org.atmosphere.gwt.server.deflate.Deflater Maven / Gradle / Ivy
/*
* Copyright 2012 Jeanfrancois Arcand
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
// $Id: Deflater.java 122 2007-08-18 08:25:04Z pornin $
/*
* Copyright (c) 2007 Thomas Pornin
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
package org.atmosphere.gwt.server.deflate;
import java.io.IOException;
import java.io.OutputStream;
/**
* This class implements the core DEFLATE process, i.e. the compression of data into DEFLATE blocks.
*
* @author Thomas Pornin
* @version $Revision: 122 $
*/
public final class Deflater {
/*
* In this class, all state variables and arrays have been designed such that the default values (all-zero) are
* fine.
*/
/* =========================================================== */
/*
* Input data mangement.
*
* The window keeps a copy of the previously encountered uncompressed data bytes. In the beginning, the window is
* empty, then filled up to a certain limit (a power of 2, at most 32768). Beyond that limit, it is managed as a
* circular buffer.
*
* To each data byte we associate a triplet, consisting of that byte and the next two bytes. We assemble triplets
* into 24-bit values, such that the lower 8 bits are the most recently received. Each window slot contains a
* triplet; hence, each input data byte appears in three distinct, successive slots in the window.
*
* Window triplets are linked as hash chains, with the hashLink[] array. The hashTable[] array contains the chain
* entry points.
*
* We also copy input bytes into the ucBuffer[] array (up to some limit). These are used to produce uncompressed
* data blocks if it turns out that the compressor cannot find anything better. The size limit is computed so that
* when an uncompressed data block must be produced, then the size limit on ucBuffer[] has not been reached. Note:
* technically, we could limit ucBuffer[] to the window length and complete the uncompressed block by reconstructing
* the input bytes from the symbols in buffer[]. This would be interesting if we used a large buffer[] array. But
* such a large symbol buffer is undesirable since it prevents the dynamic Huffman codes from adapting to changes in
* the file content type.
*/
/**
* The window buffer. Entry of index "n" contains the triplet of bytes beginning at index "n".
*/
private int[] window;
/**
* windowPtr contains the window index where the next triplet will go.
*/
private int windowPtr;
/**
* This state variable is initially 0; it is set to 1 after the first data byte has been received, and 2 once the
* second data byte has been received.
*/
private int windowState;
/**
* recentBytes is a 16-bit value which contains the last two received bytes.
*/
private int recentBytes;
/**
* Hash chains: element "n" in this array contains the backward distance to the previous triplet with the same hash
* (or 0, if there is none). Due to the window buffer reuse, the previous triplet may have been overwritten: the
* code which walks a chain must make sure that it stays within the window size.
*/
private char[] windowLink;
/**
* For the hash value "v", hashTable[v] contains the value "j". If j == 0, then there is
* no current chain for this hash value; otherwise, the chain head is in the window, at index "j-1". It may happen
* that the chain head entry has been overwritten: the insertion code checks the designated entry when linking a new
* triplet.
*/
private char[] hashTable;
/**
* The buffer which receives a copy of the uncompressed data. That buffer is circular.
*/
private byte[] ucBuffer;
/**
* The length of the accumulated data in ucBuffer.
*/
private int ucBufferPtr;
/**
* The current to-match sequence length. If its value is 0, 1 or 2, then we do not have a triplet yet and there is
* no match. Otherwise, with a value of 3 or more, than there is a match with a previous sequence which begins at
* index seqPtr and distance seqDist.
*/
private int seqLen;
/**
* The index at which the current match begins (ignored if seqLen is 2 or less).
*/
private int seqPtr;
/**
* The distance between the current matched sequence and its source. Ignored if seqLen is 2 or less.
*/
private int seqDist;
/* =========================================================== */
/*
* Compression parameters.
*
* These parameters alter both the compression ratio and the compression speed.
*/
/**
* The maximum hash chain explored length when looking for a triplet.
*/
private int maxChainLengthTriplet;
/**
* The maximum backward distance when looking for a triplet.
*/
private int maxDistanceTriplet;
/**
* The maximum hash chain explored length when looking for a previous longer sequence.
*/
private int maxChainLengthSeq1;
/**
* The maximum backward distance when looking for a previous longer sequence.
*/
private int maxDistanceSeq1;
/**
* If the current sequence exceeds this length, then the explored chain length when looking for a previous longer
* distance is reduced (divided by four).
*/
private int goodSequenceLength;
/**
* If the current sequence exceeds this length, then a lazy match is not attempted.
*/
private int maxLazyLength;
/**
* The maximum hash chain explored length when looking for a sequence in lazy match mode.
*/
private int maxChainLengthSeq2;
/**
* The maximum backward distance when looking for a sequence in lazy match mode.
*/
private int maxDistanceSeq2;
/**
* If true, then no LZ77 sharing will be performed. Compression will come only from the Huffman codes.
*/
private boolean huffOnly;
/* =========================================================== */
/*
* Output data management.
*
* Output symbols are accumulated in a buffer. Each entry is a 32-bit word consisting of: -- literal value in the
* literal+length alphabet (9 bits) -- extra length bits (5 bits) -- distance symbol (5 bits) -- extra distance
* length (13 bits) (values ordered from least- to most-significant bits)
*
* If the literal value is not a sequence copy symbol (i.e. it has value 255 or less) then the other fields are
* zero. Note that the end-of-block special literal (value 256) is never written in that buffer.
*
* The lengths of the buffer[] and ucBuffer[] arrays are linked. Basically, if there are bufferLen symbols in
* buffer[], then these could be encoded as (at worst) 32bufferLen bits, in a type 1 block (plus the three-bit block
* header). Hence, a type 0 block may be used only if the uncompressed data length is no more than 32bufferLen-32
* bits, because this is the payload length for an uncompressed block of size 32bufferLen bits (then again excluding
* the three-bit header, and the additional byte-alignment padding bits). Therefore, ucBuffer.length needs not be
* larger than 4buffer.length (we need 258 more extra bytes to accomodate a currently matched sequence).
*
* We furthermore limit buffer.length to 16384, thus guaranteeing that when type 0 blocks are selected, no more than
* 65532 bytes are to be written out, which fits in a single block. The drawback is that uncompressible data may
* fill buffer[] after only 16384 literal bytes, which yields an overhead four times larger than the optimal
* overhead. This is not a serious issue: it turns out that zlib has the same overhead and is quite happy with it.
*
* Actual writes to the output stream use an internal buffer so that unbuffered transport streams can be used.
* Compression is inherently a buffered process.
*/
/**
* The output buffer for symbols.
*/
private int[] buffer;
/**
* The number of symbols currently accumulated in the buffer.
*/
private int bufferPtr;
/**
* The underlying transport stream for compressed data.
*/
private OutputStream out;
/**
* This byte value accumulates up to 7 bits, to be sent as part of the next complete byte.
*/
private int outByte;
/**
* The number of accumulated bits in outByte (between 0 and 7, inclusive).
*/
private int outPtr;
/**
* This buffer is used internally to accumulate compressed data bytes before sending them to the transport stream.
*/
private byte[] outBuf;
/**
* This pointer value marks the current limit to the data stored in outBuf[].
*/
private int outBufPtr;
/**
* This flag is set to true when processing a dictionary.
