mirror of
https://github.com/go-gitea/gitea
synced 2024-11-16 07:04:25 +00:00
702 lines
18 KiB
Go
702 lines
18 KiB
Go
// 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"
|
|
)
|
|
|
|
const (
|
|
// The largest offset code.
|
|
offsetCodeCount = 30
|
|
|
|
// 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
|
|
|
|
// bufferFlushSize indicates the buffer size
|
|
// after which bytes are flushed to the writer.
|
|
// Should preferably be a multiple of 6, since
|
|
// we accumulate 6 bytes between writes to the buffer.
|
|
bufferFlushSize = 240
|
|
|
|
// bufferSize is the actual output byte buffer size.
|
|
// It must have additional headroom for a flush
|
|
// which can contain up to 8 bytes.
|
|
bufferSize = bufferFlushSize + 8
|
|
)
|
|
|
|
// 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 {
|
|
// writer is the underlying writer.
|
|
// Do not use it directly; use the write method, which ensures
|
|
// that Write errors are sticky.
|
|
writer io.Writer
|
|
|
|
// Data waiting to be written is bytes[0:nbytes]
|
|
// and then the low nbits of bits.
|
|
bits uint64
|
|
nbits uint
|
|
bytes [bufferSize]byte
|
|
codegenFreq [codegenCodeCount]int32
|
|
nbytes int
|
|
literalFreq []int32
|
|
offsetFreq []int32
|
|
codegen []uint8
|
|
literalEncoding *huffmanEncoder
|
|
offsetEncoding *huffmanEncoder
|
|
codegenEncoding *huffmanEncoder
|
|
err error
|
|
}
|
|
|
|
func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
|
|
return &huffmanBitWriter{
|
|
writer: w,
|
|
literalFreq: make([]int32, maxNumLit),
|
|
offsetFreq: make([]int32, offsetCodeCount),
|
|
codegen: make([]uint8, maxNumLit+offsetCodeCount+1),
|
|
literalEncoding: newHuffmanEncoder(maxNumLit),
|
|
codegenEncoding: newHuffmanEncoder(codegenCodeCount),
|
|
offsetEncoding: newHuffmanEncoder(offsetCodeCount),
|
|
}
|
|
}
|
|
|
|
func (w *huffmanBitWriter) reset(writer io.Writer) {
|
|
w.writer = writer
|
|
w.bits, w.nbits, w.nbytes, w.err = 0, 0, 0, nil
|
|
w.bytes = [bufferSize]byte{}
|
|
}
|
|
|
|
func (w *huffmanBitWriter) flush() {
|
|
if w.err != nil {
|
|
w.nbits = 0
|
|
return
|
|
}
|
|
n := w.nbytes
|
|
for w.nbits != 0 {
|
|
w.bytes[n] = byte(w.bits)
|
|
w.bits >>= 8
|
|
if w.nbits > 8 { // Avoid underflow
|
|
w.nbits -= 8
|
|
} else {
|
|
w.nbits = 0
|
|
}
|
|
n++
|
|
}
|
|
w.bits = 0
|
|
w.write(w.bytes[:n])
|
|
w.nbytes = 0
|
|
}
|
|
|
|
func (w *huffmanBitWriter) write(b []byte) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
_, w.err = w.writer.Write(b)
|
|
}
|
|
|
|
func (w *huffmanBitWriter) writeBits(b int32, nb uint) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
w.bits |= uint64(b) << w.nbits
|
|
w.nbits += nb
|
|
if w.nbits >= 48 {
|
|
bits := w.bits
|
|
w.bits >>= 48
|
|
w.nbits -= 48
|
|
n := w.nbytes
|
|
bytes := w.bytes[n : n+6]
|
|
bytes[0] = byte(bits)
|
|
bytes[1] = byte(bits >> 8)
|
|
bytes[2] = byte(bits >> 16)
|
|
bytes[3] = byte(bits >> 24)
|
|
bytes[4] = byte(bits >> 32)
|
|
bytes[5] = byte(bits >> 40)
|
|
n += 6
|
|
if n >= bufferFlushSize {
|
|
w.write(w.bytes[:n])
|
|
n = 0
|
|
}
|
|
w.nbytes = n
|
|
}
|
|
}
|
|
|
|
func (w *huffmanBitWriter) writeBytes(bytes []byte) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
n := w.nbytes
|
|
if w.nbits&7 != 0 {
|
|
w.err = InternalError("writeBytes with unfinished bits")
|
|
return
|
|
}
|
|
for w.nbits != 0 {
|
|
w.bytes[n] = byte(w.bits)
|
|
w.bits >>= 8
|
|
w.nbits -= 8
|
|
n++
|
|
}
|
|
if n != 0 {
|
|
w.write(w.bytes[:n])
|
|
}
|
|
w.nbytes = 0
|
|
w.write(bytes)
|
|
}
|
|
|
|
// RFC 1951 3.2.7 specifies a special run-length encoding for specifying
|
|
// 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
|
|
// litenc, offenc The literal and offset encoder to use
|
|
func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int, litEnc, offEnc *huffmanEncoder) {
|
|
for i := range w.codegenFreq {
|
|
w.codegenFreq[i] = 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.
