+				got_snake = 1;
+			kvdf[d] = i1;
+			if (odd && bmin <= d && d <= bmax && kvdb[d] <= i1) {
+				spl->i1 = i1;
+				spl->i2 = i2;
+				spl->min_lo = spl->min_hi = 1;
+				return ec;
+			}
+		}
+
+		/*
+		 * We need to extent the diagonal "domain" by one. If the next
+		 * values exits the box boundaries we need to change it in the
+		 * opposite direction because (max - min) must be a power of two.
+		 * Also we initialize the external K value to -1 so that we can
+		 * avoid extra conditions check inside the core loop.
+		 */
+		if (bmin > dmin)
+			kvdb[--bmin - 1] = XDL_LINE_MAX;
+		else
+			++bmin;
+		if (bmax < dmax)
+			kvdb[++bmax + 1] = XDL_LINE_MAX;
+		else
+			--bmax;
+
+		for (d = bmax; d >= bmin; d -= 2) {
+			if (kvdb[d - 1] < kvdb[d + 1])
+				i1 = kvdb[d - 1];
+			else
+				i1 = kvdb[d + 1] - 1;
+			prev1 = i1;
+			i2 = i1 - d;
+			for (; i1 > off1 && i2 > off2 && ha1[i1 - 1] == ha2[i2 - 1]; i1--, i2--);
+			if (prev1 - i1 > xenv->snake_cnt)
+				got_snake = 1;
+			kvdb[d] = i1;
+			if (!odd && fmin <= d && d <= fmax && i1 <= kvdf[d]) {
+				spl->i1 = i1;
+				spl->i2 = i2;
+				spl->min_lo = spl->min_hi = 1;
+				return ec;
+			}
+		}
+
+		if (need_min)
+			continue;
+
+		/*
+		 * If the edit cost is above the heuristic trigger and if
+		 * we got a good snake, we sample current diagonals to see
+		 * if some of the, have reached an "interesting" path. Our
+		 * measure is a function of the distance from the diagonal
+		 * corner (i1 + i2) penalized with the distance from the
+		 * mid diagonal itself. If this value is above the current
+		 * edit cost times a magic factor (XDL_K_HEUR) we consider
+		 * it interesting.
+		 */
+		if (got_snake && ec > xenv->heur_min) {
+			for (best = 0, d = fmax; d >= fmin; d -= 2) {
+				dd = d > fmid ? d - fmid: fmid - d;
+				i1 = kvdf[d];
+				i2 = i1 - d;
+				v = (i1 - off1) + (i2 - off2) - dd;
+
+				if (v > XDL_K_HEUR * ec && v > best &&
+				    off1 + xenv->snake_cnt <= i1 && i1 < lim1 &&
+				    off2 + xenv->snake_cnt <= i2 && i2 < lim2) {
+					for (k = 1; ha1[i1 - k] == ha2[i2 - k]; k++)
+						if (k == xenv->snake_cnt) {
+							best = v;
+							spl->i1 = i1;
+							spl->i2 = i2;
+							break;
+						}
+				}
+			}
+			if (best > 0) {
+				spl->min_lo = 1;
+				spl->min_hi = 0;
+				return ec;
+			}
+
+			for (best = 0, d = bmax; d >= bmin; d -= 2) {
+				dd = d > bmid ? d - bmid: bmid - d;
+				i1 = kvdb[d];
+				i2 = i1 - d;
+				v = (lim1 - i1) + (lim2 - i2) - dd;
+
+				if (v > XDL_K_HEUR * ec && v > best &&
+				    off1 < i1 && i1 <= lim1 - xenv->snake_cnt &&
+				    off2 < i2 && i2 <= lim2 - xenv->snake_cnt) {
+					for (k = 0; ha1[i1 + k] == ha2[i2 + k]; k++)
+						if (k == xenv->snake_cnt - 1) {
+							best = v;
+							spl->i1 = i1;
+							spl->i2 = i2;
+							break;
+						}
+				}
+			}
+			if (best > 0) {
+				spl->min_lo = 0;
+				spl->min_hi = 1;
+				return ec;
+			}
+		}
+
+		/*
+		 * Enough is enough. We spent too much time here and now we collect
+		 * the furthest reaching path using the (i1 + i2) measure.
+		 */
+		if (ec >= xenv->mxcost) {
+			long fbest, fbest1, bbest, bbest1;
+
+			fbest = fbest1 = -1;
+			for (d = fmax; d >= fmin; d -= 2) {
+				i1 = XDL_MIN(kvdf[d], lim1);
+				i2 = i1 - d;
+				if (lim2 < i2)
+					i1 = lim2 + d, i2 = lim2;
+				if (fbest < i1 + i2) {
+					fbest = i1 + i2;
+					fbest1 = i1;
+				}
+			}
+
+			bbest = bbest1 = XDL_LINE_MAX;
+			for (d = bmax; d >= bmin; d -= 2) {
+				i1 = XDL_MAX(off1, kvdb[d]);
+				i2 = i1 - d;
+				if (i2 < off2)
+					i1 = off2 + d, i2 = off2;
+				if (i1 + i2 < bbest) {
+					bbest = i1 + i2;
+					bbest1 = i1;
+				}
+			}
+
+			if ((lim1 + lim2) - bbest < fbest - (off1 + off2)) {
+				spl->i1 = fbest1;
+				spl->i2 = fbest - fbest1;
+				spl->min_lo = 1;
+				spl->min_hi = 0;
+			} else {
+				spl->i1 = bbest1;
+				spl->i2 = bbest - bbest1;
+				spl->min_lo = 0;
+				spl->min_hi = 1;
+			}
+			return ec;
+		}
+	}
+}
+
+
+/*
+ * Rule: "Divide et Impera". Recursively split the box in sub-boxes by calling
+ * the box splitting function. Note that the real job (marking changed lines)
+ * is done in the two boundary reaching checks.
+ */
+int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
+		 diffdata_t *dd2, long off2, long lim2,
+		 long *kvdf, long *kvdb, int need_min, xdalgoenv_t *xenv) {
+	unsigned long const *ha1 = dd1->ha, *ha2 = dd2->ha;
+
+	/*
+	 * Shrink the box by walking through each diagonal snake (SW and NE).
+	 */
+	for (; off1 < lim1 && off2 < lim2 && ha1[off1] == ha2[off2]; off1++, off2++);
+	for (; off1 < lim1 && off2 < lim2 && ha1[lim1 - 1] == ha2[lim2 - 1]; lim1--, lim2--);
+
+	/*
+	 * If one dimension is empty, then all records on the other one must
+	 * be obviously changed.
+	 */
+	if (off1 == lim1) {
+		char *rchg2 = dd2->rchg;
+		long *rindex2 = dd2->rindex;
+
+		for (; off2 < lim2; off2++)
+			rchg2[rindex2[off2]] = 1;
+	} else if (off2 == lim2) {
+		char *rchg1 = dd1->rchg;
+		long *rindex1 = dd1->rindex;
+
+		for (; off1 < lim1; off1++)
+			rchg1[rindex1[off1]] = 1;
+	} else {
+		xdpsplit_t spl;
+		spl.i1 = spl.i2 = 0;
+
+		/*
+		 * Divide ...
+		 */
+		if (xdl_split(ha1, off1, lim1, ha2, off2, lim2, kvdf, kvdb,
+			      need_min, &spl, xenv) < 0) {
+
+			return -1;
+		}
+
+		/*
+		 * ... et Impera.
+		 */
+		if (xdl_recs_cmp(dd1, off1, spl.i1, dd2, off2, spl.i2,
+				 kvdf, kvdb, spl.min_lo, xenv) < 0 ||
+		    xdl_recs_cmp(dd1, spl.i1, lim1, dd2, spl.i2, lim2,
+				 kvdf, kvdb, spl.min_hi, xenv) < 0) {
+
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+
+int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		xdfenv_t *xe) {
+	long ndiags;
+	long *kvd, *kvdf, *kvdb;
+	xdalgoenv_t xenv;
+	diffdata_t dd1, dd2;
+
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_PATIENCE_DIFF)
+		return xdl_do_patience_diff(mf1, mf2, xpp, xe);
+
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
+		return xdl_do_histogram_diff(mf1, mf2, xpp, xe);
+
+	if (xdl_prepare_env(mf1, mf2, xpp, xe) < 0) {
+
+		return -1;
+	}
+
+	/*
+	 * Allocate and setup K vectors to be used by the differential algorithm.
+	 * One is to store the forward path and one to store the backward path.
+	 */
+	ndiags = xe->xdf1.nreff + xe->xdf2.nreff + 3;
+	if (!(kvd = (long *) xdl_malloc((2 * ndiags + 2) * sizeof(long)))) {
+
+		xdl_free_env(xe);
+		return -1;
+	}
+	kvdf = kvd;
+	kvdb = kvdf + ndiags;
+	kvdf += xe->xdf2.nreff + 1;
+	kvdb += xe->xdf2.nreff + 1;
+
+	xenv.mxcost = xdl_bogosqrt(ndiags);
+	if (xenv.mxcost < XDL_MAX_COST_MIN)
+		xenv.mxcost = XDL_MAX_COST_MIN;
+	xenv.snake_cnt = XDL_SNAKE_CNT;
+	xenv.heur_min = XDL_HEUR_MIN_COST;
+
+	dd1.nrec = xe->xdf1.nreff;
+	dd1.ha = xe->xdf1.ha;
+	dd1.rchg = xe->xdf1.rchg;
+	dd1.rindex = xe->xdf1.rindex;
+	dd2.nrec = xe->xdf2.nreff;
+	dd2.ha = xe->xdf2.ha;
+	dd2.rchg = xe->xdf2.rchg;
+	dd2.rindex = xe->xdf2.rindex;
+
+	if (xdl_recs_cmp(&dd1, 0, dd1.nrec, &dd2, 0, dd2.nrec,
+			 kvdf, kvdb, (xpp->flags & XDF_NEED_MINIMAL) != 0, &xenv) < 0) {
+
+		xdl_free(kvd);
+		xdl_free_env(xe);
+		return -1;
+	}
+
+	xdl_free(kvd);
+
+	return 0;
+}
+
+
+static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1, long chg2) {
+	xdchange_t *xch;
+
+	if (!(xch = (xdchange_t *) xdl_malloc(sizeof(xdchange_t))))
+		return NULL;
+
+	xch->next = xscr;
+	xch->i1 = i1;
+	xch->i2 = i2;
+	xch->chg1 = chg1;
+	xch->chg2 = chg2;
+	xch->ignore = 0;
+
+	return xch;
+}
+
+
+static int recs_match(xrecord_t *rec1, xrecord_t *rec2, long flags)
+{
+	return (rec1->ha == rec2->ha &&
+		xdl_recmatch(rec1->ptr, rec1->size,
+			     rec2->ptr, rec2->size,
+			     flags));
+}
+
+/*
+ * If a line is indented more than this, xget_indent() just returns this value.
+ * This avoids having to do absurd amounts of work for data that are not
+ * human-readable text, and also ensures that the output of xget_indent fits within
+ * an int.
+ */
+#define MAX_INDENT 200
+
+/*
+ * Return the amount of indentation of the specified line, treating TAB as 8
+ * columns. Return -1 if line is empty or contains only whitespace. Clamp the
+ * output value at MAX_INDENT.
+ */
+static int xget_indent(xrecord_t *rec)
+{
+	long i;
+	int ret = 0;
+
+	for (i = 0; i < rec->size; i++) {
+		char c = rec->ptr[i];
+
+		if (!XDL_ISSPACE(c))
+			return ret;
+		else if (c == ' ')
+			ret += 1;
+		else if (c == '\t')
+			ret += 8 - ret % 8;
+		/* ignore other whitespace characters */
+
+		if (ret >= MAX_INDENT)
+			return MAX_INDENT;
+	}
+
+	/* The line contains only whitespace. */
+	return -1;
+}
+
+/*
+ * If more than this number of consecutive blank rows are found, just return this
+ * value. This avoids requiring O(N^2) work for pathological cases, and also
+ * ensures that the output of score_split fits in an int.
+ */
+#define MAX_BLANKS 20
+
+/* Characteristics measured about a hypothetical split position. */
+struct split_measurement {
+	/*
+	 * Is the split at the end of the file (aside from any blank lines)?
+	 */
+	int end_of_file;
+
+	/*
+	 * How much is the line immediately following the split indented (or -1 if
+	 * the line is blank):
+	 */
+	int indent;
+
+	/*
+	 * How many consecutive lines above the split are blank?
+	 */
+	int pre_blank;
+
+	/*
+	 * How much is the nearest non-blank line above the split indented (or -1
+	 * if there is no such line)?
+	 */
+	int pre_indent;
+
+	/*
+	 * How many lines after the line following the split are blank?
+	 */
+	int post_blank;
+
+	/*
+	 * How much is the nearest non-blank line after the line following the
+	 * split indented (or -1 if there is no such line)?
