// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package flate
import (
"io";
"math";
"os";
"strconv";
)
const (
// The largest offset code.
offsetCodeCount = 30;
// The largest offset code in the extensions.
extendedOffsetCodeCount = 42;
// The special code used to mark the end of a block.
endBlockMarker = 256;
// The first length code.
lengthCodesStart = 257;
// The number of codegen codes.
codegenCodeCount = 19;
badCode = 255;
)
// The number of extra bits needed by length code X - LENGTH_CODES_START.
var lengthExtraBits = []int8{
/* 257 */ 0, 0, 0,
/* 260 */ 0, 0, 0, 0, 0, 1, 1, 1, 1, 2,
/* 270 */ 2, 2, 2, 3, 3, 3, 3, 4, 4, 4,
/* 280 */ 4, 5, 5, 5, 5, 0,
}
// The length indicated by length code X - LENGTH_CODES_START.
var lengthBase = []uint32{
0, 1, 2, 3, 4, 5, 6, 7, 8, 10,
12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
64, 80, 96, 112, 128, 160, 192, 224, 255,
}
// offset code word extra bits.
var offsetExtraBits = []int8{
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,
/* extended window */
14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20,
}
var offsetBase = []uint32{
/* normal deflate */
0x000000, 0x000001, 0x000002, 0x000003, 0x000004,
0x000006, 0x000008, 0x00000c, 0x000010, 0x000018,
0x000020, 0x000030, 0x000040, 0x000060, 0x000080,
0x0000c0, 0x000100, 0x000180, 0x000200, 0x000300,
0x000400, 0x000600, 0x000800, 0x000c00, 0x001000,
0x001800, 0x002000, 0x003000, 0x004000, 0x006000,
/* extended window */
0x008000, 0x00c000, 0x010000, 0x018000, 0x020000,
0x030000, 0x040000, 0x060000, 0x080000, 0x0c0000,
0x100000, 0x180000, 0x200000, 0x300000,
}
// The odd order in which the codegen code sizes are written.
var codegenOrder = []uint32{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}
type huffmanBitWriter struct {
w io.Writer;
// Data waiting to be written is bytes[0:nbytes]
// and then the low nbits of bits.
bits uint32;
nbits uint32;
bytes [64]byte;
nbytes int;
literalFreq []int32;
offsetFreq []int32;
codegen []uint8;
codegenFreq []int32;
literalEncoding *huffmanEncoder;
offsetEncoding *huffmanEncoder;
codegenEncoding *huffmanEncoder;
err os.Error;
}
type WrongValueError struct {
name string;
from int32;
to int32;
value int32;
}
func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
return &huffmanBitWriter{
w: w,
literalFreq: make([]int32, maxLit),
offsetFreq: make([]int32, extendedOffsetCodeCount),
codegen: make([]uint8, maxLit+extendedOffsetCodeCount+1),
codegenFreq: make([]int32, codegenCodeCount),
literalEncoding: newHuffmanEncoder(maxLit),
offsetEncoding: newHuffmanEncoder(extendedOffsetCodeCount),
codegenEncoding: newHuffmanEncoder(codegenCodeCount),
}
}
func (err WrongValueError) String() string {
return "huffmanBitWriter: " + err.name + " should belong to [" + strconv.Itoa64(int64(err.from)) + ";" +
strconv.Itoa64(int64(err.to)) + "] but actual value is " + strconv.Itoa64(int64(err.value))
}
func (w *huffmanBitWriter) flushBits() {
if w.err != nil {
w.nbits = 0;
return;
}
bits := w.bits;
w.bits >>= 16;
w.nbits -= 16;
n := w.nbytes;
w.bytes[n] = byte(bits);
w.bytes[n+1] = byte(bits >> 8);
if n += 2; n >= len(w.bytes) {
_, w.err = w.w.Write(&w.bytes);
n = 0;
}
w.nbytes = n;
}
func (w *huffmanBitWriter) flush() {
if w.err != nil {
w.nbits = 0;
return;
}
n := w.nbytes;
if w.nbits > 8 {
w.bytes[n] = byte(w.bits);
w.bits >>= 8;
w.nbits -= 8;
n++;
}
if w.nbits > 0 {
w.bytes[n] = byte(w.bits);
w.nbits = 0;
n++;
}
w.bits = 0;
_, w.err = w.w.Write(w.bytes[0:n]);
w.nbytes = 0;
}
func (w *huffmanBitWriter) writeBits(b, nb int32) {
w.bits |= uint32(b) << w.nbits;
if w.nbits += uint32(nb); w.nbits >= 16 {
w.flushBits()
}
}
func (w *huffmanBitWriter) writeBytes(bytes []byte) {
if w.err != nil {
return
}
n := w.nbytes;
if w.nbits == 8 {
w.bytes[n] = byte(w.bits);
w.nbits = 0;
n++;
}
if w.nbits != 0 {
w.err = InternalError("writeBytes with unfinished bits");
return;
}
if n != 0 {
_, w.err = w.w.Write(w.bytes[0:n]);
if w.err != nil {
return
}
}
w.nbytes = 0;
_, w.err = w.w.Write(bytes);
}
// RFC 1951 3.2.7 specifies a special run-length encoding for specifiying
// the literal and offset lengths arrays (which are concatenated into a single
// array). This method generates that run-length encoding.