|
|
cgnl := codegen[:numLiterals]
|
|
for i := range cgnl {
|
|
cgnl[i] = uint8(litEnc.codes[i].len)
|
|
}
|
|
|
|
cgnl = codegen[numLiterals : numLiterals+numOffsets]
|
|
for i := range cgnl {
|
|
cgnl[i] = uint8(offEnc.codes[i].len)
|
|
}
|
|
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 := 6
|
|
if n > count {
|
|
n = count
|
|
}
|
|
codegen[outIndex] = 16
|
|
outIndex++
|
|
codegen[outIndex] = uint8(n - 3)
|
|
outIndex++
|
|
w.codegenFreq[16]++
|
|
count -= n
|
|
}
|
|
} else {
|
|
for count >= 11 {
|
|
n := 138
|
|
if n > count {
|
|
n = count
|
|
}
|
|
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
|
|
}
|
|
|
|
// dynamicSize returns the size of dynamically encoded data in bits.
|
|
func (w *huffmanBitWriter) dynamicSize(litEnc, offEnc *huffmanEncoder, extraBits int) (size, numCodegens int) {
|
|
numCodegens = len(w.codegenFreq)
|
|
for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
|
|
numCodegens--
|
|
}
|
|
header := 3 + 5 + 5 + 4 + (3 * numCodegens) +
|
|
w.codegenEncoding.bitLength(w.codegenFreq[:]) +
|
|
int(w.codegenFreq[16])*2 +
|
|
int(w.codegenFreq[17])*3 +
|
|
int(w.codegenFreq[18])*7
|
|
size = header +
|
|
litEnc.bitLength(w.literalFreq) +
|
|
offEnc.bitLength(w.offsetFreq) +
|
|
extraBits
|
|
|
|
return size, numCodegens
|
|
}
|
|
|
|
// fixedSize returns the size of dynamically encoded data in bits.
|
|
func (w *huffmanBitWriter) fixedSize(extraBits int) int {
|
|
return 3 +
|
|
fixedLiteralEncoding.bitLength(w.literalFreq) +
|
|
fixedOffsetEncoding.bitLength(w.offsetFreq) +
|
|
extraBits
|
|
}
|
|
|
|
// storedSize calculates the stored size, including header.
|
|
// The function returns the size in bits and whether the block
|
|
// fits inside a single block.
|
|
func (w *huffmanBitWriter) storedSize(in []byte) (int, bool) {
|
|
if in == nil {
|
|
return 0, false
|
|
}
|
|
if len(in) <= maxStoreBlockSize {
|
|
return (len(in) + 5) * 8, true
|
|
}
|
|
return 0, false
|
|
}
|
|
|
|
func (w *huffmanBitWriter) writeCode(c hcode) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
w.bits |= uint64(c.code) << w.nbits
|
|
w.nbits += uint(c.len)
|
|
if w.nbits >= 48 {
|
|
bits := w.bits
|
|
w.bits >>= 48
|
|
w.nbits -= 48
|
|
n := w.nbytes
|
|
bytes := w.bytes[n : n+6]
|
|
bytes[0] = byte(bits)
|
|
bytes[1] = byte(bits >> 8)
|
|
bytes[2] = byte(bits >> 16)
|
|
bytes[3] = byte(bits >> 24)
|
|
bytes[4] = byte(bits >> 32)
|
|
bytes[5] = byte(bits >> 40)
|
|
n += 6
|
|
if n >= bufferFlushSize {
|
|
w.write(w.bytes[:n])
|
|
n = 0
|
|
}
|
|
w.nbytes = n
|
|
}
|
|
}
|
|
|
|
// 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 The 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)
|
|
w.writeBits(int32(numOffsets-1), 5)
|
|
w.writeBits(int32(numCodegens-4), 4)
|
|
|
|
for i := 0; i < numCodegens; i++ {
|
|
value := uint(w.codegenEncoding.codes[codegenOrder[i]].len)
|
|
w.writeBits(int32(value), 3)
|
|
}
|
|
|
|
i := 0
|
|
for {
|
|
var codeWord int = int(w.codegen[i])
|
|
i++
|
|
if codeWord == badCode {
|
|
break
|
|
}
|
|
w.writeCode(w.codegenEncoding.codes[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)
|
|
}
|
|
|
|
// writeBlock will write a block of tokens with the smallest encoding.