*/
private boolean noOutput;
/* =========================================================== */
/**
* Compression level 1: do not apply LZ77; only Huffman codes are computed. This is faster than SPEED
* but with a degraded compression ratio.
*/
public static final int HUFF = 1;
/**
* Compression level 2: optimize for speed.
*/
public static final int SPEED = 2;
/**
* Compression level 3: compromise between speed and compression ratio. This is the default level.
*/
public static final int MEDIUM = 3;
/**
* Compression level 4: try to achieve best compression ratio, possibly at the expense of compression speed. This
* level may occasionaly yield slightly worse results than the MEDIUM level.
*/
public static final int COMPACT = 4;
/**
* Build a deflater with the default parameters (MEDIUM level, 15-bit window).
*/
public Deflater() {
this(0, 15);
}
/**
* Build a deflater with the provided compression strategy (either SPEED, MEDIUM or
* COMPACT). A standard 15-bit window is used. If the compression level is 0, then the default
* compression level is selected.
*
* @param level the compression strategy
*/
public Deflater(int level) {
this(level, 15);
}
/**
* Build a deflater with the provided compression strategy (either SPEED, MEDIUM or
* COMPACT) and the provided window size. The window size is expressed in bits and may range from 9 to
* 15 (inclusive). The DEFLATE format uses a 15-bit window; by using a smaller window, the produced stream can be
* inflated with less memory (but compression ratio is lowered). If the compression level is 0, then the default
* compression level is selected.
*
* @param level the compression strategy
* @param windowBits the window bit size (9 to 15)
*/
public Deflater(int level, int windowBits) {
if (windowBits < 9 || windowBits > 15)
throw new IllegalArgumentException("invalid LZ77 window bit length: " + windowBits);
/*
* The internal buffer should not be too large, because it prevents the Huffman codes from adapting to data
* internal changes. When the internal buffer is too small, the block headers and dynamic tree representations
* become too expensive. The maximum value is 16384; to use something greater, the type 0 block code in
* endBlock() would have to be adapted.
*/
int bufferLen = 16384;
int windowLen = 1 << windowBits;
window = new int[windowLen];
windowLink = new char[windowLen];
hashTable = new char[windowLen];
maxDistanceTriplet = windowLen - 261;
maxDistanceSeq1 = windowLen - 261;
maxDistanceSeq2 = windowLen - 261;
if (level == 0)
level = MEDIUM;
switch (level) {
case SPEED:
maxChainLengthTriplet = 16;
maxChainLengthSeq1 = 8;
goodSequenceLength = 8;
maxLazyLength = 4;
maxChainLengthSeq2 = 4;
break;
case MEDIUM:
maxChainLengthTriplet = 128;
maxChainLengthSeq1 = 128;
goodSequenceLength = 64;
maxLazyLength = 64;
maxChainLengthSeq2 = 32;
break;
case COMPACT:
maxChainLengthTriplet = 1024;
maxChainLengthSeq1 = 1024;
goodSequenceLength = 258;
maxLazyLength = 258;
maxChainLengthSeq2 = 1024;
break;
case HUFF:
huffOnly = true;
break;
default:
throw new IllegalArgumentException("unknown compression level: " + level);
}
buffer = new int[bufferLen];
ucBuffer = new byte[4 * bufferLen + 258];
outBuf = new byte[4096];
}
/**
* Get the current output transport stream.
*
* @return the current output stream
*/
public OutputStream getOut() {
return out;
}
/**
* Set the current output transport stream. This method must be called before compressing data.
*
* @param out the new transport stream
*/
public void setOut(OutputStream out) {
this.out = out;
}
/* =========================================================== */
/*
* LZ77 implementation.
*/
/**
* Compute a 32-bit copy symbol, for the provided sequence length and source distance.
*
* @param len the sequence length
* @param dist the source sequence distance
* @return the copy symbol
*/
private static int makeCopySymbol(int len, int dist) {
int symlen, elen;
if (len <= 10) {
symlen = 254 + len;
elen = 0;
} else if (len == 258) {
symlen = 285;
elen = 0;
} else {
/*
* This may be optimized with a dichotomic search.
*/
int i;
for (i = 9; i < 29; i++)
if (LENGTH[i] > len)
break;
symlen = 256 + i;
elen = len - LENGTH[i - 1];
}
int symdist, edist;
if (dist <= 4) {
symdist = dist - 1;
edist = 0;
} else {
/*
* This may be optimized with a dichotomic search.
*/
int i;
for (i = 5; i < 30; i++)
if (DIST[i] > dist)
break;
symdist = i - 1;
edist = dist - DIST[i - 1];
}
return symlen + (elen << 9) + (symdist << 14) + (edist << 19);
}
/**
* Find a previous sequence, identical to the sequence at index orig and length len, such
* that this previous sequence is continued by three bytes equal to the provided end value.
* IMPORTANT: the "original" sequence must actually be longer than len by two bytes,
* which match the high two bytes of end.
*
* @param win the window buffer
* @param winMask the window buffer length, minus one
* @param wlink the window link buffer
* @param orig the original sequence begin index
* @param dist the distance associated with the original sequence
* @param len the original sequence length
* @param end the sequence end triplet
* @param maxLen the maximum explored chain length
* @param maxDist the maximum accepted distance
* @return the previous longer sequence distance, or 0 if not found
*/
private static int findPreviousSequence(int[] win, int winMask, char[] wlink, int orig, int dist, int len, int end, int maxLen, int maxDist) {
int n = orig;
int chainLength = maxLen;
loop:
while (chainLength-- > 0) {
int d = wlink[n];
if (d == 0)
return 0;
dist += d;
if (dist > maxDist)
return 0;
n = (n - d) & winMask;
int tm = len;
int j = orig, k = n;
if (tm >= 3) {
while (tm >= 3) {
if (win[j] != win[k])
continue loop;
tm -= 3;
j = (j + 3) & winMask;
k = (k + 3) & winMask;
}
switch (tm) {
case 1:
j = (j - 2) & winMask;
k = (k - 2) & winMask;
if (win[j] != win[k])
continue loop;
k = (k + 3) & winMask;
break;
case 2:
j = (j - 1) & winMask;
k = (k - 1) & winMask;
if (win[j] != win[k])
continue loop;
k = (k + 3) & winMask;
break;
}
} else {
if (win[j] != win[k])
continue loop;
k = (k + tm) & winMask;
}
if (win[k] == end)
return dist;
}
return 0;
}
/**
* Update the ucBuffer array with the provided uncompressed data. This must be done before ending the
* block.
*
* @param buf the source data buffer
* @param off1 the source start offset (inclusive)
* @param off2 the source end offset (exclusive)
*/
private void updateUCBuffer(byte[] buf, int off1, int off2) {
int uLen = ucBuffer.length;
int sInc = (uLen >>> 1);
while (off1 < off2) {
int free = uLen - ucBufferPtr;
int tc = off2 - off1;
if (tc > sInc)
tc = sInc;
if (tc > free) {
System.arraycopy(buf, off1, ucBuffer, ucBufferPtr, free);
System.arraycopy(buf, off1 + free, ucBuffer, 0, tc - free);
ucBufferPtr = tc - free;
} else {
System.arraycopy(buf, off1, ucBuffer, ucBufferPtr, tc);
ucBufferPtr += tc;
}
off1 += tc;
}
}
/**
* Process some more data. When the internal buffer is full, or when the compressor code deems it appropriate, the
* data is compressed and sent on the transport stream. This method is most efficient when data is input by big
* enough chunks (at least a dozen bytes per call).
