那些踩過得神坑:<備註,這個demo的例子有一處是不對的.>

LzmaDecode中的第四個引數:nCompBufLen 應該給第三個引數的實際緩衝區大小.!!!,我操.分析原始碼.和返回值,百度沒有.

本文章介紹的是 LZMA SDK 9.20

7z LZMA 至少需要這三個原始檔
LzmaEnc.c
LzmaDec.c
LzFind.c

和這五個標頭檔案

LzFind.h
LzHash.h
LzmaDec.h
LzmaEnc.h
Types.h

LZMA2 需要在此基礎上附加兩個原始檔

Lzma2Dec.c
Lzma2Enc.c

以及兩個標頭檔案

Lzma2Dec.h
Lzma2Enc.h

LZMA 流介面有 6 個函式，引數含義可顧名思義

CLzmaEncHandle LzmaEnc_Create(ISzAlloc *alloc);
void LzmaEnc_Destroy(CLzmaEncHandle p, ISzAlloc *alloc, ISzAlloc *allocBig);
SRes LzmaEnc_SetProps(CLzmaEncHandle p, const CLzmaEncProps *props);
SRes LzmaEnc_WriteProperties(CLzmaEncHandle p, Byte *properties, SizeT *size);
SRes LzmaEnc_Encode(CLzmaEncHandle p, ISeqOutStream *outStream, ISeqInStream *inStream,

ICompressProgress *progress, ISzAlloc *alloc, ISzAlloc *allocBig);
SRes LzmaEnc_MemEncode(CLzmaEncHandle p, Byte *dest, SizeT *destLen, const Byte *src, SizeT srcLen,
int writeEndMark, ICompressProgress *progress, ISzAlloc *alloc, ISzAlloc *allocBig);

CLzmaEncHandle 實為 void *

SRes 為狀態返回型別

ISzAlloc、ISeqInStream、ISeqOutStreaem 和 ICompressProgress 為使用者需要提供的四個介面，它們的定義如下

typedef struct
{
void *(*Alloc)(void *p, size_t size);
void (*Free)(void *p, void *address); /* address can be 0 */
} ISzAlloc;

typedef struct
{
SRes (*Read)(void *p, void *buf, size_t *size);
/* if (input(*size) != 0 && output(*size) == 0) means end_of_stream.
(output(*size) < input(*size)) is allowed */
} ISeqInStream;

typedef struct
{
size_t (*Write)(void *p, const void *buf, size_t size);
/* Returns: result - the number of actually written bytes.
(result < size) means error */
} ISeqOutStream;

typedef struct
{
SRes (*Progress)(void *p, UInt64 inSize, UInt64 outSize);
/* Returns: result. (result != SZ_OK) means break.
Value (UInt64)(Int64)-1 for size means unknown value. */
} ICompressProgress;

另外注意在實現 ISeqInStream 時，除最後兩次呼叫外，必須每次都提交 *size 位元組的資料，最後兩次中，一次提交所有剩餘資料，另一次提交 0 位元組表示結束，否則 LZMA Encoder 會崩潰。

還有一個 One-Call 介面，把上面的呼叫按照常規邏輯包裝了一下

SRes LzmaEncode(Byte *dest, SizeT *destLen, const Byte *src, SizeT srcLen,
const CLzmaEncProps *props, Byte *propsEncoded, SizeT *propsSize, int writeEndMark,
ICompressProgress *progress, ISzAlloc *alloc, ISzAlloc *allocBig);

LZMA2 的介面與 LZMA 類似，主要不同之處有兩點：

- alloc 和 allocBig 介面被放到了建構函式中
- props 中多了一些引數

http://www.7-zip.org/sdk.html

另外值得一提的是，LZMA 單執行緒在筆記本電池供電時，使用快速模式，對隨機資料的壓縮速度為 4MB/s，壓縮率約為 100%，對全零資料的壓縮速度為 70MB/s，壓縮率約為 0%。 

