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274 lines
9.1 KiB
C
274 lines
9.1 KiB
C
#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <stdio.h>
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/*Altered by Kuwanger*/
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/*************************************************************************
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* Name: lz.c
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* Author: Marcus Geelnard
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* Description: LZ77 coder/decoder implementation.
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* Reentrant: Yes
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* $Id: lz.c,v 1.4 2004/10/08 19:28:04 marcus256 Exp $
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*
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* The LZ77 compression scheme is a substitutional compression scheme
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* proposed by Abraham Lempel and Jakob Ziv in 1977. It is very simple in
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* its design, and uses no fancy bit level compression.
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*
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* This is my first attempt at an implementation of a LZ77 code/decoder.
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*
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* The principle of the LZ77 compression algorithm is to store repeated
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* occurrences of strings as references to previous occurrences of the same
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* string. The point is that the reference consumes less space than the
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* string itself, provided that the string is long enough (in this
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* implementation, the string has to be at least 4 bytes long, since the
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* minimum coded reference is 3 bytes long). Also note that the term
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* "string" refers to any kind of byte sequence (it does not have to be
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* an ASCII string, for instance).
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*
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* The coder uses a brute force approach to finding string matches in the
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* history buffer (or "sliding window", if you wish), which is very, very
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* slow. I recon the complexity is somewhere between O(n^2) and O(n^3),
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* depending on the input data.
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*
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* There is also a faster implementation that uses a large working buffer
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* in which a "jump table" is stored, which is used to quickly find
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* possible string matches (see the source code for LZ_CompressFast() for
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* more information). The faster method is an order of magnitude faster,
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* and also does a full string search in the entire input buffer (it does
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* not use a sliding window).
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*
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* The upside is that decompression is very fast, and the compression ratio
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* is often very good.
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*
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* The reference to a string is coded as a (length,offset) pair, where the
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* length indicates the length of the string, and the offset gives the
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* offset from the current data position. To distinguish between string
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* references and literal strings (uncompressed bytes), a string reference
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* is preceded by a marker byte, which is chosen as the least common byte
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* symbol in the input data stream (this marker byte is stored in the
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* output stream as the first byte).
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*
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* Occurrences of the marker byte in the stream are encoded as the marker
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* byte followed by a zero byte, which means that occurrences of the marker
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* byte have to be coded with two bytes.
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*
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* The lengths and offsets are coded in a variable length fashion, allowing
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* values of any magnitude (up to 4294967295 in this implementation).
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*
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* With this compression scheme, the worst case compression result is
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* (257/256)*insize + 1.
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*
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*-------------------------------------------------------------------------
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* Copyright (c) 2003-2004 Marcus Geelnard
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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*
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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*
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would
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* be appreciated but is not required.
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*
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* 2. Altered source versions must be plainly marked as such, and must not
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* be misrepresented as being the original software.
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*
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* 3. This notice may not be removed or altered from any source
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* distribution.
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*
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* Marcus Geelnard
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* marcus.geelnard at home.se
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*************************************************************************/
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/*************************************************************************
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* Constants used for LZ77 coding
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*************************************************************************/
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/* Maximum offset (can be any size < 2^32). Lower values gives faster
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compression, while higher values gives better compression.
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NOTE: LZ_CompressFast does not use this constant. */
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#define LZ_MAX_OFFSET 4096
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/*************************************************************************
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* INTERNAL FUNCTIONS *
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*************************************************************************/
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/*************************************************************************
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* _LZ_StringCompare() - Return maximum length string match.
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*************************************************************************/
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static unsigned int _LZ_StringCompare( unsigned char * str1,
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unsigned char * str2, unsigned int minlen, unsigned int maxlen )
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{
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unsigned int len;
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for( len = minlen; (len < maxlen) && (str1[len] == str2[len]); ++ len );
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// for( len = minlen; (len < maxlen) && (str2+len+1 < str1-1) && (str1[len] == str2[len]); ++ len );
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return len;
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}
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/*************************************************************************
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* PUBLIC FUNCTIONS *
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*************************************************************************/
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/*************************************************************************
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* LZ_Compress() - Compress a block of data using an LZ77 coder.
