//========= Copyright � 1996-2006, Valve LLC, All rights reserved. ============
//
// Purpose: Low level byte swapping routines.
//
// $NoKeywords: $
//=============================================================================
#ifndef BYTESWAP_H
#define BYTESWAP_H
#if defined(_WIN32)
#pragma once
#endif

#include "tier0/dbg.h"
#include "public/datamap.h"	// needed for typedescription_t.  note datamap.h is tier1 as well.

class CByteSwap
{
public:
	CByteSwap()
	{
		// Default behavior sets the target endian to match the machine native endian (no swap).
		SetTargetBigEndian(IsMachineBigEndian());
	}

	//-----------------------------------------------------------------------------
	// Write a single field.
	//-----------------------------------------------------------------------------
	void SwapFieldToTargetEndian(void* pOutputBuffer, void* pData, typedescription_t* pField);

	//-----------------------------------------------------------------------------
	// Write a block of fields.  Works a bit like the saverestore code.  
	//-----------------------------------------------------------------------------
	void SwapFieldsToTargetEndian(void* pOutputBuffer, void* pBaseData, datamap_t* pDataMap);

	// Swaps fields for the templated type to the output buffer.
	template<typename T> inline void SwapFieldsToTargetEndian(T* pOutputBuffer, void* pBaseData, unsigned int objectCount = 1)
	{
		for (unsigned int i = 0; i < objectCount; ++i, ++pOutputBuffer)
		{
			SwapFieldsToTargetEndian((void*)pOutputBuffer, pBaseData, &T::m_DataMap);
			pBaseData = (byte*)pBaseData + sizeof(T);
		}
	}

	// Swaps fields for the templated type in place.
	template<typename T> inline void SwapFieldsToTargetEndian(T* pOutputBuffer, unsigned int objectCount = 1)
	{
		SwapFieldsToTargetEndian<T>(pOutputBuffer, (void*)pOutputBuffer, objectCount);
	}

	//-----------------------------------------------------------------------------
	// True if the current machine is detected as big endian. 
	// (Endianness is effectively detected at compile time when optimizations are
	// enabled)
	//-----------------------------------------------------------------------------
	static bool IsMachineBigEndian()
	{
		short nIsBigEndian = 1;

		// if we are big endian, the first byte will be a 0, if little endian, it will be a one.
		return (bool)(0 == *(char*)&nIsBigEndian);
	}

	//-----------------------------------------------------------------------------
	// Sets the target byte ordering we are swapping to or from.
	//
	// Braindead Endian Reference:
	//		x86 is LITTLE Endian
	//		PowerPC is BIG Endian
	//-----------------------------------------------------------------------------
	inline void SetTargetBigEndian(bool bigEndian)
	{
		m_bBigEndian = bigEndian;
		m_bSwapBytes = IsMachineBigEndian() != bigEndian;
	}

	// Changes target endian
	inline void FlipTargetEndian(void)
	{
		m_bSwapBytes = !m_bSwapBytes;
		m_bBigEndian = !m_bBigEndian;
	}

	// Forces byte swapping state, regardless of endianess
	inline void ActivateByteSwapping(bool bActivate)
	{
		SetTargetBigEndian(IsMachineBigEndian() != bActivate);
	}

	//-----------------------------------------------------------------------------
	// Returns true if the target machine is the same as this one in endianness.
	//
	// Used to determine when a byteswap needs to take place.
	//-----------------------------------------------------------------------------
	inline bool IsSwappingBytes(void)	// Are bytes being swapped?
	{
		return m_bSwapBytes;
	}

	inline bool IsTargetBigEndian(void)	// What is the current target endian?
	{
		return m_bBigEndian;
	}

	//-----------------------------------------------------------------------------
	// IsByteSwapped()
	//
	// When supplied with a chunk of input data and a constant or magic number
	// (in native format) determines the endienness of the current machine in
	// relation to the given input data.
	//
	// Returns:
	//		1  if input is the same as nativeConstant.
	//		0  if input is byteswapped relative to nativeConstant.
	//		-1 if input is not the same as nativeConstant and not byteswapped either.
	//
	// ( This is useful for detecting byteswapping in magic numbers in structure 
	// headers for example. )
	//-----------------------------------------------------------------------------
	template<typename T> inline int SourceIsNativeEndian(T input, T nativeConstant)
	{
		// If it's the same, it isn't byteswapped:
		if (input == nativeConstant)
			return 1;

		int output;
		LowLevelByteSwap<T>(&output, &input);
		if (output == nativeConstant)
			return 0;

