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compat: add endianness helpers

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The POSIX standard doesn't currently define a `ntohll`/`htonll`
function pair to perform network-to-host and host-to-network
swaps of 64-bit data. These 64-bit swaps are necessary for the on-disk
storage of EWAH bitmaps if they are not in native byte order.

Many thanks to Ramsay Jones <ramsay@ramsay1.demon.co.uk> and
Torsten Bögershausen <tboegi@web.de> for cygwin/mingw/msvc
portability fixes.

Signed-off-by: Vicent Marti <tanoku@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Vicent Marti 2013-11-14 07:43:36 -05:00 committed by Junio C Hamano
parent ec73f5807c
commit 7e3dae4943
1 changed files with 75 additions and 1 deletions
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76
compat/bswap.h
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@ -17,7 +17,20 @@ static inline uint32_t default_swab32(uint32_t val)
((val & 0x000000ff) << 24));
}
static inline uint64_t default_bswap64(uint64_t val)
{
return (((val & (uint64_t)0x00000000000000ffULL) << 56) |
((val & (uint64_t)0x000000000000ff00ULL) << 40) |
((val & (uint64_t)0x0000000000ff0000ULL) << 24) |
((val & (uint64_t)0x00000000ff000000ULL) << 8) |
((val & (uint64_t)0x000000ff00000000ULL) >> 8) |
((val & (uint64_t)0x0000ff0000000000ULL) >> 24) |
((val & (uint64_t)0x00ff000000000000ULL) >> 40) |
((val & (uint64_t)0xff00000000000000ULL) >> 56));
}
#undef bswap32
#undef bswap64
#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
@ -32,15 +45,42 @@ static inline uint32_t git_bswap32(uint32_t x)
return result;
}
#define bswap64 git_bswap64
#if defined(__x86_64__)
static inline uint64_t git_bswap64(uint64_t x)
{
uint64_t result;
if (__builtin_constant_p(x))
result = default_bswap64(x);
else
__asm__("bswap %q0" : "=r" (result) : "0" (x));
return result;
}
#else
static inline uint64_t git_bswap64(uint64_t x)
{
union { uint64_t i64; uint32_t i32[2]; } tmp, result;
if (__builtin_constant_p(x))
result.i64 = default_bswap64(x);
else {
tmp.i64 = x;
result.i32[0] = git_bswap32(tmp.i32[1]);
result.i32[1] = git_bswap32(tmp.i32[0]);
}
return result.i64;
}
#endif
#elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
#include <stdlib.h>
#define bswap32(x) _byteswap_ulong(x)
#define bswap64(x) _byteswap_uint64(x)
#endif
#ifdef bswap32
#if defined(bswap32)
#undef ntohl
#undef htonl
@ -48,3 +88,37 @@ static inline uint32_t git_bswap32(uint32_t x)
#define htonl(x) bswap32(x)
#endif
#if defined(bswap64)
#undef ntohll
#undef htonll
#define ntohll(x) bswap64(x)
#define htonll(x) bswap64(x)
#else
#undef ntohll
#undef htonll
#if !defined(__BYTE_ORDER)
# if defined(BYTE_ORDER) && defined(LITTLE_ENDIAN) && defined(BIG_ENDIAN)
# define __BYTE_ORDER BYTE_ORDER
# define __LITTLE_ENDIAN LITTLE_ENDIAN
# define __BIG_ENDIAN BIG_ENDIAN
# endif
#endif
#if !defined(__BYTE_ORDER)
# error "Cannot determine endianness"
#endif
#if __BYTE_ORDER == __BIG_ENDIAN
# define ntohll(n) (n)
# define htonll(n) (n)
#else
# define ntohll(n) default_bswap64(n)
# define htonll(n) default_bswap64(n)
#endif
#endif