; Add commentary to recent changes

* src/image.c (png_load_body):
* src/editfns.c (styled_format):
* src/casefiddle.c (do_casify_multibyte_string):
* src/alloc.c (free_cons): Comment why we use a signed
temporary integer variable.  (Bug#37006)

1 files changed, 3 insertions, 1 deletions

diff --git a/src/editfns.c b/src/editfns.c
index 25f80bedb1c..19bbfdcd478 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3158,12 +3158,14 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
   /* Upper bound on number of format specs.  Each uses at least 2 chars.  */
   ptrdiff_t nspec_bound = SCHARS (args[0]) >> 1;
 
-  /* Allocate the info and discarded tables.  */
+  /* Use a temporary signed variable, since otherwise INT_ADD_WRAPV
+     might incorrectly return non-zero.  */
   ptrdiff_t info_size = sizeof *info, alloca_size;
   if (INT_MULTIPLY_WRAPV (nspec_bound, info_size, &info_size)
       || INT_ADD_WRAPV (formatlen, info_size, &alloca_size)
       || SIZE_MAX < alloca_size)
     memory_full (SIZE_MAX);
+  /* Allocate the info and discarded tables.  */
   info = SAFE_ALLOCA (alloca_size);
   /* discarded[I] is 1 if byte I of the format
      string was not copied into the output.