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engines/zvision/file/lzss_read_stream.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/scummsys.h"
+#include "zvision/file/lzss_read_stream.h"
+
+namespace ZVision {
+
+LzssReadStream::LzssReadStream(Common::SeekableReadStream *source)
+	: _source(source),
+	  // It's convention to set the starting cursor position to blockSize - 16
+	  _windowCursor(0x0FEE),
+	  _eosFlag(false) {
+	// All values up to _windowCursor inits by 0x20
+	memset(_window, 0x20, _windowCursor);
+	memset(_window + _windowCursor, 0, BLOCK_SIZE - _windowCursor);
+}
+
+uint32 LzssReadStream::decompressBytes(byte *destination, uint32 numberOfBytes) {
+	uint32 destinationCursor = 0;
+
+	while (destinationCursor < numberOfBytes) {
+		byte flagbyte = _source->readByte();
+		if (_source->eos())
+			break;
+		uint mask = 1;
+
+		for (int i = 0; i < 8; ++i) {
+			if ((flagbyte & mask) == mask) {
+				byte data = _source->readByte();
+				if (_source->eos()) {
+					return destinationCursor;
+				}
+
+				_window[_windowCursor] = data;
+				destination[destinationCursor++] = data;
+
+				// Increment and wrap the window cursor
+				_windowCursor = (_windowCursor + 1) & 0xFFF;
+			} else {
+				byte low = _source->readByte();
+				if (_source->eos()) {
+					return destinationCursor;
+				}
+
+				byte high = _source->readByte();
+				if (_source->eos()) {
+					return destinationCursor;
+				}
+
+				uint16 length = (high & 0xF) + 2;
+				uint16 offset = low | ((high & 0xF0) << 4);
+
+				for (int j = 0; j <= length; ++j) {
+					byte temp = _window[(offset + j) & 0xFFF];
+					_window[_windowCursor] = temp;
+					destination[destinationCursor++] = temp;
+					_windowCursor = (_windowCursor + 1) & 0xFFF;
+				}
+			}
+
+			mask = mask << 1;
+		}
+	}
+
+	return destinationCursor;
+}
+
+bool LzssReadStream::eos() const {
+	return _eosFlag;
+}
+
+uint32 LzssReadStream::read(void *dataPtr, uint32 dataSize) {
+	uint32 bytesRead = decompressBytes(static_cast<byte *>(dataPtr), dataSize);
+	if (bytesRead < dataSize) {
+		// Flag that we're at EOS
+		_eosFlag = true;
+	}
+
+	return dataSize;
+}
+
+} // End of namespace ZVision