Yuuki/Lockpick_RCM
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

Implement payload compression

Browse source
This commit is contained in:
shchmue 2021-05-12 16:47:06 -06:00
parent a7712b173c
commit 918b00ce07
20 changed files with 2305 additions and 28 deletions
Download patch file Download diff file Expand all files Collapse all files

546
tools/lz/lz.c Normal file
View file

@ -0,0 +1,546 @@
//
// Name: lz.c
// Author: Marcus Geelnard
// Description: LZ77 coder/decoder implementation.
// Reentrant: Yes
// $ATH_LICENSE_NULL$
//
// The LZ77 compression scheme is a substitutional compression scheme
// proposed by Abraham Lempel and Jakob Ziv in 1977. It is very simple in
// its design, and uses no fancy bit level compression.
//
// This is my first attempt at an implementation of a LZ77 code/decoder.
//
// The principle of the LZ77 compression algorithm is to store repeated
// occurrences of strings as references to previous occurrences of the same
// string. The point is that the reference consumes less space than the
// string itself, provided that the string is long enough (in this
// implementation, the string has to be at least 4 bytes long, since the
// minimum coded reference is 3 bytes long). Also note that the term
// "string" refers to any kind of byte sequence (it does not have to be
// an ASCII string, for instance).
//
// The coder uses a brute force approach to finding string matches in the
// history buffer (or "sliding window", if you wish), which is very, very
// slow. I recon the complexity is somewhere between O(n^2) and O(n^3),
// depending on the input data.
//
// There is also a faster implementation that uses a large working buffer
// in which a "jump table" is stored, which is used to quickly find
// possible string matches (see the source code for LZ_CompressFast() for
// more information). The faster method is an order of magnitude faster,
// but still quite slow compared to other compression methods.
//
// The upside is that decompression is very fast, and the compression ratio
// is often very good.
//
// The reference to a string is coded as a (length,offset) pair, where the
// length indicates the length of the string, and the offset gives the
// offset from the current data position. To distinguish between string
// references and literal strings (uncompressed bytes), a string reference
// is preceded by a marker byte, which is chosen as the least common byte
// symbol in the input data stream (this marker byte is stored in the
// output stream as the first byte).
//
// Occurrences of the marker byte in the stream are encoded as the marker
// byte followed by a zero byte, which means that occurrences of the marker
// byte have to be coded with two bytes.
//
// The lengths and offsets are coded in a variable length fashion, allowing
// values of any magnitude (up to 4294967295 in this implementation).
//
// With this compression scheme, the worst case compression result is
// (257/256)*insize + 1.
//
//------------------------------------------------------------------------
// Copyright (c) 2003-2006 Marcus Geelnard
//
// This software is provided 'as-is', without any express or implied
// warranty. In no event will the authors be held liable for any damages
// arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute it
// freely, subject to the following restrictions:
//
// 1. The origin of this software must not be misrepresented; you must not
// claim that you wrote the original software. If you use this software
// in a product, an acknowledgment in the product documentation would
// be appreciated but is not required.
//
// 2. Altered source versions must be plainly marked as such, and must not
// be misrepresented as being the original software.
//
// 3. This notice may not be removed or altered from any source
// distribution.
//
// Marcus Geelnard
// marcus.geelnard at home.se
//
//
// This file has been altered from the original version.
//
/*************************************************************************
* Constants used for LZ77 coding
*************************************************************************/
/* Maximum offset (can be any size < 2^31). Lower values give faster
compression, while higher values gives better compression. The default
value of 100000 is quite high. Experiment to see what works best for
you. */
#define LZ_MAX_OFFSET 100000
/*************************************************************************
* INTERNAL FUNCTIONS *
*************************************************************************/
/*************************************************************************
* _LZ_StringCompare() - Return maximum length string match.
