/////////////////////////////////////////////////////////////////////////////
// SckLzw.cpp   LZW For GIF 編碼和解碼實現文件                             //
// CopyRight(C)   1996,2008   TCSY 公司                                    //
// Pentium Working Room   ShanChengKun   2003.08.18   更新                 //
/////////////////////////////////////////////////////////////////////////////
#include "stdafx.h"
#include "SckLzw.h"

//===========================================================================
// 通用LZW編碼，編碼階段不需要String Table，只需要m_wTableIndex來獲知寫位數
//===========================================================================
DWORD CSckLzw::LZW_Encode(const BYTE *InBuffer,      // 輸入數據流
						  DWORD  dwLength,           // 原數據大小
						  BYTE *OutBuffer)           // 壓縮后數據
{
	WORD *pHash = new WORD [LZW_MAX_HASH_SIZE];      // Hash索引表
	if(!pHash || !InBuffer || !OutBuffer) {if(pHash) delete[] pHash; return 0;}
	memset(pHash, 0x00, LZW_MAX_HASH_SIZE * sizeof(WORD)); // Hash Table置位0
	memset(OutBuffer, 0x00, dwLength * 2 + 2048);    // 目標全部清零

	m_wTableIndex     = LZW_END + 1;                 // 初始化字符表
	m_byCurrBits      = LZW_MIN_CODE_LEN + 1;        // 當前階段碼長
	m_pCurrIn         = InBuffer;                    // 原始輸入當前
	m_pCurrOut        = OutBuffer;                   // 當前指針輸出

	DWORD dwCurrPixel = 0, dwHashIndex = 0;          // 當前寫入點數
	BYTE  byOutBit    = 0;                           // 輸出緩沖位置
	WORD  wPrefix     = m_pCurrIn[dwCurrPixel++];    // Hash索引前綴
	WORD  wSuffix     = 0;                           // Hash索引后綴

	Encode_WriteIndexOut(LZW_CLEAR, byOutBit);       // 寫Clear首字節
	while(dwCurrPixel < dwLength)
	{
		wSuffix = m_pCurrIn[dwCurrPixel++];          // 提取當前數據
		dwHashIndex = (wPrefix << 8) | wSuffix;      // 構造Hash地址

		// 已在表中，取出索引， Hash Table中存放的是String Table的Index
		if (pHash[dwHashIndex] != 0)                 // 編碼可匹配
		{
			wPrefix = pHash[dwHashIndex];            // 取出索引值
		}

		// 不在表中，把wPrefix + wSuffix添加到String Table中
		else                                         // 沒有則添加
		{
			Encode_WriteIndexOut(wPrefix, byOutBit);
			pHash[dwHashIndex] = m_wTableIndex++;
			wPrefix = wSuffix;

			if ((m_wTableIndex == 0x009) || (m_wTableIndex == 0x011) ||
				(m_wTableIndex == 0x021) || (m_wTableIndex == 0x041) ||
				(m_wTableIndex == 0x081) || (m_wTableIndex == 0x101) ||
				(m_wTableIndex == 0x201) || (m_wTableIndex == 0x401) ||
				(m_wTableIndex == 0x801))
				m_byCurrBits++;

			// String Table(編碼表)已經填滿
			else if (m_wTableIndex == LZW_MAX_TABLE_SIZE)
			{
				Encode_WriteIndexOut (wSuffix,   byOutBit);
				Encode_WriteIndexOut (LZW_CLEAR, byOutBit);

				m_wTableIndex = LZW_END + 1;
				m_byCurrBits  = LZW_MIN_CODE_LEN + 1;
				memset(pHash, 0x00, LZW_MAX_HASH_SIZE * sizeof(WORD));

				wPrefix = m_pCurrIn[dwCurrPixel++];
			}
		}
	}
	Encode_WriteIndexOut (wPrefix, byOutBit);
	Encode_WriteIndexOut (LZW_END, byOutBit);
	delete[] pHash; pHash = NULL;
	return (m_pCurrOut - OutBuffer + 1);             // 釋放并返回
}

//===========================================================================
// 解碼到目標8位色位圖，目標為8位色，自身遞歸調用
//===========================================================================
void CSckLzw::Decode_WriteStringOut(LZW_STRING * pString, WORD wPrefix, DWORD &dwCurrPixel)
{
	if(wPrefix < LZW_CLEAR)
	{
		m_pCurrOut[dwCurrPixel++] = (BYTE)pString[wPrefix].wSuffix;
	}
	else
	{
		Decode_WriteStringOut(pString, pString[wPrefix].wPrefix, dwCurrPixel);
		Decode_WriteStringOut(pString, pString[wPrefix].wSuffix, dwCurrPixel);
	}
}

//===========================================================================
// 通用LZW解碼
//===========================================================================
DWORD CSckLzw::LZW_Decode (const BYTE *InBuffer,     // 輸入的數據流
						   BYTE *OutBuffer)          // 解壓后的數據
{
	LZW_STRING *pString = new LZW_STRING[LZW_MAX_TABLE_SIZE + 32];
	if(!pString || !InBuffer || !OutBuffer) return 0;// 字符串表空間
	memset(pString, 0xFF, (LZW_MAX_TABLE_SIZE + 32) * sizeof(LZW_STRING));
	register WORD i;                                 // 初始化串后綴
	for(i=0; i<LZW_CLEAR; i++) pString[i].wSuffix = i;

	m_wTableIndex     = LZW_END + 1;                 // 初始化字符表
	m_byCurrBits      = LZW_MIN_CODE_LEN + 1;        // 當前階段碼長
	m_pCurrIn         = InBuffer;                    // 原始輸入當前
	m_pCurrOut        = OutBuffer;                   // 當前指針輸出

	DWORD dwCurrPixel = 0;                           // 當前寫入點數
	BYTE  byInBit     = 0;                           // 輸入從0開始
	WORD  wPrefix, wSuffix = LZW_CLEAR, wTemp;       // 表索引前后綴

	while((wPrefix = Decode_GetNextCode(byInBit)) != LZW_END)
	{
		if(wPrefix == LZW_CLEAR)
		{
			memset(pString, 0xFF, (LZW_MAX_TABLE_SIZE + 32) * sizeof(LZW_STRING));
			for(i=0; i<LZW_CLEAR; i++) pString[i].wSuffix = i;
			m_wTableIndex = LZW_END + 1;
			m_byCurrBits  = LZW_MIN_CODE_LEN + 1;
			while((wPrefix = Decode_GetNextCode(byInBit)) == LZW_CLEAR);
		}
		else
		{
			wTemp = (wPrefix < m_wTableIndex) ? wPrefix : wSuffix;
			while(pString[wTemp].wPrefix != 0xFFFF) wTemp = pString[wTemp].wPrefix;
			pString[m_wTableIndex  ].wPrefix = wSuffix;
			pString[m_wTableIndex++].wSuffix = pString[wTemp].wSuffix;

			if ((m_wTableIndex == 0x008) || (m_wTableIndex == 0x010) ||
				(m_wTableIndex == 0x020) || (m_wTableIndex == 0x040) ||
				(m_wTableIndex == 0x080) || (m_wTableIndex == 0x100) ||
				(m_wTableIndex == 0x200) || (m_wTableIndex == 0x400) ||
				(m_wTableIndex == 0x800))
				m_byCurrBits++;
		}
		Decode_WriteStringOut(pString, wPrefix, dwCurrPixel);
		wSuffix = wPrefix;
	}
	delete[] pString; pString = NULL;                // 釋放字符表
	return dwCurrPixel;                              // 返回原大小
}

/////////////////////////////////////////////////////////////////////////////