viml/profile: revert proftime_T to unsigned type #10521

- reltimestr(): Produce negative value by comparing the unsigned
  proftime_T value to INT64_MAX.

https://github.com/neovim/neovim/issues/10452#issuecomment-511155132
1. The interfaces of nearly all platforms return uint64_t. INT64_MAX is
   only half of that.
2. Low-level interfaces like this typically define that there is no
   fixed starting point. The only guarantees are that it's (a)
   monotonically increasing at a rate that (b) matches real time.

ref 06af88cd72ea
fix #10452

4 files changed, 40 insertions, 34 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 67aaf3c25c..1a690fdf8f 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -13840,7 +13840,7 @@ static void f_reltimestr(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   rettv->v_type = VAR_STRING;
   rettv->vval.v_string = NULL;
   if (list2proftime(&argvars[0], &tm) == OK) {
-    rettv->vval.v_string = (char_u *) xstrdup(profile_msg(tm));
+    rettv->vval.v_string = (char_u *)xstrdup(profile_msg(tm));
   }
 }
 
diff --git a/src/nvim/profile.c b/src/nvim/profile.c
index 52e03c895e..a6314e7b9d 100644
--- a/src/nvim/profile.c
+++ b/src/nvim/profile.c
@@ -24,9 +24,7 @@ static proftime_T prof_wait_time;
 /// @return the current time
 proftime_T profile_start(void) FUNC_ATTR_WARN_UNUSED_RESULT
 {
-  uint64_t now = os_hrtime();
-  assert(now <= INT64_MAX);
-  return (proftime_T)now;
+  return os_hrtime();
 }
 
 /// Computes the time elapsed.
@@ -34,9 +32,7 @@ proftime_T profile_start(void) FUNC_ATTR_WARN_UNUSED_RESULT
 /// @return Elapsed time from `tm` until now.
 proftime_T profile_end(proftime_T tm) FUNC_ATTR_WARN_UNUSED_RESULT
 {
-  uint64_t now = os_hrtime();
-  assert(now <= INT64_MAX);
-  return profile_sub((proftime_T)now, tm);
+  return profile_sub(os_hrtime(), tm);
 }
 
 /// Gets a string representing time `tm`.
@@ -48,7 +44,8 @@ proftime_T profile_end(proftime_T tm) FUNC_ATTR_WARN_UNUSED_RESULT
 const char *profile_msg(proftime_T tm) FUNC_ATTR_WARN_UNUSED_RESULT
 {
   static char buf[50];
-  snprintf(buf, sizeof(buf), "%10.6lf", (double)tm / 1000000000.0);
+  snprintf(buf, sizeof(buf), "%10.6lf",
+           (double)profile_signed(tm) / 1000000000.0);
   return buf;
 }
 
@@ -65,12 +62,8 @@ proftime_T profile_setlimit(int64_t msec) FUNC_ATTR_WARN_UNUSED_RESULT
     return profile_zero();
   }
   assert(msec <= (INT64_MAX / 1000000LL) - 1);
-  proftime_T nsec = msec * 1000000LL;
-  uint64_t now = os_hrtime();
-  assert(now <= INT64_MAX);
-  int64_t rv;
-  STRICT_ADD((proftime_T)now, nsec, &rv, int64_t);
-  return rv;
+  proftime_T nsec = (proftime_T)msec * 1000000ULL;
+  return os_hrtime() + nsec;
 }
 
 /// Checks if current time has passed `tm`.
@@ -83,9 +76,8 @@ bool profile_passed_limit(proftime_T tm) FUNC_ATTR_WARN_UNUSED_RESULT
     // timer was not set
     return false;
   }
-  uint64_t now = os_hrtime();
-  assert(now <= INT64_MAX);
-  return profile_cmp((proftime_T)now, tm) < 0;
+
+  return profile_cmp(os_hrtime(), tm) < 0;
 }
 
 /// Gets the zero time.
@@ -113,19 +105,20 @@ proftime_T profile_divide(proftime_T tm, int count) FUNC_ATTR_CONST
 /// @return `tm1` + `tm2`
 proftime_T profile_add(proftime_T tm1, proftime_T tm2) FUNC_ATTR_CONST
 {
-  int64_t rv;
-  STRICT_ADD(tm1, tm2, &rv, int64_t);
-  return rv;
+  return tm1 + tm2;
 }
 