*************************************************************************/
static unsigned int _LZ_StringCompare( unsigned char * str1,
unsigned char * str2, unsigned int minlen, unsigned int maxlen )
{
unsigned int len;
for( len = minlen; (len < maxlen) && (str1[len] == str2[len]); ++ len );
return len;
}
/*************************************************************************
* _LZ_WriteVarSize() - Write unsigned integer with variable number of
* bytes depending on value.
*************************************************************************/
static int _LZ_WriteVarSize( unsigned int x, unsigned char * buf )
{
unsigned int y;
int num_bytes, i, b;
/* Determine number of bytes needed to store the number x */
y = x >> 3;
for( num_bytes = 5; num_bytes >= 2; -- num_bytes )
{
if( y & 0xfe000000 ) break;
y <<= 7;
}
/* Write all bytes, seven bits in each, with 8:th bit set for all */
/* but the last byte. */
for( i = num_bytes-1; i >= 0; -- i )
{
b = (x >> (i*7)) & 0x0000007f;
if( i > 0 )
{
b |= 0x00000080;
}
*buf ++ = (unsigned char) b;
}
/* Return number of bytes written */
return num_bytes;
}
/*************************************************************************
* _LZ_ReadVarSize() - Read unsigned integer with variable number of
* bytes depending on value.
*************************************************************************/
static int _LZ_ReadVarSize( unsigned int * x, unsigned char * buf )
{
unsigned int y, b, num_bytes;
/* Read complete value (stop when byte contains zero in 8:th bit) */
y = 0;
num_bytes = 0;
do
{
b = (unsigned int) (*buf ++);
y = (y << 7) | (b & 0x0000007f);
++ num_bytes;
}
while( b & 0x00000080 );
/* Store value in x */
*x = y;
/* Return number of bytes read */
return num_bytes;
}
/*************************************************************************
* PUBLIC FUNCTIONS *
*************************************************************************/
/*************************************************************************
* LZ_Compress() - Compress a block of data using an LZ77 coder.
* in - Input (uncompressed) buffer.
* out - Output (compressed) buffer. This buffer must be 0.4% larger
* than the input buffer, plus one byte.
* insize - Number of input bytes.
* The function returns the size of the compressed data.
*************************************************************************/
int LZ_Compress( unsigned char *in, unsigned char *out,
unsigned int insize )
{
unsigned char marker, symbol;
unsigned int inpos, outpos, bytesleft, i;
unsigned int maxoffset, offset, bestoffset;
unsigned int maxlength, length, bestlength;
unsigned int histogram[ 256 ];
unsigned char *ptr1, *ptr2;
/* Do we have anything to compress? */
if( insize < 1 )
{
return 0;
}
/* Create histogram */
for( i = 0; i < 256; ++ i )
{
histogram[ i ] = 0;
}
for( i = 0; i < insize; ++ i )
{
++ histogram[ in[ i ] ];
}
/* Find the least common byte, and use it as the marker symbol */
marker = 0;
for( i = 1; i < 256; ++ i )
{
if( histogram[ i ] < histogram[ marker ] )
{
marker = i;
}
}
/* Remember the marker symbol for the decoder */
out[ 0 ] = marker;
/* Start of compression */
inpos = 0;
outpos = 1;
/* Main compression loop */
bytesleft = insize;
do
{
/* Determine most distant position */
if( inpos > LZ_MAX_OFFSET ) maxoffset = LZ_MAX_OFFSET;
else maxoffset = inpos;
/* Get pointer to current position */
ptr1 = &in[ inpos ];
/* Search history window for maximum length string match */
bestlength = 3;
