1 /* $NetBSD: consttime_memequal.c,v 1.5 2014/06/24 16:39:39 drochner Exp $ */ 2 3 /* 4 * Written by Matthias Drochner <drochner@NetBSD.org>. 5 * Public domain. 6 */ 7 8 #if !defined(_KERNEL) && !defined(_STANDALONE) 9 #include "namespace.h" 10 #include <string.h> 11 #ifdef __weak_alias 12 __weak_alias(consttime_memequal,_consttime_memequal) 13 #endif 14 #else 15 #include <lib/libkern/libkern.h> 16 #endif 17 18 int 19 consttime_memequal(const void *b1, const void *b2, size_t len) 20 { 21 const char *c1 = b1, *c2 = b2; 22 int res = 0; 23 24 while (len --) 25 res |= *c1++ ^ *c2++; 26 27 /* 28 * If the compiler for your favourite architecture generates a 29 * conditional branch for `!res', it will be a data-dependent 30 * branch, in which case this should be replaced by 31 * 32 * return (1 - (1 & ((res - 1) >> 8))); 33 * 34 * or rewritten in assembly. 35 */ 36 return !res; 37 } 38