162 lines
4.2 KiB
C
162 lines
4.2 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_bswap.h
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* Byte swapping.
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*
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* Macros for reversing the byte order of 16, 32 and 64-bit unsigned integers.
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* For example, 0xAABBCCDD becomes 0xDDCCBBAA. These are just wrappers for
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* built-in functions provided by the compiler where support exists.
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*
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* Note that all of these functions accept unsigned integers as arguments and
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* return the same. Use caution when using these wrapper macros with signed
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* integers.
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*
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* Copyright (c) 2015-2019, PostgreSQL Global Development Group
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*
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* src/include/port/pg_bswap.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PG_BSWAP_H
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#define PG_BSWAP_H
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/*
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* In all supported versions msvc provides _byteswap_* functions in stdlib.h,
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* already included by c.h.
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*/
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/* implementation of uint16 pg_bswap16(uint16) */
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#if defined(HAVE__BUILTIN_BSWAP16)
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#define pg_bswap16(x) __builtin_bswap16(x)
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#elif defined(_MSC_VER)
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#define pg_bswap16(x) _byteswap_ushort(x)
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#else
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static inline uint16
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pg_bswap16(uint16 x)
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{
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return
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((x << 8) & 0xff00) |
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((x >> 8) & 0x00ff);
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}
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#endif /* HAVE__BUILTIN_BSWAP16 */
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/* implementation of uint32 pg_bswap32(uint32) */
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#if defined(HAVE__BUILTIN_BSWAP32)
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#define pg_bswap32(x) __builtin_bswap32(x)
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#elif defined(_MSC_VER)
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#define pg_bswap32(x) _byteswap_ulong(x)
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#else
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static inline uint32
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pg_bswap32(uint32 x)
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{
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return
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((x << 24) & 0xff000000) |
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((x << 8) & 0x00ff0000) |
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((x >> 8) & 0x0000ff00) |
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((x >> 24) & 0x000000ff);
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}
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#endif /* HAVE__BUILTIN_BSWAP32 */
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/* implementation of uint64 pg_bswap64(uint64) */
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#if defined(HAVE__BUILTIN_BSWAP64)
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#define pg_bswap64(x) __builtin_bswap64(x)
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#elif defined(_MSC_VER)
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#define pg_bswap64(x) _byteswap_uint64(x)
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#else
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static inline uint64
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pg_bswap64(uint64 x)
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{
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return
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((x << 56) & UINT64CONST(0xff00000000000000)) |
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((x << 40) & UINT64CONST(0x00ff000000000000)) |
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((x << 24) & UINT64CONST(0x0000ff0000000000)) |
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((x << 8) & UINT64CONST(0x000000ff00000000)) |
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((x >> 8) & UINT64CONST(0x00000000ff000000)) |
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((x >> 24) & UINT64CONST(0x0000000000ff0000)) |
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((x >> 40) & UINT64CONST(0x000000000000ff00)) |
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((x >> 56) & UINT64CONST(0x00000000000000ff));
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}
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#endif /* HAVE__BUILTIN_BSWAP64 */
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/*
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* Portable and fast equivalents for ntohs, ntohl, htons, htonl,
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* additionally extended to 64 bits.
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*/
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#ifdef WORDS_BIGENDIAN
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#define pg_hton16(x) (x)
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#define pg_hton32(x) (x)
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#define pg_hton64(x) (x)
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#define pg_ntoh16(x) (x)
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#define pg_ntoh32(x) (x)
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#define pg_ntoh64(x) (x)
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#else
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#define pg_hton16(x) pg_bswap16(x)
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#define pg_hton32(x) pg_bswap32(x)
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#define pg_hton64(x) pg_bswap64(x)
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#define pg_ntoh16(x) pg_bswap16(x)
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#define pg_ntoh32(x) pg_bswap32(x)
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#define pg_ntoh64(x) pg_bswap64(x)
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#endif /* WORDS_BIGENDIAN */
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/*
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* Rearrange the bytes of a Datum from big-endian order into the native byte
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* order. On big-endian machines, this does nothing at all. Note that the C
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* type Datum is an unsigned integer type on all platforms.
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*
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* One possible application of the DatumBigEndianToNative() macro is to make
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* bitwise comparisons cheaper. A simple 3-way comparison of Datums
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* transformed by the macro (based on native, unsigned comparisons) will return
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* the same result as a memcmp() of the corresponding original Datums, but can
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* be much cheaper. It's generally safe to do this on big-endian systems
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* without any special transformation occurring first.
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*
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* If SIZEOF_DATUM is not defined, then postgres.h wasn't included and these
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* macros probably shouldn't be used, so we define nothing. Note that
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* SIZEOF_DATUM == 8 would evaluate as 0 == 8 in that case, potentially
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* leading to the wrong implementation being selected and confusing errors, so
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* defining nothing is safest.
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*/
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#ifdef SIZEOF_DATUM
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#ifdef WORDS_BIGENDIAN
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#define DatumBigEndianToNative(x) (x)
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#else /* !WORDS_BIGENDIAN */
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#if SIZEOF_DATUM == 8
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#define DatumBigEndianToNative(x) pg_bswap64(x)
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#else /* SIZEOF_DATUM != 8 */
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#define DatumBigEndianToNative(x) pg_bswap32(x)
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#endif /* SIZEOF_DATUM == 8 */
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#endif /* WORDS_BIGENDIAN */
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#endif /* SIZEOF_DATUM */
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#endif /* PG_BSWAP_H */
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