+	 */
+	int post_indent;
+};
+
+struct split_score {
+	/* The effective indent of this split (smaller is preferred). */
+	int effective_indent;
+
+	/* Penalty for this split (smaller is preferred). */
+	int penalty;
+};
+
+/*
+ * Fill m with information about a hypothetical split of xdf above line split.
+ */
+static void measure_split(const xdfile_t *xdf, long split,
+			  struct split_measurement *m)
+{
+	long i;
+
+	if (split >= xdf->nrec) {
+		m->end_of_file = 1;
+		m->indent = -1;
+	} else {
+		m->end_of_file = 0;
+		m->indent = xget_indent(xdf->recs[split]);
+	}
+
+	m->pre_blank = 0;
+	m->pre_indent = -1;
+	for (i = split - 1; i >= 0; i--) {
+		m->pre_indent = xget_indent(xdf->recs[i]);
+		if (m->pre_indent != -1)
+			break;
+		m->pre_blank += 1;
+		if (m->pre_blank == MAX_BLANKS) {
+			m->pre_indent = 0;
+			break;
+		}
+	}
+
+	m->post_blank = 0;
+	m->post_indent = -1;
+	for (i = split + 1; i < xdf->nrec; i++) {
+		m->post_indent = xget_indent(xdf->recs[i]);
+		if (m->post_indent != -1)
+			break;
+		m->post_blank += 1;
+		if (m->post_blank == MAX_BLANKS) {
+			m->post_indent = 0;
+			break;
+		}
+	}
+}
+
+/*
+ * The empirically-determined weight factors used by score_split() below.
+ * Larger values means that the position is a less favorable place to split.
+ *
+ * Note that scores are only ever compared against each other, so multiplying
+ * all of these weight/penalty values by the same factor wouldn't change the
+ * heuristic's behavior. Still, we need to set that arbitrary scale *somehow*.
+ * In practice, these numbers are chosen to be large enough that they can be
+ * adjusted relative to each other with sufficient precision despite using
+ * integer math.
+ */
+
+/* Penalty if there are no non-blank lines before the split */
+#define START_OF_FILE_PENALTY 1
+
+/* Penalty if there are no non-blank lines after the split */
+#define END_OF_FILE_PENALTY 21
+
+/* Multiplier for the number of blank lines around the split */
+#define TOTAL_BLANK_WEIGHT (-30)
+
+/* Multiplier for the number of blank lines after the split */
+#define POST_BLANK_WEIGHT 6
+
+/*
+ * Penalties applied if the line is indented more than its predecessor
+ */
+#define RELATIVE_INDENT_PENALTY (-4)
+#define RELATIVE_INDENT_WITH_BLANK_PENALTY 10
+
+/*
+ * Penalties applied if the line is indented less than both its predecessor and
+ * its successor
+ */
+#define RELATIVE_OUTDENT_PENALTY 24
+#define RELATIVE_OUTDENT_WITH_BLANK_PENALTY 17
+
+/*
+ * Penalties applied if the line is indented less than its predecessor but not
+ * less than its successor
+ */
+#define RELATIVE_DEDENT_PENALTY 23
+#define RELATIVE_DEDENT_WITH_BLANK_PENALTY 17
+
+/*
+ * We only consider whether the sum of the effective indents for splits are
+ * less than (-1), equal to (0), or greater than (+1) each other. The resulting
+ * value is multiplied by the following weight and combined with the penalty to
+ * determine the better of two scores.
+ */
+#define INDENT_WEIGHT 60
+
+/*
+ * How far do we slide a hunk at most?
+ */
+#define INDENT_HEURISTIC_MAX_SLIDING 100
+
+/*
+ * Compute a badness score for the hypothetical split whose measurements are
+ * stored in m. The weight factors were determined empirically using the tools and
+ * corpus described in
+ *
+ *     https://github.com/mhagger/diff-slider-tools
+ *
+ * Also see that project if you want to improve the weights based on, for example,
+ * a larger or more diverse corpus.
+ */
+static void score_add_split(const struct split_measurement *m, struct split_score *s)
+{
+	/*
+	 * A place to accumulate penalty factors (positive makes this index more
+	 * favored):
+	 */
+	int post_blank, total_blank, indent, any_blanks;
+
+	if (m->pre_indent == -1 && m->pre_blank == 0)
+		s->penalty += START_OF_FILE_PENALTY;
+
+	if (m->end_of_file)
+		s->penalty += END_OF_FILE_PENALTY;
+
+	/*
+	 * Set post_blank to the number of blank lines following the split,
+	 * including the line immediately after the split:
+	 */
+	post_blank = (m->indent == -1) ? 1 + m->post_blank : 0;
+	total_blank = m->pre_blank + post_blank;
+
+	/* Penalties based on nearby blank lines: */
+	s->penalty += TOTAL_BLANK_WEIGHT * total_blank;
+	s->penalty += POST_BLANK_WEIGHT * post_blank;
+
+	if (m->indent != -1)
+		indent = m->indent;
+	else
+		indent = m->post_indent;
+
+	any_blanks = (total_blank != 0);
+
+	/* Note that the effective indent is -1 at the end of the file: */
+	s->effective_indent += indent;
+
+	if (indent == -1) {
+		/* No additional adjustments needed. */
+	} else if (m->pre_indent == -1) {
+		/* No additional adjustments needed. */
+	} else if (indent > m->pre_indent) {
+		/*
+		 * The line is indented more than its predecessor.
+		 */
+		s->penalty += any_blanks ?
+			RELATIVE_INDENT_WITH_BLANK_PENALTY :
+			RELATIVE_INDENT_PENALTY;
+	} else if (indent == m->pre_indent) {
+		/*
+		 * The line has the same indentation level as its predecessor.
+		 * No additional adjustments needed.
+		 */
+	} else {
+		/*
+		 * The line is indented less than its predecessor. It could be
+		 * the block terminator of the previous block, but it could
+		 * also be the start of a new block (e.g., an "else" block, or
+		 * maybe the previous block didn't have a block terminator).
+		 * Try to distinguish those cases based on what comes next:
+		 */
+		if (m->post_indent != -1 && m->post_indent > indent) {
+			/*
+			 * The following line is indented more. So it is likely
+			 * that this line is the start of a block.
+			 */
+			s->penalty += any_blanks ?
+				RELATIVE_OUTDENT_WITH_BLANK_PENALTY :
+				RELATIVE_OUTDENT_PENALTY;
+		} else {
+			/*
+			 * That was probably the end of a block.
+			 */
+			s->penalty += any_blanks ?
+				RELATIVE_DEDENT_WITH_BLANK_PENALTY :
+				RELATIVE_DEDENT_PENALTY;
+		}
+	}
+}
+
+static int score_cmp(struct split_score *s1, struct split_score *s2)
+{
+	/* -1 if s1.effective_indent < s2->effective_indent, etc. */
+	int cmp_indents = ((s1->effective_indent > s2->effective_indent) -
+			   (s1->effective_indent < s2->effective_indent));
+
+	return INDENT_WEIGHT * cmp_indents + (s1->penalty - s2->penalty);
+}
+
+/*
+ * Represent a group of changed lines in an xdfile_t (i.e., a contiguous group
+ * of lines that was inserted or deleted from the corresponding version of the
+ * file). We consider there to be such a group at the beginning of the file, at
+ * the end of the file, and between any two unchanged lines, though most such
+ * groups will usually be empty.
+ *
+ * If the first line in a group is equal to the line following the group, then
+ * the group can be slid down. Similarly, if the last line in a group is equal
+ * to the line preceding the group, then the group can be slid up. See
+ * group_slide_down() and group_slide_up().
+ *
+ * Note that loops that are testing for changed lines in xdf->rchg do not need
+ * index bounding since the array is prepared with a zero at position -1 and N.
+ */
+struct xdlgroup {
+	/*
+	 * The index of the first changed line in the group, or the index of
+	 * the unchanged line above which the (empty) group is located.
+	 */
+	long start;
+
+	/*
+	 * The index of the first unchanged line after the group. For an empty
+	 * group, end is equal to start.
+	 */
+	long end;
+};
+
+/*
+ * Initialize g to point at the first group in xdf.
+ */
+static void group_init(xdfile_t *xdf, struct xdlgroup *g)
+{
+	g->start = g->end = 0;
+	while (xdf->rchg[g->end])
+		g->end++;
+}
+
+/*
+ * Move g to describe the next (possibly empty) group in xdf and return 0. If g
+ * is already at the end of the file, do nothing and return -1.
+ */
+static inline int group_next(xdfile_t *xdf, struct xdlgroup *g)
+{
+	if (g->end == xdf->nrec)
+		return -1;
+
+	g->start = g->end + 1;
+	for (g->end = g->start; xdf->rchg[g->end]; g->end++)
+		;
+
+	return 0;
+}
+
+/*
+ * Move g to describe the previous (possibly empty) group in xdf and return 0.
+ * If g is already at the beginning of the file, do nothing and return -1.
+ */
+static inline int group_previous(xdfile_t *xdf, struct xdlgroup *g)
+{
+	if (g->start == 0)
+		return -1;
+
+	g->end = g->start - 1;
+	for (g->start = g->end; xdf->rchg[g->start - 1]; g->start--)
+		;
+
+	return 0;
+}
+
+/*
+ * If g can be slid toward the end of the file, do so, and if it bumps into a
+ * following group, expand this group to include it. Return 0 on success or -1
+ * if g cannot be slid down.
+ */
+static int group_slide_down(xdfile_t *xdf, struct xdlgroup *g, long flags)
+{
+	if (g->end < xdf->nrec &&
+	    recs_match(xdf->recs[g->start], xdf->recs[g->end], flags)) {
+		xdf->rchg[g->start++] = 0;
+		xdf->rchg[g->end++] = 1;
+
+		while (xdf->rchg[g->end])
+			g->end++;
+
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+/*
+ * If g can be slid toward the beginning of the file, do so, and if it bumps
+ * into a previous group, expand this group to include it. Return 0 on success
+ * or -1 if g cannot be slid up.
+ */
+static int group_slide_up(xdfile_t *xdf, struct xdlgroup *g, long flags)
+{
+	if (g->start > 0 &&
+	    recs_match(xdf->recs[g->start - 1], xdf->recs[g->end - 1], flags)) {
+		xdf->rchg[--g->start] = 1;
+		xdf->rchg[--g->end] = 0;
+
+		while (xdf->rchg[g->start - 1])
+			g->start--;
+
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+static void xdl_bug(const char *msg)
+{
+	fprintf(stderr, "BUG: %s\n", msg);
+	exit(1);
+}
+
+/*
+ * Move back and forward change groups for a consistent and pretty diff output.
+ * This also helps in finding joinable change groups and reducing the diff
+ * size.
+ */
+int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
+	struct xdlgroup g, go;
+	long earliest_end, end_matching_other;
+	long groupsize;
+
+	group_init(xdf, &g);
+	group_init(xdfo, &go);
+
+	while (1) {
+		/* If the group is empty in the to-be-compacted file, skip it: */
+		if (g.end == g.start)
+			goto next;
+
+		/*
+		 * Now shift the change up and then down as far as possible in
+		 * each direction. If it bumps into any other changes, merge them.
+		 */
+		do {
+			groupsize = g.end - g.start;
+
+			/*
+			 * Keep track of the last "end" index that causes this
+			 * group to align with a group of changed lines in the
+			 * other file. -1 indicates that we haven't found such
+			 * a match yet:
+			 */
+			end_matching_other = -1;
+
+			/* Shift the group backward as much as possible: */
+			while (!group_slide_up(xdf, &g, flags))
+				if (group_previous(xdfo, &go))
+					xdl_bug("group sync broken sliding up");
+
+			/*
+			 * This is this highest that this group can be shifted.
+			 * Record its end index:
+			 */
+			earliest_end = g.end;
+
+			if (go.end > go.start)
+				end_matching_other = g.end;
+
+			/* Now shift the group forward as far as possible: */
+			while (1) {
+				if (group_slide_down(xdf, &g, flags))
+					break;
+				if (group_next(xdfo, &go))
+					xdl_bug("group sync broken sliding down");
+
+				if (go.end > go.start)
+					end_matching_other = g.end;
+			}
+		} while (groupsize != g.end - g.start);
+
+		/*
+		 * If the group can be shifted, then we can possibly use this
+		 * freedom to produce a more intuitive diff.
+		 *
+		 * The group is currently shifted as far down as possible, so the
+		 * heuristics below only have to handle upwards shifts.
+		 */
+
+		if (g.end == earliest_end) {
+			/* no shifting was possible */
+		} else if (end_matching_other != -1) {
+			/*
+			 * Move the possibly merged group of changes back to line
+			 * up with the last group of changes from the other file
+			 * that it can align with.
+			 */
+			while (go.end == go.start) {
+				if (group_slide_up(xdf, &g, flags))
+					xdl_bug("match disappeared");
+				if (group_previous(xdfo, &go))
+					xdl_bug("group sync broken sliding to match");
+			}
+		} else if (flags & XDF_INDENT_HEURISTIC) {
+			/*
+			 * Indent heuristic: a group of pure add/delete lines
+			 * implies two splits, one between the end of the "before"
+			 * context and the start of the group, and another between
+			 * the end of the group and the beginning of the "after"
+			 * context. Some splits are aesthetically better and some
+			 * are worse. We compute a badness "score" for each split,
+			 * and add the scores for the two splits to define a
+			 * "score" for each position that the group can be shifted
+			 * to. Then we pick the shift with the lowest score.
