mirror of
https://github.com/go-gitea/gitea.git
synced 2024-11-01 08:47:40 -04:00
912 lines
24 KiB
Go
912 lines
24 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 = [32]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 = [32]uint8{
|
|
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 = [64]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 = [64]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 uint16
|
|
nbytes uint8
|
|
literalEncoding *huffmanEncoder
|
|
offsetEncoding *huffmanEncoder
|
|
codegenEncoding *huffmanEncoder
|
|
err error
|
|
lastHeader int
|
|
// Set between 0 (reused block can be up to 2x the size)
|
|
logNewTablePenalty uint
|
|
lastHuffMan bool
|
|
bytes [256]byte
|
|
literalFreq [lengthCodesStart + 32]uint16
|
|
offsetFreq [32]uint16
|
|
codegenFreq [codegenCodeCount]uint16
|
|
|
|
// codegen must have an extra space for the final symbol.
|
|
codegen [literalCount + offsetCodeCount + 1]uint8
|
|
}
|
|
|
|
// Huffman reuse.
|
|
//
|
|
// The huffmanBitWriter supports reusing huffman tables and thereby combining block sections.
|
|
//
|
|
// This is controlled by several variables:
|
|
//
|
|
// If lastHeader is non-zero the Huffman table can be reused.
|
|
// This also indicates that a Huffman table has been generated that can output all
|
|
// possible symbols.
|
|
// It also indicates that an EOB has not yet been emitted, so if a new tabel is generated
|
|
// an EOB with the previous table must be written.
|
|
//
|
|
// If lastHuffMan is set, a table for outputting literals has been generated and offsets are invalid.
|
|
//
|
|
// An incoming block estimates the output size of a new table using a 'fresh' by calculating the
|
|
// optimal size and adding a penalty in 'logNewTablePenalty'.
|
|
// A Huffman table is not optimal, which is why we add a penalty, and generating a new table
|
|
// is slower both for compression and decompression.
|
|
|
|
func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
|
|
return &huffmanBitWriter{
|
|
writer: w,
|
|
literalEncoding: newHuffmanEncoder(literalCount),
|
|
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.lastHeader = 0
|
|
w.lastHuffMan = false
|
|
}
|
|
|
|
func (w *huffmanBitWriter) canReuse(t *tokens) (offsets, lits bool) {
|
|
offsets, lits = true, true
|
|
a := t.offHist[:offsetCodeCount]
|
|
b := w.offsetFreq[:len(a)]
|
|
for i := range a {
|
|
if b[i] == 0 && a[i] != 0 {
|
|
offsets = false
|
|
break
|
|
}
|
|
}
|
|
|
|
a = t.extraHist[:literalCount-256]
|
|
b = w.literalFreq[256:literalCount]
|
|
b = b[:len(a)]
|
|
for i := range a {
|
|
if b[i] == 0 && a[i] != 0 {
|
|
lits = false
|
|
break
|
|
}
|
|
}
|
|
if lits {
|
|
a = t.litHist[:]
|
|
b = w.literalFreq[:len(a)]
|
|
for i := range a {
|
|
if b[i] == 0 && a[i] != 0 {
|
|
lits = false
|
|
break
|
|
}
|
|
}
|
|
}
|
|
return
|
|
}
|
|
|
|
func (w *huffmanBitWriter) flush() {
|
|
if w.err != nil {
|
|
w.nbits = 0
|
|
return
|
|
}
|
|
if w.lastHeader > 0 {
|
|
// We owe an EOB
|
|
w.writeCode(w.literalEncoding.codes[endBlockMarker])
|
|
w.lastHeader = 0
|
|
}
|
|
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 uint16) {
|
|
w.bits |= uint64(b) << (w.nbits & 63)
|
|
w.nbits += nb
|
|
if w.nbits >= 48 {
|
|
w.writeOutBits()
|
|
}
|
|
}
|
|
|
|
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
|
|
}
|
|
|
|
func (w *huffmanBitWriter) codegens() int {
|
|
numCodegens := len(w.codegenFreq)
|
|
for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
|
|
numCodegens--
|
|
}
|
|
return numCodegens
|
|
}
|
|
|
|
func (w *huffmanBitWriter) headerSize() (size, numCodegens int) {
|
|
numCodegens = len(w.codegenFreq)
|
|
for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
|
|
numCodegens--
|
|
}
|
|
return 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, numCodegens
|
|
}
|
|
|
|
// dynamicSize returns the size of dynamically encoded data in bits.
