Initial commit

engines/awe/unpack.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/textconsole.h"
+#include "awe/unpack.h"
+
+namespace Awe {
+
+struct UnpackCtx {
+	int size;
+	uint32 crc;
+	uint32 bits;
+	uint8 *dst;
+	const uint8 *src;
+};
+
+static bool nextBit(UnpackCtx *uc) {
+	bool carry = (uc->bits & 1) != 0;
+	uc->bits >>= 1;
+	if (uc->bits == 0) { // getnextlwd
+		uc->bits = READ_BE_UINT32(uc->src); uc->src -= 4;
+		uc->crc ^= uc->bits;
+		carry = (uc->bits & 1) != 0;
+		uc->bits = (1 << 31) | (uc->bits >> 1);
+	}
+	return carry;
+}
+
+static int getBits(UnpackCtx *uc, int count) { // rdd1bits
+	int bits = 0;
+	for (int i = 0; i < count; ++i) {
+		bits <<= 1;
+		if (nextBit(uc)) {
+			bits |= 1;
+		}
+	}
+	return bits;
+}
+
+static void copyLiteral(UnpackCtx *uc, int bitsCount, int len) { // getd3chr
+	int count = getBits(uc, bitsCount) + len + 1;
+	uc->size -= count;
+	if (uc->size < 0) {
+		count += uc->size;
+		uc->size = 0;
+	}
+	for (int i = 0; i < count; ++i) {
+		*(uc->dst - i) = (uint8)getBits(uc, 8);
+	}
+	uc->dst -= count;
+}
+
+static void copyReference(UnpackCtx *uc, int bitsCount, int count) { // copyd3bytes
+	uc->size -= count;
+	if (uc->size < 0) {
+		count += uc->size;
+		uc->size = 0;
+	}
+	const int offset = getBits(uc, bitsCount);
+	for (int i = 0; i < count; ++i) {
+		*(uc->dst - i) = *(uc->dst - i + offset);
+	}
+	uc->dst -= count;
+}
+
+bool bytekiller_unpack(uint8 *dst, int dstSize, const uint8 *src, int srcSize) {
+	UnpackCtx uc;
+	uc.src = src + srcSize - 4;
+	uc.size = READ_BE_UINT32(uc.src); uc.src -= 4;
+	if (uc.size > dstSize) {
+		warning("Unexpected unpack size %d, buffer size %d", uc.size, dstSize);
+		return false;
+	}
+	uc.dst = dst + uc.size - 1;
+	uc.crc = READ_BE_UINT32(uc.src); uc.src -= 4;
+	uc.bits = READ_BE_UINT32(uc.src); uc.src -= 4;
+	uc.crc ^= uc.bits;
+	do {
+		if (!nextBit(&uc)) {
+			if (!nextBit(&uc)) {
+				copyLiteral(&uc, 3, 0);
+			} else {
+				copyReference(&uc, 8, 2);
+			}
+		} else {
+			const int code = getBits(&uc, 2);
+			switch (code) {
+			case 3:
+				copyLiteral(&uc, 8, 8);
+				break;
+			case 2:
+				copyReference(&uc, 12, getBits(&uc, 8) + 1);
+				break;
+			case 1:
+				copyReference(&uc, 10, 4);
+				break;
+			case 0:
+				copyReference(&uc, 9, 3);
+				break;
+			}
+		}
+	} while (uc.size > 0);
+	assert(uc.size == 0);
+	return uc.crc == 0;
+}
+
+} // namespace Awe