+			 */
+			long shift, best_shift = -1;
+			struct split_score best_score;
+
+			shift = earliest_end;
+			if (g.end - groupsize - 1 > shift)
+				shift = g.end - groupsize - 1;
+			if (g.end - INDENT_HEURISTIC_MAX_SLIDING > shift)
+				shift = g.end - INDENT_HEURISTIC_MAX_SLIDING;
+			for (; shift <= g.end; shift++) {
+				struct split_measurement m;
+				struct split_score score = {0, 0};
+
+				measure_split(xdf, shift, &m);
+				score_add_split(&m, &score);
+				measure_split(xdf, shift - groupsize, &m);
+				score_add_split(&m, &score);
+				if (best_shift == -1 ||
+				    score_cmp(&score, &best_score) <= 0) {
+					best_score.effective_indent = score.effective_indent;
+					best_score.penalty = score.penalty;
+					best_shift = shift;
+				}
+			}
+
+			while (g.end > best_shift) {
+				if (group_slide_up(xdf, &g, flags))
+					xdl_bug("best shift unreached");
+				if (group_previous(xdfo, &go))
+					xdl_bug("group sync broken sliding to blank line");
+			}
+		}
+
+	next:
+		/* Move past the just-processed group: */
+		if (group_next(xdf, &g))
+			break;
+		if (group_next(xdfo, &go))
+			xdl_bug("group sync broken moving to next group");
+	}
+
+	if (!group_next(xdfo, &go))
+		xdl_bug("group sync broken at end of file");
+
+	return 0;
+}
+
+
+int xdl_build_script(xdfenv_t *xe, xdchange_t **xscr) {
+	xdchange_t *cscr = NULL, *xch;
+	char *rchg1 = xe->xdf1.rchg, *rchg2 = xe->xdf2.rchg;
+	long i1, i2, l1, l2;
+
+	/*
+	 * Trivial. Collects "groups" of changes and creates an edit script.
+	 */
+	for (i1 = xe->xdf1.nrec, i2 = xe->xdf2.nrec; i1 >= 0 || i2 >= 0; i1--, i2--)
+		if (rchg1[i1 - 1] || rchg2[i2 - 1]) {
+			for (l1 = i1; rchg1[i1 - 1]; i1--);
+			for (l2 = i2; rchg2[i2 - 1]; i2--);
+
+			if (!(xch = xdl_add_change(cscr, i1, i2, l1 - i1, l2 - i2))) {
+				xdl_free_script(cscr);
+				return -1;
+			}
+			cscr = xch;
+		}
+
+	*xscr = cscr;
+
+	return 0;
+}
+
+
+void xdl_free_script(xdchange_t *xscr) {
+	xdchange_t *xch;
+
+	while ((xch = xscr) != NULL) {
+		xscr = xscr->next;
+		xdl_free(xch);
+	}
+}
+
+static int xdl_call_hunk_func(xdfenv_t *xe UNUSED, xdchange_t *xscr, xdemitcb_t *ecb,
+			      xdemitconf_t const *xecfg)
+{
+	xdchange_t *xch, *xche;
+
+	for (xch = xscr; xch; xch = xche->next) {
+		xche = xdl_get_hunk(&xch, xecfg);
+		if (!xch)
+			break;
+		if (xecfg->hunk_func(xch->i1, xche->i1 + xche->chg1 - xch->i1,
+				     xch->i2, xche->i2 + xche->chg2 - xch->i2,
+				     ecb->priv) < 0)
+			return -1;
+	}
+	return 0;
+}
+
+static void xdl_mark_ignorable(xdchange_t *xscr, xdfenv_t *xe, long flags)
+{
+	xdchange_t *xch;
+
+	for (xch = xscr; xch; xch = xch->next) {
+		int ignore = 1;
+		xrecord_t **rec;
+		long i;
+
+		rec = &xe->xdf1.recs[xch->i1];
+		for (i = 0; i < xch->chg1 && ignore; i++)
+			ignore = xdl_blankline(rec[i]->ptr, rec[i]->size, flags);
+
+		rec = &xe->xdf2.recs[xch->i2];
+		for (i = 0; i < xch->chg2 && ignore; i++)
+			ignore = xdl_blankline(rec[i]->ptr, rec[i]->size, flags);
+
+		xch->ignore = ignore;
+	}
+}
+
+int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+	     xdemitconf_t const *xecfg, xdemitcb_t *ecb) {
+	xdchange_t *xscr;
+	xdfenv_t xe;
+	emit_func_t ef = xecfg->hunk_func ? xdl_call_hunk_func : xdl_emit_diff;
+
+	if (xdl_do_diff(mf1, mf2, xpp, &xe) < 0) {
+
+		return -1;
+	}
+	if (xdl_change_compact(&xe.xdf1, &xe.xdf2, xpp->flags) < 0 ||
+	    xdl_change_compact(&xe.xdf2, &xe.xdf1, xpp->flags) < 0 ||
+	    xdl_build_script(&xe, &xscr) < 0) {
+
+		xdl_free_env(&xe);
+		return -1;
+	}
+	if (xscr) {
+		if (xpp->flags & XDF_IGNORE_BLANK_LINES)
+			xdl_mark_ignorable(xscr, &xe, xpp->flags);
+
+		if (ef(&xe, xscr, ecb, xecfg) < 0) {
+
+			xdl_free_script(xscr);
+			xdl_free_env(&xe);
+			return -1;
+		}
+		xdl_free_script(xscr);
+	}
+	xdl_free_env(&xe);
+
+	return 0;
+}
diff --git a/src/nvim/xdiff/xdiffi.h b/src/nvim/xdiff/xdiffi.h
new file mode 100644
index 0000000000..8f1c7c8b04
--- /dev/null
+++ b/src/nvim/xdiff/xdiffi.h
@@ -0,0 +1,64 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XDIFFI_H)
+#define XDIFFI_H
+
+
+typedef struct s_diffdata {
+	long nrec;
+	unsigned long const *ha;
+	long *rindex;
+	char *rchg;
+} diffdata_t;
+
+typedef struct s_xdalgoenv {
+	long mxcost;
+	long snake_cnt;
+	long heur_min;
+} xdalgoenv_t;
+
+typedef struct s_xdchange {
+	struct s_xdchange *next;
+	long i1, i2;
+	long chg1, chg2;
+	int ignore;
+} xdchange_t;
+
+
+
+int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
+		 diffdata_t *dd2, long off2, long lim2,
+		 long *kvdf, long *kvdb, int need_min, xdalgoenv_t *xenv);
+int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		xdfenv_t *xe);
+int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags);
+int xdl_build_script(xdfenv_t *xe, xdchange_t **xscr);
+void xdl_free_script(xdchange_t *xscr);
+int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+		  xdemitconf_t const *xecfg);
+int xdl_do_patience_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		xdfenv_t *env);
+int xdl_do_histogram_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		xdfenv_t *env);
+
+#endif /* #if !defined(XDIFFI_H) */
diff --git a/src/nvim/xdiff/xemit.c b/src/nvim/xdiff/xemit.c
new file mode 100644
index 0000000000..d8a6f1ed38
--- /dev/null
+++ b/src/nvim/xdiff/xemit.c
@@ -0,0 +1,332 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003	Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include "xinclude.h"
+
+static long xdl_get_rec(xdfile_t *xdf, long ri, char const **rec) {
+
+	*rec = xdf->recs[ri]->ptr;
+
+	return xdf->recs[ri]->size;
+}
+
+
+static int xdl_emit_record(xdfile_t *xdf, long ri, char const *pre, xdemitcb_t *ecb) {
+	long size, psize = (long)strlen(pre);
+	char const *rec;
+
+	size = xdl_get_rec(xdf, ri, &rec);
+	if (xdl_emit_diffrec(rec, size, pre, psize, ecb) < 0) {
+
+		return -1;
+	}
+
+	return 0;
+}
+
+
+/*
+ * Starting at the passed change atom, find the latest change atom to be included
+ * inside the differential hunk according to the specified configuration.
+ * Also advance xscr if the first changes must be discarded.
+ */
+xdchange_t *xdl_get_hunk(xdchange_t **xscr, xdemitconf_t const *xecfg)
+{
+	xdchange_t *xch, *xchp, *lxch;
+	long max_common = 2 * xecfg->ctxlen + xecfg->interhunkctxlen;
+	long max_ignorable = xecfg->ctxlen;
+	unsigned long ignored = 0; /* number of ignored blank lines */
+
+	/* remove ignorable changes that are too far before other changes */
+	for (xchp = *xscr; xchp && xchp->ignore; xchp = xchp->next) {
+		xch = xchp->next;
+
+		if (xch == NULL ||
+		    xch->i1 - (xchp->i1 + xchp->chg1) >= max_ignorable)
+			*xscr = xch;
+	}
+
+	if (*xscr == NULL)
+		return NULL;
+
+	lxch = *xscr;
+
+	for (xchp = *xscr, xch = xchp->next; xch; xchp = xch, xch = xch->next) {
+		long distance = xch->i1 - (xchp->i1 + xchp->chg1);
+		if (distance > max_common)
+			break;
+
+		if (distance < max_ignorable && (!xch->ignore || lxch == xchp)) {
+			lxch = xch;
+			ignored = 0;
+		} else if (distance < max_ignorable && xch->ignore) {
+			ignored += xch->chg2;
+		} else if (lxch != xchp &&
+			   xch->i1 + (long)ignored - (lxch->i1 + lxch->chg1) > max_common) {
+			break;
+		} else if (!xch->ignore) {
+			lxch = xch;
+			ignored = 0;
+		} else {
+			ignored += xch->chg2;
+		}
+	}
+
+	return lxch;
+}
+
+
+#if 0
+static long def_ff(const char *rec, long len, char *buf, long sz, void *priv UNUSED)
+{
+	if (len > 0 &&
+			(isalpha((unsigned char)*rec) || /* identifier? */
+			 *rec == '_' || /* also identifier? */
+			 *rec == '$')) { /* identifiers from VMS and other esoterico */
+		if (len > sz)
+			len = sz;
+		while (0 < len && isspace((unsigned char)rec[len - 1]))
+			len--;
+		memcpy(buf, rec, len);
+		return len;
+	}
+	return -1;
+}
+#endif
+
+#if 0
+static long match_func_rec(xdfile_t *xdf, xdemitconf_t const *xecfg, long ri,
+			   char *buf, long sz)
+{
+	const char *rec;
+	long len = xdl_get_rec(xdf, ri, &rec);
+	if (!xecfg->find_func)
+		return def_ff(rec, len, buf, sz, xecfg->find_func_priv);
+	return xecfg->find_func(rec, len, buf, sz, xecfg->find_func_priv);
+}
+#endif
+
+#if 0
+static int is_func_rec(xdfile_t *xdf, xdemitconf_t const *xecfg, long ri)
+{
+	char dummy[1];
+	return match_func_rec(xdf, xecfg, ri, dummy, sizeof(dummy)) >= 0;
+}
+#endif
+
+struct func_line {
+	long len;
+	char buf[80];
+};
+
+#if 0
+static long get_func_line(xdfenv_t *xe, xdemitconf_t const *xecfg,
+			  struct func_line *func_line, long start, long limit)
+{
+	long l, size, step = (start > limit) ? -1 : 1;
+	char *buf, dummy[1];
+
+	buf = func_line ? func_line->buf : dummy;
+	size = func_line ? sizeof(func_line->buf) : sizeof(dummy);
+
+	for (l = start; l != limit && 0 <= l && l < xe->xdf1.nrec; l += step) {
+		long len = match_func_rec(&xe->xdf1, xecfg, l, buf, size);
+		if (len >= 0) {
+			if (func_line)
+				func_line->len = len;
+			return l;
+		}
+	}
+	return -1;
+}
+#endif
+
+#if 0
+static int is_empty_rec(xdfile_t *xdf, long ri)
+{
+	const char *rec;
+	long len = xdl_get_rec(xdf, ri, &rec);
+
+	while (len > 0 && XDL_ISSPACE(*rec)) {
+		rec++;
+		len--;
+	}
+	return !len;
+}
+#endif
+
+int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+		  xdemitconf_t const *xecfg) {
+	long s1, s2, e1, e2, lctx;
+	xdchange_t *xch, *xche;
+#if 0
+	long funclineprev = -1;
+#endif
+	struct func_line func_line;
+
+	func_line.len = 0;
+
+	for (xch = xscr; xch; xch = xche->next) {
+		xche = xdl_get_hunk(&xch, xecfg);
+		if (!xch)
+			break;
+
+		s1 = XDL_MAX(xch->i1 - xecfg->ctxlen, 0);
+		s2 = XDL_MAX(xch->i2 - xecfg->ctxlen, 0);
+
+#if 0
+		if (xecfg->flags & XDL_EMIT_FUNCCONTEXT) {
+			long fs1, i1 = xch->i1;
+
+			/* Appended chunk? */
+			if (i1 >= xe->xdf1.nrec) {
+				long i2 = xch->i2;
+
+				/*
+				 * We don't need additional context if
+				 * a whole function was added.
