/* $NetBSD: consttime_memequal.c,v 1.6 2015/03/18 20:11:35 riastradh Exp $ */

/*
* Written by Matthias Drochner <[email protected]>.
* 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));
}