|
|
func (w *huffmanBitWriter) dynamicReuseSize(litEnc, offEnc *huffmanEncoder) (size int) {
|
|
size = litEnc.bitLength(w.literalFreq[:]) +
|
|
offEnc.bitLength(w.offsetFreq[:])
|
|
return size
|
|
}
|
|
|
|
// dynamicSize returns the size of dynamically encoded data in bits.
|
|
func (w *huffmanBitWriter) dynamicSize(litEnc, offEnc *huffmanEncoder, extraBits int) (size, numCodegens int) {
|
|
header, numCodegens := w.headerSize()
|
|
size = header +
|
|
litEnc.bitLength(w.literalFreq[:]) +
|
|
offEnc.bitLength(w.offsetFreq[:]) +
|
|
extraBits
|
|
return size, numCodegens
|
|
}
|
|
|
|
// extraBitSize will return the number of bits that will be written
|
|
// as "extra" bits on matches.
|
|
func (w *huffmanBitWriter) extraBitSize() int {
|
|
total := 0
|
|
for i, n := range w.literalFreq[257:literalCount] {
|
|
total += int(n) * int(lengthExtraBits[i&31])
|
|
}
|
|
for i, n := range w.offsetFreq[:offsetCodeCount] {
|
|
total += int(n) * int(offsetExtraBits[i&31])
|
|
}
|
|
return total
|
|
}
|
|
|
|
// 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) {
|
|
// The function does not get inlined if we "& 63" the shift.
|
|
w.bits |= uint64(c.code) << w.nbits
|
|
w.nbits += c.len
|
|
if w.nbits >= 48 {
|
|
w.writeOutBits()
|
|
}
|
|
}
|
|
|
|
// writeOutBits will write bits to the buffer.
|
|
func (w *huffmanBitWriter) writeOutBits() {
|
|
bits := w.bits
|
|
w.bits >>= 48
|
|
w.nbits -= 48
|
|
n := w.nbytes
|
|
w.bytes[n] = byte(bits)
|
|
w.bytes[n+1] = byte(bits >> 8)
|
|
w.bytes[n+2] = byte(bits >> 16)
|
|
w.bytes[n+3] = byte(bits >> 24)
|
|
w.bytes[n+4] = byte(bits >> 32)
|
|
w.bytes[n+5] = byte(bits >> 40)
|
|
n += 6
|
|
if n >= bufferFlushSize {
|
|
if w.err != nil {
|
|
n = 0
|
|
return
|
|
}
|
|
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 = uint32(w.codegen[i])
|
|
i++
|
|
if codeWord == badCode {
|
|
break
|
|
}
|
|
w.writeCode(w.codegenEncoding.codes[codeWord])
|
|
|
|
switch codeWord {
|
|
case 16:
|
|
w.writeBits(int32(w.codegen[i]), 2)
|
|
i++
|
|
case 17:
|
|
w.writeBits(int32(w.codegen[i]), 3)
|
|
i++
|
|
case 18:
|
|
w.writeBits(int32(w.codegen[i]), 7)
|
|
i++
|
|
}
|
|
}
|
|
}
|
|
|
|
// writeStoredHeader will write a stored header.
|
|
// If the stored block is only used for EOF,
|
|
// it is replaced with a fixed huffman block.
|
|
func (w *huffmanBitWriter) writeStoredHeader(length int, isEof bool) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
if w.lastHeader > 0 {
|
|
// We owe an EOB
|
|
w.writeCode(w.literalEncoding.codes[endBlockMarker])
|
|
w.lastHeader = 0
|
|
}
|
|
|
|
// To write EOF, use a fixed encoding block. 10 bits instead of 5 bytes.