*
* @param buf the data buffer
* @param off the data offset
* @param len the data length (in bytes)
* @throws IOException on I/O error with the transport stream
*/
public void process(byte[] buf, int off, int len) throws IOException {
if (len == 0)
return;
int origOff = off;
/*
* If in "Huffman only" mode, then we use an alternate loop.
*/
if (huffOnly) {
int[] sb = buffer;
int sbPtr = bufferPtr;
int sbLen = sb.length;
while (len-- > 0) {
int bv = buf[off++] & 0xFF;
sb[sbPtr++] = bv;
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
}
bufferPtr = sbPtr;
updateUCBuffer(buf, origOff, off);
return;
}
/*
* We have some special code for the first two bytes ever.
*/
if (windowState < 2) {
int bv = buf[off++] & 0xFF;
len--;
if (windowState == 0) {
recentBytes = bv;
seqLen = 1;
if (len == 0) {
updateUCBuffer(buf, origOff, off);
return;
}
bv = buf[off++] & 0xFF;
len--;
}
recentBytes = (recentBytes << 8) | bv;
windowState = 2;
seqLen = 2;
if (len == 0) {
updateUCBuffer(buf, origOff, off);
return;
}
}
/*
* We cache most instance fields in local variables. This helps the JIT compiler produce efficient code.
*/
int[] win = window;
int winMask = win.length - 1;
int winPtr = windowPtr;
int recent = recentBytes;
char[] wlink = windowLink;
char[] ht = hashTable;
int htMask = ht.length - 1;
int sLen = seqLen;
int sPtr = seqPtr;
int sDist = seqDist;
int[] sb = buffer;
int sbPtr = bufferPtr;
int sbLen = sb.length;
int maxCL0 = maxChainLengthTriplet;
int maxDistCL0 = maxDistanceTriplet;
int maxCL1 = maxChainLengthSeq1;
int maxDistCL1 = maxDistanceSeq1;
int goodSLen = goodSequenceLength;
int maxLLen = maxLazyLength;
int maxCL2 = maxChainLengthSeq2;
int maxDistCL2 = maxDistanceSeq2;
loop:
while (len-- > 0) {
int b0 = buf[off++] & 0xFF;
/*
* Compute the current triplet.
*/
int triplet = (recent << 8) | b0;
recent = triplet & 0xFFFF;
/*
* Update the window and set hash links.
*/
win[winPtr] = triplet;
int h = (triplet + (triplet >>> 4) + (triplet >>> 8) + (triplet >>> 9) - (triplet >>> 16)) & htMask;
int link = ht[h] - 1;
int dist;
if (link < 0) {
dist = 0;
} else {
int pv = win[link];
int ph = (pv + (pv >>> 4) + (pv >>> 8) + (pv >>> 9) - (pv >>> 16)) & htMask;
if (ph == h) {
dist = (winPtr - link) & winMask;
} else {
dist = 0;
}
}
ht[h] = (char) (winPtr + 1);
wlink[winPtr] = (char) dist;
int thisPtr = winPtr;
winPtr = (winPtr + 1) & winMask;
/*
* If the current sequence length is 0 or 1, then we do not have a complete triplet yet, and there is
* nothing more to do.
*/
if (sLen < 2) {
sLen++;
continue loop;
}
/*
* If we just completed a triplet, then we look for a previous triplet. If we find one, then we begin a
* match sequence; otherwise, we emit a literal for the first byte of our triplet, and we continue. There is
* a corner case when the previous triplet is at the maximum distance: in that situation, we must emit the
* copy symbol immediately.
*/
if (sLen == 2) {
if (dist == 0) {
sb[sbPtr++] = triplet >>> 16;
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
continue loop;
}
sDist = dist;
findTriplet:
do {
int n = link;
int chainLen = maxCL0;
while (chainLen-- > 0) {
if (win[n] == triplet)
break findTriplet;
int d = wlink[n];
if (d == 0)
break;
sDist += d;
if (sDist > maxDistCL0)
break;
n = (n - d) & winMask;
}
sDist = 0;
}
while (false);
if (sDist == 0) {
sb[sbPtr++] = triplet >>> 16;
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
} else {
sPtr = (thisPtr - sDist) & winMask;
sLen = 3;
if (sPtr == winPtr) {
sb[sbPtr++] = makeCopySymbol(sLen, sDist);
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
sLen = 0;
}
}
continue loop;
}
/*
* We are currently matching a sequence. We try to augment it. If we can, then we just do that; but we must
* mind the maximum sequence length and also its distance.
*/
if (win[(thisPtr - sDist) & winMask] == triplet) {
sLen++;
if (sPtr == winPtr || sLen == 258) {
sb[sbPtr++] = makeCopySymbol(sLen, sDist);
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
sLen = 0;
}
continue loop;
}
/*
* The current sequence cannot be agumented. We try to find a longer match in the previous sequences.
*/
int sDistNew = findPreviousSequence(win, winMask, wlink, sPtr, sDist, sLen - 2, triplet, sLen > goodSLen ? (maxCL1 >>> 2) : maxCL1, maxDistCL1);
if (sDistNew > 0) {
sDist = sDistNew;
sPtr = (thisPtr - (sLen - 2) - sDistNew) & winMask;
sLen++;
if (sPtr == winPtr || sLen == 258) {
sb[sbPtr++] = makeCopySymbol(sLen, sDist);
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
sLen = 0;
}
continue loop;
}
/*
* We could not find a longer sequence. We must flush something. We try to find a longer sequence beginning
* at the next byte (that's what RFC 1951 calls lazy matching).
*/
if (sLen <= maxLLen) {
int refPtr = (thisPtr - (sLen - 2) + 1) & winMask;
int mdc = maxDistCL2;
if (mdc > sDist)
mdc = sDist;
sDistNew = findPreviousSequence(win, winMask, wlink, refPtr, 0, sLen - 3, triplet, maxCL2, mdc);
if (sDistNew > 0) {
sb[sbPtr++] = win[sPtr] >>> 16;
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
sDist = sDistNew;
sPtr = (refPtr - sDistNew) & winMask;
if (sPtr == winPtr) {
sb[sbPtr++] = makeCopySymbol(sLen, sDist);
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
sLen = 0;
}
continue loop;
}
}
/*
* The current sequence is finished and we could not find any better. We filter out three-byte sequences
* which are too far: for these sequences, the copy symbol with its distance code and extra bits may be more
* expensive than simply writing out the literal bytes.
*
* The threshold for this test has been determined by compressing many files and seeing how the result
* compares with what gzip produces. It seems that the "right" value is 6144.
*/
if (sLen == 3 && sDist > 6144) {
int ot = win[sPtr];
for (int k = 16; k >= 0; k -= 8) {
sb[sbPtr++] = (ot >>> k) & 0xFF;
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
}
} else {
sb[sbPtr++] = makeCopySymbol(sLen, sDist);
if (sbPtr == sbLen) {
updateUCBuffer(buf, origOff, off);
origOff = off;
endBlock(false, sbPtr);
sbPtr = 0;
}
}
sLen = 1;
}
/*
* Flush out the local copies of the instance fields.