|
|
// The original input can be supplied, and if the huffman encoded data
|
|
// is larger than the original bytes, the data will be written as a
|
|
// stored block.
|
|
// If the input is nil, the tokens will always be Huffman encoded.
|
|
func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
|
|
tokens = append(tokens, endBlockMarker)
|
|
numLiterals, numOffsets := w.indexTokens(tokens)
|
|
|
|
var extraBits int
|
|
storedSize, storable := w.storedSize(input)
|
|
if storable {
|
|
// 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 += int(w.literalFreq[lengthCode]) * int(lengthExtraBits[lengthCode-lengthCodesStart])
|
|
}
|
|
for offsetCode := 4; offsetCode < numOffsets; offsetCode++ {
|
|
// First four offset codes have extra size = 0.
|
|
extraBits += int(w.offsetFreq[offsetCode]) * int(offsetExtraBits[offsetCode])
|
|
}
|
|
}
|
|
|
|
// Figure out smallest code.
|
|
// Fixed Huffman baseline.
|
|
var literalEncoding = fixedLiteralEncoding
|
|
var offsetEncoding = fixedOffsetEncoding
|
|
var size = w.fixedSize(extraBits)
|
|
|
|
// Dynamic Huffman?
|
|
var numCodegens int
|
|
|
|
// Generate codegen and codegenFrequencies, which indicates how to encode
|
|
// the literalEncoding and the offsetEncoding.
|
|
w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
|
|
w.codegenEncoding.generate(w.codegenFreq[:], 7)
|
|
dynamicSize, numCodegens := w.dynamicSize(w.literalEncoding, w.offsetEncoding, extraBits)
|
|
|
|
if dynamicSize < size {
|
|
size = dynamicSize
|
|
literalEncoding = w.literalEncoding
|
|
offsetEncoding = w.offsetEncoding
|
|
}
|
|
|
|
// Stored bytes?
|
|
if storable && storedSize < size {
|
|
w.writeStoredHeader(len(input), eof)
|
|
w.writeBytes(input)
|
|
return
|
|
}
|
|
|
|
// Huffman.
|
|
if literalEncoding == fixedLiteralEncoding {
|
|
w.writeFixedHeader(eof)
|
|
} else {
|
|
w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
|
|
}
|
|
|
|
// Write the tokens.
|
|
w.writeTokens(tokens, literalEncoding.codes, offsetEncoding.codes)
|
|
}
|
|
|
|
// writeBlockDynamic encodes a block using a dynamic Huffman table.
|
|
// This should be used if the symbols used have a disproportionate
|
|
// histogram distribution.
|
|
// If input is supplied and the compression savings are below 1/16th of the
|
|
// input size the block is stored.
|
|
func (w *huffmanBitWriter) writeBlockDynamic(tokens []token, eof bool, input []byte) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
|
|
tokens = append(tokens, endBlockMarker)
|
|
numLiterals, numOffsets := w.indexTokens(tokens)
|
|
|
|
// Generate codegen and codegenFrequencies, which indicates how to encode
|
|
// the literalEncoding and the offsetEncoding.
|
|
w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
|
|
w.codegenEncoding.generate(w.codegenFreq[:], 7)
|
|
size, numCodegens := w.dynamicSize(w.literalEncoding, w.offsetEncoding, 0)
|
|
|
|
// Store bytes, if we don't get a reasonable improvement.
|
|
if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
|
|
w.writeStoredHeader(len(input), eof)
|
|
w.writeBytes(input)
|
|
return
|
|
}
|
|
|
|
// Write Huffman table.
|
|
w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
|
|
|
|
// Write the tokens.
|
|
w.writeTokens(tokens, w.literalEncoding.codes, w.offsetEncoding.codes)
|
|
}
|
|
|
|
// indexTokens indexes a slice of tokens, and updates
|
|
// literalFreq and offsetFreq, and generates literalEncoding
|
|
// and offsetEncoding.
|
|
// The number of literal and offset tokens is returned.
|
|
func (w *huffmanBitWriter) indexTokens(tokens []token) (numLiterals, numOffsets int) {
|
|
for i := range w.literalFreq {
|
|
w.literalFreq[i] = 0
|
|
}
|
|
for i := range w.offsetFreq {
|
|
w.offsetFreq[i] = 0
|
|
}
|
|
|
|
for _, t := range tokens {
|
|
if t < matchType {
|
|
w.literalFreq[t.literal()]++
|
|
continue
|
|
}
|
|
length := t.length()
|
|
offset := t.offset()
|
|
w.literalFreq[lengthCodesStart+lengthCode(length)]++
|
|
w.offsetFreq[offsetCode(offset)]++
|
|
}
|
|
|
|
// 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 > 0 && w.offsetFreq[numOffsets-1] == 0 {
|
|
numOffsets--
|
|
}
|
|
if numOffsets == 0 {
|
|
// We haven't found a single match. If we want to go with the dynamic encoding,
|
|
// we should count at least one offset to be sure that the offset huffman tree could be encoded.