|
|
if length == 0 && isEof {
|
|
w.writeFixedHeader(isEof)
|
|
// EOB: 7 bits, value: 0
|
|
w.writeBits(0, 7)
|
|
w.flush()
|
|
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
|
|
}
|
|
if w.lastHeader > 0 {
|
|
// We owe an EOB
|
|
w.writeCode(w.literalEncoding.codes[endBlockMarker])
|
|
w.lastHeader = 0
|
|
}
|
|
|
|
// 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 *tokens, eof bool, input []byte) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
|
|
tokens.AddEOB()
|
|
if w.lastHeader > 0 {
|
|
// We owe an EOB
|
|
w.writeCode(w.literalEncoding.codes[endBlockMarker])
|
|
w.lastHeader = 0
|
|
}
|
|
numLiterals, numOffsets := w.indexTokens(tokens, false)
|
|
w.generate(tokens)
|
|
var extraBits int
|
|
storedSize, storable := w.storedSize(input)
|
|
if storable {
|
|
extraBits = w.extraBitSize()
|
|
}
|
|
|
|
// 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.Slice(), 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 *tokens, eof bool, input []byte, sync bool) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
|
|
sync = sync || eof
|
|
if sync {
|
|
tokens.AddEOB()
|
|
}
|
|
|
|
// We cannot reuse pure huffman table, and must mark as EOF.
|
|
if (w.lastHuffMan || eof) && w.lastHeader > 0 {
|
|
// We will not try to reuse.
|
|
w.writeCode(w.literalEncoding.codes[endBlockMarker])
|
|
w.lastHeader = 0
|
|
w.lastHuffMan = false
|
|
}
|
|
if !sync {
|
|
tokens.Fill()
|
|
}
|
|
numLiterals, numOffsets := w.indexTokens(tokens, !sync)
|
|
|
|
var size int
|
|
// Check if we should reuse.
|
|
if w.lastHeader > 0 {
|
|
// Estimate size for using a new table.
|
|
// Use the previous header size as the best estimate.
|
|
newSize := w.lastHeader + tokens.EstimatedBits()
|
|
newSize += newSize >> w.logNewTablePenalty
|
|
|
|
// The estimated size is calculated as an optimal table.
|
|
// We add a penalty to make it more realistic and re-use a bit more.
|
|
reuseSize := w.dynamicReuseSize(w.literalEncoding, w.offsetEncoding) + w.extraBitSize()
|
|
|
|
// Check if a new table is better.
|
|
if newSize < reuseSize {
|
|
// Write the EOB we owe.
|
|
w.writeCode(w.literalEncoding.codes[endBlockMarker])
|
|
size = newSize
|
|
w.lastHeader = 0
|
|
} else {
|
|
size = reuseSize
|
|
}
|
|
// Check if we get a reasonable size decrease.
|
|
if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
|
|
w.writeStoredHeader(len(input), eof)
|
|
w.writeBytes(input)
|
|
w.lastHeader = 0
|
|
return
|
|
}
|
|
}
|
|
|
|
// We want a new block/table
|
|
if w.lastHeader == 0 {
|
|
w.generate(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)
|
|
var numCodegens int
|
|
size, numCodegens = w.dynamicSize(w.literalEncoding, w.offsetEncoding, w.extraBitSize())
|
|
// 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)
|
|
w.lastHeader = 0
|
|
return
|
|
}
|
|
|
|
// Write Huffman table.
|
|
w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
|
|
w.lastHeader, _ = w.headerSize()
|
|
w.lastHuffMan = false
|
|
}
|
|
|
|
if sync {
|
|
w.lastHeader = 0
|
|
}
|
|
// Write the tokens.
