git/compat/bswap.h
Jeff King c3d8da571f read-cache: use get_be32 instead of hand-rolled ntoh_l
Commit d60c49c (read-cache.c: allow unaligned mapping of the
index file, 2012-04-03) introduced helpers to access
unaligned data. However, we already have get_be32, which has
a few advantages:

  1. It's already written, so we avoid duplication.

  2. It's probably faster, since it does the endian
     conversion and the alignment fix at the same time.

  3. The get_be32 code is well-tested, having been in
     block-sha1 for a long time. By contrast, our custom
     helpers were probably almost never used, since the user
     needed to manually define a macro to enable them.

We have to add a get_be16 implementation to the existing
get_be32, but that is very simple to do.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2014-01-23 14:03:48 -08:00

160 lines
3.9 KiB
C

/*
* Let's make sure we always have a sane definition for ntohl()/htonl().
* Some libraries define those as a function call, just to perform byte
* shifting, bringing significant overhead to what should be a simple
* operation.
*/
/*
* Default version that the compiler ought to optimize properly with
* constant values.
*/
static inline uint32_t default_swab32(uint32_t val)
{
return (((val & 0xff000000) >> 24) |
((val & 0x00ff0000) >> 8) |
((val & 0x0000ff00) << 8) |
((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__))
#define bswap32 git_bswap32
static inline uint32_t git_bswap32(uint32_t x)
{
uint32_t result;
if (__builtin_constant_p(x))
result = default_swab32(x);
else
__asm__("bswap %0" : "=r" (result) : "0" (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
#if defined(bswap32)
#undef ntohl
#undef htonl
#define ntohl(x) bswap32(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
/*
* Performance might be improved if the CPU architecture is OK with
* unaligned 32-bit loads and a fast ntohl() is available.
* Otherwise fall back to byte loads and shifts which is portable,
* and is faster on architectures with memory alignment issues.
*/
#if defined(__i386__) || defined(__x86_64__) || \
defined(_M_IX86) || defined(_M_X64) || \
defined(__ppc__) || defined(__ppc64__) || \
defined(__powerpc__) || defined(__powerpc64__) || \
defined(__s390__) || defined(__s390x__)
#define get_be16(p) ntohs(*(unsigned short *)(p))
#define get_be32(p) ntohl(*(unsigned int *)(p))
#define put_be32(p, v) do { *(unsigned int *)(p) = htonl(v); } while (0)
#else
#define get_be16(p) ( \
(*((unsigned char *)(p) + 0) << 8) | \
(*((unsigned char *)(p) + 1) << 0) )
#define get_be32(p) ( \
(*((unsigned char *)(p) + 0) << 24) | \
(*((unsigned char *)(p) + 1) << 16) | \
(*((unsigned char *)(p) + 2) << 8) | \
(*((unsigned char *)(p) + 3) << 0) )
#define put_be32(p, v) do { \
unsigned int __v = (v); \
*((unsigned char *)(p) + 0) = __v >> 24; \
*((unsigned char *)(p) + 1) = __v >> 16; \
*((unsigned char *)(p) + 2) = __v >> 8; \
*((unsigned char *)(p) + 3) = __v >> 0; } while (0)
#endif