gif文件解析

详细资料：http://blog.csdn.net/wzy198852/article/details/17266507

MD5：98206F88B84CCC399C840C8EEC902CCF

 GIF文件结构定义模块：

#ifndef _GIF_COMMON_H
#define _GIF_COMMON_H

#ifndef BYTE
#define BYTE unsigned char
#endif

#ifndef CHAR
#define CHAR char
#endif

#ifndef SHORT
#define SHORT short
#endif

#ifndef LONG
#define LONG long
#endif

typedef struct GIFColor {
    BYTE gifRed;
    BYTE gifGreen;
    BYTE gifBlue;
    BYTE gifResv;
}GIFColor;

typedef struct GIFHeader {
    CHAR gifSignature[3];    // GIF署名: "GIF"
    CHAR gifVersion[2];        // GIF版本号: "87a" or "89a"
    BYTE gifResv[3];        // 保留字段
}GIFHeader;

typedef struct GIFLSDescriptor {
    SHORT gifLSWidth;        // 逻辑屏幕宽度
    SHORT gifLSHeight;        // 逻辑屏幕高度

    BYTE gifGlobalColorTableFlg : 1;    // 全局颜色列表标志: 置位表示有全局颜色列表，pixel值有意义
    BYTE gifColorResolution : 3;        // 颜色深度: cr + 1
    BYTE gifSortFlg : 1;    // 分类标志: 置位表示全局颜色列表分类排序
    BYTE gifPixel : 3;        // 全局颜色列表索引数: 2^(pixel+1)
    BYTE gifBgColorIdx;        // 背景颜色索引，如果无全局颜色列表，该值无意义
    BYTE gifAspectRadio;    // 像素宽高比
    BYTE gifResv[2];
}GIFLSDescriptor;

typedef struct GIFColorTable {
    BYTE gifColorTable[256];
}GIFColorTable;

typedef struct GIFImageDescriptor {
    BYTE gifImageFlg;        // 图像标识符开始标志: 0x2c(';')
    BYTE gifResv1[3];

    SHORT gifXOffset;        // X方向偏移量
    SHORT gifYOffset;        // Y方向偏移量
    SHORT gifImageWidth;    // 图像宽度
    SHORT gifImageHeight;    // 图像高度

    BYTE gifLocalColorTableFlg : 1;        // 局部颜色列表标志，置位时图像标识符后紧跟一个局部颜色表，
                                           供紧跟在它之后的一幅图像使用；值否时使用全局颜色列表，忽略pixel值。
    BYTE gifInterlaceFlg : 1;            // 交织标志，置位时图像数据使用交织方式排列，否则使用顺序排列
    BYTE gifSortFlg : 1;    // 分类标志，置位表示局部颜色列表分类排序
    BYTE gifResv : 2;        // 保留位，必须为 0
    BYTE gifPixel;            // 局部颜色列表索引数: 2^(pixel+1)
    BYTE gifResv2[3];        
}GIFImageDescriptor;

typedef struct GIFImageDataSubBlock {
    BYTE gifSubBlockSize;    // 块大小
    BYTE gifResv[3];
    BYTE *gifCodedData;        // 编码数据
}GIFImageDataSubBlock;

typedef struct GIFImageData {
    BYTE gifLZWCodeTableSize;        // LZW初始编码表大小的位数
    SHORT gifSubBlockNum;            // 数据块数
    BYTE gifResv1;
    GIFImageDataSubBlock *gifImageDataSubBlocks;    // 数据块
    BYTE gifImageDataEndFlg;        // 数据编码结束: 0
    BYTE gifResv2[3];
}GIFImageData;

typedef struct GIFImageChunk {
    /* 图像标识符 */
    GIFImageDescriptor gifImageDescriptor;
    /* 图像局部颜色列表，gifLocalColorTableFlg=1时有效 */
    GIFColorTable gifLocalColorTable;
    /* 图像数据 */
    GIFImageData gifImageData;
}GIFImageChunk;

typedef struct GIFStruct {
    /* 1 文件头 */
    GIFHeader gifHeader;

    /* 2 GIF数据流 */
    /* 2.1 逻辑屏幕标志符 */
    GIFLSDescriptor gifLSDescriptor;
    /* 2.2 全局颜色列表，gifGlobalColorTableFlg=1时有效 */
    GIFColorTable gifGlobalColorTable;
    /* 2.3 图像 */
    SHORT gifImageChunkNum;        // 图像数
    BYTE gifResv[2];
    GIFImageChunk *gifImageChunks;



