From: Hans Boehm <Hans.Boehm@hp.com>
Date: Thu, 15 Mar 2012 17:09:05 +0000 (+0400)
Subject: Speedup calloc size overflow check by preventing division if small values
X-Git-Tag: gc7_3alpha2~53
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=83231d0ab5ed60015797c3d1ad9056295ac3b2bb;p=gc

Speedup calloc size overflow check by preventing division if small values

* malloc.c (GC_SQRT_SIZE_MAX): New macro.
* malloc.c (calloc): Add fast initial size overflow check to avoid
integer division for reasonably small values passed.
---

diff --git a/malloc.c b/malloc.c
index cb49a5cf..c9b9eb6a 100644
--- a/malloc.c
+++ b/malloc.c
@@ -381,9 +381,12 @@ void * malloc(size_t lb)
 # define GC_SIZE_MAX (~(size_t)0)
 #endif
 
+#define GC_SQRT_SIZE_MAX ((1U << (WORDSZ / 2)) - 1)
+
 void * calloc(size_t n, size_t lb)
 {
-    if (lb && n > GC_SIZE_MAX / lb)
+    if ((lb | n) > GC_SQRT_SIZE_MAX /* fast initial test */
+        && lb && n > GC_SIZE_MAX / lb)
       return NULL;
 #   if defined(GC_LINUX_THREADS) /* && !defined(USE_PROC_FOR_LIBRARIES) */
         /* libpthread allocated some memory that is only pointed to by  */