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c3d8da571f
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>
160 lines
3.9 KiB
C
160 lines
3.9 KiB
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 uint32_t default_swab32(uint32_t 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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static inline uint64_t default_bswap64(uint64_t val)
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{
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return (((val & (uint64_t)0x00000000000000ffULL) << 56) |
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((val & (uint64_t)0x000000000000ff00ULL) << 40) |
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((val & (uint64_t)0x0000000000ff0000ULL) << 24) |
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((val & (uint64_t)0x00000000ff000000ULL) << 8) |
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((val & (uint64_t)0x000000ff00000000ULL) >> 8) |
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((val & (uint64_t)0x0000ff0000000000ULL) >> 24) |
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((val & (uint64_t)0x00ff000000000000ULL) >> 40) |
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((val & (uint64_t)0xff00000000000000ULL) >> 56));
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}
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#undef bswap32
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#undef bswap64
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#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
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#define bswap32 git_bswap32
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static inline uint32_t git_bswap32(uint32_t x)
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{
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uint32_t result;
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if (__builtin_constant_p(x))
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result = default_swab32(x);
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else
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__asm__("bswap %0" : "=r" (result) : "0" (x));
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return result;
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}
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#define bswap64 git_bswap64
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#if defined(__x86_64__)
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static inline uint64_t git_bswap64(uint64_t x)
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{
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uint64_t result;
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if (__builtin_constant_p(x))
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result = default_bswap64(x);
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else
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__asm__("bswap %q0" : "=r" (result) : "0" (x));
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return result;
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}
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#else
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static inline uint64_t git_bswap64(uint64_t x)
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{
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union { uint64_t i64; uint32_t i32[2]; } tmp, result;
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if (__builtin_constant_p(x))
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result.i64 = default_bswap64(x);
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else {
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tmp.i64 = x;
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result.i32[0] = git_bswap32(tmp.i32[1]);
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result.i32[1] = git_bswap32(tmp.i32[0]);
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}
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return result.i64;
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}
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#endif
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#elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
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#include <stdlib.h>
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#define bswap32(x) _byteswap_ulong(x)
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#define bswap64(x) _byteswap_uint64(x)
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#endif
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#if defined(bswap32)
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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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#if defined(bswap64)
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#undef ntohll
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#undef htonll
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#define ntohll(x) bswap64(x)
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#define htonll(x) bswap64(x)
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#else
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#undef ntohll
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#undef htonll
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#if !defined(__BYTE_ORDER)
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# if defined(BYTE_ORDER) && defined(LITTLE_ENDIAN) && defined(BIG_ENDIAN)
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# define __BYTE_ORDER BYTE_ORDER
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# define __LITTLE_ENDIAN LITTLE_ENDIAN
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# define __BIG_ENDIAN BIG_ENDIAN
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# endif
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#endif
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#if !defined(__BYTE_ORDER)
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# error "Cannot determine endianness"
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#endif
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#if __BYTE_ORDER == __BIG_ENDIAN
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# define ntohll(n) (n)
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# define htonll(n) (n)
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#else
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# define ntohll(n) default_bswap64(n)
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# define htonll(n) default_bswap64(n)
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#endif
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#endif
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/*
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* Performance might be improved if the CPU architecture is OK with
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* unaligned 32-bit loads and a fast ntohl() is available.
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* Otherwise fall back to byte loads and shifts which is portable,
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* and is faster on architectures with memory alignment issues.
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*/
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#if defined(__i386__) || defined(__x86_64__) || \
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defined(_M_IX86) || defined(_M_X64) || \
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defined(__ppc__) || defined(__ppc64__) || \
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defined(__powerpc__) || defined(__powerpc64__) || \
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defined(__s390__) || defined(__s390x__)
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#define get_be16(p) ntohs(*(unsigned short *)(p))
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#define get_be32(p) ntohl(*(unsigned int *)(p))
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#define put_be32(p, v) do { *(unsigned int *)(p) = htonl(v); } while (0)
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#else
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#define get_be16(p) ( \
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(*((unsigned char *)(p) + 0) << 8) | \
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(*((unsigned char *)(p) + 1) << 0) )
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#define get_be32(p) ( \
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(*((unsigned char *)(p) + 0) << 24) | \
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(*((unsigned char *)(p) + 1) << 16) | \
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(*((unsigned char *)(p) + 2) << 8) | \
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(*((unsigned char *)(p) + 3) << 0) )
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#define put_be32(p, v) do { \
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unsigned int __v = (v); \
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*((unsigned char *)(p) + 0) = __v >> 24; \
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*((unsigned char *)(p) + 1) = __v >> 16; \
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*((unsigned char *)(p) + 2) = __v >> 8; \
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*((unsigned char *)(p) + 3) = __v >> 0; } while (0)
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#endif
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