//
// The result is written into the codegen array, and the frequencies
// of each code is written into the codegenFreq array.
// Codes 0-15 are single byte codes. Codes 16-18 are followed by additional
// information. Code badCode is an end marker
//
// numLiterals The number of literals in literalEncoding
// numOffsets The number of offsets in offsetEncoding
func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int) {
fillInt32s(w.codegenFreq, 0);
// Note that we are using codegen both as a temporary variable for holding
// a copy of the frequencies, and as the place where we put the result.
// This is fine because the output is always shorter than the input used
// so far.
codegen := w.codegen; // cache
// Copy the concatenated code sizes to codegen. Put a marker at the end.
copyUint8s(codegen[0:numLiterals], w.literalEncoding.codeBits);
copyUint8s(codegen[numLiterals:numLiterals+numOffsets], w.offsetEncoding.codeBits);
codegen[numLiterals+numOffsets] = badCode;
size := codegen[0];
count := 1;
outIndex := 0;
for inIndex := 1; size != badCode; inIndex++ {
// INVARIANT: We have seen "count" copies of size that have not yet
// had output generated for them.
nextSize := codegen[inIndex];
if nextSize == size {
count++;
continue;
}
// We need to generate codegen indicating "count" of size.
if size != 0 {
codegen[outIndex] = size;
outIndex++;
w.codegenFreq[size]++;
count--;
for count >= 3 {
n := min(count, 6);
codegen[outIndex] = 16;
outIndex++;
codegen[outIndex] = uint8(n - 3);
outIndex++;
w.codegenFreq[16]++;
count -= n;
}
} else {
for count >= 11 {
n := min(count, 138);
codegen[outIndex] = 18;
outIndex++;
codegen[outIndex] = uint8(n - 11);
outIndex++;
w.codegenFreq[18]++;
count -= n;
}
if count >= 3 {
// count >= 3 && count <= 10
codegen[outIndex] = 17;
outIndex++;
codegen[outIndex] = uint8(count - 3);
outIndex++;
w.codegenFreq[17]++;
count = 0;
}
}
count--;
for ; count >= 0; count-- {
codegen[outIndex] = size;
outIndex++;
w.codegenFreq[size]++;
}
// Set up invariant for next time through the loop.
size = nextSize;
count = 1;
}
// Marker indicating the end of the codegen.
codegen[outIndex] = badCode;
}
func (w *huffmanBitWriter) writeCode(code *huffmanEncoder, literal uint32) {
if w.err != nil {
return
}
w.writeBits(int32(code.code[literal]), int32(code.codeBits[literal]));
}
// Write the header of a dynamic Huffman block to the output stream.
//
// numLiterals The number of literals specified in codegen
// numOffsets The number of offsets specified in codegen
// numCodegens Tne number of codegens used in codegen
func (w *huffmanBitWriter) writeDynamicHeader(numLiterals int, numOffsets int, numCodegens int, isEof bool) {
if w.err != nil {
return
}
var firstBits int32 = 4;
if isEof {
firstBits = 5
}
w.writeBits(firstBits, 3);
w.writeBits(int32(numLiterals-257), 5);
if numOffsets > offsetCodeCount {
// Extended version of deflater
w.writeBits(int32(offsetCodeCount+((numOffsets-(1+offsetCodeCount))>>3)), 5);
w.writeBits(int32((numOffsets-(1+offsetCodeCount))&0x7), 3);
} else {
w.writeBits(int32(numOffsets-1), 5)
}
w.writeBits(int32(numCodegens-4), 4);
for i := 0; i < numCodegens; i++ {
value := w.codegenEncoding.codeBits[codegenOrder[i]];
w.writeBits(int32(value), 3);
}
i := 0;
for {
var codeWord int = int(w.codegen[i]);
i++;
if codeWord == badCode {
break
}
// The low byte contains the actual code to generate.
w.writeCode(w.codegenEncoding, uint32(codeWord));
switch codeWord {
case 16:
w.writeBits(int32(w.codegen[i]), 2);
i++;
break;
case 17:
w.writeBits(int32(w.codegen[i]), 3);
i++;
break;
case 18:
w.writeBits(int32(w.codegen[i]), 7);
i++;
break;
}
}
}
func (w *huffmanBitWriter) writeStoredHeader(length int, isEof bool) {
if w.err != nil {
return
}
var flag int32;
if isEof {
flag = 1
}
w.writeBits(flag, 3);
w.flush();
w.writeBits(int32(length), 16);
w.writeBits(int32(^uint16(length)), 16);
}
func (w *huffmanBitWriter) writeFixedHeader(isEof bool) {
if w.err != nil {
return
}
// Indicate that we are a fixed Huffman block
var value int32 = 2;
if isEof {
value = 3
}
w.writeBits(value, 3);
}
func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
if w.err != nil {
return
}
fillInt32s(w.literalFreq, 0);
fillInt32s(w.offsetFreq, 0);
n := len(tokens);
tokens = tokens[0 : n+1];
tokens[n] = endBlockMarker;
totalLength := -1; // Subtract 1 for endBlock.
