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/* $NetBSD: consttime_memequal.c,v 1.6 2015/03/18 20:11:35 riastradh Exp $ */
/*
* Written by Matthias Drochner <drochner@NetBSD.org>.
* Public domain.
*/
#if !defined(_KERNEL) && !defined(_STANDALONE)
#include "namespace.h"
#include <string.h>
#ifdef __weak_alias
__weak_alias(consttime_memequal,_consttime_memequal)
#endif
#else
#include <lib/libkern/libkern.h>
#endif
int
consttime_memequal(const void *b1, const void *b2, size_t len)
{
const unsigned char *c1 = b1, *c2 = b2;
unsigned int res = 0;
while (len--)
res |= *c1++ ^ *c2++;
/*
* Map 0 to 1 and [1, 256) to 0 using only constant-time
* arithmetic.
*
* This is not simply `!res' because although many CPUs support
* branchless conditional moves and many compilers will take
* advantage of them, certain compilers generate branches on
* certain CPUs for `!res'.
*/
return (1 & ((res - 1) >> 8));
}
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