136 lines
3.4 KiB
C++
136 lines
3.4 KiB
C++
/* ScummVM - Graphic Adventure Engine
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*
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* ScummVM is the legal property of its developers, whose names
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* are too numerous to list here. Please refer to the COPYRIGHT
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* file distributed with this source distribution.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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#include "common/endian.h"
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#include "common/util.h"
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#include "ultima/shared/core/lzw.h"
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namespace Ultima {
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namespace Shared {
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void LZW::decompress(Common::ReadStream *source, Common::WriteStream *dest) {
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int32 destSize = source->readUint32LE();
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_source = source;
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_currentByte = source->readByte();
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byte litByte = 0;
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uint16 oldCode = 0;
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uint16 copyLength, maxCodeValue, code, nextCode, lastCode;
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byte *copyBuf = new byte[8192];
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struct {
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uint16 code; byte value;
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} codeTable[8192];
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memset(codeTable, 0, sizeof(codeTable));
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_codeLength = 9;
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nextCode = 258;
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maxCodeValue = 512;
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copyLength = 0;
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_sourceBitsLeft = 8;
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for (;;) {
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code = getCode();
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if (code == 257)
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break;
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if (code == 256) {
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_codeLength = 9;
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nextCode = 258;
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maxCodeValue = 512;
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lastCode = getCode();
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oldCode = lastCode;
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litByte = lastCode;
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dest->writeByte(litByte);
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} else {
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lastCode = code;
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if (code >= nextCode) {
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lastCode = oldCode;
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copyBuf[copyLength++] = litByte;
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}
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while (lastCode > 255) {
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copyBuf[copyLength++] = codeTable[lastCode].value;
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lastCode = codeTable[lastCode].code;
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}
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litByte = lastCode;
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copyBuf[copyLength++] = lastCode;
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while (copyLength > 0)
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dest->writeByte(copyBuf[--copyLength]);
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codeTable[nextCode].value = lastCode;
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codeTable[nextCode].code = oldCode;
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nextCode++;
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oldCode = code;
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if (nextCode >= maxCodeValue && _codeLength <= 12) {
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_codeLength++;
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maxCodeValue <<= 1;
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}
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}
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}
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delete[] copyBuf;
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assert(dest->pos() == destSize);
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}
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uint16 LZW::getCode() {
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const byte bitMasks[9] = {
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0x00, 0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F, 0x0FF
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};
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byte resultBitsLeft = _codeLength;
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byte resultBitsPos = 0;
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uint16 result = 0;
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byte currentByte = _currentByte;
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byte currentBits = 0;
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// Get bits of current byte
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while (resultBitsLeft) {
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if (resultBitsLeft < _sourceBitsLeft) {
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// we need less than we have left
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currentBits = (currentByte >> (8 - _sourceBitsLeft)) &bitMasks[resultBitsLeft];
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result |= (currentBits << resultBitsPos);
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_sourceBitsLeft -= resultBitsLeft;
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resultBitsLeft = 0;
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} else {
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// we need as much as we have left or more
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resultBitsLeft -= _sourceBitsLeft;
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currentBits = currentByte >> (8 - _sourceBitsLeft);
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result |= (currentBits << resultBitsPos);
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resultBitsPos += _sourceBitsLeft;
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// Go to next byte
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_currentByte = _source->readByte();
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_sourceBitsLeft = 8;
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if (resultBitsLeft) {
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currentByte = _currentByte;
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}
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}
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}
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return result;
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}
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} // End of namespace Shared
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} // End of namespace Ultima
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