51ea55190b
We rely on ntohl() and htonl() to perform byte swapping in many places. However, some platforms have libraries providing really poor implementations of those which might cause significant performance issues, especially with the block-sha1 code. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
37 lines
879 B
C
37 lines
879 B
C
/*
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* Let's make sure we always have a sane definition for ntohl()/htonl().
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* Some libraries define those as a function call, just to perform byte
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* shifting, bringing significant overhead to what should be a simple
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* operation.
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*/
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/*
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* Default version that the compiler ought to optimize properly with
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* constant values.
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*/
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static inline unsigned int default_swab32(unsigned int val)
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{
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return (((val & 0xff000000) >> 24) |
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((val & 0x00ff0000) >> 8) |
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((val & 0x0000ff00) << 8) |
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((val & 0x000000ff) << 24));
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}
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#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
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#define bswap32(x) ({ \
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unsigned int __res; \
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if (__builtin_constant_p(x)) { \
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__res = default_swab32(x); \
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} else { \
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__asm__("bswap %0" : "=r" (__res) : "0" (x)); \
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} \
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__res; })
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#undef ntohl
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#undef htonl
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#define ntohl(x) bswap32(x)
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#define htonl(x) bswap32(x)
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#endif
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