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/*
 * Copyright (c) 2015, Harald Kuhr
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name "TwelveMonkeys" nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.twelvemonkeys.imageio.plugins.tiff;

import com.twelvemonkeys.io.enc.Encoder;

import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.util.Arrays;

/**
 * LZWEncoder
 * 

* Inspired by LZWTreeEncoder by Wen Yu and the * algorithm described by Bob Montgomery * which * "[...] uses a tree method to search if a new string is already in the table, * which is much simpler, faster, and easier to understand than hashing." * * @author Harald Kuhr * @author last modified by $Author: haraldk$ * @version $Id: LZWEncoder.java,v 1.0 02.12.13 14:13 haraldk Exp$ */ final class LZWEncoder implements Encoder { /** Clear: Re-initialize tables. */ static final int CLEAR_CODE = 256; /** End of Information. */ static final int EOI_CODE = 257; private static final int MIN_BITS = 9; private static final int MAX_BITS = 12; private static final int TABLE_SIZE = 1 << MAX_BITS; // A child is made up of a parent (or prefix) code plus a suffix byte // and siblings are strings with a common parent(or prefix) and different // suffix bytes private final short[] CHILDREN = new short[TABLE_SIZE]; private final short[] SIBLINGS = new short[TABLE_SIZE]; private final short[] SUFFIXES = new short[TABLE_SIZE]; // Initial setup private int parent = -1; private int bitsPerCode = MIN_BITS; private int nextValidCode = EOI_CODE + 1; private int maxCode = maxValue(bitsPerCode); // Buffer for partial codes private int bits = 0; private int bitPos = 0; // Keep track of how many bytes we will write, to make sure we write EOI at correct position private long remaining; LZWEncoder(final long length) { remaining = length; } @Override public void encode(final OutputStream stream, final ByteBuffer buffer) throws IOException { encodeBytes(stream, buffer); if (remaining <= 0) { // Write EOI when er are done (the API isn't very supportive of this at the moment) writeCode(stream, parent); writeCode(stream, EOI_CODE); // Flush partial codes by writing 0 pad if (bitPos > 0) { writeCode(stream, 0); } } } void encodeBytes(final OutputStream stream, final ByteBuffer buffer) throws IOException { int length = buffer.remaining(); if (length == 0) { return; } if (parent == -1) { // Init stream writeCode(stream, CLEAR_CODE); parent = buffer.get() & 0xff; } while (buffer.hasRemaining()) { int value = buffer.get() & 0xff; int child = CHILDREN[parent]; if (child > 0) { if (SUFFIXES[child] == value) { parent = child; } else { int sibling = child; while (true) { if (SIBLINGS[sibling] > 0) { sibling = SIBLINGS[sibling]; if (SUFFIXES[sibling] == value) { parent = sibling; break; } } else { SIBLINGS[sibling] = (short) nextValidCode; SUFFIXES[nextValidCode] = (short) value; writeCode(stream, parent); parent = value; nextValidCode++; increaseCodeSizeOrResetIfNeeded(stream); break; } } } } else { CHILDREN[parent] = (short) nextValidCode; SUFFIXES[nextValidCode] = (short) value; writeCode(stream, parent); parent = value; nextValidCode++; increaseCodeSizeOrResetIfNeeded(stream); } } remaining -= length; } private void increaseCodeSizeOrResetIfNeeded(final OutputStream stream) throws IOException { if (nextValidCode > maxCode) { if (bitsPerCode == MAX_BITS) { // Reset stream by writing Clear code writeCode(stream, CLEAR_CODE); // Reset tables resetTables(); } else { // Increase code size bitsPerCode++; maxCode = maxValue(bitsPerCode); } } } private void resetTables() { Arrays.fill(CHILDREN, (short) 0); Arrays.fill(SIBLINGS, (short) 0); bitsPerCode = MIN_BITS; maxCode = maxValue(bitsPerCode); nextValidCode = EOI_CODE + 1; } private void writeCode(final OutputStream stream, final int code) throws IOException { // System.err.printf("LZWEncoder.writeCode: 0x%04x\n", code); bits = (bits << bitsPerCode) | (code & maxCode); bitPos += bitsPerCode; while (bitPos >= 8) { int b = (bits >> (bitPos - 8)) & 0xff; // System.err.printf("write: 0x%02x\n", b); stream.write(b); bitPos -= 8; } bits &= bitmaskFor(bitPos); } private static int maxValue(final int codeLen) { return (1 << codeLen) - 1; } private static int bitmaskFor(final int bits) { return maxValue(bits); } }





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