+				 */
+				while (i2 < xe->xdf2.nrec) {
+					if (is_func_rec(&xe->xdf2, xecfg, i2))
+						goto post_context_calculation;
+					i2++;
+				}
+
+				/*
+				 * Otherwise get more context from the
+				 * pre-image.
+				 */
+				i1 = xe->xdf1.nrec - 1;
+			}
+
+			fs1 = get_func_line(xe, xecfg, NULL, i1, -1);
+			while (fs1 > 0 && !is_empty_rec(&xe->xdf1, fs1 - 1) &&
+			       !is_func_rec(&xe->xdf1, xecfg, fs1 - 1))
+				fs1--;
+			if (fs1 < 0)
+				fs1 = 0;
+			if (fs1 < s1) {
+				s2 -= s1 - fs1;
+				s1 = fs1;
+			}
+		}
+
+ post_context_calculation:
+#endif
+		lctx = xecfg->ctxlen;
+		lctx = XDL_MIN(lctx, xe->xdf1.nrec - (xche->i1 + xche->chg1));
+		lctx = XDL_MIN(lctx, xe->xdf2.nrec - (xche->i2 + xche->chg2));
+
+		e1 = xche->i1 + xche->chg1 + lctx;
+		e2 = xche->i2 + xche->chg2 + lctx;
+
+#if 0
+		if (xecfg->flags & XDL_EMIT_FUNCCONTEXT) {
+			long fe1 = get_func_line(xe, xecfg, NULL,
+						 xche->i1 + xche->chg1,
+						 xe->xdf1.nrec);
+			while (fe1 > 0 && is_empty_rec(&xe->xdf1, fe1 - 1))
+				fe1--;
+			if (fe1 < 0)
+				fe1 = xe->xdf1.nrec;
+			if (fe1 > e1) {
+				e2 += fe1 - e1;
+				e1 = fe1;
+			}
+
+			/*
+			 * Overlap with next change?  Then include it
+			 * in the current hunk and start over to find
+			 * its new end.
+			 */
+			if (xche->next) {
+				long l = XDL_MIN(xche->next->i1,
+						 xe->xdf1.nrec - 1);
+				if (l - xecfg->ctxlen <= e1 ||
+				    get_func_line(xe, xecfg, NULL, l, e1) < 0) {
+					xche = xche->next;
+					goto post_context_calculation;
+				}
+			}
+		}
+#endif
+
+		/*
+		 * Emit current hunk header.
+		 */
+
+#if 0
+		if (xecfg->flags & XDL_EMIT_FUNCNAMES) {
+			get_func_line(xe, xecfg, &func_line,
+				      s1 - 1, funclineprev);
+			funclineprev = s1 - 1;
+		}
+#endif
+		if (xdl_emit_hunk_hdr(s1 + 1, e1 - s1, s2 + 1, e2 - s2,
+				      func_line.buf, func_line.len, ecb) < 0)
+			return -1;
+
+		/*
+		 * Emit pre-context.
+		 */
+		for (; s2 < xch->i2; s2++)
+			if (xdl_emit_record(&xe->xdf2, s2, " ", ecb) < 0)
+				return -1;
+
+		for (s1 = xch->i1, s2 = xch->i2;; xch = xch->next) {
+			/*
+			 * Merge previous with current change atom.
+			 */
+			for (; s1 < xch->i1 && s2 < xch->i2; s1++, s2++)
+				if (xdl_emit_record(&xe->xdf2, s2, " ", ecb) < 0)
+					return -1;
+
+			/*
+			 * Removes lines from the first file.
+			 */
+			for (s1 = xch->i1; s1 < xch->i1 + xch->chg1; s1++)
+				if (xdl_emit_record(&xe->xdf1, s1, "-", ecb) < 0)
+					return -1;
+
+			/*
+			 * Adds lines from the second file.
+			 */
+			for (s2 = xch->i2; s2 < xch->i2 + xch->chg2; s2++)
+				if (xdl_emit_record(&xe->xdf2, s2, "+", ecb) < 0)
+					return -1;
+
+			if (xch == xche)
+				break;
+			s1 = xch->i1 + xch->chg1;
+			s2 = xch->i2 + xch->chg2;
+		}
+
+		/*
+		 * Emit post-context.
+		 */
+		for (s2 = xche->i2 + xche->chg2; s2 < e2; s2++)
+			if (xdl_emit_record(&xe->xdf2, s2, " ", ecb) < 0)
+				return -1;
+	}
+
+	return 0;
+}
diff --git a/src/nvim/xdiff/xemit.h b/src/nvim/xdiff/xemit.h
new file mode 100644
index 0000000000..1b9887e670
--- /dev/null
+++ b/src/nvim/xdiff/xemit.h
@@ -0,0 +1,36 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XEMIT_H)
+#define XEMIT_H
+
+
+typedef int (*emit_func_t)(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+			   xdemitconf_t const *xecfg);
+
+xdchange_t *xdl_get_hunk(xdchange_t **xscr, xdemitconf_t const *xecfg);
+int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+		  xdemitconf_t const *xecfg);
+
+
+
+#endif /* #if !defined(XEMIT_H) */
diff --git a/src/nvim/xdiff/xhistogram.c b/src/nvim/xdiff/xhistogram.c
new file mode 100644
index 0000000000..3fb8974dd4
--- /dev/null
+++ b/src/nvim/xdiff/xhistogram.c
@@ -0,0 +1,386 @@
+/*
+ * Copyright (C) 2010, Google Inc.
+ * and other copyright owners as documented in JGit's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "xinclude.h"
+#include "xtypes.h"
+#include "xdiff.h"
+
+#define MAX_PTR	INT_MAX
+#define MAX_CNT	INT_MAX
+
+#define LINE_END(n) (line##n + count##n - 1)
+#define LINE_END_PTR(n) (*line##n + *count##n - 1)
+
+struct histindex {
+	struct record {
+		unsigned int ptr, cnt;
+		struct record *next;
+	} **records, /* an occurrence */
+	  **line_map; /* map of line to record chain */
+	chastore_t rcha;
+	unsigned int *next_ptrs;
+	unsigned int table_bits,
+		     records_size,
+		     line_map_size;
+
+	unsigned int max_chain_length,
+		     key_shift,
+		     ptr_shift;
+
+	unsigned int cnt,
+		     has_common;
+
+	xdfenv_t *env;
+	xpparam_t const *xpp;
+};
+
+struct region {
+	unsigned int begin1, end1;
+	unsigned int begin2, end2;
+};
+
+#define LINE_MAP(i, a) (i->line_map[(a) - i->ptr_shift])
+
+#define NEXT_PTR(index, ptr) \
+	(index->next_ptrs[(ptr) - index->ptr_shift])
+
+#define CNT(index, ptr) \
+	((LINE_MAP(index, ptr))->cnt)
+
+#define REC(env, s, l) \
+	(env->xdf##s.recs[l - 1])
+
+static int cmp_recs(xpparam_t const *xpp,
+	xrecord_t *r1, xrecord_t *r2)
+{
+	return r1->ha == r2->ha &&
+		xdl_recmatch(r1->ptr, r1->size, r2->ptr, r2->size,
+			    xpp->flags);
+}
+
+#define CMP_ENV(xpp, env, s1, l1, s2, l2) \
+	(cmp_recs(xpp, REC(env, s1, l1), REC(env, s2, l2)))
+
+#define CMP(i, s1, l1, s2, l2) \
+	(cmp_recs(i->xpp, REC(i->env, s1, l1), REC(i->env, s2, l2)))
+
+#define TABLE_HASH(index, side, line) \
+	XDL_HASHLONG((REC(index->env, side, line))->ha, index->table_bits)
+
+static int scanA(struct histindex *index, int line1, int count1)
+{
+	int ptr, tbl_idx;
+	unsigned int chain_len;
+	struct record **rec_chain, *rec;
+
+	for (ptr = LINE_END(1); line1 <= ptr; ptr--) {
+		tbl_idx = TABLE_HASH(index, 1, ptr);
+		rec_chain = index->records + tbl_idx;
+		rec = *rec_chain;
+
+		chain_len = 0;
+		while (rec) {
+			if (CMP(index, 1, rec->ptr, 1, ptr)) {
+				/*
+				 * ptr is identical to another element. Insert
+				 * it onto the front of the existing element
+				 * chain.
+				 */
+				NEXT_PTR(index, ptr) = rec->ptr;
+				rec->ptr = ptr;
+				/* cap rec->cnt at MAX_CNT */
+				rec->cnt = XDL_MIN(MAX_CNT, rec->cnt + 1);
+				LINE_MAP(index, ptr) = rec;
+				goto continue_scan;
+			}
+
+			rec = rec->next;
+			chain_len++;
+		}
+
+		if (chain_len == index->max_chain_length)
+			return -1;
+
+		/*
+		 * This is the first time we have ever seen this particular
+		 * element in the sequence. Construct a new chain for it.