*/
windowPtr = winPtr;
recentBytes = recent;
seqLen = sLen;
seqPtr = sPtr;
seqDist = sDist;
bufferPtr = sbPtr;
/*
* Do not forget the original data bytes.
*/
updateUCBuffer(buf, origOff, off);
}
/**
* Prepare for a flush / terminate: the current dangling sequence is output.
*
* @throws IOException on I/O error with the transport stream
*/
private void prepareFlush() throws IOException {
switch (seqLen) {
case 0:
break;
case 1:
buffer[bufferPtr++] = recentBytes & 0xFF;
if (bufferPtr == buffer.length)
endBlock(false, bufferPtr);
break;
case 2:
buffer[bufferPtr++] = (recentBytes >>> 8) & 0xFF;
if (bufferPtr == buffer.length)
endBlock(false, bufferPtr);
buffer[bufferPtr++] = recentBytes & 0xFF;
if (bufferPtr == buffer.length)
endBlock(false, bufferPtr);
break;
default:
buffer[bufferPtr++] = makeCopySymbol(seqLen, seqDist);
if (bufferPtr == buffer.length)
endBlock(false, bufferPtr);
break;
}
seqLen = 0;
}
/* =========================================================== */
/*
* Huffman trees.
*
* The optimal Huffman tree cannot always be used, because we have additional constraints on the code lengths. The
* generic algorithm is called "package-merge" but it is relatively expensive (O(Ln) where L is the maximum code
* length and n is the alphabet size. We rather implement a "tree tweak": we begin with the optimal Huffman tree,
* and then we tweak it until it fits in the length constraints (it turns out that zlib uses a very similar trick).
*
* The tricky point is that once we have sorted the symbol by frequencies, then we just need to compute the number
* of codes for each code length. The actual code lengths for all symbols are easy to compute back by giving the
* longer codes to the least often encountered symbols (we may somehow obtain a locally optimal yet different tree,
* but this is no problem since in fine we will convert the tree to the canonical Huffman codes anyway). That idea
* apparently comes from someone called Haruhiko Okumura.
*
* Tree tweaking is applied when the optimal tree has "overdeep" leaves. Basically, we have a number of non-leaf
* nodes at the maximum depth (call "p" that number of nodes). Each is the root for a subtree containing q_i leaves
* which are all overdeep (1 <= i <= q). If we have q = \sum_i q_i overdeep leaves, then we must relocate those q
* leaves: -- p leaves will use the locations held by the subtree roots at maximum depth; -- q-p leaves will have to
* be relocated elsewhere. Hence, a first pass is used to obtain the number of codes for all valid code lengths; in
* that pass, the subtree roots at maximum depth are accounted as leaves (this handles the p "natural" relocations),
* and the value of q-p is returned. Relocation for those values works thus: to relocate a leaf, find a valid code
* of length l (strictly lower than the maximum length) and replace it with two codes of length l+1: the code is
* lengthened by one bit, which leaves room for one brother. We iterate over all leaves to relocate, choosing each
* time the longest possible code.
*
* It shall be noted that for the values used in DEFLATE, it is not possible that _all_ optimal codes exceed the
* maximum code length. Actually, the tweaking mechanism cannot fail with the parameters which will be used.
*
* The sorting step uses the Heap Sort, because it is an elegant algorithm which uses O(1) additional space and has
* a nice O(n log n) guaranteed worst case. A QuickSort would be faster on average, but I like the Heap Sort better,
* and this part is not a CPU bottleneck anyway.
*/
/**
* Sort the provided array of integer values (ascending order). Only the values between indexes off
* (inclusive) and off + len (exclusive) are touched; other array elements are neither considered nor
* modified.
*
* @param val the array to sort
* @param off the array offset
* @param len the number of elements to sort
*/
private static void heapSort(int[] val, int off, int len) {
if (len <= 1)
return;
/*
* We use virtual indexes, between 1 and len (inclusive). In our internal heap, the two children of node of
* virtual index "i" have virtual indexes "2*i" and "2*i+1".
*/
int corr = off - 1;
/*
* Build the heap by inserting all values at the bottom, and then making them float up as necessary.
*/
for (int i = 2; i <= len; i++) {
int j = i;
int v = val[corr + j];
while (j > 1) {
int k = j >>> 1;
int f = val[corr + k];
if (f > v)
break;
val[corr + j] = f;
val[corr + k] = v;
j = k;
}
}
/*
* Repeatedly, extract the heap root (maximum element) and rebuild the heap by promoting the bottom element and
* having it sink to its proper place.
*/
for (int i = len; i > 1; i--) {
int v = val[corr + i];
val[corr + i] = val[corr + 1];
val[corr + 1] = v;
int j = 1;
for (; ; ) {
int kl = j << 1;
int kr = kl + 1;
if (kl >= i)
break;
int si;
int sv;
if (kr >= i) {
si = kl;
sv = val[corr + kl];
} else {
int cl = val[corr + kl];
int cr = val[corr + kr];
if (cl > cr) {
si = kl;
sv = cl;
} else {
si = kr;
sv = cr;
}
}
if (v > sv)
break;
val[corr + j] = sv;
val[corr + si] = v;
j = si;
}
}
}
/**
*
* Compute the optimal Huffman tree, then tweak it so that it fits within the specified maximum code length.
* Returned value is the resulting code length for each symbol. From these lengths, the canonical Huffman code can
* be rebuilt.
*
*
*
* The alphabet size is assumed to be equal to freq.length.
*
*
*
* The following properties MUST be met:
*
* - frequencies are positive integers (0 is allowed, and qualifies a symbol which does not occur at all);
* - the sum of all frequencies must be strictly lower than 2097152 (i.e. that sum must fit in a 21-bit unsigned
* integer field).
*
*
*
* @param freq the symbol frequencies
* @param maxCodeLen the maximum code length
* @return the resulting code lengths
*/
private static int[] makeHuffmanCodes(int[] freq, int maxCodeLen) {
int alphLen = freq.length;
/*
* We sort symbols by frequencies. Each value in freqTmp[] consists of: -- symbol value (9 bits) -- flag
* "literal" set (1 bit, equal to 1) -- symbol frequency (21 bits)
*
* Since the frequencies use the upper bits, we can compare those values directly. A side effect is that no two
* values will be considered as equal to each other, even for two symbols which occur with the same frequency;
* this is harmless.
*/
int[] freqTmp = new int[alphLen];
for (int i = 0; i < alphLen; i++)
freqTmp[i] = i + (1 << 9) + (freq[i] << 10);
heapSort(freqTmp, 0, alphLen);
/*
* We skip the values with frequency zero; they will not take part in the tree construction. We handle
* immediately the special case where only one symbol occurs.
*/
int freqTmpPtr = 0;
while (freqTmpPtr < alphLen && (freqTmp[freqTmpPtr] >>> 10) == 0)
freqTmpPtr++;
if (freqTmpPtr == alphLen) {
/*
* No symbol occurs (degenerate case).
