tomcrypt/src/misc/mem_neq.c

/* LibTomCrypt, modular cryptographic library -- Tom St Denis
 *
 * LibTomCrypt is a library that provides various cryptographic
 * algorithms in a highly modular and flexible manner.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 */
#include "tomcrypt.h"

/**
   @file mem_neq.c
   Compare two blocks of memory for inequality.
   Steffen Jaeckel
*/

/**
   Compare two blocks of memory for inequality.

   The usage is similar to that of standard memcmp, but you can only test
   if the memory is equal or not - you can not determine by how much the
   first different byte differs.

   @param a     The first memory region
   @param b     The second memory region
   @param len   The length of the area to compare (octets)

   @return 0 when a and b are equal for len bytes, else they are not equal.
*/
int mem_neq(const void *a, const void *b, size_t len)
{
   unsigned char ret = 0;
   const unsigned char* pa;
   const unsigned char* pb;

   LTC_ARGCHK(a != NULL);
   LTC_ARGCHK(b != NULL);

   pa = a;
   pb = b;

   while (len-- > 0) {
      ret |= *pa ^ *pb;
      ++pa;
      ++pb;
   }

   ret |= ret >> 4;
   ret |= ret >> 2;
   ret |= ret >> 1;
   ret &= 1;

   return ret;
}

/* $Source$ */
/* $Revision$ */
/* $Date$ */