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package org.eclipse.swt.internal.image;
import java.io.*;
import org.eclipse.swt.*;
/*
* Licensed Materials - Property of IBM,
* (c) Copyright IBM Corp. 1998, 2000 All Rights Reserved
*/
public class PngDecodingDataStream {
PngIdatChunk currentChunk;
PngChunkReader chunkReader;
byte currentByte;
int nextByteIndex;
int nextBitIndex;
PngLzBlockReader lzBlockReader;
int adlerValue;
static final int PRIME = 65521;
static final int MAX_BIT = 7;
PngDecodingDataStream(PngIdatChunk idatChunk, PngChunkReader chunkReader) {
super();
this.currentChunk = idatChunk;
this.chunkReader = chunkReader;
nextByteIndex = 0;
nextBitIndex = MAX_BIT + 1;
adlerValue = 1;
lzBlockReader = new PngLzBlockReader(this);
readCompressedDataHeader();
lzBlockReader.readNextBlockHeader();
}
/**
* This method should be called when the image decoder thinks
* that all of the compressed image data has been read. This
* method will ensure that the next data value is an end of
* block marker. If there are more blocks after this one,
* the method will read them and ensure that they are empty.
*/
void assertImageDataAtEnd() {
lzBlockReader.assertCompressedDataAtEnd();
}
int getNextIdatBits(int length) {
int value = 0;
for (int i = 0; i < length; i++) {
value |= (getNextIdatBit() << i);
}
return value;
}
byte getNextIdatBit() {
if (nextBitIndex > MAX_BIT) {
currentByte = getNextIdatByte();
nextBitIndex = 0;
}
int mask = 1 << nextBitIndex;
nextBitIndex++;
return ((currentByte & mask) > 0) ? (byte) 1 : (byte) 0;
}
private PngIdatChunk getNextChunk() {
PngChunk chunk = chunkReader.readNextChunk();
if (chunk == null) error();
if (chunk.getChunkType() != PngChunk.CHUNK_IDAT) error();
return (PngIdatChunk) chunk;
}
byte getNextIdatByte() {
if (nextByteIndex > currentChunk.getLength() - 1) {
currentChunk = getNextChunk();
nextByteIndex = 0;
}
byte nextByte = currentChunk.getDataByteAtOffset(nextByteIndex);
nextByteIndex++;
nextBitIndex = MAX_BIT + 1;
return nextByte;
}
private void updateAdler(byte value) {
int low = adlerValue & 0xFFFF;
int high = (adlerValue >> 16) & 0xFFFF;
int valueInt = value & 0xFF;
low = (low + valueInt) % PRIME;
high = (low + high) % PRIME;
adlerValue = (high << 16) | low;
}
byte getNextDecodedByte() {
byte nextDecodedByte = lzBlockReader.getNextByte();
updateAdler(nextDecodedByte);
return nextDecodedByte;
}
void error() {
SWT.error(SWT.ERROR_INVALID_IMAGE);
}
private void readCompressedDataHeader() {
byte headerByte1 = getNextIdatByte();
byte headerByte2 = getNextIdatByte();
int number = (headerByte1 << 8) | (headerByte2 & 0xFF);
if (number % 31 != 0) error();
int compressionMethod = headerByte1 & 0x0F;
if (compressionMethod != 8) error();
int windowSizeHint = (headerByte1 & 0xF0) >> 4;
if (windowSizeHint > 7) error();
int windowSize = (1 << (windowSizeHint + 8));
lzBlockReader.setWindowSize(windowSize);
int dictionary = (headerByte2 & (1 << 5));
if (dictionary != 0) error();
int compressionLevel = (headerByte2 & 0xC0) >> 6;
}
void checkAdler() {
int storedAdler = ((getNextIdatByte() & 0xFF) << 24)
| ((getNextIdatByte() & 0xFF) << 16)
| ((getNextIdatByte() & 0xFF) << 8)
| (getNextIdatByte() & 0xFF);
if (storedAdler != adlerValue) error();
}
}
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