+		 */
+		if (!(rec = xdl_cha_alloc(&index->rcha)))
+			return -1;
+		rec->ptr = ptr;
+		rec->cnt = 1;
+		rec->next = *rec_chain;
+		*rec_chain = rec;
+		LINE_MAP(index, ptr) = rec;
+
+continue_scan:
+		; /* no op */
+	}
+
+	return 0;
+}
+
+static int try_lcs(struct histindex *index, struct region *lcs, int b_ptr,
+	int line1, int count1, int line2, int count2)
+{
+	unsigned int b_next = b_ptr + 1;
+	struct record *rec = index->records[TABLE_HASH(index, 2, b_ptr)];
+	unsigned int as, ae, bs, be, np, rc;
+	int should_break;
+
+	for (; rec; rec = rec->next) {
+		if (rec->cnt > index->cnt) {
+			if (!index->has_common)
+				index->has_common = CMP(index, 1, rec->ptr, 2, b_ptr);
+			continue;
+		}
+
+		as = rec->ptr;
+		if (!CMP(index, 1, as, 2, b_ptr))
+			continue;
+
+		index->has_common = 1;
+		for (;;) {
+			should_break = 0;
+			np = NEXT_PTR(index, as);
+			bs = b_ptr;
+			ae = as;
+			be = bs;
+			rc = rec->cnt;
+
+			while (line1 < (int)as && line2 < (int)bs
+				&& CMP(index, 1, as - 1, 2, bs - 1)) {
+				as--;
+				bs--;
+				if (1 < rc)
+					rc = XDL_MIN(rc, CNT(index, as));
+			}
+			while ((int)ae < LINE_END(1) && (int)be < LINE_END(2)
+				&& CMP(index, 1, ae + 1, 2, be + 1)) {
+				ae++;
+				be++;
+				if (1 < rc)
+					rc = XDL_MIN(rc, CNT(index, ae));
+			}
+
+			if (b_next <= be)
+				b_next = be + 1;
+			if (lcs->end1 - lcs->begin1 < ae - as || rc < index->cnt) {
+				lcs->begin1 = as;
+				lcs->begin2 = bs;
+				lcs->end1 = ae;
+				lcs->end2 = be;
+				index->cnt = rc;
+			}
+
+			if (np == 0)
+				break;
+
+			while (np <= ae) {
+				np = NEXT_PTR(index, np);
+				if (np == 0) {
+					should_break = 1;
+					break;
+				}
+			}
+
+			if (should_break)
+				break;
+
+			as = np;
+		}
+	}
+	return b_next;
+}
+
+static int fall_back_to_classic_diff(xpparam_t const *xpp, xdfenv_t *env,
+		int line1, int count1, int line2, int count2)
+{
+	xpparam_t xpparam;
+	xpparam.flags = xpp->flags & ~XDF_DIFF_ALGORITHM_MASK;
+
+	return xdl_fall_back_diff(env, &xpparam,
+				  line1, count1, line2, count2);
+}
+
+static inline void free_index(struct histindex *index)
+{
+	xdl_free(index->records);
+	xdl_free(index->line_map);
+	xdl_free(index->next_ptrs);
+	xdl_cha_free(&index->rcha);
+}
+
+static int find_lcs(xpparam_t const *xpp, xdfenv_t *env,
+		    struct region *lcs,
+		    int line1, int count1, int line2, int count2)
+{
+	int b_ptr;
+	int sz, ret = -1;
+	struct histindex index;
+
+	memset(&index, 0, sizeof(index));
+
+	index.env = env;
+	index.xpp = xpp;
+
+	index.records = NULL;
+	index.line_map = NULL;
+	/* in case of early xdl_cha_free() */
+	index.rcha.head = NULL;
+
+	index.table_bits = xdl_hashbits(count1);
+	sz = index.records_size = 1 << index.table_bits;
+	sz *= sizeof(struct record *);
+	if (!(index.records = (struct record **) xdl_malloc(sz)))
+		goto cleanup;
+	memset(index.records, 0, sz);
+
+	sz = index.line_map_size = count1;
+	sz *= sizeof(struct record *);
+	if (!(index.line_map = (struct record **) xdl_malloc(sz)))
+		goto cleanup;
+	memset(index.line_map, 0, sz);
+
+	sz = index.line_map_size;
+	sz *= sizeof(unsigned int);
+	if (!(index.next_ptrs = (unsigned int *) xdl_malloc(sz)))
+		goto cleanup;
+	memset(index.next_ptrs, 0, sz);
+
+	/* lines / 4 + 1 comes from xprepare.c:xdl_prepare_ctx() */
+	if (xdl_cha_init(&index.rcha, sizeof(struct record), count1 / 4 + 1) < 0)
+		goto cleanup;
+
+	index.ptr_shift = line1;
+	index.max_chain_length = 64;
+
+	if (scanA(&index, line1, count1))
+		goto cleanup;
+
+	index.cnt = index.max_chain_length + 1;
+
+	for (b_ptr = line2; b_ptr <= LINE_END(2); )
+		b_ptr = try_lcs(&index, lcs, b_ptr, line1, count1, line2, count2);
+
+	if (index.has_common && index.max_chain_length < index.cnt)
+		ret = 1;
+	else
+		ret = 0;
+
+cleanup:
+	free_index(&index);
+	return ret;
+}
+
+static int histogram_diff(xpparam_t const *xpp, xdfenv_t *env,
+	int line1, int count1, int line2, int count2)
+{
+	struct region lcs;
+	int lcs_found;
+	int result;
+redo:
+	result = -1;
+
+	if (count1 <= 0 && count2 <= 0)
+		return 0;
+
+	if (LINE_END(1) >= MAX_PTR)
+		return -1;
+
+	if (!count1) {
+		while(count2--)
+			env->xdf2.rchg[line2++ - 1] = 1;
+		return 0;
+	} else if (!count2) {
+		while(count1--)
+			env->xdf1.rchg[line1++ - 1] = 1;
+		return 0;
+	}
+
+	memset(&lcs, 0, sizeof(lcs));
+	lcs_found = find_lcs(xpp, env, &lcs, line1, count1, line2, count2);
+	if (lcs_found < 0)
+		goto out;
+	else if (lcs_found)
+		result = fall_back_to_classic_diff(xpp, env, line1, count1, line2, count2);
+	else {
+		if (lcs.begin1 == 0 && lcs.begin2 == 0) {
+			while (count1--)
+				env->xdf1.rchg[line1++ - 1] = 1;
+			while (count2--)
+				env->xdf2.rchg[line2++ - 1] = 1;
+			result = 0;
+		} else {
+			result = histogram_diff(xpp, env,
+						line1, lcs.begin1 - line1,
+						line2, lcs.begin2 - line2);
+			if (result)
+				goto out;
+			/*
+			 * result = histogram_diff(xpp, env,
+			 *            lcs.end1 + 1, LINE_END(1) - lcs.end1,
+			 *            lcs.end2 + 1, LINE_END(2) - lcs.end2);
+			 * but let's optimize tail recursion ourself:
+			*/
+			count1 = LINE_END(1) - lcs.end1;
+			line1 = lcs.end1 + 1;
+			count2 = LINE_END(2) - lcs.end2;
+			line2 = lcs.end2 + 1;
+			goto redo;
+		}
+	}
+out:
+	return result;
+}
+
+int xdl_do_histogram_diff(mmfile_t *file1, mmfile_t *file2,
+	xpparam_t const *xpp, xdfenv_t *env)
+{
+	if (xdl_prepare_env(file1, file2, xpp, env) < 0)
+		return -1;
+
+	return histogram_diff(xpp, env,
+		env->xdf1.dstart + 1, env->xdf1.dend - env->xdf1.dstart + 1,
+		env->xdf2.dstart + 1, env->xdf2.dend - env->xdf2.dstart + 1);
+}
diff --git a/src/nvim/xdiff/xinclude.h b/src/nvim/xdiff/xinclude.h
new file mode 100644
index 0000000000..46b8608314
--- /dev/null
+++ b/src/nvim/xdiff/xinclude.h
@@ -0,0 +1,61 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+/* defines HAVE_ATTRIBUTE_UNUSED */
+#ifdef HAVE_CONFIG_H
+# include "../auto/config.h"
+#endif
+
+/* Mark unused function arguments with UNUSED, so that gcc -Wunused-parameter
+ * can be used to check for mistakes. */
+#ifdef HAVE_ATTRIBUTE_UNUSED
+# define UNUSED __attribute__((unused))
+#else
+# define UNUSED
+#endif
+
+#if defined(_MSC_VER)
+# define inline __inline
+#endif
+
+#if !defined(XINCLUDE_H)
+#define XINCLUDE_H
+
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#if !defined(_WIN32)
+#include <unistd.h>
+#endif
+#include <string.h>
+#include <limits.h>
+
+#include "xmacros.h"
+#include "xdiff.h"
+#include "xtypes.h"
+#include "xutils.h"
+#include "xprepare.h"
+#include "xdiffi.h"
+#include "xemit.h"
+
+
+#endif /* #if !defined(XINCLUDE_H) */
diff --git a/src/nvim/xdiff/xmacros.h b/src/nvim/xdiff/xmacros.h
new file mode 100644
index 0000000000..2809a28ca9
--- /dev/null
+++ b/src/nvim/xdiff/xmacros.h
@@ -0,0 +1,54 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XMACROS_H)
+#define XMACROS_H
+
+
+
+
+#define XDL_MIN(a, b) ((a) < (b) ? (a): (b))
+#define XDL_MAX(a, b) ((a) > (b) ? (a): (b))
+#define XDL_ABS(v) ((v) >= 0 ? (v): -(v))
+#define XDL_ISDIGIT(c) ((c) >= '0' && (c) <= '9')
+#define XDL_ISSPACE(c) (isspace((unsigned char)(c)))
+#define XDL_ADDBITS(v,b)	((v) + ((v) >> (b)))
+#define XDL_MASKBITS(b)		((1UL << (b)) - 1)
+#define XDL_HASHLONG(v,b)	(XDL_ADDBITS((unsigned long)(v), b) & XDL_MASKBITS(b))
+#define XDL_PTRFREE(p) do { if (p) { xdl_free(p); (p) = NULL; } } while (0)
+#define XDL_LE32_PUT(p, v) \
+do { \
+	unsigned char *__p = (unsigned char *) (p); \
+	*__p++ = (unsigned char) (v); \
+	*__p++ = (unsigned char) ((v) >> 8); \
+	*__p++ = (unsigned char) ((v) >> 16); \
+	*__p = (unsigned char) ((v) >> 24); \
+} while (0)
+#define XDL_LE32_GET(p, v) \
+do { \
+	unsigned char const *__p = (unsigned char const *) (p); \
+	(v) = (unsigned long) __p[0] | ((unsigned long) __p[1]) << 8 | \
+		((unsigned long) __p[2]) << 16 | ((unsigned long) __p[3]) << 24; \
+} while (0)
+
+
+#endif /* #if !defined(XMACROS_H) */
diff --git a/src/nvim/xdiff/xpatience.c b/src/nvim/xdiff/xpatience.c
new file mode 100644
index 0000000000..2c65aac386
--- /dev/null
+++ b/src/nvim/xdiff/xpatience.c
@@ -0,0 +1,393 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003-2016 Davide Libenzi, Johannes E. Schindelin
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+#include "xinclude.h"
+#include "xtypes.h"
+#include "xdiff.h"
+
+/*
+ * The basic idea of patience diff is to find lines that are unique in
+ * both files.  These are intuitively the ones that we want to see as
+ * common lines.
+ *
+ * The maximal ordered sequence of such line pairs (where ordered means
+ * that the order in the sequence agrees with the order of the lines in
+ * both files) naturally defines an initial set of common lines.
+ *
+ * Now, the algorithm tries to extend the set of common lines by growing
+ * the line ranges where the files have identical lines.
+ *
+ * Between those common lines, the patience diff algorithm is applied
+ * recursively, until no unique line pairs can be found; these line ranges
+ * are handled by the well-known Myers algorithm.
+ */
+
+#define NON_UNIQUE ULONG_MAX
+
+/*
+ * This is a hash mapping from line hash to line numbers in the first and
+ * second file.
+ */
+struct hashmap {
+	int nr, alloc;
+	struct entry {
+		unsigned long hash;
+		/*
+		 * 0 = unused entry, 1 = first line, 2 = second, etc.
+		 * line2 is NON_UNIQUE if the line is not unique
+		 * in either the first or the second file.
+		 */
+		unsigned long line1, line2;
+		/*
+		 * "next" & "previous" are used for the longest common
+		 * sequence;
+		 * initially, "next" reflects only the order in file1.
+		 */
+		struct entry *next, *previous;
+
+		/*
+		 * If 1, this entry can serve as an anchor. See
+		 * Documentation/diff-options.txt for more information.
+		 */
+		unsigned anchor : 1;
+	} *entries, *first, *last;
+	/* were common records found? */
+	unsigned long has_matches;
+	mmfile_t *file1, *file2;
+	xdfenv_t *env;
+	xpparam_t const *xpp;
+};
+
+static int is_anchor(xpparam_t const *xpp, const char *line)
+{
+	size_t i;
+	for (i = 0; i < xpp->anchors_nr; i++) {
+		if (!strncmp(line, xpp->anchors[i], strlen(xpp->anchors[i])))
+			return 1;
+	}
+	return 0;
+}
+
+/* The argument "pass" is 1 for the first file, 2 for the second. */
+static void insert_record(xpparam_t const *xpp, int line, struct hashmap *map,
+			  int pass)
+{
+	xrecord_t **records = pass == 1 ?
+		map->env->xdf1.recs : map->env->xdf2.recs;
+	xrecord_t *record = records[line - 1], *other;
+	/*
+	 * After xdl_prepare_env() (or more precisely, due to
+	 * xdl_classify_record()), the "ha" member of the records (AKA lines)
+	 * is _not_ the hash anymore, but a linearized version of it.  In
+	 * other words, the "ha" member is guaranteed to start with 0 and
+	 * the second record's ha can only be 0 or 1, etc.
+	 *
+	 * So we multiply ha by 2 in the hope that the hashing was
+	 * "unique enough".
+	 */
+	int index = (int)((record->ha << 1) % map->alloc);
+
+	while (map->entries[index].line1) {
+		other = map->env->xdf1.recs[map->entries[index].line1 - 1];
+		if (map->entries[index].hash != record->ha ||
+				!xdl_recmatch(record->ptr, record->size,
+					other->ptr, other->size,
+					map->xpp->flags)) {
+			if (++index >= map->alloc)
+				index = 0;
+			continue;
+		}
+		if (pass == 2)
+			map->has_matches = 1;
+		if (pass == 1 || map->entries[index].line2)
+			map->entries[index].line2 = NON_UNIQUE;
+		else
+			map->entries[index].line2 = line;
+		return;
+	}
+	if (pass == 2)
+		return;
+	map->entries[index].line1 = line;
+	map->entries[index].hash = record->ha;
+	map->entries[index].anchor = is_anchor(xpp, map->env->xdf1.recs[line - 1]->ptr);
+	if (!map->first)
+		map->first = map->entries + index;
+	if (map->last) {
+		map->last->next = map->entries + index;
+		map->entries[index].previous = map->last;
+	}
+	map->last = map->entries + index;
+	map->nr++;
+}
+
+/*
+ * This function has to be called for each recursion into the inter-hunk
+ * parts, as previously non-unique lines can become unique when being
+ * restricted to a smaller part of the files.
+ *
+ * It is assumed that env has been prepared using xdl_prepare().
+ */
+static int fill_hashmap(mmfile_t *file1, mmfile_t *file2,
+		xpparam_t const *xpp, xdfenv_t *env,
+		struct hashmap *result,
+		int line1, int count1, int line2, int count2)
+{
+	result->file1 = file1;
+	result->file2 = file2;
+	result->xpp = xpp;
+	result->env = env;
+
+	/* We know exactly how large we want the hash map */
+	result->alloc = count1 * 2;
+	result->entries = (struct entry *)
+		xdl_malloc(result->alloc * sizeof(struct entry));
+	if (!result->entries)
+		return -1;
+	memset(result->entries, 0, result->alloc * sizeof(struct entry));
+
+	/* First, fill with entries from the first file */
+	while (count1--)
+		insert_record(xpp, line1++, result, 1);
+
+	/* Then search for matches in the second file */
+	while (count2--)
+		insert_record(xpp, line2++, result, 2);
+
+	return 0;
+}
+
+/*
+ * Find the longest sequence with a smaller last element (meaning a smaller
+ * line2, as we construct the sequence with entries ordered by line1).