    /* 3 文件终结器 */
};

#endif

文件读取缓存模块：

#include <stdio.h>
#include <stdlib.h>

#ifndef GIF
#define CHAR char
#define BYTE unsigned char
#define SHORT short
#define INT int
#define LONG long
#define GIF

#define SUCCESS 0
#define FAILURE 1
#define INVALID -1

#define CHECK_NULL_RET(expr, ret) if(NULL == (expr)) return ret
#define CHECK_RET(expr, ret) if(expr) return ret
#define CHECK_FALSE_RET(expr, ret) if(!(expr)) return ret

#endif

#define FIRST_BUFF_SIZE     2048
#define SECOND_BUFF_SIZE     FIRST_BUFF_SIZE
#define BUFF_SIZE             (FIRST_BUFF_SIZE+SECOND_BUFF_SIZE)
#define READ_ONCE_SIZE     FIRST_BUFF_SIZE

FILE *fin;                     // 输入文件
BYTE readBuff[BUFF_SIZE];    // 缓存区，分为第一缓存和第二缓存，对应FIRST_BUFF和SECOND_BUFF
INT startIdx;                // 有效数据起始索引(包含当前)，默认值为INVALID(-1)
INT endIdx;                    // 有效数据结束索引(包含当前)，默认值为INVALID(-1)
INT readIdx;                // 下一次读取起始索引(包含当前)，默认值为INVALID(-1)

#define GET_VALID_SIZE() (endIdx - readIdx + 1)

INT RBFillBuff()
{
    INT realReadBytes;
    INT unusedLen;
    CHECK_NULL_RET(fin, FAILURE);

    if(readIdx <= endIdx) // 有未读数据
    {
        memmove(readBuff, &readBuff[readIdx], endIdx-readIdx+1);
        startIdx = readIdx = 0;
        endIdx = endIdx - readIdx;
    }
    else // 无未读数据
    {
        startIdx = endIdx = -1;
        readIdx = 0;
    }
    CHECK_FALSE_RET(endIdx < FIRST_BUFF_SIZE, SUCCESS);
    
    realReadBytes = fread(&readBuff[endIdx+1], 1, READ_ONCE_SIZE, fin);
    CHECK_FALSE_RET(realReadBytes > 0, FAILURE);

    startIdx = readIdx = 0;
    endIdx = endIdx + realReadBytes;
    
    return SUCCESS;
}

VOID RBFreeFile() 
{ 
    if(fin != NULL) 
    { 
        fclose(fin); 
        fin = NULL; 
    } 
}

/* 缓存模块初始化 */
INT RBModuleInit(CHAR *filePath)
{
    startIdx = endIdx = -1;
    readIdx = 0;
    
    CHECK_NULL_RET(filePath, FAILURE);
    
    fin = fopen(filePath, "rb");
    CHECK_NULL_RET(fin, FAILURE);
    RBFillBuff();
}

INT RBGetBytes(BYTE *buff, int len)
{
    INT ret;
    CHECK_NULL_RET(buff, FAILURE);
    CHECK_FALSE_RET(len > 0 && len < FIRST_BUFF_SIZE, FAILURE);
    if(len > GET_VALID_SIZE())
    {
        if(FAILURE == RBFillBuff())
        {
            return FAILURE;
        }
    }
    CHECK_FALSE_RET(len <= GET_VALID_SIZE(), FAILURE);
    memcpy(buff, &readBuff[readIdx], len);
    readIdx += len;
    
    return SUCCESS;
}


INT RBGetByte(BYTE *value)
{
    return RBGetBytes(value, 1);
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct Elem {
    unsigned char value;
    int preIdx;
}Elem;

int tabSize;
Elem lzwTab[256];

#define LZWSIZE 2

int LzwInit(int size)
{
    int loop = 0;
    for(loop = 0; loop < size; loop++)
    {
        lzwTab[loop].value = loop;
        lzwTab[loop].preIdx = -1;
    }
    tabSize = size;
    return 1;
}

int AddElement(unsigned char currChar, int lastIdx)
{
    lzwTab[tabSize].value = currChar;
    lzwTab[tabSize].preIdx = lastIdx;
    tabSize++;
    return 1;
}

int SearchStrInTable(unsigned char currChar, int lastIdx)
{
    int loop = 0;
    for(loop = 0; loop < tabSize; loop++)
    {
        if((lzwTab[loop].value == currChar) && (lzwTab[loop].preIdx == lastIdx))
        {
            return loop;
        }
    }
    return -1;
}

int LzwEncode(const unsigned char *inStream, int inLen, int *outStream, int *outLen)
{
    
    unsigned char currChar = 0;
    int lastIdx = -1;
    int currIdx = -1;

    int readIdx = 0;
    int writeIdx = 0;

