LZ77压缩算法(C语言版)

最新推荐文章于 2024-03-06 10:04:00 发布

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最新推荐文章于 2024-03-06 10:04:00 发布 · 8.4k 阅读

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CC 4.0 BY-SA版权

文章标签：

#算法 #语言 #c #buffer #winapi #fp

本文档展示了如何使用C语言实现LZ77压缩和解压缩算法。代码包括了Write1ToBitStream、Write0ToBitStream、ReadBitFromBitStream等位操作函数，以及WriteGolombCode和ReadGolombCode用于Golomb编码和解码的函数。通过调用lz77compress和lz77decompress函数，可以对文件进行压缩和解压缩，并且提供了一个简单的测试程序来测量压缩和解压缩的时间。

测试压缩一个425K的文件需要9.4秒，压缩后的文件为177K。

/*********************************************************************
*
* Project description:
* Lz77 compression/decompression algorithm.
*
*********************************************************************/

#include <windows.h>
#include <conio.h>
#include <stdio.h>
#include <assert.h>

#define OFFSET_CODING_LENGTH (10)
#define MAX_WND_SIZE 1024
//#define MAX_WND_SIZE (1<<OFFSET_CODING_LENGTH)
#define OFFSET_MASK_CODE (MAX_WND_SIZE-1)

const ULONG m=3;

UCHAR __buffer1__[0x200000];
UCHAR __buffer2__[0x200000];

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

void
Write1ToBitStream(
PUCHAR pBuffer,
ULONG ulBitOffset
)
{
ULONG ulByteBoundary;
ULONG ulOffsetInByte;

ulByteBoundary = ulBitOffset>>3 ;
ulOffsetInByte = ulBitOffset&7;

*(pBuffer+ulByteBoundary) |= (1<<ulOffsetInByte);
}

void
Write0ToBitStream(
PUCHAR pBuffer,
ULONG ulBitOffset
)
{
ULONG ulByteBoundary;
ULONG ulOffsetInByte;

ulByteBoundary = ulBitOffset>>3 ;
ulOffsetInByte = ulBitOffset&7;

*(pBuffer+ulByteBoundary) &= (~(1<<ulOffsetInByte));
}

ULONG
ReadBitFromBitStream(
PUCHAR pBuffer,
ULONG ulBitOffset
)
{
ULONG ulByteBoundary;
ULONG ulOffsetInByte;

ulByteBoundary = ulBitOffset>>3 ;
ulOffsetInByte = ulBitOffset&7;

return ((*(PULONG)(pBuffer+ulByteBoundary))>>ulOffsetInByte)&1 ;
}

ULONG WINAPI
WriteGolombCode(
ULONG x,
PUCHAR pBuffer,
ULONG ulBitOffset
)
{
ULONG q, r;
int i;

q = (x-1)>>m;
r = x-(q<<m)-1;

for(i=0; (ULONG)i<q; i++, ulBitOffset++)
{
Write1ToBitStream(pBuffer, ulBitOffset);
}
Write0ToBitStream(pBuffer, ulBitOffset);
ulBitOffset++;

for(i=0; i<m; i++, ulBitOffset++)
{
if( (r>>i)&1 )
{
Write1ToBitStream(pBuffer, ulBitOffset);
}
else
{
Write0ToBitStream(pBuffer, ulBitOffset);
}
}

return m+q+1;
}

ULONG
ReadGolombCode(
PULONG pulCodingLength,
PUCHAR pBuffer,
ULONG ulBitOffset
)
{
ULONG q, r;
ULONG bit;
int i;

for(q=0; ;q++)
{
bit = (ULONG)ReadBitFromBitStream(pBuffer, ulBitOffset);
ulBitOffset++;
if( !bit )
{
break;
}
}

for(i=0, r=0; (ULONG)i<m; i++, ulBitOffset++)
{
bit = (ULONG)ReadBitFromBitStream(pBuffer, ulBitOffset);
bit <<= i;
r |= bit;
}

*pulCodingLength = m + q + 1;

return r+(q<<m)+1;
}

ULONG
CompareStrings(
PUCHAR string1,
PUCHAR string2,
ULONG length
)
{
&nbs

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