for _, t := range tokens {
switch t.typ() {
case literalType:
w.literalFreq[t.literal()]++;
totalLength++;
break;
case matchType:
length := t.length();
offset := t.offset();
totalLength += int(length + 3);
w.literalFreq[lengthCodesStart+lengthCode(length)]++;
w.offsetFreq[offsetCode(offset)]++;
break;
}
}
w.literalEncoding.generate(w.literalFreq, 15);
w.offsetEncoding.generate(w.offsetFreq, 15);
// get the number of literals
numLiterals := len(w.literalFreq);
for w.literalFreq[numLiterals-1] == 0 {
numLiterals--
}
// get the number of offsets
numOffsets := len(w.offsetFreq);
for numOffsets > 1 && w.offsetFreq[numOffsets-1] == 0 {
numOffsets--
}
storedBytes := 0;
if input != nil {
storedBytes = len(input)
}
var extraBits int64;
var storedSize int64;
if storedBytes <= maxStoreBlockSize && input != nil {
storedSize = int64((storedBytes + 5) * 8);
// We only bother calculating the costs of the extra bits required by
// the length of offset fields (which will be the same for both fixed
// and dynamic encoding), if we need to compare those two encodings
// against stored encoding.
for lengthCode := lengthCodesStart + 8; lengthCode < numLiterals; lengthCode++ {
// First eight length codes have extra size = 0.
extraBits += int64(w.literalFreq[lengthCode]) * int64(lengthExtraBits[lengthCode-lengthCodesStart])
}
for offsetCode := 4; offsetCode < numOffsets; offsetCode++ {
// First four offset codes have extra size = 0.
extraBits += int64(w.offsetFreq[offsetCode]) * int64(offsetExtraBits[offsetCode])
}
} else {
storedSize = math.MaxInt32
}
// Figure out which generates smaller code, fixed Huffman, dynamic
// Huffman, or just storing the data.
var fixedSize int64 = math.MaxInt64;
if numOffsets <= offsetCodeCount {
fixedSize = int64(3) +
fixedLiteralEncoding.bitLength(w.literalFreq) +
fixedOffsetEncoding.bitLength(w.offsetFreq) +
extraBits
}
// Generate codegen and codegenFrequencies, which indicates how to encode
// the literalEncoding and the offsetEncoding.
w.generateCodegen(numLiterals, numOffsets);
w.codegenEncoding.generate(w.codegenFreq, 7);
numCodegens := len(w.codegenFreq);
for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
numCodegens--
}
extensionSummand := 0;
if numOffsets > offsetCodeCount {
extensionSummand = 3
}
dynamicHeader := int64(3+5+5+4+(3*numCodegens)) +
// Following line is an extension.
int64(extensionSummand) +
w.codegenEncoding.bitLength(w.codegenFreq) +
int64(extraBits) +
int64(w.codegenFreq[16]*2) +
int64(w.codegenFreq[17]*3) +
int64(w.codegenFreq[18]*7);
dynamicSize := dynamicHeader +
w.literalEncoding.bitLength(w.literalFreq) +
w.offsetEncoding.bitLength(w.offsetFreq);
if storedSize < fixedSize && storedSize < dynamicSize {
w.writeStoredHeader(storedBytes, eof);
w.writeBytes(input[0:storedBytes]);
return;
}
var literalEncoding *huffmanEncoder;
var offsetEncoding *huffmanEncoder;
if fixedSize <= dynamicSize {
w.writeFixedHeader(eof);
literalEncoding = fixedLiteralEncoding;
offsetEncoding = fixedOffsetEncoding;
} else {
// Write the header.
w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof);
literalEncoding = w.literalEncoding;
offsetEncoding = w.offsetEncoding;
}
// Write the tokens.
for _, t := range tokens {
switch t.typ() {
case literalType:
w.writeCode(literalEncoding, t.literal());
break;
case matchType:
// Write the length
length := t.length();
lengthCode := lengthCode(length);
w.writeCode(literalEncoding, lengthCode+lengthCodesStart);
extraLengthBits := int32(lengthExtraBits[lengthCode]);
if extraLengthBits > 0 {
extraLength := int32(length - lengthBase[lengthCode]);
w.writeBits(extraLength, extraLengthBits);
}
// Write the offset
offset := t.offset();
offsetCode := offsetCode(offset);
w.writeCode(offsetEncoding, offsetCode);
extraOffsetBits := int32(offsetExtraBits[offsetCode]);
if extraOffsetBits > 0 {
extraOffset := int32(offset - offsetBase[offsetCode]);
w.writeBits(extraOffset, extraOffsetBits);
}
break;
default:
panic("unknown token type: " + string(t))
}
}
}
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