*/
return new int[alphLen];
}
if (freqTmpPtr == (alphLen - 1)) {
/*
* Only onw symbol occurs.
*/
int[] clen = new int[alphLen];
clen[freqTmp[freqTmpPtr] & 0x1FF] = 1;
return clen;
}
/*
* We use an additional FIFO in which we store the built tree nodes. All nodes make it to that fifo, and we do
* not move elements inside it; rather, we shift the limit indexes. There are at most alphLen-1 nodes in the
* tree (possibly less if some symbols are not used).
*/
int[] fifo = new int[alphLen - 1];
int fifoHead = 0, fifoRear = 0;
/*
* The tree is stored in an array. Each array element specifies a non-leaf node and consists of two 10-bit
* values, for the left and right node children, respectively. Each such 10-bit value specifies either a leaf
* symbol (9-bit value, 10th bit set) or the index for a non-leaf child node (9-bit index, 10th bit cleared).
* The tree root index is stored in rootIndex when the tree is finished.
*
* The tree is complete (no missing child anywhere) and has at most alphLen leaves (since we skip symbols which
* do not occur, the actual tree can be smaller); hence, it may have up to alphLen-1 non-leaf nodes.
*/
int[] tree = new int[alphLen - 1];
int treePtr = 0;
int rootIndex;
/*
* Tree building uses the classical Huffman code construction algorithm. We have two queues, the one in
* freqTmp[] (the yet unprocessed leaves) and the one in fifo[] (the built subtrees). At each step, we take the
* two least frequent elements (not necessarily one from each queue) and assemble them into a new subtree, which
* we insert in the fifo. The algorithm ends when freqTmp[] is empty (all symbols attached) and fifo[] contains
* a single subtree (which is the complete tree).
*/
for (; ; ) {
if (freqTmpPtr == alphLen && fifoRear == (fifoHead + 1)) {
rootIndex = fifo[fifoHead] & 0x1FF;
break;
}
int n0, n1;
if (fifoRear == fifoHead) {
n0 = freqTmp[freqTmpPtr++];
n1 = freqTmp[freqTmpPtr++];
} else if (freqTmpPtr == alphLen) {
n0 = fifo[fifoHead++];
n1 = fifo[fifoHead++];
} else {
int f = fifo[fifoHead];
int q = freqTmp[freqTmpPtr];
if (f < q) {
n0 = f;
fifoHead++;
} else {
n0 = q;
freqTmpPtr++;
}
if (fifoHead == fifoRear) {
n1 = freqTmp[freqTmpPtr++];
} else if (freqTmpPtr == alphLen) {
n1 = fifo[fifoHead++];
} else {
f = fifo[fifoHead];
q = freqTmp[freqTmpPtr];
if (f < q) {
n1 = f;
fifoHead++;
} else {
n1 = q;
freqTmpPtr++;
}
}
}
int ni = (n0 & ~0x3FF) + (n1 & ~0x3FF) + treePtr;
fifo[fifoRear++] = ni;
int nv = (n0 & 0x3FF) + ((n1 & 0x3FF) << 10);
tree[treePtr++] = nv;
}
/*
* Now, we gather the count for each code length, and the number of overdeep leaves which must be relocated.
*/
int[] blCount = new int[maxCodeLen + 1];
int overdeep = getCodeLengths(tree, rootIndex, 0, blCount, maxCodeLen);
/*
* We relocate the overdeep leaves.
*
* "dpi" contains the code length where we find nodes to demote (i.e. for which we lengthen the code) in order
* to find some room for a relocated leaf. That length is kept as long as possible, provided that it is strictly
* lower than maxCodeLen, and that there remain codes with that length.
*/
int dpi = maxCodeLen;
while (overdeep-- > 0) {
if (dpi == maxCodeLen) {
do {
dpi--;
}
while (blCount[dpi] == 0);
}
blCount[dpi]--;
blCount[++dpi] += 2;
}
/*
* We rebuild the code lengths. We just walk the symbols sorted by frequencies, and give them code lengths,
* according to the counts in blCount[].
*/
int[] codeLen = new int[alphLen];
int p = 0;
while ((freqTmp[p] >>> 10) == 0)
p++;
for (int bits = maxCodeLen; bits > 0; bits--) {
for (int k = blCount[bits]; k > 0; k--) {
int sym = freqTmp[p++] & 0x1FF;
codeLen[sym] = bits;
}
}
/*
* We have finished: we computed the code lengths for all symbols. These code lengths are for an optimized (not
* necessarily optimal) Huffman tree which fits in the allowed maximum code length.
*/
return codeLen;
}
/**
* Count the code lengths for the provided subtree; the counts are accumulated in the blCount[] array.
* Non-leaf nodes at exactly the maximum depth are accounted as leaves with the maximum code length. The number of
* overdeep leaves which must be relocated is returned.
*
* @param tree the tree array
* @param idx the subtree root index (or leaf code)
* @param depth the subtree root depth
* @param blCount the code length count accumulator array
* @param maxCodeLen the maximum code length
* @return the number of overdeep leaves to relocate
*/
private static int getCodeLengths(int[] tree, int idx, int depth, int[] blCount, int maxCodeLen) {
if ((idx & 0x200) != 0) {
if (depth > maxCodeLen) {
return 1;
} else {
blCount[depth]++;
return 0;
}
}
int s;
if (depth == maxCodeLen) {
blCount[maxCodeLen]++;
s = -1;
} else {
s = 0;
}
int n = tree[idx];
int l = n & 0x3FF;
int r = (n >>> 10) & 0x3FF;
s += getCodeLengths(tree, l, depth + 1, blCount, maxCodeLen);
s += getCodeLengths(tree, r, depth + 1, blCount, maxCodeLen);
return s;
}
/**
* The fixed Huffman codes, for the literal+length alphabet.
*/
private static final int[] FIXED_LIT_CODE;
static {
int[] fixedLitCodeLen = new int[288];
for (int i = 0; i < 144; i++)
fixedLitCodeLen[i] = 8;
for (int i = 144; i < 256; i++)
fixedLitCodeLen[i] = 9;
for (int i = 256; i < 280; i++)
fixedLitCodeLen[i] = 7;
for (int i = 280; i < 288; i++)
fixedLitCodeLen[i] = 8;
FIXED_LIT_CODE = makeCanonicalHuff(fixedLitCodeLen, 15);
}
/**
* The fixed Huffman codes, for the distance alphabet.
*/
private static final int[] FIXED_DIST_CODE;
static {
int[] fixedDistCodeLen = new int[32];
for (int i = 0; i < 32; i++)
fixedDistCodeLen[i] = 5;
FIXED_DIST_CODE = makeCanonicalHuff(fixedDistCodeLen, 15);
}
/**
* RLE-compress two Huffman trees (for the literal+length and distance alphabets, represented as arrays of code
* lengths). This results in values from 0 to 18 (5 low bits), where values 16, 17 and 18 have extra bits (bit 5 and
* beyond). The frequencies for the resulting values are also accumulated in the freq[] array.