+ */
+static int binary_search(struct entry **sequence, int longest,
+		struct entry *entry)
+{
+	int left = -1, right = longest;
+
+	while (left + 1 < right) {
+		int middle = left + (right - left) / 2;
+		/* by construction, no two entries can be equal */
+		if (sequence[middle]->line2 > entry->line2)
+			right = middle;
+		else
+			left = middle;
+	}
+	/* return the index in "sequence", _not_ the sequence length */
+	return left;
+}
+
+/*
+ * The idea is to start with the list of common unique lines sorted by
+ * the order in file1.  For each of these pairs, the longest (partial)
+ * sequence whose last element's line2 is smaller is determined.
+ *
+ * For efficiency, the sequences are kept in a list containing exactly one
+ * item per sequence length: the sequence with the smallest last
+ * element (in terms of line2).
+ */
+static struct entry *find_longest_common_sequence(struct hashmap *map)
+{
+	struct entry **sequence = (struct entry **)xdl_malloc(map->nr * sizeof(struct entry *));
+	int longest = 0, i;
+	struct entry *entry;
+	/*
+	 * If not -1, this entry in sequence must never be overridden.
+	 * Therefore, overriding entries before this has no effect, so
+	 * do not do that either.
+	 */
+	int anchor_i = -1;
+
+	/* Added to silence Coverity. */
+	if (sequence == NULL)
+		return map->first;
+
+	for (entry = map->first; entry; entry = entry->next) {
+		if (!entry->line2 || entry->line2 == NON_UNIQUE)
+			continue;
+		i = binary_search(sequence, longest, entry);
+		entry->previous = i < 0 ? NULL : sequence[i];
+		++i;
+		if (i <= anchor_i)
+			continue;
+		sequence[i] = entry;
+		if (entry->anchor) {
+			anchor_i = i;
+			longest = anchor_i + 1;
+		} else if (i == longest) {
+			longest++;
+		}
+	}
+
+	/* No common unique lines were found */
+	if (!longest) {
+		xdl_free(sequence);
+		return NULL;
+	}
+
+	/* Iterate starting at the last element, adjusting the "next" members */
+	entry = sequence[longest - 1];
+	entry->next = NULL;
+	while (entry->previous) {
+		entry->previous->next = entry;
+		entry = entry->previous;
+	}
+	xdl_free(sequence);
+	return entry;
+}
+
+static int match(struct hashmap *map, int line1, int line2)
+{
+	xrecord_t *record1 = map->env->xdf1.recs[line1 - 1];
+	xrecord_t *record2 = map->env->xdf2.recs[line2 - 1];
+	return xdl_recmatch(record1->ptr, record1->size,
+		record2->ptr, record2->size, map->xpp->flags);
+}
+
+static int patience_diff(mmfile_t *file1, mmfile_t *file2,
+		xpparam_t const *xpp, xdfenv_t *env,
+		int line1, int count1, int line2, int count2);
+
+static int walk_common_sequence(struct hashmap *map, struct entry *first,
+		int line1, int count1, int line2, int count2)
+{
+	int end1 = line1 + count1, end2 = line2 + count2;
+	int next1, next2;
+
+	for (;;) {
+		/* Try to grow the line ranges of common lines */
+		if (first) {
+			next1 = first->line1;
+			next2 = first->line2;
+			while (next1 > line1 && next2 > line2 &&
+					match(map, next1 - 1, next2 - 1)) {
+				next1--;
+				next2--;
+			}
+		} else {
+			next1 = end1;
+			next2 = end2;
+		}
+		while (line1 < next1 && line2 < next2 &&
+				match(map, line1, line2)) {
+			line1++;
+			line2++;
+		}
+
+		/* Recurse */
+		if (next1 > line1 || next2 > line2) {
+			struct hashmap submap;
+
+			memset(&submap, 0, sizeof(submap));
+			if (patience_diff(map->file1, map->file2,
+					map->xpp, map->env,
+					line1, next1 - line1,
+					line2, next2 - line2))
+				return -1;
+		}
+
+		if (!first)
+			return 0;
+
+		while (first->next &&
+				first->next->line1 == first->line1 + 1 &&
+				first->next->line2 == first->line2 + 1)
+			first = first->next;
+
+		line1 = first->line1 + 1;
+		line2 = first->line2 + 1;
+
+		first = first->next;
+	}
+}
+
+static int fall_back_to_classic_diff(struct hashmap *map,
+		int line1, int count1, int line2, int count2)
+{
+	xpparam_t xpp;
+	xpp.flags = map->xpp->flags & ~XDF_DIFF_ALGORITHM_MASK;
+
+	return xdl_fall_back_diff(map->env, &xpp,
+				  line1, count1, line2, count2);
+}
+
+/*
+ * Recursively find the longest common sequence of unique lines,
+ * and if none was found, ask xdl_do_diff() to do the job.
+ *
+ * This function assumes that env was prepared with xdl_prepare_env().
+ */
+static int patience_diff(mmfile_t *file1, mmfile_t *file2,
+		xpparam_t const *xpp, xdfenv_t *env,
+		int line1, int count1, int line2, int count2)
+{
+	struct hashmap map;
+	struct entry *first;
+	int result = 0;
+
+	/* trivial case: one side is empty */
+	if (!count1) {
+		while(count2--)
+			env->xdf2.rchg[line2++ - 1] = 1;
+		return 0;
+	} else if (!count2) {
+		while(count1--)
+			env->xdf1.rchg[line1++ - 1] = 1;
+		return 0;
+	}
+
+	memset(&map, 0, sizeof(map));
+	if (fill_hashmap(file1, file2, xpp, env, &map,
+			line1, count1, line2, count2))
+		return -1;
+
+	/* are there any matching lines at all? */
+	if (!map.has_matches) {
+		while(count1--)
+			env->xdf1.rchg[line1++ - 1] = 1;
+		while(count2--)
+			env->xdf2.rchg[line2++ - 1] = 1;
+		xdl_free(map.entries);
+		return 0;
+	}
+
+	first = find_longest_common_sequence(&map);
+	if (first)
+		result = walk_common_sequence(&map, first,
+			line1, count1, line2, count2);
+	else
+		result = fall_back_to_classic_diff(&map,
+			line1, count1, line2, count2);
+
+	xdl_free(map.entries);
+	return result;
+}
+
+int xdl_do_patience_diff(mmfile_t *file1, mmfile_t *file2,
+		xpparam_t const *xpp, xdfenv_t *env)
+{
+	if (xdl_prepare_env(file1, file2, xpp, env) < 0)
+		return -1;
+
+	/* environment is cleaned up in xdl_diff() */
+	return patience_diff(file1, file2, xpp, env,
+			1, env->xdf1.nrec, 1, env->xdf2.nrec);
+}
diff --git a/src/nvim/xdiff/xprepare.c b/src/nvim/xdiff/xprepare.c
new file mode 100644
index 0000000000..abeb8fb84e
--- /dev/null
+++ b/src/nvim/xdiff/xprepare.c
@@ -0,0 +1,483 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include "xinclude.h"
+
+
+#define XDL_KPDIS_RUN 4
+#define XDL_MAX_EQLIMIT 1024
+#define XDL_SIMSCAN_WINDOW 100
+#define XDL_GUESS_NLINES1 256
+#define XDL_GUESS_NLINES2 20
+
+
+typedef struct s_xdlclass {
+	struct s_xdlclass *next;
+	unsigned long ha;
+	char const *line;
+	long size;
+	long idx;
+	long len1, len2;
+} xdlclass_t;
+
+typedef struct s_xdlclassifier {
+	unsigned int hbits;
+	long hsize;
+	xdlclass_t **rchash;
+	chastore_t ncha;
+	xdlclass_t **rcrecs;
+	long alloc;
+	long count;
+	long flags;
+} xdlclassifier_t;
+
+
+
+
+static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags);
+static void xdl_free_classifier(xdlclassifier_t *cf);
+static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t **rhash,
+			       unsigned int hbits, xrecord_t *rec);
+static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_t const *xpp,
+			   xdlclassifier_t *cf, xdfile_t *xdf);
+static void xdl_free_ctx(xdfile_t *xdf);
+static int xdl_clean_mmatch(char const *dis, long i, long s, long e);
+static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2);
+static int xdl_trim_ends(xdfile_t *xdf1, xdfile_t *xdf2);
+static int xdl_optimize_ctxs(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2);
+
+
+
+
+static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags) {
+	cf->flags = flags;
+
+	cf->hbits = xdl_hashbits((unsigned int) size);
+	cf->hsize = 1 << cf->hbits;
+
+	if (xdl_cha_init(&cf->ncha, sizeof(xdlclass_t), size / 4 + 1) < 0) {
+
+		return -1;
+	}
+	if (!(cf->rchash = (xdlclass_t **) xdl_malloc(cf->hsize * sizeof(xdlclass_t *)))) {
+
+		xdl_cha_free(&cf->ncha);
+		return -1;
+	}
+	memset(cf->rchash, 0, cf->hsize * sizeof(xdlclass_t *));
+
+	cf->alloc = size;
+	if (!(cf->rcrecs = (xdlclass_t **) xdl_malloc(cf->alloc * sizeof(xdlclass_t *)))) {
+
+		xdl_free(cf->rchash);
+		xdl_cha_free(&cf->ncha);
+		return -1;
+	}
+
+	cf->count = 0;
+
+	return 0;
+}
+
+
+static void xdl_free_classifier(xdlclassifier_t *cf) {
+
+	xdl_free(cf->rcrecs);
+	xdl_free(cf->rchash);
+	xdl_cha_free(&cf->ncha);
+}
+
+
+static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t **rhash,
+			       unsigned int hbits, xrecord_t *rec) {
+	long hi;
+	char const *line;
+	xdlclass_t *rcrec;
+	xdlclass_t **rcrecs;
+
+	line = rec->ptr;
+	hi = (long) XDL_HASHLONG(rec->ha, cf->hbits);
+	for (rcrec = cf->rchash[hi]; rcrec; rcrec = rcrec->next)
+		if (rcrec->ha == rec->ha &&
+				xdl_recmatch(rcrec->line, rcrec->size,
+					rec->ptr, rec->size, cf->flags))
+			break;
+
+	if (!rcrec) {
+		if (!(rcrec = xdl_cha_alloc(&cf->ncha))) {
+
+			return -1;
+		}
+		rcrec->idx = cf->count++;
+		if (cf->count > cf->alloc) {
+			cf->alloc *= 2;
+			if (!(rcrecs = (xdlclass_t **) xdl_realloc(cf->rcrecs, cf->alloc * sizeof(xdlclass_t *)))) {
+
+				return -1;
+			}
+			cf->rcrecs = rcrecs;
+		}
+		cf->rcrecs[rcrec->idx] = rcrec;
+		rcrec->line = line;
+		rcrec->size = rec->size;
+		rcrec->ha = rec->ha;
+		rcrec->len1 = rcrec->len2 = 0;
+		rcrec->next = cf->rchash[hi];
+		cf->rchash[hi] = rcrec;
+	}
+
+	(pass == 1) ? rcrec->len1++ : rcrec->len2++;
+
+	rec->ha = (unsigned long) rcrec->idx;
+
+	hi = (long) XDL_HASHLONG(rec->ha, hbits);
+	rec->next = rhash[hi];
+	rhash[hi] = rec;
+
+	return 0;
+}
+
+
+static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_t const *xpp,
+			   xdlclassifier_t *cf, xdfile_t *xdf) {
+	unsigned int hbits;
+	long nrec, hsize, bsize;
+	unsigned long hav;
+	char const *blk, *cur, *top, *prev;
+	xrecord_t *crec;
+	xrecord_t **recs, **rrecs;
+	xrecord_t **rhash;
+	unsigned long *ha;
+	char *rchg;
+	long *rindex;
+
+	ha = NULL;
+	rindex = NULL;
+	rchg = NULL;
+	rhash = NULL;
+	recs = NULL;
+
+	if (xdl_cha_init(&xdf->rcha, sizeof(xrecord_t), narec / 4 + 1) < 0)
+		goto abort;
+	if (!(recs = (xrecord_t **) xdl_malloc(narec * sizeof(xrecord_t *))))
+		goto abort;
+
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
+		hbits = hsize = 0;
+	else {
+		hbits = xdl_hashbits((unsigned int) narec);
+		hsize = 1 << hbits;
+		if (!(rhash = (xrecord_t **) xdl_malloc(hsize * sizeof(xrecord_t *))))
+			goto abort;
+		memset(rhash, 0, hsize * sizeof(xrecord_t *));
+	}
+
+	nrec = 0;
+	if ((cur = blk = xdl_mmfile_first(mf, &bsize)) != NULL) {
+		for (top = blk + bsize; cur < top; ) {
+			prev = cur;
+			hav = xdl_hash_record(&cur, top, xpp->flags);
+			if (nrec >= narec) {
+				narec *= 2;
+				if (!(rrecs = (xrecord_t **) xdl_realloc(recs, narec * sizeof(xrecord_t *))))
+					goto abort;
+				recs = rrecs;
+			}
+			if (!(crec = xdl_cha_alloc(&xdf->rcha)))
+				goto abort;
+			crec->ptr = prev;
+			crec->size = (long) (cur - prev);
+			crec->ha = hav;
+			recs[nrec++] = crec;
+
+			if ((XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF) &&
+			    xdl_classify_record(pass, cf, rhash, hbits, crec) < 0)
+				goto abort;
+		}
+	}
+
+	if (!(rchg = (char *) xdl_malloc((nrec + 2) * sizeof(char))))
+		goto abort;
+	memset(rchg, 0, (nrec + 2) * sizeof(char));
+
+	if (!(rindex = (long *) xdl_malloc((nrec + 1) * sizeof(long))))
+		goto abort;
+	if (!(ha = (unsigned long *) xdl_malloc((nrec + 1) * sizeof(unsigned long))))
+		goto abort;
+
+	xdf->nrec = nrec;
+	xdf->recs = recs;
+	xdf->hbits = hbits;
+	xdf->rhash = rhash;
+	xdf->rchg = rchg + 1;
+	xdf->rindex = rindex;
+	xdf->nreff = 0;
+	xdf->ha = ha;
+	xdf->dstart = 0;
+	xdf->dend = nrec - 1;
+
+	return 0;
+
+abort:
+	xdl_free(ha);
+	xdl_free(rindex);
+	xdl_free(rchg);
+	xdl_free(rhash);
+	xdl_free(recs);
+	xdl_cha_free(&xdf->rcha);
+	return -1;
+}
+
+
+static void xdl_free_ctx(xdfile_t *xdf) {
+
+	xdl_free(xdf->rhash);
+	xdl_free(xdf->rindex);
+	xdl_free(xdf->rchg - 1);
+	xdl_free(xdf->ha);
+	xdl_free(xdf->recs);
+	xdl_cha_free(&xdf->rcha);
+}
+
+
+int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		    xdfenv_t *xe) {
+	long enl1, enl2, sample;
+	xdlclassifier_t cf;
+
+	memset(&cf, 0, sizeof(cf));
+
+	/*
+	 * For histogram diff, we can afford a smaller sample size and
+	 * thus a poorer estimate of the number of lines, as the hash
+	 * table (rhash) won't be filled up/grown. The number of lines
+	 * (nrecs) will be updated correctly anyway by
+	 * xdl_prepare_ctx().
