org.eclipse.swt.internal.image.PngHuffmanTable Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of org.eclipse.swt.gtk.hpux.ia64 Show documentation
SWT is an open source widget toolkit for Java designed to provide efficient, portable access to the user-interface facilities of the operating systems on which it is implemented.
The newest version!
/*******************************************************************************
 * Copyright (c) 2000, 2011 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.internal.image;

import java.io.*;

public class PngHuffmanTable {
	CodeLengthInfo[] codeLengthInfo;
	int[] codeValues;
	
	static final int MAX_CODE_LENGTH = 15;
	static final int BAD_CODE = 0xFFFFFFF;
	static final int incs[] = {1391376, 463792, 198768, 86961, 33936, 13776, 4592, 1968, 861, 336, 112, 48, 21, 7, 3, 1};

PngHuffmanTable (int[] lengths) {
	super();
	initialize(lengths);
	generateTable(lengths);
}

private void initialize(int[] lengths) {
	codeValues = new int[lengths.length];
	for (int i = 0; i < codeValues.length; i++) {
		codeValues[i] = i;
	}
	
	// minCodesByLength[n] : The smallest Huffman code of length n + 1.
	// maxCodesByLength[n] : The largest Huffman code of length n + 1.
	// indexesByLength[n] : Index into the values array. First value with a code of length n + 1.
	codeLengthInfo = new CodeLengthInfo[MAX_CODE_LENGTH];
	for (int i = 0; i < MAX_CODE_LENGTH; i++) {
		codeLengthInfo[i] = new CodeLengthInfo();
		codeLengthInfo[i].length = i;
		codeLengthInfo[i].baseIndex = 0;
		codeLengthInfo[i].min = BAD_CODE;
		codeLengthInfo[i].max = -1;
	}
}
	
private void generateTable(int[] lengths) {
	// Sort the values using shellsort. Primary key is code size. Secondary key is value.
	int codeValuesTemp;
	for (int k = 0; k < 16; k++) {
		for (int h = incs[k], i = h; i < lengths.length; i++) {
			int v = lengths[i];
			codeValuesTemp = codeValues[i];
			int j = i;
			while (j >= h && (lengths[j - h] > v || (lengths[j - h] == v && codeValues[j - h] > codeValuesTemp))) {
				lengths[j] = lengths[j - h];
				codeValues[j] = codeValues[j - h];
				j -= h;
			}
			lengths[j] = v;
			codeValues[j] = codeValuesTemp;
		}
	}

	// These values in these arrays correspond to the elements of the
	// "values" array. The Huffman code for codeValues[N] is codes[N]
	// and the length of the code is lengths[N].
	int[] codes = new int[lengths.length];
	int lastLength = 0;
	int code = 0;
	for (int i = 0; i < lengths.length; i++) {
		while (lastLength != lengths[i]) {
			lastLength++;
			code <<= 1;
		}
		if (lastLength != 0) {
			codes[i] = code;
			code++;
		}
	}
	
	int last = 0;
	for (int i = 0; i < lengths.length; i++) {
		if (last != lengths[i]) {
			last = lengths[i];
			codeLengthInfo[last - 1].baseIndex = i;
			codeLengthInfo[last - 1].min = codes[i];
		}
		if (last != 0) codeLengthInfo[last - 1].max = codes[i];
	}
}

int getNextValue(PngDecodingDataStream stream) throws IOException {
	int code = stream.getNextIdatBit();
	int codelength = 0;

	// Here we are taking advantage of the fact that 1 bits are used as
	// a prefix to the longer codeValues.
	while (codelength < MAX_CODE_LENGTH && code > codeLengthInfo[codelength].max) {
		code = ((code << 1) | stream.getNextIdatBit());
        codelength++;
	}
	if (codelength >= MAX_CODE_LENGTH) stream.error();

	// Now we have a Huffman code of length (codelength + 1) that
	// is somewhere in the range
	// minCodesByLength[codelength]..maxCodesByLength[codelength].
	// This code is the (offset + 1)'th code of (codelength + 1);
	int offset = code - codeLengthInfo[codelength].min;

	// indexesByLength[codelength] is the first code of length (codelength + 1)
	// so now we can look up the value for the Huffman code in the table.
	int index = codeLengthInfo[codelength].baseIndex + offset;
	return codeValues[index];
}	
	
static class CodeLengthInfo {
	int length;
	int max;
	int min;
	int baseIndex;
}

}