From: Jakub Jelinek <jakub@redhat.com>
To: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>
Cc: libc-hacker@sources.redhat.com
Subject: [PATCH] optimize calloc
Date: Sat, 03 Aug 2002 05:03:00 -0000 [thread overview]
Message-ID: <20020803140349.N20867@sunsite.ms.mff.cuni.cz> (raw)
In-Reply-To: <20020802121321.25638.qmail@md.dent.med.uni-muenchen.de>; from wmglo@dent.med.uni-muenchen.de on Fri, Aug 02, 2002 at 12:13:21PM -0000
On Fri, Aug 02, 2002 at 12:13:21PM -0000, Wolfram Gloger wrote:
> > Why not 2^32? size_t is unsigned.
>
> Yes, however malloc can only handle chunks of a little less than 2^31
> currently, so the _int_malloc later will fail anyway... But that is
> ok, having a power of two as the compared value wins against this
> micro-optimisation:
>
> > So you mean something like:
> > bytes = n * elem_size;
> > if (__builtin_expect ((a | b) >= 65536, 0)) {
> > if (bytes / elem_size != n) {
> > MALLOC_FAILURE_ACTION;
> > return 0;
> > }
> > }
>
> Hey, nice, avoids the second comparision and ||. Looks like we have a
> winner?
Ok, here is the patch:
2002-08-03 Jakub Jelinek <jakub@redhat.com>
* malloc/malloc.c (public_cALLOc): Only divide if one of arguments
is bigger than 65535.
--- libc/malloc/malloc.c.jj 2002-08-02 11:47:41.000000000 +0200
+++ libc/malloc/malloc.c 2002-08-03 13:47:50.000000000 +0200
@@ -488,6 +488,9 @@ Void_t *(*__morecore)(ptrdiff_t) = __def
#endif /* _LIBC */
#endif /* USE_DL_PREFIX */
+#ifndef _LIBC
+#define __builtin_expect(expr, val) (expr)
+#endif
/*
HAVE_MEMCPY should be defined if you are not otherwise using
@@ -3466,9 +3469,11 @@ public_cALLOc(size_t n, size_t elem_size
/* size_t is unsigned so the behavior on overflow is defined. */
bytes = n * elem_size;
- if (bytes / elem_size != n) {
- MALLOC_FAILURE_ACTION;
- return 0;
+ if (__builtin_expect ((n | elem_size) >= 65536, 0)) {
+ if (bytes / elem_size != n) {
+ MALLOC_FAILURE_ACTION;
+ return 0;
+ }
}
if (hook != NULL) {
Jakub
next prev parent reply other threads:[~2002-08-03 12:03 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-08-01 15:46 [PATCH] xdr_array and calloc security fix Jakub Jelinek
2002-08-02 0:20 ` Ulrich Drepper
2002-08-02 2:29 ` Wolfram Gloger
2002-08-02 2:43 ` Ulrich Drepper
2002-08-02 2:50 ` Ulrich Drepper
2002-08-02 2:56 ` Jakub Jelinek
2002-08-02 4:07 ` Andreas Schwab
2002-08-02 4:46 ` Jakub Jelinek
2002-08-02 4:57 ` Wolfram Gloger
2002-08-02 5:05 ` Jakub Jelinek
2002-08-02 5:13 ` Wolfram Gloger
2002-08-03 5:03 ` Jakub Jelinek [this message]
2002-08-03 12:02 ` [PATCH] optimize calloc Ulrich Drepper
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