+	 */
+	sample = (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF
+		  ? XDL_GUESS_NLINES2 : XDL_GUESS_NLINES1);
+
+	enl1 = xdl_guess_lines(mf1, sample) + 1;
+	enl2 = xdl_guess_lines(mf2, sample) + 1;
+
+	if (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF &&
+	    xdl_init_classifier(&cf, enl1 + enl2 + 1, xpp->flags) < 0)
+		return -1;
+
+	if (xdl_prepare_ctx(1, mf1, enl1, xpp, &cf, &xe->xdf1) < 0) {
+
+		xdl_free_classifier(&cf);
+		return -1;
+	}
+	if (xdl_prepare_ctx(2, mf2, enl2, xpp, &cf, &xe->xdf2) < 0) {
+
+		xdl_free_ctx(&xe->xdf1);
+		xdl_free_classifier(&cf);
+		return -1;
+	}
+
+	if ((XDF_DIFF_ALG(xpp->flags) != XDF_PATIENCE_DIFF) &&
+	    (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF) &&
+	    xdl_optimize_ctxs(&cf, &xe->xdf1, &xe->xdf2) < 0) {
+
+		xdl_free_ctx(&xe->xdf2);
+		xdl_free_ctx(&xe->xdf1);
+		xdl_free_classifier(&cf);
+		return -1;
+	}
+
+	if (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF)
+		xdl_free_classifier(&cf);
+
+	return 0;
+}
+
+
+void xdl_free_env(xdfenv_t *xe) {
+
+	xdl_free_ctx(&xe->xdf2);
+	xdl_free_ctx(&xe->xdf1);
+}
+
+
+static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
+	long r, rdis0, rpdis0, rdis1, rpdis1;
+
+	/*
+	 * Limits the window the is examined during the similar-lines
+	 * scan. The loops below stops when dis[i - r] == 1 (line that
+	 * has no match), but there are corner cases where the loop
+	 * proceed all the way to the extremities by causing huge
+	 * performance penalties in case of big files.
+	 */
+	if (i - s > XDL_SIMSCAN_WINDOW)
+		s = i - XDL_SIMSCAN_WINDOW;
+	if (e - i > XDL_SIMSCAN_WINDOW)
+		e = i + XDL_SIMSCAN_WINDOW;
+
+	/*
+	 * Scans the lines before 'i' to find a run of lines that either
+	 * have no match (dis[j] == 0) or have multiple matches (dis[j] > 1).
+	 * Note that we always call this function with dis[i] > 1, so the
+	 * current line (i) is already a multimatch line.
+	 */
+	for (r = 1, rdis0 = 0, rpdis0 = 1; (i - r) >= s; r++) {
+		if (!dis[i - r])
+			rdis0++;
+		else if (dis[i - r] == 2)
+			rpdis0++;
+		else
+			break;
+	}
+	/*
+	 * If the run before the line 'i' found only multimatch lines, we
+	 * return 0 and hence we don't make the current line (i) discarded.
+	 * We want to discard multimatch lines only when they appear in the
+	 * middle of runs with nomatch lines (dis[j] == 0).
+	 */
+	if (rdis0 == 0)
+		return 0;
+	for (r = 1, rdis1 = 0, rpdis1 = 1; (i + r) <= e; r++) {
+		if (!dis[i + r])
+			rdis1++;
+		else if (dis[i + r] == 2)
+			rpdis1++;
+		else
+			break;
+	}
+	/*
+	 * If the run after the line 'i' found only multimatch lines, we
+	 * return 0 and hence we don't make the current line (i) discarded.
+	 */
+	if (rdis1 == 0)
+		return 0;
+	rdis1 += rdis0;
+	rpdis1 += rpdis0;
+
+	return rpdis1 * XDL_KPDIS_RUN < (rpdis1 + rdis1);
+}
+
+
+/*
+ * Try to reduce the problem complexity, discard records that have no
+ * matches on the other file. Also, lines that have multiple matches
+ * might be potentially discarded if they happear in a run of discardable.
+ */
+static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
+	long i, nm, nreff, mlim;
+	xrecord_t **recs;
+	xdlclass_t *rcrec;
+	char *dis, *dis1, *dis2;
+
+	if (!(dis = (char *) xdl_malloc(xdf1->nrec + xdf2->nrec + 2))) {
+
+		return -1;
+	}
+	memset(dis, 0, xdf1->nrec + xdf2->nrec + 2);
+	dis1 = dis;
+	dis2 = dis1 + xdf1->nrec + 1;
+
+	if ((mlim = xdl_bogosqrt(xdf1->nrec)) > XDL_MAX_EQLIMIT)
+		mlim = XDL_MAX_EQLIMIT;
+	for (i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart]; i <= xdf1->dend; i++, recs++) {
+		rcrec = cf->rcrecs[(*recs)->ha];
+		nm = rcrec ? rcrec->len2 : 0;
+		dis1[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+	}
+
+	if ((mlim = xdl_bogosqrt(xdf2->nrec)) > XDL_MAX_EQLIMIT)
+		mlim = XDL_MAX_EQLIMIT;
+	for (i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart]; i <= xdf2->dend; i++, recs++) {
+		rcrec = cf->rcrecs[(*recs)->ha];
+		nm = rcrec ? rcrec->len1 : 0;
+		dis2[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+	}
+
+	for (nreff = 0, i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart];
+	     i <= xdf1->dend; i++, recs++) {
+		if (dis1[i] == 1 ||
+		    (dis1[i] == 2 && !xdl_clean_mmatch(dis1, i, xdf1->dstart, xdf1->dend))) {
+			xdf1->rindex[nreff] = i;
+			xdf1->ha[nreff] = (*recs)->ha;
+			nreff++;
+		} else
+			xdf1->rchg[i] = 1;
+	}
+	xdf1->nreff = nreff;
+
+	for (nreff = 0, i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart];
+	     i <= xdf2->dend; i++, recs++) {
+		if (dis2[i] == 1 ||
+		    (dis2[i] == 2 && !xdl_clean_mmatch(dis2, i, xdf2->dstart, xdf2->dend))) {
+			xdf2->rindex[nreff] = i;
+			xdf2->ha[nreff] = (*recs)->ha;
+			nreff++;
+		} else
+			xdf2->rchg[i] = 1;
+	}
+	xdf2->nreff = nreff;
+
+	xdl_free(dis);
+
+	return 0;
+}
+
+
+/*
+ * Early trim initial and terminal matching records.
+ */
+static int xdl_trim_ends(xdfile_t *xdf1, xdfile_t *xdf2) {
+	long i, lim;
+	xrecord_t **recs1, **recs2;
+
+	recs1 = xdf1->recs;
+	recs2 = xdf2->recs;
+	for (i = 0, lim = XDL_MIN(xdf1->nrec, xdf2->nrec); i < lim;
+	     i++, recs1++, recs2++)
+		if ((*recs1)->ha != (*recs2)->ha)
+			break;
+
+	xdf1->dstart = xdf2->dstart = i;
+
+	recs1 = xdf1->recs + xdf1->nrec - 1;
+	recs2 = xdf2->recs + xdf2->nrec - 1;
+	for (lim -= i, i = 0; i < lim; i++, recs1--, recs2--)
+		if ((*recs1)->ha != (*recs2)->ha)
+			break;
+
+	xdf1->dend = xdf1->nrec - i - 1;
+	xdf2->dend = xdf2->nrec - i - 1;
+
+	return 0;
+}
+
+
+static int xdl_optimize_ctxs(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
+
+	if (xdl_trim_ends(xdf1, xdf2) < 0 ||
+	    xdl_cleanup_records(cf, xdf1, xdf2) < 0) {
+
+		return -1;
+	}
+
+	return 0;
+}
diff --git a/src/nvim/xdiff/xprepare.h b/src/nvim/xdiff/xprepare.h
new file mode 100644
index 0000000000..947d9fc1bb
--- /dev/null
+++ b/src/nvim/xdiff/xprepare.h
@@ -0,0 +1,34 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XPREPARE_H)
+#define XPREPARE_H
+
+
+
+int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		    xdfenv_t *xe);
+void xdl_free_env(xdfenv_t *xe);
+
+
+
+#endif /* #if !defined(XPREPARE_H) */
diff --git a/src/nvim/xdiff/xtypes.h b/src/nvim/xdiff/xtypes.h
new file mode 100644
index 0000000000..8442bd436e
--- /dev/null
+++ b/src/nvim/xdiff/xtypes.h
@@ -0,0 +1,67 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XTYPES_H)
+#define XTYPES_H
+
+
+
+typedef struct s_chanode {
+	struct s_chanode *next;
+	long icurr;
+} chanode_t;
+
+typedef struct s_chastore {
+	chanode_t *head, *tail;
+	long isize, nsize;
+	chanode_t *ancur;
+	chanode_t *sncur;
+	long scurr;
+} chastore_t;
+
+typedef struct s_xrecord {
+	struct s_xrecord *next;
+	char const *ptr;
+	long size;
+	unsigned long ha;
+} xrecord_t;
+
+typedef struct s_xdfile {
+	chastore_t rcha;
+	long nrec;
+	unsigned int hbits;
+	xrecord_t **rhash;
+	long dstart, dend;
+	xrecord_t **recs;
+	char *rchg;
+	long *rindex;
+	long nreff;
+	unsigned long *ha;
+} xdfile_t;
+
+typedef struct s_xdfenv {
+	xdfile_t xdf1, xdf2;
+} xdfenv_t;
+
+
+
+#endif /* #if !defined(XTYPES_H) */
diff --git a/src/nvim/xdiff/xutils.c b/src/nvim/xdiff/xutils.c
new file mode 100644
index 0000000000..25a090fb73
--- /dev/null
+++ b/src/nvim/xdiff/xutils.c
@@ -0,0 +1,425 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003	Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include <limits.h>
+#include <assert.h>
+#include "xinclude.h"
+
+
+
+
+long xdl_bogosqrt(long n) {
+	long i;
+
+	/*
+	 * Classical integer square root approximation using shifts.
