gamos/file.cpp

/* 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 "gamos/gamos.h"

namespace Gamos {

Archive::Archive() {
};

Archive::~Archive() {
};

bool Archive::open(const Common::Path &name) {
	bool res = File::open(name);

	if (!res)
		return false;

	seek(-12, SEEK_END);

	_dirOffset = 12 + readUint32LE();
	skip(4);
	uint32 magic = readUint32LE();

	if (magic != 0x3d53563d) // =VS=
		return false;

	seek(-_dirOffset, SEEK_END);

	_dirCount = readUint32LE();
	_dataOffset = readUint32LE();

	seek(-(_dirOffset + _dirCount * 5), SEEK_END);

	_directories.resize(_dirCount);

	for (uint i = 0; i < _dirCount; ++i) {
		ArchiveDir &dir = _directories[i];

		dir.offset = readUint32LE();
		dir.id = readByte();
	}

	return true;
}

bool Archive::seekDir(uint id) {
	int16 idx = findDirByID(id);
	if (idx < 0)
		return false;

	const ArchiveDir &dir = _directories[idx];

	if (!seek(_dataOffset + dir.offset, SEEK_SET))
		return false;

	return true;
}

int32 Archive::readPackedInt() {
	byte b = readByte();
	if (!(b & 0x80))
		return b;

	byte num = 0;
	byte skipsz = 0;
	if (!(b & 0x20))
		num = b & 0x1f;
	else
		num = 1 + ((b >> 2) & 3);

	if (num > 4) {
		skipsz = num - 4;
		num = 4;
	}

	int32 val = 0;
	for (int i = 0; i < num; ++i)
		val |= readByte() << (i << 3);

	if (skipsz) {
		skip(skipsz);
		/* warning !!!! */
		warning("readPackedInt skipped %d", skipsz);
	}

	static int32 negs[4] {0, -1, -1025, -263169};
	static int32 adds[4] {0, 0x80, 0x480, 0x40480};

	if (b & 0x20) {
		val += (b & 3) * (1 << ((num << 3) & 0x1f));
		if (b & 0x10)
			val = negs[num] - val;
		else
			val += adds[num];
	}

	return val;
}

RawData *Archive::readCompressedData() {
	RawData *data = new RawData();
	if (!readCompressedData(data)) {
		delete data;
		data = nullptr;
	}
	return data;
}

bool Archive::readCompressedData(RawData *out) {
	const byte t = readByte();
	if ((t & 0x80) == 0)
		return false;

	_lastReadDecompressedSize = 0;
	_lastReadSize = 0;

	if (t & 0x40) {
		/* small uncompressed data */
		_lastReadSize = t & 0x1F;
	} else {
		/* read size */
		const byte szsize = (t & 3) + 1;

		/* big data size */
		for (uint i = 0; i < szsize; ++i)
			_lastReadSize |= readByte() << (i << 3);

		/* is compressed */
		if (t & 0xC) {
			for (uint i = 0; i < szsize; ++i)
				_lastReadDecompressedSize |= readByte() << (i << 3);
		}
	}

	if (!_lastReadSize)
		return false;

	_lastReadDataOffset = pos();
	out->resize(_lastReadSize);
	read(out->data(), _lastReadSize);

	if (!_lastReadDecompressedSize)
		return true;

	/* looks hacky but we just allocate array for decompressed and swap it with compressed */
	RawData compressed(_lastReadDecompressedSize);
	out->swap(compressed);

	decompress(&compressed, out);
	return true;
}

void Archive::decompress(RawData const *in, RawData *out) {
	uint pos = 0;
	uint outPos = 0;

	while (pos < in->size()) {
		byte ctrlBits = (*in)[pos];
		pos++;

		for (int bitsLeft = 8; bitsLeft > 0; --bitsLeft) {
			if (pos >= in->size())
				return;

			if (ctrlBits & 1) {
				(*out)[outPos] = (*in)[pos];
				outPos++;
				pos++;
			} else {
				byte b1 = (*in)[pos];
				byte b2 = (*in)[pos + 1];
				pos += 2;

				byte num = (b2 & 0xF) + 3;
				uint16 distance = b1 | ((b2 & 0xF0) << 4);

				for (int i = 0; i < num; ++i) {
					(*out)[outPos] = (*out)[outPos - distance];
					outPos++;
				}
			}

			ctrlBits >>= 1;
		}
	}
}


}