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Re: xmalloc.c's xcalloc performs unnecessary test for N*S overflow
From: |
Paul Eggert |
Subject: |
Re: xmalloc.c's xcalloc performs unnecessary test for N*S overflow |
Date: |
Fri, 17 Jun 2005 10:42:26 -0700 |
User-agent: |
Gnus/5.1006 (Gnus v5.10.6) Emacs/21.4 (gnu/linux) |
Jim Meyering <address@hidden> writes:
> This makes me think it'd be worthwhile to support a new section in
> the modules file listing `Recommended' modules.
Yes, that would be nice. It's been suggested before but nobody has
had the time yet to do it. gnulib-tool might bring in recommended
modules automatically on request, for example.
> But why reuse the HAVE_CALLOC symbol at all?
> It's name isn't really accurate in this context.
> How about this instead:
Yes, that would be better (and thanks for catching the bug -- I did
say my patch was untested :-). Though I think it'd be better to
reverse the sense and call it "HAVE_GNU_CALLOC" or something like
that. How about the following (also untested) patch?
2005-06-17 Paul Eggert <address@hidden>
* xmalloc (HAVE_GNU_CALLOC): New macro.
(xcalloc): Omit needless tests if ! HAVE_GNU_CALLOC.
--- xmalloc.c 2005-05-13 23:03:58 -0700
+++ /tmp/xmalloc.c 2005-06-17 10:28:06 -0700
@@ -30,6 +30,15 @@
# define SIZE_MAX ((size_t) -1)
#endif
+/* 1 if calloc is known to be compatible with GNU calloc. This
+ matters if we are not also using the calloc module, which defines
+ HAVE_CALLOC and supports the GNU API even on non-GNU platforms. */
+#ifdef HAVE_CALLOC
+# define HAVE_GNU_CALLOC 1
+#else
+# define HAVE_GNU_CALLOC 0
+#endif
+
/* Allocate an array of N objects, each with S bytes of memory,
dynamically, with error checking. S must be nonzero. */
@@ -204,8 +213,11 @@ 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. But omit overflow and size-zero tests if
+ HAVE_GNU_CALLOC, since GNU calloc catches overflow and never
+ returns NULL if successful. */
+ if ((! HAVE_GNU_CALLOC && xalloc_oversized (n, s))
+ || (! (p = calloc (n, s)) && (HAVE_GNU_CALLOC || n != 0)))
xalloc_die ();
return p;
}