gplib/include/gp/bitops.hpp

#pragma once
#include <stddef.h>
#include <stdint.h>

namespace gp{
	namespace _impl{
    	constexpr uint32_t uint32_ = 0x01020304;
    	constexpr uint8_t magic_ = (const uint8_t&)uint32_;
	}
	
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wfour-char-constants"
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wmultichar"
	enum class endian : uint16_t
	{
#ifdef _WIN32
		little = 0,
		big = 1,
		native = little
#elseif defined(__BYTE_ORDER__)
		little = __ORDER_LITTLE_ENDIAN__,
		big = __ORDER_BIG_ENDIAN__,
		native = __BYTE_ORDER__
#else
		little = true,
		big = false,
		native = ('ABCD'==0x41424344UL)
	};
#endif
#pragma GCC diagnostic pop
#pragma clang diagnostic pop

	
	template <typename T>
	T swap_endian(T value)
	{
		union
		{
			T v;
			uint8_t u8[sizeof(T)];
		} src, dest;
	
		src.v = value;
		
		for (size_t idx = 0;idx<sizeof(T);idx++)
		{
			dest.u8[idx] = src.u8[sizeof(T)-idx-1];
		}
		
		return dest.v;
	}

	template<typename T, endian mode = endian::big>
	struct endian_wrapper {
		T value;
		endian_wrapper(){};
		endian_wrapper(T v) : value{
			mode == endian::native ? v : swap_endian(v)
		}{}
		endian_wrapper(endian_wrapper& v) : value{
			v.value
		}{}

		endian_wrapper& operator=(T p) {
			value = mode == endian::native ? p : swap_endian(p);
			return *this;
		}

		operator T(){
			return mode == endian::native ? value : swap_endian(value);
		}
	};
}