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