maint: refactor integer overflow checking

Rely on more-modern Gnulib capabilities instead of doing
integer overflow checking by hand, in some cases.
* lib/cmpbuf.c (buffer_lcm):
* src/io.c (slurp, find_identical_ends):
Use INT_ADD_WRAPV and INT_MULTIPLY_WRAPV rather than checking
overflow by hand.
* src/diff3.c (process_diff):
* src/dir.c (dir_read):
* src/io.c (find_identical_ends, read_files):
Use xnmalloc rather than checking overflow by hand.
(read_files): Rely on xcalloc to do overflow checking.

1 files changed, 1 insertions, 2 deletions

diff --git a/lib/cmpbuf.c b/lib/cmpbuf.c
index 7cee45a..f7c34e2 100644
--- a/lib/cmpbuf.c
+++ b/lib/cmpbuf.c
@@ -104,6 +104,5 @@ buffer_lcm (size_t a, size_t b, size_t lcm_max)
 
   /* Yield a if there is an overflow.  */
   q = a / n;
-  lcm = q * b;
-  return lcm <= lcm_max && lcm / b == q ? lcm : a;
+  return !INT_MULTIPLY_WRAPV (q, b, &lcm) && lcm <= lcm_max ? lcm : a;
 }