bestoffset = 0;
for( offset = 3; offset <= maxoffset; ++ offset )
{
/* Get pointer to candidate string */
ptr2 = &ptr1[ -(int)offset ];
/* Quickly determine if this is a candidate (for speed) */
if( (ptr1[ 0 ] == ptr2[ 0 ]) &&
(ptr1[ bestlength ] == ptr2[ bestlength ]) )
{
/* Determine maximum length for this offset */
maxlength = (bytesleft < offset ? bytesleft : offset);
/* Count maximum length match at this offset */
length = _LZ_StringCompare( ptr1, ptr2, 0, maxlength );
/* Better match than any previous match? */
if( length > bestlength )
{
bestlength = length;
bestoffset = offset;
}
}
}
/* Was there a good enough match? */
if( (bestlength >= 8) ||
((bestlength == 4) && (bestoffset <= 0x0000007f)) ||
((bestlength == 5) && (bestoffset <= 0x00003fff)) ||
((bestlength == 6) && (bestoffset <= 0x001fffff)) ||
((bestlength == 7) && (bestoffset <= 0x0fffffff)) )
{
out[ outpos ++ ] = (unsigned char) marker;
outpos += _LZ_WriteVarSize( bestlength, &out[ outpos ] );
outpos += _LZ_WriteVarSize( bestoffset, &out[ outpos ] );
inpos += bestlength;
bytesleft -= bestlength;
}
else
{
/* Output single byte (or two bytes if marker byte) */
symbol = in[ inpos ++ ];
out[ outpos ++ ] = symbol;
if( symbol == marker )
{
out[ outpos ++ ] = 0;
}
-- bytesleft;
}
}
while( bytesleft > 3 );
/* Dump remaining bytes, if any */
while( inpos < insize )
{
if( in[ inpos ] == marker )
{
out[ outpos ++ ] = marker;
out[ outpos ++ ] = 0;
}
else
{
out[ outpos ++ ] = in[ inpos ];
}
++ inpos;
}
return outpos;
}
/*************************************************************************
* LZ_CompressFast() - Compress a block of data using an LZ77 coder.
* in - Input (uncompressed) buffer.
* out - Output (compressed) buffer. This buffer must be 0.4% larger
* than the input buffer, plus one byte.
* insize - Number of input bytes.
* work - Pointer to a temporary buffer (internal working buffer), which
* must be able to hold (insize+65536) unsigned integers.
* The function returns the size of the compressed data.
*************************************************************************/
int LZ_CompressFast( unsigned char *in, unsigned char *out,
unsigned int insize, unsigned int *work )
{
unsigned char marker, symbol;
unsigned int inpos, outpos, bytesleft, i, index, symbols;
unsigned int offset, bestoffset;
unsigned int maxlength, length, bestlength;
unsigned int histogram[ 256 ], *lastindex, *jumptable;
unsigned char *ptr1, *ptr2;
/* Do we have anything to compress? */
if( insize < 1 )
{
return 0;
}
/* Assign arrays to the working area */
lastindex = work;
jumptable = &work[ 65536 ];
/* Build a "jump table". Here is how the jump table works:
jumptable[i] points to the nearest previous occurrence of the same
symbol pair as in[i]:in[i+1], so in[i] == in[jumptable[i]] and
in[i+1] == in[jumptable[i]+1], and so on... Following the jump table
gives a dramatic boost for the string search'n'match loop compared
to doing a brute force search. The jump table is built in O(n) time,
so it is a cheap operation in terms of time, but it is expensice in
terms of memory consumption. */
for( i = 0; i < 65536; ++ i )
{
lastindex[ i ] = 0xffffffff;
}
for( i = 0; i < insize-1; ++ i )
{
symbols = (((unsigned int)in[i]) << 8) | ((unsigned int)in[i+1]);
index = lastindex[ symbols ];
lastindex[ symbols ] = i;
jumptable[ i ] = index;
}
jumptable[ insize-1 ] = 0xffffffff;
/* Create histogram */
for( i = 0; i < 256; ++ i )
{
histogram[ i ] = 0;
}
