Add support for GCC's byteswap builtins. They were added in 4.3 and

work for 32 and 64 bit integers. Using these instead of inline asm may
offer better scheduling on x86, and additionally offers native
byteswapping on other platforms (PPC, ARM, etc).

1 files changed, 29 insertions, 4 deletions

diff --git a/src/utils/bswap.h b/src/utils/bswap.h
index 49962f076..7865d59d0 100644
--- a/src/utils/bswap.h
+++ b/src/utils/bswap.h
@@ -18,37 +18,56 @@
 
 namespace Botan {
 
-/*
-* Byte Swapping Functions
+/**
+* Swap a 16 bit integer
 */
 inline u16bit reverse_bytes(u16bit input)
    {
    return rotate_left(input, 8);
    }
 
+/**
+* Swap a 32 bit integer
+*/
 inline u32bit reverse_bytes(u32bit input)
    {
-#if BOTAN_USE_GCC_INLINE_ASM && defined(BOTAN_TARGET_CPU_IS_X86_FAMILY)
+#if BOTAN_GCC_VERSION >= 420
+
+   // GCC intrinsic added in 4.3, works for a number of CPUs
+   return __builtin_bswap32(input);
+
+#elif BOTAN_USE_GCC_INLINE_ASM && defined(BOTAN_TARGET_CPU_IS_X86_FAMILY)
 
    // GCC-style inline assembly for x86 or x86-64
    asm("bswapl %0" : "=r" (input) : "0" (input));
    return input;
 
 #elif defined(_MSC_VER) && defined(BOTAN_TARGET_ARCH_IS_IA32)
+
    // Visual C++ inline asm for 32-bit x86, by Yves Jerschow
    __asm mov eax, input;
    __asm bswap eax;
 
 #else
+
    // Generic implementation
    return (rotate_right(input, 8) & 0xFF00FF00) |
           (rotate_left (input, 8) & 0x00FF00FF);
+
 #endif
    }
 
+/**
+* Swap a 64 bit integer
+*/
 inline u64bit reverse_bytes(u64bit input)
    {
-#if BOTAN_USE_GCC_INLINE_ASM && defined(BOTAN_TARGET_ARCH_IS_AMD64)
+#if BOTAN_GCC_VERSION >= 430
+
+   // GCC intrinsic added in 4.3, works for a number of CPUs
+   return __builtin_bswap64(input);
+
+#elif BOTAN_USE_GCC_INLINE_ASM && defined(BOTAN_TARGET_ARCH_IS_AMD64)
    // GCC-style inline assembly for x86-64
    asm("bswapq %0" : "=r" (input) : "0" (input));
    return input;
@@ -69,6 +88,9 @@ inline u64bit reverse_bytes(u64bit input)
 #endif
    }
 
+/**
+* Swap 4 Ts in an array
+*/
 template<typename T>
 inline void bswap_4(T x[4])
    {
@@ -80,6 +102,9 @@ inline void bswap_4(T x[4])
 
 #if defined(BOTAN_TARGET_CPU_HAS_SSE2)
 
+/**
+* Swap 4 u32bits in an array using SSE2 shuffle instructions
+*/
 template<>
 inline void bswap_4(u32bit x[4])
    {