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/*
* Copyright (c) 2009 Kungliga Tekniska Högskolan
* (Royal Institute of Technology, Stockholm, Sweden).
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* 3. Neither the name of the Institute nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <config.h>
#include "roken.h"
/**
* Constant time compare to memory regions. The reason for making it
* constant time is to make sure that timeing information leak from
* where in the function the diffrence is.
*
* ct_memcmp() can't be used to order memory regions like memcmp(),
* for example, use ct_memcmp() with qsort().
*
* We use volatile to avoid optimizations where the compiler and/or
* linker turn this ct_memcmp() into a plain memcmp(). The pointers
* themselves are also marked volatile (not just the memory pointed at)
* because in some GCC versions there is a bug which can be worked
* around by doing this.
*
* @param p1 memory region 1 to compare
* @param p2 memory region 2 to compare
* @param len length of memory
*
* @return 0 when the memory regions are equal, non zero if not
*
* @ingroup roken
*/
int
ct_memcmp(const volatile void * volatile p1,
const volatile void * volatile p2,
size_t len)
{
/*
* There's no need for s1 and s2 to be volatile; only p1 and p2 have
* to be in order to work around GCC bugs.
*
* However, s1 and s2 do have to point to volatile, as we don't know
* if the object was originally defined as volatile, and if it was
* then we'd get undefined behavior here if s1/s2 were declared to
* point to non-volatile memory.
*/
const volatile unsigned char *s1 = p1;
const volatile unsigned char *s2 = p2;
size_t i;
int r = 0;
for (i = 0; i < len; i++)
r |= (s1[i] ^ s2[i]);
return !!r;
}
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