small patch: CRYPTO_memcmp

[Michael W. Bombardieri]

Hi tech@,

Sending this patch for comment...

CRYPTO_memcmp() is different to memcmp() because it can only check
for equality, not greater-than/less-than.
If we check the string in reverse order we can remove a variable
from the comparison loop.

Does this look ok?

- Michael



Index: cryptlib.c
===================================================================
RCS file: /cvs/src/lib/libssl/src/crypto/cryptlib.c,v
retrieving revision 1.23
diff -u -r1.23 cryptlib.c
--- cryptlib.c  21 Apr 2014 11:19:28 -0000      1.23
+++ cryptlib.c  23 Apr 2014 01:19:39 -0000
@@ -727,15 +727,13 @@
 }
 
 int
-CRYPTO_memcmp(const void *in_a, const void *in_b, size_t len)
+CRYPTO_memcmp(const void *in_a, const void *in_b, size_t n)
 {
-       size_t i;
        const unsigned char *a = in_a;
        const unsigned char *b = in_b;
        unsigned char x = 0;
 
-       for (i = 0; i < len; i++)
-               x |= a[i] ^ b[i];
-
+       while (n-- > 0)
+               x |= a[n] ^ b[n];
        return x;
 }