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engines/agi/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/>.
+ *
+ */
+
+/***************************************************************************
+** decomp.c
+**
+** Routines that deal with AGI version 3 specific features.
+** The original LZW code is from DJJ, October 1989, p.86.
+** It has been modified to handle AGI compression.
+**
+** (c) 1997  Lance Ewing
+***************************************************************************/
+
+#include "agi/agi.h"
+#include "agi/lzw.h"
+
+#include "common/textconsole.h"
+
+namespace Agi {
+
+
+class LZWDecoder {
+private:
+
+	enum {
+		MAXBITS     = 12,
+		TABLE_SIZE  = 18041,    // strange number
+		START_BITS  = 9
+	};
+
+	int32 BITS, MAX_VALUE, MAX_CODE;
+	uint32 *prefixCode;
+	uint8 *appendCharacter;
+	uint8 *decodeStack;
+	int32 inputBitCount;    // Number of bits in input bit buffer
+	uint32 inputBitBuffer;
+
+public:
+	LZWDecoder();
+	~LZWDecoder();
+
+	void lzwExpand(uint8 *in, uint8 *out, int32 len);
+
+private:
+	int setBits(int32 value);
+	uint8 *decodeString(uint8 *buffer, uint32 code);
+	uint32 inputCode(uint8 **input);
+};
+
+LZWDecoder::LZWDecoder() {
+	decodeStack = (uint8 *)calloc(1, 8192);
+	prefixCode = (uint32 *)malloc(TABLE_SIZE * sizeof(uint32));
+	appendCharacter = (uint8 *)malloc(TABLE_SIZE * sizeof(uint8));
+	inputBitCount = 0;  // Number of bits in input bit buffer
+	inputBitBuffer = 0L;
+	BITS = MAX_VALUE = MAX_CODE = 0;
+}
+
+LZWDecoder::~LZWDecoder() {
+	free(decodeStack);
+	free(prefixCode);
+	free(appendCharacter);
+}
+
+/**
+ * Adjust the number of bits used to store codes to the value passed in.
+ */
+int LZWDecoder::setBits(int32 value) {
+	if (value == MAXBITS)
+		return true;
+
+	BITS = value;
+	MAX_VALUE = (1 << BITS) - 1;
+	MAX_CODE = MAX_VALUE - 1;
+
+	return false;
+}
+
+/**
+ * Return the string that the code taken from the input buffer
+ * represents. The string is returned as a stack, i.e. the characters are
+ * in reverse order.
+ */
+uint8 *LZWDecoder::decodeString(uint8 *buffer, uint32 code) {
+	uint32 i;
+
+	for (i = 0; code > 255;) {
+		*buffer++ = appendCharacter[code];
+		code = prefixCode[code];
+		if (i++ >= 4000) {
+			error("lzw: error in code expansion");
+		}
+	}
+	*buffer = code;
+
+	return buffer;
+}
+
+/**
+ * Return the next code from the input buffer.
+ */
+uint32 LZWDecoder::inputCode(uint8 **input) {
+	uint32 r;
+
+	while (inputBitCount <= 24) {
+		inputBitBuffer |= (uint32) * (*input)++ << inputBitCount;
+		inputBitCount += 8;
+	}
+	r = (inputBitBuffer & 0x7FFF) % (1 << BITS);
+	inputBitBuffer >>= BITS;
+	inputBitCount -= BITS;
+
+	return r;
+}
+
+/**
+ * Uncompress the data contained in the input buffer and store
+ * the result in the output buffer. The fileLength parameter says how
+ * many bytes to uncompress. The compression itself is a form of LZW that
+ * adjusts the number of bits that it represents its codes in as it fills
+ * up the available codes. Two codes have special meaning:
+ *
+ *  code 256 = start over
+ *  code 257 = end of data
+ */
+void LZWDecoder::lzwExpand(uint8 *in, uint8 *out, int32 len) {
+	int32 c, lzwnext, lzwnew, lzwold;
+	uint8 *s, *end;
+
+	LZWDecoder d;
+
+	setBits(START_BITS); // Starts at 9-bits
+	lzwnext = 257;       // Next available code to define
+
+	end = (uint8 *)(out + (uint32)len);
+
+	lzwold = inputCode(&in); // Read in the first code
+	c = lzwold;
+	lzwnew = inputCode(&in);
+
+	while ((out < end) && (lzwnew != 0x101)) {
+		if (lzwnew == 0x100) {
+			// Code to "start over"
+			lzwnext = 258;
+			setBits(START_BITS);
+			lzwold = inputCode(&in);
+			c = lzwold;
+			*out++ = (char)c;
+			lzwnew = inputCode(&in);
+		} else {
+			if (lzwnew >= lzwnext) {
+				// Handles special LZW scenario
+				*decodeStack = c;
+				s = decodeString(decodeStack + 1, lzwold);
+			} else
+				s = decodeString(decodeStack, lzwnew);
+
+			// Reverse order of decoded string and
+			// store in out buffer
+			c = *s;
+			while (s >= decodeStack)
+				*out++ = *s--;
+
+			if (lzwnext > MAX_CODE)
+				setBits(BITS + 1);
+
+			prefixCode[lzwnext] = lzwold;
+			appendCharacter[lzwnext] = c;
+			lzwnext++;
+			lzwold = lzwnew;
+
+			lzwnew = inputCode(&in);
+		}
+	}
+}
+
+void lzwExpand(uint8 *in, uint8 *out, int32 len) {
+	LZWDecoder d;
+	d.lzwExpand(in, out, len);
+}
+
+} // End of namespace Agi