Use rol/ror x86 instructions on GCC/Clang

Neither is very good at recognizing rotate sequences. For cases where
the rotation value is a constant they do fine, but for variable rotations
they do horribly. Using inline asm here improved performance of both
CAST-128 and CAST-256 by ~20% on my system with both GCC and Clang.

1 files changed, 24 insertions, 2 deletions

diff --git a/src/lib/utils/rotate.h b/src/lib/utils/rotate.h
index cb92daf96..6aeb631b3 100644
--- a/src/lib/utils/rotate.h
+++ b/src/lib/utils/rotate.h
@@ -18,7 +18,7 @@ namespace Botan {
 * @param rot the number of bits to rotate
 * @return input rotated left by rot bits
 */
-template<typename T> inline T rotate_left(T input, size_t rot)
+template<typename T> inline T rotate_left(T input, uint8_t rot)
    {
    rot %= 8 * sizeof(T);
    return (rot == 0) ? input : static_cast<T>((input << rot) | (input >> (8*sizeof(T)-rot)));;
@@ -30,12 +30,34 @@ template<typename T> inline T rotate_left(T input, size_t rot)
 * @param rot the number of bits to rotate
 * @return input rotated right by rot bits
 */
-template<typename T> inline T rotate_right(T input, size_t rot)
+template<typename T> inline T rotate_right(T input, uint8_t rot)
    {
    rot %= 8 * sizeof(T);
    return (rot == 0) ? input : static_cast<T>((input >> rot) | (input << (8*sizeof(T)-rot)));
    }
 
+#if BOTAN_USE_GCC_INLINE_ASM
+
+#if defined(BOTAN_TARGET_ARCH_IS_X86_64) || defined(BOTAN_TARGET_ARCH_IS_X86_32)
+
+template<>
+inline uint32_t rotate_left(uint32_t input, uint8_t rot)
+   {
+   asm("roll %1,%0" : "+r" (input) : "c" (rot));
+   return input;
+   }
+
+template<>
+inline uint32_t rotate_right(uint32_t input, uint8_t rot)
+   {
+   asm("rorl %1,%0" : "+r" (input) : "c" (rot));
+   return input;
+   }
+
+#endif
+
+#endif
+
 }
 
 #endif