org.apache.poi.hdgf.HDGFLZWCompressor Maven / Gradle / Ivy
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this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
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package org.apache.poi.hdgf;
import static org.apache.poi.util.LZWDecompresser.DICT_MASK;
import static org.apache.poi.util.LZWDecompresser.DICT_SIZE;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
/**
* Helper class to handle the Visio compatible streaming LZW compression.
* Need our own class to handle keeping track of the code buffer, pending bytes to write out etc.
*
* TODO Fix this, as it starts to go wrong on large streams
*/
/* package */ final class HDGFLZWCompressor {
// We use 12 bit codes:
// * 0-255 are real bytes
// * 256-4095 are the substring codes
// Java handily initialises our buffer / dictionary
// to all zeros
private final byte[] dict = new byte[DICT_SIZE];
// The next block of data to be written out, minus its mask byte
private final byte[] buffer = new byte[16];
// And how long it is
// (Un-compressed codes are 1 byte each, compressed codes are two)
private int bufferLen;
// The raw length of a code is limited to 4 bits + 2
private final byte[] rawCode = new byte[18];
// And how much we're using
private int rawCodeLen;
// How far through the input and output streams we are
private int posInp;
private int posOut;
// What the next mask byte to output will be
private int nextMask;
// And how many bits we've already set
private int maskBitsSet;
private final OutputStream res;
public HDGFLZWCompressor(OutputStream res) {
this.res = res;
}
/**
* Returns the last place that the bytes from rawCode are found
* at in the buffer, or -1 if they can't be found
*/
private int findRawCodeInBuffer() {
// Work our way through all the codes until we
// find the right one. Visio starts from the end
for (int i = rawCodeLen+1; i < DICT_SIZE; i++) {
int pos = (posInp - i) & DICT_MASK;
// in the example data it seems, that the compressor doesn't like to wrap beyond DICT_SIZE
// if (pos + rawCodeLen > DICT_SIZE) continue;
boolean matches = true;
for (int j = 0; j < rawCodeLen; j++) {
if (dict[(pos + j) & DICT_MASK] != rawCode[j]) {
// Doesn't fit, can't be a match
matches = false;
break;
}
}
// Was this position a match?
if (matches) {
return pos;
}
}
// Not found
return -1;
}
/**
* Output the compressed representation for the bytes
* found in rawCode
*/
private void outputCompressed() throws IOException {
// It's not worth compressing only 1 or two bytes, due to the overheads
// So if asked, just output uncompressed
if (rawCodeLen < 3) {
final int rcl = rawCodeLen;
for (int i = 0; i < rcl; i++) {
outputUncompressed(rawCode[i]);
}
return;
}
// Grab where the data lives
int codesAt = findRawCodeInBuffer();
codesAt = (codesAt-18) & DICT_MASK;
// Increment the mask bit count, we've done another code
maskBitsSet++;
// Add the length+code to the buffer
// (The position is the first 12 bits, the length is the last 4 bits)
int bp1 = (codesAt & 0xFF);
int bp2 = (rawCodeLen - 3) + ((codesAt - bp1) >>> 4);
buffer[bufferLen++] = (byte) bp1;
buffer[bufferLen++] = (byte) bp2;
assert(maskBitsSet <= 8);
// If we're now at 8 codes, output
if (maskBitsSet == 8) {
output8Codes();
}
rawCodeLen = 0;
}
/**
* Output the un-compressed byte
*/
private void outputUncompressed(byte b) throws IOException {
// Set the mask bit for us
nextMask += (1 << maskBitsSet);
maskBitsSet++;
// And add us to the buffer + dictionary
buffer[bufferLen++] = b;
// If we're now at 8 codes, output
if (maskBitsSet == 8) {
output8Codes();
}
rawCodeLen = 0;
}
/**
* We've got 8 code worth to write out, so
* output along with the header
*/
private void output8Codes() throws IOException {
// Output the mask and the data
res.write(nextMask);
res.write(buffer, 0, bufferLen);
posOut += 1 + bufferLen;
// Reset things
nextMask = 0;
maskBitsSet = 0;
bufferLen = 0;
}
/**
* Does the compression
*/
public void compress(InputStream src) throws IOException {
int dataI = -1;
while (true) {
if (dataI > -1) {
// copy the last read byte into the dictionary.
// the example data compressor used self references, so we don't wait for filling the dictionary
// until we know if it's a un-/compressed token.
dict[(posInp++) & DICT_MASK] = (byte)dataI;
}
// This is an unsigned byte read from the stream
// It needs to be unsigned, so that bit stuff works
dataI = src.read();
// If we've run out of data, output anything that's pending then finish
if (dataI == -1) {
if (rawCodeLen > 0) {
outputCompressed();
if (maskBitsSet > 0) {
output8Codes();
}
}
break;
}
// This is a byte as looked up in the dictionary
// It needs to be signed, as it'll get passed on to the output stream
byte dataB = (byte) dataI;
// Try adding this new byte onto rawCode, and see if all of that is still found
// in the buffer dictionary or not
rawCode[rawCodeLen++] = dataB;
int rawAt = findRawCodeInBuffer();
if (rawAt > -1) {
// If we found it and are now at 18 bytes, we need to output our pending code block
if (rawCodeLen == 18) {
outputCompressed();
}
// If we did find all of rawCode with our new byte added on,
// we can wait to see what happens with the next byte
continue;
}
// If we get here, then the rawCode + this byte weren't found in the dictionary
// If there was something in rawCode before, then that was
// found in the dictionary, so output that compressed
rawCodeLen--;
if (rawCodeLen > 0) {
// Output the old rawCode
outputCompressed();
// Can this byte start a new rawCode, or does it need outputting itself?
rawCode[0] = dataB;
rawCodeLen = 1;
if (findRawCodeInBuffer() > -1) {
// Fits in, wait for next byte
continue;
}
// Doesn't fit, output
outputUncompressed(dataB);
} else {
// Nothing in rawCode before, so this byte isn't in the buffer dictionary
// Output it un-compressed
outputUncompressed(dataB);
}
}
}
}