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engines/nancy/decompress.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/memstream.h"
+#include "common/textconsole.h"
+
+#include "engines/nancy/decompress.h"
+
+namespace Nancy {
+
+Decompressor::Decompressor() :
+	_bufpos(0),
+	_err(false),
+	_val(0),
+	_output(nullptr),
+	_input(nullptr),
+	_pos(nullptr),
+	_end(nullptr) {}
+
+Decompressor::~Decompressor() {
+	delete[] _input;
+}
+
+void Decompressor::init(Common::SeekableReadStream &input, Common::WriteStream &output) {
+	memset(_buf, ' ', kBufSize);
+	_bufpos = kBufStart;
+	_err = false;
+	_val = 0;
+
+	// We store the input data in a raw buffer, since we need to check if we're at the end of the
+	// stream on _every_ read byte. This way we avoid doing a vtable lookup per byte, which makes
+	// decompression roughly twice as fast
+	delete[] _input;
+	_input = new byte[input.size() + 1];
+	input.read(_input, input.size());
+	_pos = _input;
+	_end = _input + input.size();
+	_output = &output;
+}
+
+bool Decompressor::readByte(byte &b) {
+	b = *_pos++ - _val++;
+	return _pos <= _end;
+}
+
+bool Decompressor::writeByte(byte b) {
+	_output->writeByte(b);
+	_buf[_bufpos++] = b;
+	_bufpos &= kBufSize - 1;
+	return true;
+}
+
+bool Decompressor::decompress(Common::SeekableReadStream &input, Common::MemoryWriteStream &output) {
+	init(input, output);
+	uint16 bits = 0;
+
+	if (input.err()) {
+		warning("Failed to decompress resource");
+		return false;
+	}
+
+	while (1) {
+		byte b;
+
+		bits >>= 1;
+
+		// The highest 8 bits are used to keep track of how many bits are left to process
+		if (!(bits & 0x100)) {
+			// Out of bits
+			if (!readByte(b))
+				break;
+			bits = 0xff00 | b;
+		}
+
+		if (bits & 1) {
+			// Literal byte
+			if (!readByte(b))
+				break;
+			writeByte(b);
+		} else {
+			// Copy from buffer
+			byte b2;
+			if (!readByte(b) || !readByte(b2))
+				break;
+
+			uint16 offset = b | ((b2 & 0xf0) << 4);
+			uint16 len = (b2 & 0xf) + 3;
+
+			for (uint i = 0; i < len; i++)
+				writeByte(_buf[(offset + i) & (kBufSize - 1)]);
+		}
+	}
+
+	if (output.err() || output.pos() != output.size()) {
+		// Workaround for nancy3 file "SLN RollPanOpn.avf", which outputs 2 bytes less than it should
+		if (output.size() - output.pos() <= 2) {
+			return true;
+		}
+
+		warning("Failed to decompress resource");
+		return false;
+	}
+
+	return true;
+}
+
+} // End of namespace Nancy