1 files changed, 54 insertions, 0 deletions
diff --git a/src/nvim/eval/typval.c b/src/nvim/eval/typval.c
index 794debf771..8b51500e18 100644
--- a/src/nvim/eval/typval.c
+++ b/src/nvim/eval/typval.c
@@ -2776,6 +2776,60 @@ bool tv_blob_equal(const blob_T *const b1, const blob_T *const b2)
   return true;
 }
 
+int tv_blob_slice_or_index(const blob_T *blob, int is_range, varnumber_T n1, varnumber_T n2,
+                           bool exclusive, typval_T *rettv)
+{
+  int len = tv_blob_len(rettv->vval.v_blob);
+  if (is_range) {
+    // The resulting variable is a sub-blob.  If the indexes
+    // are out of range the result is empty.
+    if (n1 < 0) {
+      n1 = len + n1;
+      if (n1 < 0) {
+        n1 = 0;
+      }
+    }
+    if (n2 < 0) {
+      n2 = len + n2;
+    } else if (n2 >= len) {
+      n2 = len - (exclusive ? 0 : 1);
+    }
+    if (exclusive) {
+      n2--;
+    }
+    if (n1 >= len || n2 < 0 || n1 > n2) {
+      tv_clear(rettv);
+      rettv->v_type = VAR_BLOB;
+      rettv->vval.v_blob = NULL;
+    } else {
+      blob_T *const new_blob = tv_blob_alloc();
+      ga_grow(&new_blob->bv_ga, (int)(n2 - n1 + 1));
+      new_blob->bv_ga.ga_len = (int)(n2 - n1 + 1);
+      for (int i = (int)n1; i <= (int)n2; i++) {
+        tv_blob_set(new_blob, i - (int)n1, tv_blob_get(rettv->vval.v_blob, i));
+      }
+      tv_clear(rettv);
+      tv_blob_set_ret(rettv, new_blob);
+    }
+  } else {
+    // The resulting variable is a byte value.
+    // If the index is too big or negative that is an error.
+    if (n1 < 0) {
+      n1 = len + n1;
+    }
+    if (n1 < len && n1 >= 0) {
+      const int v = (int)tv_blob_get(rettv->vval.v_blob, (int)n1);
+      tv_clear(rettv);
+      rettv->v_type = VAR_NUMBER;
+      rettv->vval.v_number = v;
+    } else {
+      semsg(_(e_blobidx), (int64_t)n1);
+      return FAIL;
+    }
+  }
+  return OK;
+}
+
 /// Check if "n1" is a valid index for a blob with length "bloblen".
 int tv_blob_check_index(int bloblen, varnumber_T n1, bool quiet)
 {