C++ LZMA : LZMA2压缩文件的解压缩功能
C++ LZMA : LZMA2压缩文件的解压缩功能
提问于 2014-01-22 17:38:31
我正在尝试创建一个函数来解压缩LZAM2压缩的数据。我的灵感来源于本教程，它对LZMA非常有用，我尝试将它改编为LZMA2。我成功地为LZMA2创建了压缩函数，但解压缩函数没有成功。
以下是压缩函数：
static void Compress2Inc(std::vector<unsigned char> &outBuf,
const std::vector<unsigned char> &inBuf)
{
CLzma2EncHandle enc = Lzma2Enc_Create(&SzAllocForLzma, &SzAllocForLzma2);
assert(enc);
CLzma2EncProps props;
Lzma2EncProps_Init(&props);
props.lzmaProps.writeEndMark = 1; // 0 or 1
SRes res = Lzma2Enc_SetProps(enc, &props);
assert(res == SZ_OK);
unsigned propsSize = LZMA_PROPS_SIZE;
outBuf.resize(propsSize);
res = Lzma2Enc_WriteProperties(enc);
//cout << res;
//assert(res == SZ_OK && propsSize == LZMA_PROPS_SIZE);
VectorInStream inStream = { &VectorInStream_Read, &inBuf, 0 };
VectorOutStream outStream = { &VectorOutStream_Write, &outBuf };
res = Lzma2Enc_Encode(enc,
(ISeqOutStream*)&outStream, (ISeqInStream*)&inStream,
0);
assert(res == SZ_OK);
Lzma2Enc_Destroy(enc);
}其中：
static void *AllocForLzma2(void *, size_t size) { return BigAlloc(size); }
static void FreeForLzma2(void *, void *address) { BigFree(address); }
static ISzAlloc SzAllocForLzma2 = { AllocForLzma2, FreeForLzma2 };
static void *AllocForLzma(void *, size_t size) { return MyAlloc(size); }
static void FreeForLzma(void *, void *address) { MyFree(address); }
static ISzAlloc SzAllocForLzma = { AllocForLzma, FreeForLzma };
typedef struct
{
ISeqInStream SeqInStream;
const std::vector<unsigned char> *Buf;
unsigned BufPos;
} VectorInStream;
SRes VectorInStream_Read(void *p, void *buf, size_t *size)
{
VectorInStream *ctx = (VectorInStream*)p;
*size = min(*size, ctx->Buf->size() - ctx->BufPos);
if (*size)
memcpy(buf, &(*ctx->Buf)[ctx->BufPos], *size);
ctx->BufPos += *size;
return SZ_OK;
}
typedef struct
{
ISeqOutStream SeqOutStream;
std::vector<unsigned char> *Buf;
} VectorOutStream;
size_t VectorOutStream_Write(void *p, const void *buf, size_t size)
{
VectorOutStream *ctx = (VectorOutStream*)p;
if (size)
{
unsigned oldSize = ctx->Buf->size();
ctx->Buf->resize(oldSize + size);
memcpy(&(*ctx->Buf)[oldSize], buf, size);
}
return size;
}这是到目前为止我对解压缩函数的看法，但是Lzma2Dec_DecodeToBuf函数返回错误代码1(SZ_ERROR_DATA)，只是在web上找不到任何关于这一点的信息。
static void Uncompress2Inc(std::vector<unsigned char> &outBuf,
const std::vector<unsigned char> &inBuf)
{
CLzma2Dec dec;
Lzma2Dec_Construct(&dec);
SRes res = Lzma2Dec_Allocate(&dec, outBuf.size(), &SzAllocForLzma);
assert(res == SZ_OK);
Lzma2Dec_Init(&dec);
outBuf.resize(UNCOMPRESSED_SIZE);
unsigned outPos = 0, inPos = LZMA_PROPS_SIZE;
ELzmaStatus status;
const unsigned BUF_SIZE = 10240;
while (outPos < outBuf.size())
{
unsigned destLen = min(BUF_SIZE, outBuf.size() - outPos);
unsigned srcLen = min(BUF_SIZE, inBuf.size() - inPos);
unsigned srcLenOld = srcLen, destLenOld = destLen;
res = Lzma2Dec_DecodeToBuf(&dec,
&outBuf[outPos], &destLen,
&inBuf[inPos], &srcLen,
(outPos + destLen == outBuf.size()) ? LZMA_FINISH_END : LZMA_FINISH_ANY,
&status);
assert(res == SZ_OK);
inPos += srcLen;
outPos += destLen;
if (status == LZMA_STATUS_FINISHED_WITH_MARK)
break;
}
Lzma2Dec_Free(&dec, &SzAllocForLzma);
outBuf.resize(outPos);
}我正在使用从Visual Studio 2008下载的LZMA SDK和这里。有人这里也有同样的问题，但我不能利用他的代码.