    LzwInit(LZWSIZE); // 初始化编码表

    for(readIdx = 0; readIdx < inLen; readIdx++) // 遍历输入流
    {
        currChar = inStream[readIdx]; // 当前字符，与lastIdx组成当前字符串
        currIdx = SearchStrInTable(currChar, lastIdx); // 查找当前字符串索引
        if(currIdx == -1) // 未找到
        {
            outStream[writeIdx++] = lastIdx; // 输出前缀索引到编码流
            AddElement(currChar, lastIdx);    // 添加当前字符串到编码表
            lastIdx = SearchStrInTable(currChar, -1); // 以当前字符的索引作为lastIdx，为下一轮做准备
        }
        else
        {
            lastIdx = currIdx;
        }
    }
    outStream[writeIdx++] = lastIdx;
    *outLen = writeIdx;

    return 1;
}

int SearchCodeInTable(int currCode, unsigned char *strBuff)
{
    if(currCode >= tabSize)
    {
        return 0;
    }
    else
    {
        int writeIdx = 0;
        while(currCode >= 0)
        {
            strBuff[writeIdx++] = lzwTab[currCode].value;
            currCode = lzwTab[currCode].preIdx;
        }

        unsigned char *strHead = strBuff;
        unsigned char *strTail = strBuff + writeIdx - 1;
        unsigned char strTemp;
        while(strHead < strTail)
        {
            strTemp = *strHead;
            *strHead = *strTail;
            *strTail = strTemp;

            strHead++;
            strTail--;
        }
        return writeIdx;
    }
}

int WriteString(unsigned char *outStream, unsigned char *strBuff, int strLen, int *outLen)
{
    memcpy(outStream + (*outLen), strBuff, strLen);
    *outLen += strLen;
    return 1;
}

int LzwDecode(const int *inStream, int inLen, unsigned char *outStream, int *outLen)
{
    int currCode;
    int lastCode = -1;
    int readIdx = 0;
    int strLen = 0;
    unsigned char *strBuff = new unsigned char[256];
    *outLen = 0;

    LzwInit(LZWSIZE); // 初始化编码表

    for(readIdx = 0; readIdx < inLen; readIdx++)
    {
        currCode = inStream[readIdx];
        strLen = SearchCodeInTable(currCode, strBuff);
        if(strLen == 0) // 没找到
        {
            strBuff[strLen++] = strBuff[0];
            WriteString(outStream, strBuff, strLen, outLen);
            if(lastCode != -1)
            {
                AddElement(strBuff[0], lastCode);
            }
            lastCode = currCode;
        }
        else // 找到
        {
            WriteString(outStream, strBuff, strLen, outLen);
            AddElement(strBuff[0], lastCode);
            lastCode = currCode;
        }
    }
    return 1;
}

int test()
{
    unsigned char srcData[] = {1,0,0,1,1,1,0,1,0,1,0,0,0,1,1,0,1,1,0,1,1,0,1};
    int encodeData[32];
    unsigned char decodeData[32];
    int srcDataLen = 23;
    int encodeDataLen;
    int decodeDataLen;

    printf("Start encode...
");
    LzwEncode(srcData, srcDataLen, encodeData, &encodeDataLen);
    printf("End encode, encodeDataLen=%d.
", encodeDataLen);
    printf("encodeData:");
    for(int i=0; i<encodeDataLen; i++)
    {
        printf("%d ", encodeData[i]);
    }

    printf("
Start decode...
");
    LzwDecode(encodeData, encodeDataLen, decodeData, &decodeDataLen);
    printf("End decode, decodeDataLen=%d.
", decodeDataLen);
    printf("decodeData:");
    for(int i=0; i<decodeDataLen; i++)
    {
        printf("%d ", decodeData[i]);
    }
    printf("
");
    return 1;
}

int main()
{
    test();

    system("pause");
    return 0;
}