+	 */
+	for (i = 1; n > 0; n >>= 2)
+		i <<= 1;
+
+	return i;
+}
+
+
+int xdl_emit_diffrec(char const *rec, long size, char const *pre, long psize,
+		     xdemitcb_t *ecb) {
+	int i = 2;
+	mmbuffer_t mb[3];
+
+	mb[0].ptr = (char *) pre;
+	mb[0].size = psize;
+	mb[1].ptr = (char *) rec;
+	mb[1].size = size;
+	if (size > 0 && rec[size - 1] != '\n') {
+		mb[2].ptr = (char *) "\n\\ No newline at end of file\n";
+		mb[2].size = (long)strlen(mb[2].ptr);
+		i++;
+	}
+	if (ecb->outf(ecb->priv, mb, i) < 0) {
+
+		return -1;
+	}
+
+	return 0;
+}
+
+void *xdl_mmfile_first(mmfile_t *mmf, long *size)
+{
+	*size = mmf->size;
+	return mmf->ptr;
+}
+
+
+long xdl_mmfile_size(mmfile_t *mmf)
+{
+	return mmf->size;
+}
+
+
+int xdl_cha_init(chastore_t *cha, long isize, long icount) {
+
+	cha->head = cha->tail = NULL;
+	cha->isize = isize;
+	cha->nsize = icount * isize;
+	cha->ancur = cha->sncur = NULL;
+	cha->scurr = 0;
+
+	return 0;
+}
+
+
+void xdl_cha_free(chastore_t *cha) {
+	chanode_t *cur, *tmp;
+
+	for (cur = cha->head; (tmp = cur) != NULL;) {
+		cur = cur->next;
+		xdl_free(tmp);
+	}
+}
+
+
+void *xdl_cha_alloc(chastore_t *cha) {
+	chanode_t *ancur;
+	void *data;
+
+	if (!(ancur = cha->ancur) || ancur->icurr == cha->nsize) {
+		if (!(ancur = (chanode_t *) xdl_malloc(sizeof(chanode_t) + cha->nsize))) {
+
+			return NULL;
+		}
+		ancur->icurr = 0;
+		ancur->next = NULL;
+		if (cha->tail)
+			cha->tail->next = ancur;
+		if (!cha->head)
+			cha->head = ancur;
+		cha->tail = ancur;
+		cha->ancur = ancur;
+	}
+
+	data = (char *) ancur + sizeof(chanode_t) + ancur->icurr;
+	ancur->icurr += cha->isize;
+
+	return data;
+}
+
+long xdl_guess_lines(mmfile_t *mf, long sample) {
+	long nl = 0, size, tsize = 0;
+	char const *data, *cur, *top;
+
+	if ((cur = data = xdl_mmfile_first(mf, &size)) != NULL) {
+		for (top = data + size; nl < sample && cur < top; ) {
+			nl++;
+			if (!(cur = memchr(cur, '\n', top - cur)))
+				cur = top;
+			else
+				cur++;
+		}
+		tsize += (long) (cur - data);
+	}
+
+	if (nl && tsize)
+		nl = xdl_mmfile_size(mf) / (tsize / nl);
+
+	return nl + 1;
+}
+
+int xdl_blankline(const char *line, long size, long flags)
+{
+	long i;
+
+	if (!(flags & XDF_WHITESPACE_FLAGS))
+		return (size <= 1);
+
+	for (i = 0; i < size && XDL_ISSPACE(line[i]); i++)
+		;
+
+	return (i == size);
+}
+
+/*
+ * Have we eaten everything on the line, except for an optional
+ * CR at the very end?
+ */
+static int ends_with_optional_cr(const char *l, long s, long i)
+{
+	int complete = s && l[s-1] == '\n';
+
+	if (complete)
+		s--;
+	if (s == i)
+		return 1;
+	/* do not ignore CR at the end of an incomplete line */
+	if (complete && s == i + 1 && l[i] == '\r')
+		return 1;
+	return 0;
+}
+
+int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags)
+{
+	int i1, i2;
+
+	if (s1 == s2 && !memcmp(l1, l2, s1))
+		return 1;
+	if (!(flags & XDF_WHITESPACE_FLAGS))
+		return 0;
+
+	i1 = 0;
+	i2 = 0;
+
+	/*
+	 * -w matches everything that matches with -b, and -b in turn
+	 * matches everything that matches with --ignore-space-at-eol,
+	 * which in turn matches everything that matches with --ignore-cr-at-eol.
+	 *
+	 * Each flavor of ignoring needs different logic to skip whitespaces
+	 * while we have both sides to compare.
+	 */
+	if (flags & XDF_IGNORE_WHITESPACE) {
+		goto skip_ws;
+		while (i1 < s1 && i2 < s2) {
+			if (l1[i1++] != l2[i2++])
+				return 0;
+		skip_ws:
+			while (i1 < s1 && XDL_ISSPACE(l1[i1]))
+				i1++;
+			while (i2 < s2 && XDL_ISSPACE(l2[i2]))
+				i2++;
+		}
+	} else if (flags & XDF_IGNORE_WHITESPACE_CHANGE) {
+		while (i1 < s1 && i2 < s2) {
+			if (XDL_ISSPACE(l1[i1]) && XDL_ISSPACE(l2[i2])) {
+				/* Skip matching spaces and try again */
+				while (i1 < s1 && XDL_ISSPACE(l1[i1]))
+					i1++;
+				while (i2 < s2 && XDL_ISSPACE(l2[i2]))
+					i2++;
+				continue;
+			}
+			if (l1[i1++] != l2[i2++])
+				return 0;
+		}
+	} else if (flags & XDF_IGNORE_WHITESPACE_AT_EOL) {
+		while (i1 < s1 && i2 < s2 && l1[i1] == l2[i2]) {
+			i1++;
+			i2++;
+		}
+	} else if (flags & XDF_IGNORE_CR_AT_EOL) {
+		/* Find the first difference and see how the line ends */
+		while (i1 < s1 && i2 < s2 && l1[i1] == l2[i2]) {
+			i1++;
+			i2++;
+		}
+		return (ends_with_optional_cr(l1, s1, i1) &&
+			ends_with_optional_cr(l2, s2, i2));
+	}
+
+	/*
+	 * After running out of one side, the remaining side must have
+	 * nothing but whitespace for the lines to match.  Note that
+	 * ignore-whitespace-at-eol case may break out of the loop
+	 * while there still are characters remaining on both lines.
+	 */
+	if (i1 < s1) {
+		while (i1 < s1 && XDL_ISSPACE(l1[i1]))
+			i1++;
+		if (s1 != i1)
+			return 0;
+	}
+	if (i2 < s2) {
+		while (i2 < s2 && XDL_ISSPACE(l2[i2]))
+			i2++;
+		return (s2 == i2);
+	}
+	return 1;
+}
+
+static unsigned long xdl_hash_record_with_whitespace(char const **data,
+		char const *top, long flags) {
+	unsigned long ha = 5381;
+	char const *ptr = *data;
+	int cr_at_eol_only = (flags & XDF_WHITESPACE_FLAGS) == XDF_IGNORE_CR_AT_EOL;
+
+	for (; ptr < top && *ptr != '\n'; ptr++) {
+		if (cr_at_eol_only) {
+			/* do not ignore CR at the end of an incomplete line */
+			if (*ptr == '\r' &&
+			    (ptr + 1 < top && ptr[1] == '\n'))
+				continue;
+		}
+		else if (XDL_ISSPACE(*ptr)) {
+			const char *ptr2 = ptr;
+			int at_eol;
+			while (ptr + 1 < top && XDL_ISSPACE(ptr[1])
+					&& ptr[1] != '\n')
+				ptr++;
+			at_eol = (top <= ptr + 1 || ptr[1] == '\n');
+			if (flags & XDF_IGNORE_WHITESPACE)
+				; /* already handled */
+			else if (flags & XDF_IGNORE_WHITESPACE_CHANGE
+				 && !at_eol) {
+				ha += (ha << 5);
+				ha ^= (unsigned long) ' ';
+			}
+			else if (flags & XDF_IGNORE_WHITESPACE_AT_EOL
+				 && !at_eol) {
+				while (ptr2 != ptr + 1) {
+					ha += (ha << 5);
+					ha ^= (unsigned long) *ptr2;
+					ptr2++;
+				}
+			}
+			continue;
+		}
+		ha += (ha << 5);
+		ha ^= (unsigned long) *ptr;
+	}
+	*data = ptr < top ? ptr + 1: ptr;
+
+	return ha;
+}
+
+unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
+	unsigned long ha = 5381;
+	char const *ptr = *data;
+
+	if (flags & XDF_WHITESPACE_FLAGS)
+		return xdl_hash_record_with_whitespace(data, top, flags);
+
+	for (; ptr < top && *ptr != '\n'; ptr++) {
+		ha += (ha << 5);
+		ha ^= (unsigned long) *ptr;
+	}
+	*data = ptr < top ? ptr + 1: ptr;
+
+	return ha;
+}
+
+unsigned int xdl_hashbits(unsigned int size) {
+	unsigned int val = 1, bits = 0;
+
+	for (; val < size && bits < CHAR_BIT * sizeof(unsigned int); val <<= 1, bits++);
+	return bits ? bits: 1;
+}
+
+
+int xdl_num_out(char *out, long val) {
+	char *ptr, *str = out;
+	char buf[32];
+
+	ptr = buf + sizeof(buf) - 1;
+	*ptr = '\0';
+	if (val < 0) {
+		*--ptr = '-';
+		val = -val;
+	}
+	for (; val && ptr > buf; val /= 10)
+		*--ptr = "0123456789"[val % 10];
+	if (*ptr)
+		for (; *ptr; ptr++, str++)
+			*str = *ptr;
+	else
+		*str++ = '0';
+	*str = '\0';
+
+	return str - out;
+}
+
+int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
+		      const char *func, long funclen, xdemitcb_t *ecb) {
+	int nb = 0;
+	mmbuffer_t mb;
+	char buf[128];
+
+	memcpy(buf, "@@ -", 4);
+	nb += 4;
+
+	nb += xdl_num_out(buf + nb, c1 ? s1: s1 - 1);
+
+	if (c1 != 1) {
+		memcpy(buf + nb, ",", 1);
+		nb += 1;
+
+		nb += xdl_num_out(buf + nb, c1);
+	}
+
+	memcpy(buf + nb, " +", 2);
+	nb += 2;
+
+	nb += xdl_num_out(buf + nb, c2 ? s2: s2 - 1);
+
+	if (c2 != 1) {
+		memcpy(buf + nb, ",", 1);
+		nb += 1;
+
+		nb += xdl_num_out(buf + nb, c2);
+	}
+
+	memcpy(buf + nb, " @@", 3);
+	nb += 3;
+	if (func && funclen) {
+		buf[nb++] = ' ';
+		if (funclen > (long)sizeof(buf) - nb - 1)
+			funclen = sizeof(buf) - nb - 1;
+		memcpy(buf + nb, func, funclen);
+		nb += funclen;
+	}
+	buf[nb++] = '\n';
+
+	mb.ptr = buf;
+	mb.size = nb;
+	if (ecb->outf(ecb->priv, &mb, 1) < 0)
+		return -1;
+
+	return 0;
+}
+
+int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
+		int line1, int count1, int line2, int count2)
+{
+	/*
+	 * This probably does not work outside Git, since
+	 * we have a very simple mmfile structure.
+	 *
+	 * Note: ideally, we would reuse the prepared environment, but
+	 * the libxdiff interface does not (yet) allow for diffing only
+	 * ranges of lines instead of the whole files.
+	 */
+	mmfile_t subfile1, subfile2;
+	xdfenv_t env;
+
+	subfile1.ptr = (char *)diff_env->xdf1.recs[line1 - 1]->ptr;
+	subfile1.size = diff_env->xdf1.recs[line1 + count1 - 2]->ptr +
+		diff_env->xdf1.recs[line1 + count1 - 2]->size - subfile1.ptr;
+	subfile2.ptr = (char *)diff_env->xdf2.recs[line2 - 1]->ptr;
+	subfile2.size = diff_env->xdf2.recs[line2 + count2 - 2]->ptr +
+		diff_env->xdf2.recs[line2 + count2 - 2]->size - subfile2.ptr;
+	if (xdl_do_diff(&subfile1, &subfile2, xpp, &env) < 0)
+		return -1;
+
+	memcpy(diff_env->xdf1.rchg + line1 - 1, env.xdf1.rchg, count1);
+	memcpy(diff_env->xdf2.rchg + line2 - 1, env.xdf2.rchg, count2);
+
+	xdl_free_env(&env);
+
+	return 0;
+}
diff --git a/src/nvim/xdiff/xutils.h b/src/nvim/xdiff/xutils.h
new file mode 100644
index 0000000000..fba7bae03c
--- /dev/null
+++ b/src/nvim/xdiff/xutils.h
@@ -0,0 +1,47 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XUTILS_H)
+#define XUTILS_H
+
+
+
+long xdl_bogosqrt(long n);
+int xdl_emit_diffrec(char const *rec, long size, char const *pre, long psize,
+		     xdemitcb_t *ecb);
+int xdl_cha_init(chastore_t *cha, long isize, long icount);
+void xdl_cha_free(chastore_t *cha);
+void *xdl_cha_alloc(chastore_t *cha);
+long xdl_guess_lines(mmfile_t *mf, long sample);
+int xdl_blankline(const char *line, long size, long flags);
+int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags);
+unsigned long xdl_hash_record(char const **data, char const *top, long flags);
+unsigned int xdl_hashbits(unsigned int size);
+int xdl_num_out(char *out, long val);
+int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
+		      const char *func, long funclen, xdemitcb_t *ecb);
+int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
+		       int line1, int count1, int line2, int count2);
+
+
+
+#endif /* #if !defined(XUTILS_H) */