[PATCH 02/12] const-time: always avoid comparison operator for byte comparison

[Jussi Kivilinna]

* configure.ac: Remove POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON
macro.
* src/const-time.h (ct_not_equal_byte): Remove
POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON ifdef.
--

Performance impact of avoiding comparison is negligible, so
remove the option for using comparison to make this easier
maintain (tested on every arch).

Signed-off-by: Jussi Kivilinna <jussi.kivilinna at iki.fi>
---
 configure.ac     | 5 -----
 src/const-time.h | 4 ----
 2 files changed, 9 deletions(-)

diff --git a/configure.ac b/configure.ac
index aead8347..4f7c3a52 100644
--- a/configure.ac
+++ b/configure.ac
@@ -121,11 +121,6 @@ AH_BOTTOM([
    properly prefixed.  */
 #define CAMELLIA_EXT_SYM_PREFIX _gcry_
 
-/* For some architectures or a specific compiler vendor, we need
-   to care about possible conditional branch in byte comparison.  */
-#if defined(__vax__) || defined(AVR) || defined(_MSC_VER)
-# define POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON 1
-#endif
 #endif /*_GCRYPT_CONFIG_H_INCLUDED*/
 ])
 
diff --git a/src/const-time.h b/src/const-time.h
index defe5ff4..4f14f86b 100644
--- a/src/const-time.h
+++ b/src/const-time.h
@@ -29,16 +29,12 @@
 static inline unsigned int
 ct_not_equal_byte (unsigned char b0, unsigned char b1)
 {
-#ifdef POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON
   unsigned int diff;
 
   diff = b0;
   diff ^= b1;
 
   return (0U - diff) >> (sizeof (unsigned int)*8 - 1);
-#else
-  return b0 != b1;
-#endif
 }
 
 /* Compare byte-arrays of length LEN, return 1 if it's not same, 0
-- 
2.40.1