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/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* $URL$
* $Id$
*
*/
/***************************************************************************
** decomp.c
**
** Routines that deal with AGI version 3 specific features.
** The original LZW code is from DJJ, October 1989, p.86.
** It has been modified to handle AGI compression.
**
** (c) 1997 Lance Ewing
***************************************************************************/
#include "agi/agi.h"
#include "agi/lzw.h"
namespace Agi {
class LZWDecoder {
private:
enum {
MAXBITS = 12,
TABLE_SIZE = 18041, // strange number
START_BITS = 9
};
int32 BITS, MAX_VALUE, MAX_CODE;
uint32 *prefixCode;
uint8 *appendCharacter;
uint8 *decodeStack;
int32 inputBitCount; // Number of bits in input bit buffer
uint32 inputBitBuffer;
public:
LZWDecoder();
~LZWDecoder();
void lzwExpand(uint8 *in, uint8 *out, int32 len);
private:
int setBits(int32 value);
uint8 *decodeString(uint8 *buffer, uint32 code);
uint32 inputCode(uint8 **input);
};
LZWDecoder::LZWDecoder() {
decodeStack = (uint8 *)calloc(1, 8192);
prefixCode = (uint32 *)malloc(TABLE_SIZE * sizeof(uint32));
appendCharacter = (uint8 *)malloc(TABLE_SIZE * sizeof(uint8));
inputBitCount = 0; // Number of bits in input bit buffer
inputBitBuffer = 0L;
}
LZWDecoder::~LZWDecoder() {
free(decodeStack);
free(prefixCode);
free(appendCharacter);
}
/**
* Adjust the number of bits used to store codes to the value passed in.
*/
int LZWDecoder::setBits(int32 value) {
if (value == MAXBITS)
return true;
BITS = value;
MAX_VALUE = (1 << BITS) - 1;
MAX_CODE = MAX_VALUE - 1;
return false;
}
/**
* Return the string that the code taken from the input buffer
* represents. The string is returned as a stack, i.e. the characters are
* in reverse order.
*/
uint8 *LZWDecoder::decodeString(uint8 *buffer, uint32 code) {
uint32 i;
for (i = 0; code > 255;) {
*buffer++ = appendCharacter[code];
code = prefixCode[code];
if (i++ >= 4000) {
error("lzw: error in code expansion.");
}
}
*buffer = code;
return buffer;
}
/**
* Return the next code from the input buffer.
*/
uint32 LZWDecoder::inputCode(uint8 **input) {
uint32 r;
while (inputBitCount <= 24) {
inputBitBuffer |= (uint32) * (*input)++ << inputBitCount;
inputBitCount += 8;
}
r = (inputBitBuffer & 0x7FFF) % (1 << BITS);
inputBitBuffer >>= BITS;
inputBitCount -= BITS;
return r;
}
/**
* Uncompress the data contained in the input buffer and store
* the result in the output buffer. The fileLength parameter says how
* many bytes to uncompress. The compression itself is a form of LZW that
* adjusts the number of bits that it represents its codes in as it fills
* up the available codes. Two codes have special meaning:
*
* code 256 = start over
* code 257 = end of data
*/
void LZWDecoder::lzwExpand(uint8 *in, uint8 *out, int32 len) {
int32 c, lzwnext, lzwnew, lzwold;
uint8 *s, *end;
LZWDecoder d;
setBits(START_BITS); // Starts at 9-bits
lzwnext = 257; // Next available code to define
end = (uint8 *)(out + (uint32)len);
lzwold = inputCode(&in); // Read in the first code
c = lzwold;
lzwnew = inputCode(&in);
while ((out < end) && (lzwnew != 0x101)) {
if (lzwnew == 0x100) {
// Code to "start over"
lzwnext = 258;
setBits(START_BITS);
lzwold = inputCode(&in);
c = lzwold;
*out++ = (char)c;
lzwnew = inputCode(&in);
} else {
if (lzwnew >= lzwnext) {
// Handles special LZW scenario
*decodeStack = c;
s = decodeString(decodeStack + 1, lzwold);
} else
s = decodeString(decodeStack, lzwnew);
// Reverse order of decoded string and
// store in out buffer
c = *s;
while (s >= decodeStack)
*out++ = *s--;
if (lzwnext > MAX_CODE)
setBits(BITS + 1);
prefixCode[lzwnext] = lzwold;
appendCharacter[lzwnext] = c;
lzwnext++;
lzwold = lzwnew;
lzwnew = inputCode(&in);
}
}
}
void lzwExpand(uint8 *in, uint8 *out, int32 len) {
LZWDecoder d;
d.lzwExpand(in, out, len);
}
} // End of namespace Agi
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