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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
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