@leroysheep / Socializer / commits / f4ac32c03a

bswap.h: provide a built-in based version of bswap32/64 if possible

The compiler is in general able to recognize the endian shift and replace it with an optimized opcode if possible. On certain architectures such as RiscV or MIPS the situation can get complicated. They don't provide an optimized opcode and masking the "higher" bits may required loading a constant which needs shifting. This causes the compiler to emit a lot of instructions for the operation. The provided builtin directive on these architecture calls a function which does the operation instead of emitting the code for operation. Bring back the change from commit 6547d1c9 (bswap.h: add support for built-in bswap functions, 2025-04-23). The bswap32/64 macro can now be defined unconditionally so it won't regress on big endian architectures. Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Sebastian Andrzej Siewior committed Jul 15, 2025 at 21:12 UTC f4ac32c03af5ac53964a05c4de435da53a59615c

1 file changed +13

compat/bswap.h

+13

index ed00f6d1d5..28635ebc69 100644 --- a/compat/bswap.h +++ b/compat/bswap.h @@ -32,6 +32,14 @@ static inline uint64_t default_bswap64(uint64_t val) ((val & (uint64_t)0xff00000000000000ULL) >> 56)); } +/* + * __has_builtin is available since Clang 10 and GCC 10. + * Below is a fallback for older compilers. + */ +#ifndef __has_builtin +# define __has_builtin(x) 0 +#endif + #undef bswap32 #undef bswap64 @@ -46,6 +54,11 @@ static inline uint64_t default_bswap64(uint64_t val) #define GIT_BIG_ENDIAN 4321 #define GIT_BYTE_ORDER GIT_LITTLE_ENDIAN +#elif __has_builtin(__builtin_bswap32) && __has_builtin(__builtin_bswap64) + +#define bswap32(x) __builtin_bswap32((x)) +#define bswap64(x) __builtin_bswap64((x)) + #endif #if defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && defined(__BIG_ENDIAN)