經過SunOS sun280 5.10驗證的例項（該例項為直接呼叫封裝好的函式）：

/* * Simple test program for LZMA SDK's "one call" interface. * */  #include <stdio.h>  #include <string.h>  #include "../../LzmaEnc.h"  #include "../../LzmaDec.h"  #include "../../Alloc.h"  #define COMP_BUFLEN 1000  #define UNCOMP_BUFLEN 5000  char* pTestData;  unsigned char pCompBuf[1000]; /* Compressed data */  unsigned char pUnCompBuf[5000]; /* Unompressed data - at the end its contents */  /* should be equal to contents of pTestData */  static void *SzAlloc(void *p, size_t size) { return MyAlloc(size); }  static void SzFree(void *p, void *address) { MyFree(address); }  int main(int argc, char* argv[])  {      pTestData = "DEADBEEF|askjd9827x34bnzkj#%wioeruxo3b84nxijlhwqdzhwerzu39b87r#_3b9p78bznor83y4fr";      size_t nTestDataLen = strlen(pTestData);      size_t nCompBufLen = COMP_BUFLEN;       size_t nUnCompBufLen = UNCOMP_BUFLEN;       unsigned char pPropsBuf[LZMA_PROPS_SIZE];       size_t nPropsBufLen = LZMA_PROPS_SIZE;       ISzAlloc stAllocator = { SzAlloc, SzFree };       CLzmaEncProps stProps;       ELzmaStatus nStatus;       SRes rc;      int err = 0;       memset(pCompBuf, 0, COMP_BUFLEN);       memset(pUnCompBuf, 0, UNCOMP_BUFLEN); /* Initialize compressor (aka encoder) properties... */       LzmaEncProps_Init(&stProps);       stProps.level = 9;       stProps.dictSize = 1 << 24;       /* ... and compress data. */       printf("dest_len:%d,src_len:%d,prop_len:%d\n",nCompBufLen,nTestDataLen,nPropsBufLen);      rc = LzmaEncode(pCompBuf+LZMA_PROPS_SIZE, &nCompBufLen, (unsigned char*)pTestData, nTestDataLen, &stProps, pPropsBuf, &nPropsBufLen, 0, NULL, &stAllocator, &stAllocator);       if ( rc != SZ_OK )       {        printf("\nLZMA compression failed (rc=%d).\n", rc);        err = 1;        }       else       {      printf("dest_address:%p,dest_len:%d,src_len:%d,dest:%s\n",pCompBuf,nCompBufLen,nTestDataLen,pCompBuf+LZMA_PROPS_SIZE+1);       }      /* Decompress compressed data from previous step */          //nCompBufLen += LZMA_PROPS_SIZE;         nUnCompBufLen = nTestDataLen;      rc = LzmaDecode(pUnCompBuf, &nUnCompBufLen, pCompBuf+LZMA_PROPS_SIZE, &nCompBufLen, pPropsBuf, nPropsBufLen, LZMA_FINISH_ANY, &nStatus, &stAllocator);       if ( rc != SZ_OK )           {            printf("\nLZMA decompression failed (rc=%d, status=%d).\n", rc, nStatus);             err = 1;           }        if ((nUnCompBufLen != nTestDataLen) || memcmp(pTestData, pUnCompBuf, nTestDataLen) )            {            printf("Compression and/or decompression failed!\n");              printf("\tInput data length [nTestDataLen] : %d\n", nTestDataLen);              printf("\tCompressed data length [nCompBufLen] : %d\n", nCompBufLen);              printf("\tUncompressed data length [nUnCompBufLen]: %d\n", nUnCompBufLen);            if ( memcmp(pTestData, pUnCompBuf, nTestDataLen) )                  printf("\tpTestData and pUnCompBuf contain different data!\n");            else              {              printf("\ndest_len:%d\n,dest_data:%s\n,src_src:%s\n",nUnCompBufLen,pUnCompBuf,pTestData);              }              err = 1;             }            printf("\ndest_len:%d\n,dest_data:%s\n,src_src:%s\n",nUnCompBufLen,pUnCompBuf,pTestData);         if ( !err )          printf("\nOK!\n");           return 0; }
詳情請瀏覽sdk說明文件或者LZMA官方論壇（http://sourceforge.net/projects/sevenzip/forums/forum/45797/topic/4698263）

備註：
         

        整整三天才搞出來，今天終於可以好好睡覺了。學程式設計的同學啊，要加強英語的學習啊。

原文轉載自:http://blog.163.com/[email protected]/blog/static/1018865812012499356225/