		Assert(0);		// if we get here, input is neither a swapped nor unswapped version of nativeConstant.
		return -1;
	}

	//-----------------------------------------------------------------------------
	// Swaps an input buffer full of type T into the given output buffer.
	//
	// Swaps [count] items from the inputBuffer to the outputBuffer.
	// If inputBuffer is omitted or NULL, then it is assumed to be the same as
	// outputBuffer - effectively swapping the contents of the buffer in place.
	//-----------------------------------------------------------------------------
	template<typename T> inline void SwapBuffer(T* outputBuffer, T* inputBuffer = NULL, int count = 1)
	{
		Assert(count >= 0);
		Assert(outputBuffer);

		// Fail gracefully in release:
		if (count <= 0 || !outputBuffer)
			return;

		// Optimization for the case when we are swapping in place.
		if (inputBuffer == NULL)
		{
			inputBuffer = outputBuffer;
		}

		// Swap everything in the buffer:
		for (int i = 0; i < count; i++)
		{
			LowLevelByteSwap<T>(&outputBuffer[i], &inputBuffer[i]);
		}
	}

	//-----------------------------------------------------------------------------
	// Swaps an input buffer full of type T into the given output buffer.
	//
	// Swaps [count] items from the inputBuffer to the outputBuffer.
	// If inputBuffer is omitted or NULL, then it is assumed to be the same as
	// outputBuffer - effectively swapping the contents of the buffer in place.
	//-----------------------------------------------------------------------------
	template<typename T> inline void SwapBufferToTargetEndian(T* outputBuffer, T* inputBuffer = NULL, int count = 1)
	{
		Assert(count >= 0);
		Assert(outputBuffer);

		// Fail gracefully in release:
		if (count <= 0 || !outputBuffer)
			return;

		// Optimization for the case when we are swapping in place.
		if (inputBuffer == NULL)
		{
			inputBuffer = outputBuffer;
		}

		// Are we already the correct endienness? ( or are we swapping 1 byte items? )
		if (!m_bSwapBytes || (sizeof(T) == 1))
		{
			// If we were just going to swap in place then return.
			if (!inputBuffer)
				return;

			// Otherwise copy the inputBuffer to the outputBuffer:
			if (outputBuffer != inputBuffer)
				memcpy(outputBuffer, inputBuffer, count * sizeof(T));
			return;

		}

		// Swap everything in the buffer:
		for (int i = 0; i < count; i++)
		{
			LowLevelByteSwap<T>(&outputBuffer[i], &inputBuffer[i]);
		}
	}

private:
	//-----------------------------------------------------------------------------
	// The lowest level byte swapping workhorse of doom.  output always contains the 
	// swapped version of input.  ( Doesn't compare machine to target endianness )
	//-----------------------------------------------------------------------------
	template<typename T> static void LowLevelByteSwap(T* output, T* input)
	{
		T temp = *output;
#if defined( _X360 )
		// Intrinsics need the source type to be fixed-point
		DWORD* word = (DWORD*)input;
		switch (sizeof(T))
		{
		case 8:
		{
			__storewordbytereverse(*(word + 1), 0, &temp);
			__storewordbytereverse(*(word + 0), 4, &temp);
		}
		break;

		case 4:
			__storewordbytereverse(*word, 0, &temp);
			break;

		case 2:
			__storeshortbytereverse(*input, 0, &temp);
			break;

		case 1:
			Q_memcpy(&temp, input, 1);
			break;

		default:
			Assert("Invalid size in CByteswap::LowLevelByteSwap" && 0);
		}
#else
		for (unsigned int i = 0; i < sizeof(T); i++)
		{
			((unsigned char*)&temp)[i] = ((unsigned char*)input)[sizeof(T) - (i + 1)];
		}
#endif
		memcpy(output, &temp, sizeof(T));
	}

#if defined( _X360 )
	// specialized for void * to get 360 XDK compile working despite changelist 281331
	//-----------------------------------------------------------------------------
	// The lowest level byte swapping workhorse of doom.  output always contains the 
	// swapped version of input.  ( Doesn't compare machine to target endianness )
	//-----------------------------------------------------------------------------
	template<> static void LowLevelByteSwap(void** output, void** input)
	{
		AssertMsgOnce(sizeof(void*) == sizeof(unsigned int), "void *'s on this platform are not four bytes!");
		__storewordbytereverse(*reinterpret_cast<unsigned int*>(input), 0, output);
	}
#endif

	unsigned int m_bSwapBytes : 1;
	unsigned int m_bBigEndian : 1;
};

#endif /* !BYTESWAP_H */