*
* @param tree1 the first tree
* @param tree1len the first tree actual length
* @param tree2 the second tree
* @param tree2len the second tree actual length
* @param freq an array which receives frequencies
* @return the compressed trees
*/
private static int[] compressTrees(int[] tree1, int tree1len, int[] tree2, int tree2len, int[] freq) {
int inLen = tree1len + tree2len;
int[] in = new int[inLen];
System.arraycopy(tree1, 0, in, 0, tree1len);
System.arraycopy(tree2, 0, in, tree1len, tree2len);
int ptr = 0;
int[] ct = new int[inLen];
int ctPtr = 0;
while (ptr < inLen) {
int v = in[ptr++];
if (v == 0) {
int r = 1;
while (r < 138 && ptr < inLen) {
if (in[ptr] != 0)
break;
r++;
ptr++;
}
switch (r) {
case 1:
ct[ctPtr++] = 0;
freq[0]++;
break;
case 2:
ct[ctPtr++] = 0;
ct[ctPtr++] = 0;
freq[0] += 2;
break;
default:
if (r <= 10) {
ct[ctPtr++] = 17 + ((r - 3) << 5);
freq[17]++;
} else {
ct[ctPtr++] = 18 + ((r - 11) << 5);
freq[18]++;
}
break;
}
} else {
int r = 0;
while (r < 6 && ptr < inLen) {
if (in[ptr] != v)
break;
r++;
ptr++;
}
ct[ctPtr++] = v;
freq[v]++;
switch (r) {
case 0:
break;
case 1:
ct[ctPtr++] = v;
freq[v]++;
break;
case 2:
ct[ctPtr++] = v;
ct[ctPtr++] = v;
freq[v] += 2;
break;
default:
ct[ctPtr++] = 16 + ((r - 3) << 5);
freq[16]++;
break;
}
}
}
int[] res = new int[ctPtr];
System.arraycopy(ct, 0, res, 0, ctPtr);
return res;
}
/**
* This array encodes the permutation for the values encoding the RLE-compressed trees.
*/
/* =========================================================== */
/*
* Block assembly and data output.
*
* The LZ77 code assembles symbols in the buffer[] array. We compute appropriate Huffman trees, and then produce the
* compressed blocks. We first get all frequencies, compute the dynamic Huffman trees, and deduce the compressed
* block size. We also use the frequencies to know what size we would get with the fixed Huffman trees. We compare
* these two sizes with each other, and with the size for uncompressed blocks; we will use whichever method yields
* the smallest size.
*
* When producing an uncompressed block, we need to rebuild the uncompressed data. The ucBuffer[] array contains the
* first uncompressed bytes for this block; the subsequent bytes can be deduced by using the buffered symbols.
*
* Technically, we could use the same technique for type 2 blocks, in order to know whether a given short sequence
* is worth copying. But this is tricky because if we decide to switch symbols at that time, then the Huffman codes
* themselves have been computed with "wrong" frequencies. Right now, we filter out those sequences heuristically in
* the LZ77 stage.
*/
/**
* Write out some bits (least significant bit exits first).
*
* @param val the bit values
* @param num the number of bits (possibly 0)
* @throws IOException on I/O error with the transport stream
*/
private void writeBits(int val, int num) throws IOException {
if (num == 0)
return;
for (; ; ) {
int fs = 8 - outPtr;
int v = outByte | (val << outPtr);
if (fs > num) {
outByte = v;
outPtr += num;
return;
} else if (fs == num) {
outBuf[outBufPtr++] = (byte) v;
if (outBufPtr == outBuf.length) {
out.write(outBuf);
outBufPtr = 0;
}
outByte = 0;
outPtr = 0;
return;
}
outBuf[outBufPtr++] = (byte) v;
if (outBufPtr == outBuf.length) {
out.write(outBuf);
outBufPtr = 0;
}
val >>>= fs;
num -= fs;
outByte = 0;
outPtr = 0;
}
}
/**
* Send buffered complete output bytes.
*
* @throws IOException on I/O error with the transport stream
*/
private void sendBuffered() throws IOException {
if (outBufPtr > 0) {
out.write(outBuf, 0, outBufPtr);
outBufPtr = 0;
}
}
/**
* End the current block and compress it. The bufferPtr field value may be incorrect; the value
* provided in the sbPtr parameter must be used instead. This method resets the bufferPtr
* field to 0.
*
* @param fin true for the final block
* @param sbPtr the correct value for bufferPtr
* @throws IOException on I/O error with the transport stream
*/
private void endBlock(boolean fin, int sbPtr) throws IOException {
if (noOutput) {
bufferPtr = 0;
return;
}
int[] sb = buffer;
int[] freqLit = new int[286];
int[] freqDist = new int[30];
/*
* Do not forget the EOB symbol.
*/
freqLit[256] = 1;
/*
* Get the uncompressed data length; also, gather frequencies.
*/
int csU = 0;
for (int i = 0; i < sbPtr; i++) {
int val = sb[i];
int sym = val & 0x1FF;
freqLit[sym]++;
if (sym < 256) {
csU += 8;
continue;
}
csU += 8 * (LENGTH[sym - 257] + ((val >>> 9) & 0x1F));
int dist = (val >>> 14) & 0x1F;
freqDist[dist]++;
}
/*
* Adjust csU to account for the header bytes. Also, save the uncompressed data length (in bytes) in uDataLen.
*/
int csUextra = 0;
for (int t = 0; t < csU; t += 65535) {
if (t == 0) {
if (outPtr > 5) {
csUextra = 48 - outPtr;
} else {
csUextra = 40 - outPtr;
}
} else {
csUextra += 40;
}
}
int uDataLen = (csU >>> 3);
csU += csUextra;
/*
* Compute the dynamic Huffman codes and get the lengths for dynamic and fixed codes.
*/
Huff huff = new Huff(freqLit, freqDist);
int csD = huff.getDynamicBitLength();
int csF = huff.getFixedBitLength();
/*
* We now have the bit lengths for uncompressed blocks (csU), fixed Huffman codes (csF) and dynamic Huffman
* codes (csD). We use the smallest. On equality, we prefer uncompressed blocks over Huffman codes, and fixed
* Huffman codes over dynamic Huffman codes.
*/
if (csU <= csF && csU <= csD) {
writeBits(fin ? 1 : 0, 3);
if (outPtr > 0)
writeBits(0, 8 - outPtr);
writeBits(uDataLen | (~uDataLen << 16), 32);
sendBuffered();
out.write(ucBuffer, 0, uDataLen);
} else if (csF <= csD) {
/*
* Fixed Huffman codes.
*/
/*
* Block header (3 bits).
*/
writeBits(fin ? 3 : 2, 3);
/*
* Now, write out the data.
*/
for (int i = 0; i < sbPtr; i++) {
int val = buffer[i];
int sym = val & 0x1FF;
if (sym < 256) {
writeBits(FIXED_LIT_CODE[sym], sym < 144 ? 8 : 9);
continue;
}
writeBits(FIXED_LIT_CODE[sym], sym < 280 ? 7 : 8);
int eLenNum = LENGTH_ENUM[sym - 257];
if (eLenNum > 0)
writeBits((val >>> 9) & 0x1F, eLenNum);
int dist = (val >>> 14) & 0x1F;
writeBits(FIXED_DIST_CODE[dist], 5);
int eDistNum = DIST_ENUM[dist];
if (eDistNum > 0)
writeBits(val >>> 19, eDistNum);
}
/*
* Write out the EOB.