|
|
w.offsetFreq[0] = 1
|
|
numOffsets = 1
|
|
}
|
|
w.literalEncoding.generate(w.literalFreq, 15)
|
|
w.offsetEncoding.generate(w.offsetFreq, 15)
|
|
return
|
|
}
|
|
|
|
// writeTokens writes a slice of tokens to the output.
|
|
// codes for literal and offset encoding must be supplied.
|
|
func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
for _, t := range tokens {
|
|
if t < matchType {
|
|
w.writeCode(leCodes[t.literal()])
|
|
continue
|
|
}
|
|
// Write the length
|
|
length := t.length()
|
|
lengthCode := lengthCode(length)
|
|
w.writeCode(leCodes[lengthCode+lengthCodesStart])
|
|
extraLengthBits := uint(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(oeCodes[offsetCode])
|
|
extraOffsetBits := uint(offsetExtraBits[offsetCode])
|
|
if extraOffsetBits > 0 {
|
|
extraOffset := int32(offset - offsetBase[offsetCode])
|
|
w.writeBits(extraOffset, extraOffsetBits)
|
|
}
|
|
}
|
|
}
|
|
|
|
// huffOffset is a static offset encoder used for huffman only encoding.
|
|
// It can be reused since we will not be encoding offset values.
|
|
var huffOffset *huffmanEncoder
|
|
|
|
func init() {
|
|
w := newHuffmanBitWriter(nil)
|
|
w.offsetFreq[0] = 1
|
|
huffOffset = newHuffmanEncoder(offsetCodeCount)
|
|
huffOffset.generate(w.offsetFreq, 15)
|
|
}
|
|
|
|
// writeBlockHuff encodes a block of bytes as either
|
|
// Huffman encoded literals or uncompressed bytes if the
|
|
// results only gains very little from compression.
|
|
func (w *huffmanBitWriter) writeBlockHuff(eof bool, input []byte) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
|
|
// Clear histogram
|
|
for i := range w.literalFreq {
|
|
w.literalFreq[i] = 0
|
|
}
|
|
|
|
// Add everything as literals
|
|
histogram(input, w.literalFreq)
|
|
|
|
w.literalFreq[endBlockMarker] = 1
|
|
|
|
const numLiterals = endBlockMarker + 1
|
|
const numOffsets = 1
|
|
|
|
w.literalEncoding.generate(w.literalFreq, 15)
|
|
|
|
// Figure out smallest code.
|
|
// Always use dynamic Huffman or Store
|
|
var numCodegens int
|
|
|
|
// Generate codegen and codegenFrequencies, which indicates how to encode
|
|
// the literalEncoding and the offsetEncoding.
|
|
w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, huffOffset)
|
|
w.codegenEncoding.generate(w.codegenFreq[:], 7)
|
|
size, numCodegens := w.dynamicSize(w.literalEncoding, huffOffset, 0)
|
|
|
|
// Store bytes, if we don't get a reasonable improvement.
|
|
if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
|
|
w.writeStoredHeader(len(input), eof)
|
|
w.writeBytes(input)
|
|
return
|
|
}
|
|
|
|
// Huffman.
|
|
w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
|
|
encoding := w.literalEncoding.codes[:257]
|
|
n := w.nbytes
|
|
for _, t := range input {
|
|
// Bitwriting inlined, ~30% speedup
|
|
c := encoding[t]
|
|
w.bits |= uint64(c.code) << w.nbits
|
|
w.nbits += uint(c.len)
|
|
if w.nbits < 48 {
|
|
continue
|
|
}
|
|
// Store 6 bytes
|
|
bits := w.bits
|
|
w.bits >>= 48
|
|
w.nbits -= 48
|
|
bytes := w.bytes[n : n+6]
|
|
bytes[0] = byte(bits)
|
|
bytes[1] = byte(bits >> 8)
|
|
bytes[2] = byte(bits >> 16)
|
|
bytes[3] = byte(bits >> 24)
|
|
bytes[4] = byte(bits >> 32)
|
|
bytes[5] = byte(bits >> 40)
|
|
n += 6
|
|
if n < bufferFlushSize {
|
|
continue
|
|
}
|
|
w.write(w.bytes[:n])
|
|
if w.err != nil {
|
|
return // Return early in the event of write failures
|
|
}
|
|
n = 0
|
|
}
|
|
w.nbytes = n
|
|
w.writeCode(encoding[endBlockMarker])
|
|
}
|