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a0df2e5a7e
The byte-swapping code automatically decides, based on the platform, whether it is sensible to cast and do a potentially unaligned ntohl(), or to pick individual bytes out of an array. It can be handy to override this decision, though, when turning on compiler flags that will complain about unaligned loads (such as -fsanitize=undefined). This patch adds a macro check to make this possible. There's no nice Makefile knob here; this is for prodding at Git's internals, and anybody using it can set "-DNO_UNALIGNED_LOADS" in the same place they are setting up "-fsanitize". Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
180 lines
4.6 KiB
C
180 lines
4.6 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) && defined(__LITTLE_ENDIAN) && defined(__BIG_ENDIAN)
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# define GIT_BYTE_ORDER __BYTE_ORDER
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# define GIT_LITTLE_ENDIAN __LITTLE_ENDIAN
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# define GIT_BIG_ENDIAN __BIG_ENDIAN
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#elif defined(BYTE_ORDER) && defined(LITTLE_ENDIAN) && defined(BIG_ENDIAN)
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# define GIT_BYTE_ORDER BYTE_ORDER
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# define GIT_LITTLE_ENDIAN LITTLE_ENDIAN
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# define GIT_BIG_ENDIAN BIG_ENDIAN
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#else
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# define GIT_BIG_ENDIAN 4321
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# define GIT_LITTLE_ENDIAN 1234
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# if defined(_BIG_ENDIAN) && !defined(_LITTLE_ENDIAN)
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# define GIT_BYTE_ORDER GIT_BIG_ENDIAN
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# elif defined(_LITTLE_ENDIAN) && !defined(_BIG_ENDIAN)
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# define GIT_BYTE_ORDER GIT_LITTLE_ENDIAN
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# elif defined(__THW_BIG_ENDIAN__) && !defined(__THW_LITTLE_ENDIAN__)
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# define GIT_BYTE_ORDER GIT_BIG_ENDIAN
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# elif defined(__THW_LITTLE_ENDIAN__) && !defined(__THW_BIG_ENDIAN__)
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# define GIT_BYTE_ORDER GIT_LITTLE_ENDIAN
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# else
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# error "Cannot determine endianness"
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# endif
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#endif
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#if GIT_BYTE_ORDER == GIT_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(NO_UNALIGNED_LOADS) && ( \
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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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