*/
writeBits(FIXED_LIT_CODE[256], 7);
} else {
/*
* Dynamic Huffman codes.
*/
int[] litCode = huff.getLitCode();
int[] litCodeLen = huff.getLitCodeLen();
int[] distCode = huff.getDistCode();
int[] distCodeLen = huff.getDistCodeLen();
int[] compTrees = huff.getCompTrees();
int compTreesLen = compTrees.length;
int[] ctCode = huff.getCTCode();
int[] ctCodeLen = huff.getCTCodeLen();
int[] permCT = huff.getPermCT();
int permCTLen = permCT.length;
/*
* Block header (3 bits).
*/
writeBits(fin ? 5 : 4, 3);
/*
* The tree lengths.
*/
writeBits(litCode.length - 257, 5);
writeBits(distCode.length - 1, 5);
writeBits(permCTLen - 4, 4);
/*
* The CT tree.
*/
for (int i = 0; i < permCTLen; i++)
writeBits(permCT[i], 3);
/*
* The two compressed trees.
*/
for (int i = 0; i < compTreesLen; i++) {
int v = compTrees[i];
int s = v & 0x1F;
writeBits(ctCode[s], ctCodeLen[s]);
int ebits;
switch (s) {
case 16:
ebits = 2;
break;
case 17:
ebits = 3;
break;
case 18:
ebits = 7;
break;
default:
continue;
}
writeBits((v >>> 5), ebits);
}
/*
* Now, write out the data.
*/
for (int i = 0; i < sbPtr; i++) {
int val = buffer[i];
int sym = val & 0x1FF;
writeBits(litCode[sym], litCodeLen[sym]);
if (sym < 256)
continue;
int eLenNum = LENGTH_ENUM[sym - 257];
if (eLenNum > 0)
writeBits((val >>> 9) & 0x1F, eLenNum);
int dist = (val >>> 14) & 0x1F;
writeBits(distCode[dist], distCodeLen[dist]);
int eDistNum = DIST_ENUM[dist];
if (eDistNum > 0)
writeBits(val >>> 19, eDistNum);
}
/*
* Write out the EOB.
*/
writeBits(litCode[256], litCodeLen[256]);
}
sendBuffered();
bufferPtr = 0;
/*
* Adjust ucBuffer[]. Some data has been processed, but some may remain (at most 258 bytes, corresponding to the
* currently matched sequence). We must take care: the buffer is circular. We use the fact that the buffer is
* more than twice as large than the maximum amout of data we move around.
*/
int uLen = ucBuffer.length;
int uRealLen = ucBufferPtr;
while (uRealLen < uDataLen)
uRealLen += uLen;
if (uDataLen < uRealLen) {
int tm = uRealLen - uDataLen;
/* DEBUG */
if (tm > 258)
throw new Error("too much data: " + tm);
if (tm <= ucBufferPtr) {
System.arraycopy(ucBuffer, ucBufferPtr - tm, ucBuffer, 0, tm);
} else {
int fpl = tm - ucBufferPtr;
System.arraycopy(ucBuffer, 0, ucBuffer, fpl, ucBufferPtr);
System.arraycopy(ucBuffer, uLen - fpl, ucBuffer, 0, fpl);
}
}
ucBufferPtr = uRealLen - uDataLen;
}
/**
* Instances of this class compute the dynamic Huffman codes for some frequencies, and report the resulting length,
* for both dynamic and static codes.
*/
private static class Huff {
private int[] litCode, litCodeLen;
private int[] distCode, distCodeLen;
private int[] compTrees;
private int[] ctCode, ctCodeLen;
private int[] permCT;
private int csD, csF;
/**
* Build the instance with the provided frequencies for the literal+length and the distance alphabets. The first
* frequency array MUST include the value 1 for the EOB symbol (value 256).
*
* @param freqLit the literal+length frequencies
* @param freqDist the distance frequencies
*/
private Huff(int[] freqLit, int[] freqDist) {
csD = 17;
csF = 3;
litCodeLen = makeHuffmanCodes(freqLit, 15);
distCodeLen = makeHuffmanCodes(freqDist, 15);
for (int i = 0; i < litCodeLen.length; i++) {
int f = freqLit[i];
int elen;
elen = (i >= 257) ? LENGTH_ENUM[i - 257] : 0;
csD += (litCodeLen[i] + elen) * f;
int fcl;
if (i < 256) {
fcl = (i < 144) ? 8 : 9;
} else {
fcl = (i < 280) ? 7 : 8;
}
csF += (fcl + elen) * f;
}
for (int i = 0; i < distCodeLen.length; i++) {
int f = freqDist[i];
int edist = DIST_ENUM[i];
csD += (distCodeLen[i] + edist) * f;
csF += (5 + edist) * f;
}
/*
* RLE-compress the two codes.
*/
litCode = makeCanonicalHuff(litCodeLen, 15);
distCode = makeCanonicalHuff(distCodeLen, 15);
if (distCode.length == 0)
distCode = new int[1];
int[] freqCT = new int[19];
compTrees = compressTrees(litCodeLen, litCode.length, distCodeLen, distCode.length, freqCT);
/*
* Compute the Huffman tree for the RLE-compressed trees.
*/
ctCodeLen = makeHuffmanCodes(freqCT, 7);
ctCode = makeCanonicalHuff(ctCodeLen, 7);
for (int i = 0; i < 19; i++) {
int ccl = ctCodeLen[i];
switch (i) {
case 16:
ccl += 2;
break;
case 17:
ccl += 3;
break;
case 18:
ccl += 7;
break;
}
csD += freqCT[i] * ccl;
}
/*
* Compute the permuted tree for the RLE-compressed trees, and its minimal length.
*/
int[] permCTtmp = new int[19];
int permCTLen = 0;
for (int i = 0; i < 19; i++) {
int len = ctCodeLen[PERM_CT[i]];
if (len > 0)
permCTLen = i + 1;
permCTtmp[i] = len;
}
permCT = new int[permCTLen];
System.arraycopy(permCTtmp, 0, permCT, 0, permCTLen);
csD += 3 * permCTLen;
}
/**
* Get the literal code values.
*
* @return the literal code values
*/
private int[] getLitCode() {
return litCode;
}
/**
* Get the literal code lengths.
*
* @return the literal code lengths
*/
private int[] getLitCodeLen() {
return litCodeLen;
}
/**
* Get the distance code lengths.
*
* @return the distance code lengths
*/
private int[] getDistCode() {
return distCode;
}
/**
* Get the distance code lengths.
*
* @return the distance code lengths
*/
private int[] getDistCodeLen() {
return distCodeLen;
}
/**
* Get the RLE-compressed tree representation.
*
* @return the RLE-compressed representation
*/
private int[] getCompTrees() {
return compTrees;
}
/**
* Get the level-2 code values.
*
* @return the level-2 code values
*/
private int[] getCTCode() {
return ctCode;
}
/**
* Get the level-2 code lengths.
*
* @return the level-2 code lengths
*/
private int[] getCTCodeLen() {
return ctCodeLen;
}
/**
* Get the level-2 code lengths, permuted.
*
* @return the permuted level-2 code lengths
*/
private int[] getPermCT() {
return permCT;
}
/**
* Get the block length, in bits, if dynamic Huffman codes are used.