for( i = 0; i < insize; ++ i )
{
++ histogram[ in[ i ] ];
}
/* Find the least common byte, and use it as the marker symbol */
marker = 0;
for( i = 1; i < 256; ++ i )
{
if( histogram[ i ] < histogram[ marker ] )
{
marker = i;
}
}
/* Remember the marker symbol for the decoder */
out[ 0 ] = marker;
/* Start of compression */
inpos = 0;
outpos = 1;
/* Main compression loop */
bytesleft = insize;
do
{
/* Get pointer to current position */
ptr1 = &in[ inpos ];
/* Search history window for maximum length string match */
bestlength = 3;
bestoffset = 0;
index = jumptable[ inpos ];
while( (index != 0xffffffff) && ((inpos - index) < LZ_MAX_OFFSET) )
{
/* Get pointer to candidate string */
ptr2 = &in[ index ];
/* Quickly determine if this is a candidate (for speed) */
if( ptr2[ bestlength ] == ptr1[ bestlength ] )
{
/* Determine maximum length for this offset */
offset = inpos - index;
maxlength = (bytesleft < offset ? bytesleft : offset);
/* Count maximum length match at this offset */
length = _LZ_StringCompare( ptr1, ptr2, 2, maxlength );
/* Better match than any previous match? */
if( length > bestlength )
{
bestlength = length;
bestoffset = offset;
}
}
/* Get next possible index from jump table */
index = jumptable[ index ];
}
/* Was there a good enough match? */
if( (bestlength >= 8) ||
((bestlength == 4) && (bestoffset <= 0x0000007f)) ||
((bestlength == 5) && (bestoffset <= 0x00003fff)) ||
((bestlength == 6) && (bestoffset <= 0x001fffff)) ||
((bestlength == 7) && (bestoffset <= 0x0fffffff)) )
{
out[ outpos ++ ] = (unsigned char) marker;
outpos += _LZ_WriteVarSize( bestlength, &out[ outpos ] );
outpos += _LZ_WriteVarSize( bestoffset, &out[ outpos ] );
inpos += bestlength;
bytesleft -= bestlength;
}
else
{
/* Output single byte (or two bytes if marker byte) */
symbol = in[ inpos ++ ];
out[ outpos ++ ] = symbol;
if( symbol == marker )
{
out[ outpos ++ ] = 0;
}
-- bytesleft;
}
}
while( bytesleft > 3 );
/* Dump remaining bytes, if any */
while( inpos < insize )
{
if( in[ inpos ] == marker )
{
out[ outpos ++ ] = marker;
out[ outpos ++ ] = 0;
}
else
{
out[ outpos ++ ] = in[ inpos ];
}
++ inpos;
}
return outpos;
}
/*************************************************************************
* LZ_Uncompress() - Uncompress a block of data using an LZ77 decoder.
* in - Input (compressed) buffer.
* out - Output (uncompressed) buffer. This buffer must be large
* enough to hold the uncompressed data.
* insize - Number of input bytes.
*************************************************************************/
int LZ_Uncompress( unsigned char *in, unsigned char *out,
unsigned int insize )
{
unsigned char marker, symbol;
unsigned int i, inpos, outpos, length, offset;
/* Do we have anything to uncompress? */
if( insize < 1 )
{
return 0;
}
/* Get marker symbol from input stream */
marker = in[ 0 ];
inpos = 1;
/* Main decompression loop */
outpos = 0;
do
{
symbol = in[ inpos ++ ];
if( symbol == marker )
{
/* We had a marker byte */
if( in[ inpos ] == 0 )
{
/* It was a single occurrence of the marker byte */
out[ outpos ++ ] = marker;
++ inpos;
}
else
{
/* Extract true length and offset */
inpos += _LZ_ReadVarSize( &length, &in[ inpos ] );
inpos += _LZ_ReadVarSize( &offset, &in[ inpos ] );
/* Copy corresponding data from history window */
for( i = 0; i < length; ++ i )
{
out[ outpos ] = out[ outpos - offset ];
++ outpos;
}
}
}
else
{
/* No marker, plain copy */
out[ outpos ++ ] = symbol;
}
}
while( inpos < insize );
return outpos;
}