Initial commit

engines/ultima/shared/core/lzw.cpp

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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 3 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, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "common/endian.h"
+#include "common/util.h"
+#include "ultima/shared/core/lzw.h"
+
+namespace Ultima {
+namespace Shared {
+
+void LZW::decompress(Common::ReadStream *source, Common::WriteStream *dest) {
+	int32 destSize = source->readUint32LE();
+	_source = source;
+	_currentByte = source->readByte();
+
+	byte litByte = 0;
+	uint16 oldCode = 0;
+	uint16 copyLength, maxCodeValue, code, nextCode, lastCode;
+
+	byte *copyBuf = new byte[8192];
+
+	struct {
+		uint16 code; byte value;
+	} codeTable[8192];
+	memset(codeTable, 0, sizeof(codeTable));
+
+	_codeLength = 9;
+	nextCode = 258;
+	maxCodeValue = 512;
+
+	copyLength = 0;
+	_sourceBitsLeft = 8;
+
+	for (;;) {
+		code = getCode();
+
+		if (code == 257)
+			break;
+
+		if (code == 256) {
+			_codeLength = 9;
+			nextCode = 258;
+			maxCodeValue = 512;
+			lastCode = getCode();
+			oldCode = lastCode;
+			litByte = lastCode;
+			dest->writeByte(litByte);
+		} else {
+			lastCode = code;
+			if (code >= nextCode) {
+				lastCode = oldCode;
+				copyBuf[copyLength++] = litByte;
+			}
+			while (lastCode > 255) {
+				copyBuf[copyLength++] = codeTable[lastCode].value;
+				lastCode = codeTable[lastCode].code;
+			}
+			litByte = lastCode;
+			copyBuf[copyLength++] = lastCode;
+			while (copyLength > 0)
+				dest->writeByte(copyBuf[--copyLength]);
+			codeTable[nextCode].value = lastCode;
+			codeTable[nextCode].code = oldCode;
+			nextCode++;
+			oldCode = code;
+			if (nextCode >= maxCodeValue && _codeLength <= 12) {
+				_codeLength++;
+				maxCodeValue <<= 1;
+			}
+		}
+	}
+
+	delete[] copyBuf;
+	assert(dest->pos() == destSize);
+}
+
+uint16 LZW::getCode() {
+	const byte bitMasks[9] = {
+		0x00, 0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F, 0x0FF
+	};
+
+	byte   resultBitsLeft = _codeLength;
+	byte   resultBitsPos = 0;
+	uint16 result = 0;
+	byte   currentByte = _currentByte;
+	byte   currentBits = 0;
+
+	// Get bits of current byte
+	while (resultBitsLeft) {
+		if (resultBitsLeft < _sourceBitsLeft) {
+			// we need less than we have left
+			currentBits = (currentByte >> (8 - _sourceBitsLeft)) &bitMasks[resultBitsLeft];
+			result |= (currentBits << resultBitsPos);
+			_sourceBitsLeft -= resultBitsLeft;
+			resultBitsLeft = 0;
+
+		} else {
+			// we need as much as we have left or more
+			resultBitsLeft -= _sourceBitsLeft;
+			currentBits = currentByte >> (8 - _sourceBitsLeft);
+			result |= (currentBits << resultBitsPos);
+			resultBitsPos += _sourceBitsLeft;
+
+			// Go to next byte
+			_currentByte = _source->readByte();
+
+			_sourceBitsLeft = 8;
+			if (resultBitsLeft) {
+				currentByte = _currentByte;
+			}
+		}
+	}
+	return result;
+}
+
+} // End of namespace Shared
+} // End of namespace Ultima