-/// Subtracts time `tm2` from `tm1` (may be negative).
+/// Subtracts time `tm2` from `tm1`.
+///
+/// Unsigned overflow (wraparound) occurs if `tm2` is greater than `tm1`.
+/// Use `profile_signed()` to get the signed integer value.
+///
+/// @see profile_signed
 ///
 /// @return `tm1` - `tm2`
 proftime_T profile_sub(proftime_T tm1, proftime_T tm2) FUNC_ATTR_CONST
 {
-  int64_t rv;
-  STRICT_SUB(tm1, tm2, &rv, int64_t);
-  return rv;
+  return tm1 - tm2;
 }
 
 /// Adds the `self` time from the total time and the `children` time.
@@ -176,22 +169,31 @@ bool profile_equal(proftime_T tm1, proftime_T tm2) FUNC_ATTR_CONST
   return tm1 == tm2;
 }
 
-/// Calculates the sign of a 64-bit integer.
+/// Converts a proftime_T value `tm` to a signed integer.
 ///
-/// @return -1, 0, or +1
-static inline int sgn64(int64_t x) FUNC_ATTR_CONST
+/// @return signed representation of the given time value
+int64_t profile_signed(proftime_T tm)
+  FUNC_ATTR_CONST
 {
-  return (int) ((x > 0) - (x < 0));
+  // (tm > INT64_MAX) is >=150 years, so we can assume it was produced by
+  // arithmetic of two proftime_T values.  For human-readable representation
+  // (and Vim-compat) we want the difference after unsigned wraparound. #10452
+  return (tm <= INT64_MAX) ? (int64_t)tm : -(int64_t)(UINT64_MAX - tm);
 }
 
 /// Compares profiling times.
 ///
 /// Times `tm1` and `tm2` must be less than 150 years apart.
 ///
-/// @return <0, 0 or >0 if `tm2` < `tm1`, `tm2` == `tm1` or `tm2` > `tm1`
+/// @return <0: `tm2` < `tm1`
+///          0: `tm2` == `tm1`
+///         >0: `tm2` > `tm1`
 int profile_cmp(proftime_T tm1, proftime_T tm2) FUNC_ATTR_CONST
 {
-  return sgn64((int64_t)(tm2 - tm1));
+  if (tm1 == tm2) {
+    return 0;
+  }
+  return profile_signed(tm2 - tm1) < 0 ? -1 : 1;
 }
 
 /// globals for use in the startuptime related functionality (time_*).
diff --git a/src/nvim/profile.h b/src/nvim/profile.h
index 2608514313..7b378577ce 100644
--- a/src/nvim/profile.h
+++ b/src/nvim/profile.h
@@ -4,7 +4,7 @@
 #include <stdint.h>
 #include <time.h>
 
-typedef int64_t proftime_T;
+typedef uint64_t proftime_T;
 
 #define TIME_MSG(s) do { \
     if (time_fd != NULL) time_msg(s, NULL); \
diff --git a/test/functional/eval/reltime_spec.lua b/test/functional/eval/reltime_spec.lua
index ef7a3a148f..d78d858fb7 100644
--- a/test/functional/eval/reltime_spec.lua
+++ b/test/functional/eval/reltime_spec.lua
@@ -38,9 +38,13 @@ describe('reltimestr(), reltimefloat()', function()
     local older_time = reltime()
     command('sleep 1m')
     local newer_time = reltime()
-    -- Should be something like -0.002123.
+
+    -- Start/end swapped: should be something like -0.002123.
     local rv = tonumber(reltimestr(reltime(newer_time, older_time)))
-    ok(rv < 0)
-    ok(rv > -10)
+    ok(rv < 0 and rv > -10)
+
+    -- Not swapped: should be something like 0.002123.
+    rv = tonumber(reltimestr(reltime(older_time, newer_time)))
+    ok(rv > 0 and rv < 10)
   end)
 end)