*
* @return the block length with dynamic codes
*/
private int getDynamicBitLength() {
return csD;
}
/**
* Get the block length, in bits, if fixed Huffman codes are used.
*
* @return the block length with fixed codes
*/
private int getFixedBitLength() {
return csF;
}
}
/* =========================================================== */
/*
* Flush handling.
*
* We need some handling for the end of stream. If we have some buffered data, then we may just end the current
* block with the "final" flag set; otherwise, we need a new empty block to set that flag.
*
* We also implement two flush modes. The "partial flush" mimics what zlib does with Z_PARTIAL_FLUSH. Recent
* versions of zlib deprecate that option, and do not document it any more, but it is needed for the implementation
* of some protocols, e.g. OpenSSH. With this flush mode, we add one or two empty blocks (with fixed Huffman trees),
* in order to make sure that the peer has enough compressed data to decompress all meaningful bytes. Whether we
* need to add one or two blocks depends on a computation, which hinges on the idea that zlib uses 9 bits of
* lookahead.
*
* The "sync flush" terminates the current block (if any) and appends an empty "uncompressed data" block. That block
* includes automatic byte alignment, and ends with the four-byte sequence 00 00 FF FF. A common convention is _not
* to include_ that four-byte sequence, in which case the receiver is responsible for adding them. PPP uses this
* convention (see RFC 1979). We implement this mode, using a parameter flag to decide whether the four-byte
* sequence must be included or not.
*/
/**
* Write out an empty type 1 block (fixed Huffman trees).
*
* @param fin true for a final block
* @throws IOException on I/O error with the transport stream
*/
private void writeEmptySH(boolean fin) throws IOException {
writeBits(fin ? 3 : 2, 10);
}
/**
* Write out an empty type 0 block (uncompressed data).
*
* @param fin true for a final block
* @param wd false to omit the 00 00 FF FF sequence
* @throws IOException on I/O error with the transport stream
*/
private void writeEmptyUD(boolean fin, boolean wd) throws IOException {
writeBits(fin ? 1 : 0, 3);
if (outPtr > 0)
writeBits(0, 8 - outPtr);
if (wd)
writeBits(0xFFFF0000, 32);
}
/**
* Terminate the current compression run. Pending buffered data, if any, is compressed as a final block, and written
* out on the transport stream. If there is no pending buffered data, then an empty, final block is added. Either
* way, any remaining partial byte is padded with zeroes and written. The transport stream is NOT flushed.
*
* @throws IOException on I/O error with the transport stream
*/
public void terminate() throws IOException {
prepareFlush();
if (bufferPtr == 0) {
writeEmptySH(true);
} else {
endBlock(true, bufferPtr);
}
if (outPtr > 0)
writeBits(0, 8 - outPtr);
sendBuffered();
}
/**
* Perform a "sync flush" in a way similar to what is done by zlib with option Z_SYNC_FLUSH. The
* current block, if any, is closed, and one empty type 0 block is added. After this call, the stream is
* byte-aligned. The type 0 block ends with the aligned four-byte sequence 00 00 FF FF; these four bytes are omitted
* if withData is false. The transport stream is NOT flushed.
*
* @param withData false to omit the 00 00 FF FF bytes
* @throws IOException on I/O error with the transport stream
*/
public void flushSync(boolean withData) throws IOException {
prepareFlush();
if (bufferPtr != 0)
endBlock(false, bufferPtr);
writeEmptyUD(false, withData);
sendBuffered();
}
/**
* LENGTH[n] contains the sequence copy length
* when the symbol 257+n has been read. The actual
* copy length may be augmented with a value from some extra bits.
*/
static final int[] LENGTH;
/**
* LENGTH_ENUM[n] contains the number of extra bits
* which shall be read, in order to augment the sequence copy
* length corresponding to the symbol257+n.
*/
static final int[] LENGTH_ENUM = {
0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0
};
/*
* Here, we initialize LENGTH[] from LENGTH_ENUM[].
*/
static {
LENGTH = new int[29];
LENGTH[0] = 3;
int l = 3;
for (int i = 1; i < 28; i++) {
l += 1 << LENGTH_ENUM[i - 1];
LENGTH[i] = l;
}
/*
* The RFC 1951 specifies that the last symbol specifies
* a copy length of 258, not 259. I don't know why.
*/
LENGTH[28] = 258;
}
/**
* DIST[n] is the copy sequence distance corresponding
* to the distance symbol n, possibly augmented by
* some extra bits.
*/
static final int[] DIST;
/**
* DIST_ENUM[n] contains the number of extra bits
* used to augment the copy sequence distance corresponding to
* the distance symbol n.
*/
static final int[] DIST_ENUM = {
0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7,
8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13
};
/*
* DIST[] is initialized from DIST_ENUM[].
*/
static {
DIST = new int[30];
DIST[0] = 1;
int d = 1;
for (int i = 1; i < 30; i++) {
d += 1 << DIST_ENUM[i - 1];
DIST[i] = d;
}
}
/**
* This array encodes the permutation for the values encoding
* the RLE-compressed trees.
*/
static final int[] PERM_CT = {
16, 17, 18, 0, 8, 7, 9, 6, 10, 5,
11, 4, 12, 3, 13, 2, 14, 1, 15
};
/**
* Build the canonical Huffman codes, given the length of each
* code. null is returned if the code is not
* correct. The returned array is trimmed to its minimal size
* (trailing codes which do not occur are removed). The codes
* are "reversed" (first bit is least significant).
*
* @param codeLen the code lengths
* @param maxCodeLen the maximum code length
* @return the codes, or null
*/
static int[] makeCanonicalHuff(int[] codeLen, int maxCodeLen) {
int alphLen = codeLen.length;
int actualAlphLen = 0;
/*
* Compute the number of codes for each length
* (by convention, there is no code of length 0).
*/
int[] blCount = new int[maxCodeLen + 1];
for (int n = 0; n < alphLen; n++) {
int len = codeLen[n];
if (len < 0 || len > maxCodeLen)
return null;
if (len > 0) {
actualAlphLen = n + 1;
blCount[len]++;
}
}
/*
* Compute the smallest code for each code length.
*/
int[] nextCode = new int[maxCodeLen + 1];
int codeVal = 0;
for (int bits = 1; bits <= maxCodeLen; bits++) {
codeVal = (codeVal + blCount[bits - 1]) << 1;
nextCode[bits] = codeVal;
}
/*
* Compute the code itself for each synbol. We also
* count the number of distinct symbols which may appear.
*/
int[] code = new int[actualAlphLen];
for (int n = 0; n < actualAlphLen; n++) {
int len = codeLen[n];
if (len != 0) {
int w = nextCode[len];
if (w >= (1 << len))
return null;
code[n] = reverse(w, len);
nextCode[len] = w + 1;
}
}
return code;
}
/**
* Bit reverse a value.
*
* @param cc the value to reverse
* @param q the value length, in bits
* @return the reversed value
*/
private static int reverse(int cc, int q) {
int v = 0;
while (q-- > 0) {
v <<= 1;
if ((cc & 1) != 0)
v++;
cc >>>= 1;
}
return v;
}
}
© 2015 - 2025 Weber Informatics LLC | Privacy Policy