Re: xmalloc.c's xcalloc performs unnecessary test for N*S overflow

[Paul Eggert]

Jim Meyering <address@hidden> writes:

> As it stands, if I use both of the xalloc and calloc modules,
> calling xcalloc ends up performing the overflow check twice,
> first in xcalloc itself (above), and then again in calloc.

Also, xcalloc contains a test n != 0 that isn't needed when
rpl_calloc is being called.

How about the following (untested) change instead?  It omits the tests
when they're unnecessary, but it doesn't establish a dependency of
xalloc on calloc.  I'd rather leave out dependencies like that if it's
easy.

2005-06-16  Paul Eggert  <address@hidden>

        * xmalloc (HAVE_CALLOC): Define to 1 if not defined.
        (xcalloc): Omit needless tests if ! HAVE_CALLOC.

--- xmalloc.c   2005-05-13 23:03:58 -0700
+++ /tmp/xmalloc.c      2005-06-16 17:14:13 -0700
@@ -30,6 +30,10 @@
 # define SIZE_MAX ((size_t) -1)
 #endif
 
+#ifndef HAVE_CALLOC
+# define HAVE_CALLOC 1
+#endif
+
 /* Allocate an array of N objects, each with S bytes of memory,
    dynamically, with error checking.  S must be nonzero.  */
 
@@ -204,8 +208,11 @@ xcalloc (size_t n, size_t s)
 {
   void *p;
   /* Test for overflow, since some calloc implementations don't have
-     proper overflow checks.  */
-  if (xalloc_oversized (n, s) || (! (p = calloc (n, s)) && n != 0))
+     proper overflow checks.  Omit some tests if !HAVE_CALLOC, since
+     rpl_calloc catches overflow and never returns NULL if
+     successful.  */
+  if ((HAVE_CALLOC && xalloc_oversized (n, s))
+      || (! (p = calloc (n, s)) && ! (HAVE_CALLOC && n == 0)))
     xalloc_die ();
   return p;
 }