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* in - Input (uncompressed) buffer.
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* out - Output (compressed) buffer. This buffer must be 0.4% larger
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* than the input buffer, plus one byte.
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* insize - Number of input bytes.
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* The function returns the size of the compressed data.
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*************************************************************************/
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int LZ_Compress( unsigned char *in, unsigned char *out,
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unsigned int insize )
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{
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unsigned char mask, bundle1, bundle2;
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int inpos, outpos, bytesleft;
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int maxoffset, offset, bestoffset;
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int maxlength, length, bestlength;
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unsigned char *ptr1, *ptr2, *flags;
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/* Do we have anything to compress? */
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if( insize < 1 )
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{
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return 0;
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}
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/* Remember the repetition marker for the decoder */
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out[0] = 0x10;
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out[1] = insize&0xFF;
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out[2] = (insize>>8)&0xFF;
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out[3] = (insize>>16)&0xFF;
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flags = &out[4];
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*flags = 0;
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mask = 128;
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/* Start of compression */
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inpos = 0;
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outpos = 5;
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/* Main compression loop */
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bytesleft = insize;
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do
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{
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/* Determine most distant position */
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if( inpos > LZ_MAX_OFFSET ) maxoffset = LZ_MAX_OFFSET;
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else maxoffset = inpos;
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/* Get pointer to current position */
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ptr1 = &in[ inpos ];
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/* Search history window for maximum length string match */
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bestlength = 2;
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bestoffset = 0;
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for( offset = 3; offset <= maxoffset; ++ offset )
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{
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/* Get pointer to candidate string */
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ptr2 = &ptr1[ -offset ];
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/* Quickly determine if this is a candidate (for speed) */
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if( (ptr1[ 0 ] == ptr2[ 0 ]) &&
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(ptr1[ bestlength ] == ptr2[ bestlength ]) )
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{
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/* Determine maximum length for this offset */
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maxlength = ((inpos+1) > 18 ? 18 : inpos + 1);
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/* Count maximum length match at this offset */
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length = _LZ_StringCompare( ptr1, ptr2, 0, maxlength );
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/* Better match than any previous match? */
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if( length > bestlength )
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{
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bestlength = length;
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bestoffset = offset;
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}
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}
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}
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/* Was there a good enough match? */
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if( bestlength > 2)
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{
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*flags |= mask;
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mask >>= 1;
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bundle2 = ((bestlength-3)<<4) | (((bestoffset-1)&0xF00)>>8);
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bundle1 = (bestoffset-1)&0xFF;
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out [ outpos++ ] = bundle2;
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out [ outpos++ ] = bundle1;
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inpos += bestlength;
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bytesleft -= bestlength;
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if (!mask) {
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mask = 128;
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flags = &out [ outpos++ ];
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*flags = 0;
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}
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}
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else
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{
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mask >>= 1;
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out[ outpos ++ ] = in[ inpos++ ];
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-- bytesleft;
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if (!mask) {
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mask = 128;
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flags = &out [ outpos++ ];
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*flags = 0;
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}
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}
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}
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while( bytesleft > 3 );
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/* Dump remaining bytes, if any */
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while( inpos < insize )
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{
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out[ outpos ++ ] = in[ inpos++ ];
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}
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while(outpos&3)
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out [ outpos ++] = 0;
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return outpos;
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}
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int main(int argc, char *argv[])
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{
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int in, out, size;
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struct stat buf;
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unsigned char *uncompressed, *compressed;
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if (argc == 3) {
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in = open(argv[1], O_RDONLY);
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out = creat(argv[2], 0600);
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fstat(in, &buf);
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uncompressed = malloc(buf.st_size);
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read(in, uncompressed, buf.st_size);
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close(in);
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compressed = malloc(buf.st_size*2);
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size = LZ_Compress(uncompressed, compressed, buf.st_size);
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write(out, "LZ77", 4);
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write(out, compressed, size);
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close(out);
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free(compressed);
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free(uncompressed);
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return 0;
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}
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printf("Usage: %s file.bin file.lz77\n", argv[0]);
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return 1;
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}
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