游戏用得到的压缩方式

在C目录中有算法文件，进入Util\LzmaLib目录，编译生成LIB库，导出了以下两函数，LzmaCompress 为压缩函数，LzmaUncompress 为解压缩函数。

MY_STDAPI LzmaCompress(unsigned char *dest, size_t *destLen, const unsigned char *src, size_t srcLen,
unsigned char *outProps, size_t *outPropsSize,
int level,
unsigned dictSize,
int lc,
int lp,
int pb,
int fb,
int numThreads
);

MY_STDAPI LzmaUncompress(unsigned char *dest, size_t *destLen, const unsigned char *src, SizeT *srcLen,
const unsigned char *props, size_t propsSize);

导入Types.h 和 Lzmalib.h 到工程中。

代码如下：

#include "stdafx.h"
#include "LzmaLib.h"

#pragma comment(lib,"lzma.lib")

int _tmain(int argc, _TCHAR* argv[])
{
FILE* pFile = _tfopen(_T("file.dat"), _T("rb"));

if (pFile == NULL)
{
_ftprintf(stderr, _T("Error to Open the file!"));
return - 1;
}

fseek(pFile, 0, SEEK_END);
size_t srcLen = ftell(pFile);
rewind(pFile);
size_t destLen = srcLen * 2;
unsigned char* psrcRead = new unsigned char[srcLen]; //原始文件数据
unsigned char* pDecomress = new unsigned char[srcLen]; //存放解压缩数据
unsigned char* pLzma = new unsigned char[destLen]; //存放压缩数据

fread(psrcRead, sizeof(char), srcLen, pFile);

unsigned char prop[5] =
{
0
};
size_t sizeProp = 5;

if (SZ_OK != LzmaCompress(pLzma, &destLen, psrcRead, srcLen, prop,
&sizeProp, 9, (1 << 24), 3, 0, 2, 32, 2))
{
//出错了
_ftprintf(stderr, _T("压缩时出错！"));
delete [] psrcRead;
delete [] pDecomress;
delete [] pLzma;
fclose(pFile);
return - 1;
}

FILE* pCompressFile = _tfopen(_T("compress.dat"), _T("wb"));
//写入压缩后的数据
if (pCompressFile == NULL)
{
_ftprintf(stderr, _T("创建文件出错!"));
delete [] psrcRead;
delete [] pDecomress;
delete [] pLzma;
fclose(pFile);
return - 1;
}
fwrite(pLzma, sizeof(char), destLen, pCompressFile);
fclose(pCompressFile);

FILE* pDecompressFile = _tfopen(_T("decompress.dat"), _T("wb"));
//写入解压缩数据
if (pDecompressFile == NULL)
{
_ftprintf(stderr, _T("写入数据出错！"));
delete [] psrcRead;
delete [] pDecomress;
delete [] pLzma;
fclose(pFile);
return - 1;
}

//注意：解压缩时props参数要使用压缩时生成的outProps，这样才能正常解压缩
if (SZ_OK != LzmaUncompress(pDecomress, &srcLen, pLzma, &destLen, prop, 5))
{
delete [] psrcRead;
delete [] pDecomress;
delete [] pLzma;

fclose(pDecompressFile);
fclose(pFile);
return - 1;
}

fwrite(pDecomress, sizeof(char), srcLen, pDecompressFile);

delete [] psrcRead;
delete [] pDecomress;
delete [] pLzma;

fclose(pDecompressFile);
fclose(pFile);

return 0;
}

zlib使用：

zlib 是通用的压缩库，提供了一套 in-memory 压缩和解压函数，并能检测解压出来的数据的完整性(integrity)。下面介绍两个最有用的函数——compress 和 uncompress。

int compress(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen);

compress函数将 source 缓冲区中的内容压缩到 dest 缓冲区。 sourceLen 表示source 缓冲区的大小(以字节计)。注意函数的第二个参数 destLen 是传址调用。当调用函数时，destLen表示 dest 缓冲区的大小，destLen > (sourceLen + 12)*100.1%。当函数退出后，destLen 表示压缩后缓冲区的实际大小。此时 destLen / sourceLen 正好是压缩率。

compress 若成功，则返回 Z_OK；若没有足够内存，则返回 Z_MEM_ERROR；若输出缓冲区不够大，则返回 Z_BUF_ERROR。

int uncompress(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen);

uncompress 函数将 source 缓冲区的内容解压缩到 dest 缓冲区。sourceLen 是 source 缓冲区的大小(以字节计)。注意函数的第二个参数 destLen 是传址调用。当调用函数时，destLen 表示 dest 缓冲区的大小， dest 缓冲区要足以容下解压后的数据。在进行解压缩时，需要提前知道被压缩的数据解压出来会有多大。这就要求在进行压缩之前，保存原始数据的大小(也就是解压后的数据的大小)。这不是 zlib 函数库的功能，需要我们做额外的工作。当函数退出后， destLen 是解压出来的数据的实际大小。

uncompress 若成功，则返回 Z_OK ；若没有足够内存，则返回 Z_MEM_ERROR；若输出缓冲区不够大，则返回 Z_BUF_ERROR。若输入数据有误，则返回 Z_DATA_ERROR。

代码如下：

#include "stdafx.h"
#include <cstring>
#include <cstdlib>
#include <iostream>
#include "zlib.h"
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
int err = 0;
Byte compr[200] = {0}, uncompr[200] = {0}; // big enough
uLong comprLen = 0, uncomprLen = 0;

const char* hello = "12345678901234567890123456789012345678901234567890";

uLong len = strlen(hello) + 1;
comprLen = sizeof(compr) / sizeof(compr[0]);

err = compress(compr, &comprLen, (const Bytef*)hello, len);

if (err != Z_OK)
{
cerr << "compess error: " << err << '\n';
exit(1);
}

cout << "orignal size: " << len
<< " , compressed size : " << comprLen << '\n';

strcpy((char*)uncompr, "garbage");

err = uncompress(uncompr, &uncomprLen, compr, comprLen);

if (err != Z_OK)
{
cerr << "uncompess error: " << err << '\n';
exit(1);
}

cout << "orignal size: " << len
<< " , uncompressed size : " << uncomprLen << '\n';

if (strcmp((char*)uncompr, hello))
{
cerr << "BAD uncompress!!!\n";
exit(1);
}
else
{
cout << "uncompress() succeed: \n" << (char*)uncompr;
}
}