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/*-------------------------------------------------------------------------
*
* pg_bswap.h
* Byte swapping.
*
* Macros for reversing the byte order of 32-bit and 64-bit unsigned integers.
* For example, 0xAABBCCDD becomes 0xDDCCBBAA. These are just wrappers for
* built-in functions provided by the compiler where support exists.
* Elsewhere, beware of multiple evaluations of the arguments!
*
* Note that the GCC built-in functions __builtin_bswap32() and
* __builtin_bswap64() are documented as accepting single arguments of type
* uint32_t and uint64_t respectively (these are also the respective return
* types). Use caution when using these wrapper macros with signed integers.
*
* Copyright (c) 2015-2016, PostgreSQL Global Development Group
*
* src/include/port/pg_bswap.h
*
*-------------------------------------------------------------------------
*/
#ifndef PG_BSWAP_H
#define PG_BSWAP_H
#ifdef HAVE__BUILTIN_BSWAP32
#define BSWAP32(x) __builtin_bswap32(x)
#else
#define BSWAP32(x) ((((x) << 24) & 0xff000000) | \
(((x) << 8) & 0x00ff0000) | \
(((x) >> 8) & 0x0000ff00) | \
(((x) >> 24) & 0x000000ff))
#endif /* HAVE__BUILTIN_BSWAP32 */
#ifdef HAVE__BUILTIN_BSWAP64
#define BSWAP64(x) __builtin_bswap64(x)
#else
#define BSWAP64(x) ((((x) << 56) & UINT64CONST(0xff00000000000000)) | \
(((x) << 40) & UINT64CONST(0x00ff000000000000)) | \
(((x) << 24) & UINT64CONST(0x0000ff0000000000)) | \
(((x) << 8) & UINT64CONST(0x000000ff00000000)) | \
(((x) >> 8) & UINT64CONST(0x00000000ff000000)) | \
(((x) >> 24) & UINT64CONST(0x0000000000ff0000)) | \
(((x) >> 40) & UINT64CONST(0x000000000000ff00)) | \
(((x) >> 56) & UINT64CONST(0x00000000000000ff)))
#endif /* HAVE__BUILTIN_BSWAP64 */
/*
* Rearrange the bytes of a Datum from big-endian order into the native byte
* order. On big-endian machines, this does nothing at all. Note that the C
* type Datum is an unsigned integer type on all platforms.
*
* One possible application of the DatumBigEndianToNative() macro is to make
* bitwise comparisons cheaper. A simple 3-way comparison of Datums
* transformed by the macro (based on native, unsigned comparisons) will return
* the same result as a memcmp() of the corresponding original Datums, but can
* be much cheaper. It's generally safe to do this on big-endian systems
* without any special transformation occurring first.
*/
#ifdef WORDS_BIGENDIAN
#define DatumBigEndianToNative(x) (x)
#else /* !WORDS_BIGENDIAN */
#if SIZEOF_DATUM == 8
#define DatumBigEndianToNative(x) BSWAP64(x)
#else /* SIZEOF_DATUM != 8 */
#define DatumBigEndianToNative(x) BSWAP32(x)
#endif /* SIZEOF_DATUM == 8 */
#endif /* WORDS_BIGENDIAN */
#endif /* PG_BSWAP_H */
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