Comment "secure memcmp" implementation

#endif

}

/* volatile unsigned char* pointers are there because

 * 1. Accessing a variable declared volatile via a pointer

 *    that lacks a volatile qualifier causes undefined behavior.

 * 2. When the variable itself is not volatile the compiler is

 *    not required to keep all those reads and can convert

 *    this into canonical memcmp() which doesn't read the whole block.

 * Pointers to volatile resolve the first problem fully. The second

 * problem cannot be resolved in any Standard-compliant way but this

 * works the problem around. Compilers typically react to

 * pointers to volatile by preserving the reads and writes through them.

 * The latter is not required by the Standard if the memory pointed to

 * is not volatile.

 * Pointers themselves are volatile in the function signature to work

 * around a subtle bug in gcc 4.6+ which causes writes through

 * pointers to volatile to not be emitted in some rare,

 * never needed in real life, pieces of code.

 */

int CRYPTO_memcmp(const volatile void * volatile in_a,

                  const volatile void * volatile in_b,

                  size_t len)