是否有人成功地使用LZMA2解压缩LZMA SDK压缩文件？
请帮帮我！
回答 1
Stack Overflow用户
回答已采纳
发布于 2014-02-08 19:03:58
暂时的解决办法是在SRes res = Lzma2Dec_Allocate(&dec, outBuf.size(), &SzAllocForLzma);函数中用SRes res = Lzma2Dec_Allocate(&dec, 8, &SzAllocForLzma);代替8，其中8是一个神奇的数字。
然而，这不是解决问题的正确方法.
第一个错误是Lzma2Enc_WriteProperties不返回结果，而是返回一个属性字节，该属性字节必须用作Uncompress2Inc函数中Lzma2Dec_Allocate调用的第二个参数。因此，我们将神奇的数字8替换为属性字节，一切都如预期的那样工作。
为了实现这一点，必须将5字节头添加到将在解码函数中提取的编码数据中。下面是一个在VS2008中工作的示例(并不是最完美的代码，但它可以工作.我会在有时间时再回来，并提供一个更好的示例)：
void Lzma2Benchmark::compressChunk(std::vector<unsigned char> &outBuf, const std::vector<unsigned char> &inBuf)
{
//! \todo This is a temporary workaround, size needs to be added to the
m_uncompressedSize = inBuf.size();
std::cout << "Uncompressed size is: " << inBuf.size() << std::endl;
DWORD tickCountBeforeCompression = GetTickCount();
CLzma2EncHandle enc = Lzma2Enc_Create(&m_szAllocForLzma, &m_szAllocForLzma2);
assert(enc);
CLzma2EncProps props;
Lzma2EncProps_Init(&props);
props.lzmaProps.writeEndMark = 1; // 0 or 1
props.lzmaProps.level = 9;
props.lzmaProps.numThreads = 3;
//props.numTotalThreads = 2;
SRes res = Lzma2Enc_SetProps(enc, &props);
assert(res == SZ_OK);
// LZMA_PROPS_SIZE == 5 bytes
unsigned propsSize = LZMA_PROPS_SIZE;
outBuf.resize(propsSize);
// I think Lzma2Enc_WriteProperties returns the encoding properties in 1 Byte
Byte properties = Lzma2Enc_WriteProperties(enc);
//! \todo This is a temporary workaround
m_propByte = properties;
//! \todo Here m_propByte and m_uncompressedSize need to be added to outBuf's 5 byte header so simply add those 2 values to outBuf and start the encoding from there.
BenchmarkUtils::VectorInStream inStream = { &BenchmarkUtils::VectorInStream_Read, &inBuf, 0 };
BenchmarkUtils::VectorOutStream outStream = { &BenchmarkUtils::VectorOutStream_Write, &outBuf };
res = Lzma2Enc_Encode(enc,
(ISeqOutStream*)&outStream,
(ISeqInStream*)&inStream,
0);
std::cout << "Compress time is: " << GetTickCount() - tickCountBeforeCompression << " milliseconds.\n";
assert(res == SZ_OK);
Lzma2Enc_Destroy(enc);
std::cout << "Compressed size is: " << outBuf.size() << std::endl;
}
void Lzma2Benchmark::unCompressChunk(std::vector<unsigned char> &outBuf, const std::vector<unsigned char> &inBuf)
{
DWORD tickCountBeforeUncompression = GetTickCount();
CLzma2Dec dec;
Lzma2Dec_Construct(&dec);
//! \todo Heere the property size and the uncompressed size need to be extracted from inBuf, which is the compressed data.
// The second parameter is a temporary workaround.
SRes res = Lzma2Dec_Allocate(&dec, m_propByte/*8*/, &m_szAllocForLzma);
assert(res == SZ_OK);
Lzma2Dec_Init(&dec);
outBuf.resize(m_uncompressedSize);
unsigned outPos = 0, inPos = LZMA_PROPS_SIZE;
ELzmaStatus status;
const unsigned BUF_SIZE = 10240;
while(outPos < outBuf.size())
{
SizeT destLen = std::min(BUF_SIZE, outBuf.size() - outPos);
SizeT srcLen = std::min(BUF_SIZE, inBuf.size() - inPos);
SizeT srcLenOld = srcLen, destLenOld = destLen;
res = Lzma2Dec_DecodeToBuf(&dec,
&outBuf[outPos],
&destLen,
&inBuf[inPos],
&srcLen,
(outPos + destLen == outBuf.size()) ? LZMA_FINISH_END : LZMA_FINISH_ANY,
&status);
assert(res == SZ_OK);
inPos += srcLen;
outPos += destLen;
if(status == LZMA_STATUS_FINISHED_WITH_MARK)
{
break;
}
}
Lzma2Dec_Free(&dec, &m_szAllocForLzma);
outBuf.resize(outPos);
std::cout << "Uncompress time is: " << GetTickCount() - tickCountBeforeUncompression << " milliseconds.\n";
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/21289985
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