Byte swapping with built-in functions

endian-swap.cpp

#include <cstddef>
#include <cstdint>
// gcc >= 4.8.1
// clang >= 3.5
uint16_t a1 = 0x0102;
uint32_t a2 = 0x01020304;
uint64_t a3 = 0x0102030405060708ull;
auto b1 = __builtin_bswap16(a1);
auto b2 = __builtin_bswap32(a2);
auto b3 = __builtin_bswap64(a3);

// MSVC
#include 
#include <stdlib.h>
_byteswap_ushort(v);
_byteswap_ulong(v);
_byteswap_uint64(v);

// Naive: (note: anonymous structs are not officially part of C++, although they seem to work on all? compilers)
// gcc -O2 is smart enough to convert all this to bswap instruction !
uint16_t swapEndian(uint16_t x) {
		union {
			struct {
				uint8_t a;
				uint8_t b;
			};
			uint16_t n;
		} y, z;

		y.n = x;
		z.a = y.b;
		z.b = y.a;
		return z.n;
	}

	uint32_t swapEndian(uint32_t x) {
		union {
			struct {
				uint8_t a;
				uint8_t b;
				uint8_t c;
				uint8_t d;
			};
			uint32_t n;
		} y, z;
		
		y.n = x;
		z.a = y.d;
		z.b = y.c;
		z.c = y.b;
		z.d = y.a;
		return z.n;
	}

	uint64_t swapEndian(uint64_t x) {
		union {
			struct {
				uint8_t a;
				uint8_t b;
				uint8_t c;
				uint8_t d;
				uint8_t e;
				uint8_t f;
				uint8_t g;
				uint8_t h;
			};
			uint64_t n;
		} y, z;

		y.n = x;
		z.a = y.h;
		z.b = y.g;
		z.c = y.f;
		z.d = y.e;
		z.e = y.d;
		z.f = y.c;
		z.g = y.b;
		z.h = y.a;
		return z.n;
	}