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db_include/port/pg_bswap.h

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+/*-------------------------------------------------------------------------
+ *
+ * pg_bswap.h
+ *	  Byte swapping.
+ *
+ * Macros for reversing the byte order of 16, 32 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.
+ *
+ * Note that all of these functions accept unsigned integers as arguments and
+ * return the same.  Use caution when using these wrapper macros with signed
+ * integers.
+ *
+ * Copyright (c) 2015-2021, PostgreSQL Global Development Group
+ *
+ * src/include/port/pg_bswap.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_BSWAP_H
+#define PG_BSWAP_H
+
+
+/*
+ * In all supported versions msvc provides _byteswap_* functions in stdlib.h,
+ * already included by c.h.
+ */
+
+
+/* implementation of uint16 pg_bswap16(uint16) */
+#if defined(HAVE__BUILTIN_BSWAP16)
+
+#define pg_bswap16(x) __builtin_bswap16(x)
+
+#elif defined(_MSC_VER)
+
+#define pg_bswap16(x) _byteswap_ushort(x)
+
+#else
+
+static inline uint16
+pg_bswap16(uint16 x)
+{
+	return
+		((x << 8) & 0xff00) |
+		((x >> 8) & 0x00ff);
+}
+
+#endif							/* HAVE__BUILTIN_BSWAP16 */
+
+
+/* implementation of uint32 pg_bswap32(uint32) */
+#if defined(HAVE__BUILTIN_BSWAP32)
+
+#define pg_bswap32(x) __builtin_bswap32(x)
+
+#elif defined(_MSC_VER)
+
+#define pg_bswap32(x) _byteswap_ulong(x)
+
+#else
+
+static inline uint32
+pg_bswap32(uint32 x)
+{
+	return
+		((x << 24) & 0xff000000) |
+		((x << 8) & 0x00ff0000) |
+		((x >> 8) & 0x0000ff00) |
+		((x >> 24) & 0x000000ff);
+}
+
+#endif							/* HAVE__BUILTIN_BSWAP32 */
+
+
+/* implementation of uint64 pg_bswap64(uint64) */
+#if defined(HAVE__BUILTIN_BSWAP64)
+
+#define pg_bswap64(x) __builtin_bswap64(x)
+
+
+#elif defined(_MSC_VER)
+
+#define pg_bswap64(x) _byteswap_uint64(x)
+
+#else
+
+static inline uint64
+pg_bswap64(uint64 x)
+{
+	return
+		((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 */
+
+
+/*
+ * Portable and fast equivalents for ntohs, ntohl, htons, htonl,
+ * additionally extended to 64 bits.
+ */
+#ifdef WORDS_BIGENDIAN
+
+#define pg_hton16(x)		(x)
+#define pg_hton32(x)		(x)
+#define pg_hton64(x)		(x)
+
+#define pg_ntoh16(x)		(x)
+#define pg_ntoh32(x)		(x)
+#define pg_ntoh64(x)		(x)
+
+#else
+
+#define pg_hton16(x)		pg_bswap16(x)
+#define pg_hton32(x)		pg_bswap32(x)
+#define pg_hton64(x)		pg_bswap64(x)
+
+#define pg_ntoh16(x)		pg_bswap16(x)
+#define pg_ntoh32(x)		pg_bswap32(x)
+#define pg_ntoh64(x)		pg_bswap64(x)
+
+#endif							/* WORDS_BIGENDIAN */
+
+
+/*
+ * 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.
+ *
+ * If SIZEOF_DATUM is not defined, then postgres.h wasn't included and these
+ * macros probably shouldn't be used, so we define nothing.  Note that
+ * SIZEOF_DATUM == 8 would evaluate as 0 == 8 in that case, potentially
+ * leading to the wrong implementation being selected and confusing errors, so
+ * defining nothing is safest.
+ */
+#ifdef SIZEOF_DATUM
+#ifdef WORDS_BIGENDIAN
+#define		DatumBigEndianToNative(x)	(x)
+#else							/* !WORDS_BIGENDIAN */
+#if SIZEOF_DATUM == 8
+#define		DatumBigEndianToNative(x)	pg_bswap64(x)
+#else							/* SIZEOF_DATUM != 8 */
+#define		DatumBigEndianToNative(x)	pg_bswap32(x)
+#endif							/* SIZEOF_DATUM == 8 */
+#endif							/* WORDS_BIGENDIAN */
+#endif							/* SIZEOF_DATUM */
+
+#endif							/* PG_BSWAP_H */