|
|
w.writeTokens(tokens.Slice(), 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(t *tokens, filled bool) (numLiterals, numOffsets int) {
|
|
copy(w.literalFreq[:], t.litHist[:])
|
|
copy(w.literalFreq[256:], t.extraHist[:])
|
|
copy(w.offsetFreq[:], t.offHist[:offsetCodeCount])
|
|
|
|
if t.n == 0 {
|
|
return
|
|
}
|
|
if filled {
|
|
return maxNumLit, maxNumDist
|
|
}
|
|
// 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
|
|
}
|
|
return
|
|
}
|
|
|
|
func (w *huffmanBitWriter) generate(t *tokens) {
|
|
w.literalEncoding.generate(w.literalFreq[:literalCount], 15)
|
|
w.offsetEncoding.generate(w.offsetFreq[:offsetCodeCount], 15)
|
|
}
|
|
|
|
// 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
|
|
}
|
|
if len(tokens) == 0 {
|
|
return
|
|
}
|
|
|
|
// Only last token should be endBlockMarker.
|
|
var deferEOB bool
|
|
if tokens[len(tokens)-1] == endBlockMarker {
|
|
tokens = tokens[:len(tokens)-1]
|
|
deferEOB = true
|
|
}
|
|
|
|
// Create slices up to the next power of two to avoid bounds checks.
|
|
lits := leCodes[:256]
|
|
offs := oeCodes[:32]
|
|
lengths := leCodes[lengthCodesStart:]
|
|
lengths = lengths[:32]
|
|
for _, t := range tokens {
|
|
if t < matchType {
|
|
w.writeCode(lits[t.literal()])
|
|
continue
|
|
}
|
|
|
|
// Write the length
|
|
length := t.length()
|
|
lengthCode := lengthCode(length)
|
|
if false {
|
|
w.writeCode(lengths[lengthCode&31])
|
|
} else {
|
|
// inlined
|
|
c := lengths[lengthCode&31]
|
|
w.bits |= uint64(c.code) << (w.nbits & 63)
|
|
w.nbits += c.len
|
|
if w.nbits >= 48 {
|
|
w.writeOutBits()
|
|
}
|
|
}
|
|
|
|
extraLengthBits := uint16(lengthExtraBits[lengthCode&31])
|
|
if extraLengthBits > 0 {
|
|
extraLength := int32(length - lengthBase[lengthCode&31])
|
|
w.writeBits(extraLength, extraLengthBits)
|
|
}
|
|
// Write the offset
|
|
offset := t.offset()
|
|
offsetCode := offsetCode(offset)
|
|
if false {
|
|
w.writeCode(offs[offsetCode&31])
|
|
} else {
|
|
// inlined
|
|
c := offs[offsetCode&31]
|
|
w.bits |= uint64(c.code) << (w.nbits & 63)
|
|
w.nbits += c.len
|
|
if w.nbits >= 48 {
|
|
w.writeOutBits()
|
|
}
|
|
}
|
|
extraOffsetBits := uint16(offsetExtraBits[offsetCode&63])
|
|
if extraOffsetBits > 0 {
|
|
extraOffset := int32(offset - offsetBase[offsetCode&63])
|
|
w.writeBits(extraOffset, extraOffsetBits)
|
|
}
|
|
}
|
|
if deferEOB {
|
|
w.writeCode(leCodes[endBlockMarker])
|
|
}
|
|
}
|
|
|
|
// 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[:offsetCodeCount], 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, sync bool) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
|
|
// Clear histogram
|
|
for i := range w.literalFreq[:] {
|
|
w.literalFreq[i] = 0
|
|
}
|
|
if !w.lastHuffMan {
|
|
for i := range w.offsetFreq[:] {
|
|
w.offsetFreq[i] = 0
|
|
}
|
|
}
|
|
|
|
// Add everything as literals
|
|
// We have to estimate the header size.
|
|
// Assume header is around 70 bytes:
|
|
// https://stackoverflow.com/a/25454430
|
|
const guessHeaderSizeBits = 70 * 8
|
|
estBits, estExtra := histogramSize(input, w.literalFreq[:], !eof && !sync)
|
|
estBits += w.lastHeader + 15
|
|
if w.lastHeader == 0 {
|
|
estBits += guessHeaderSizeBits
|
|
}
|
|
estBits += estBits >> w.logNewTablePenalty
|
|
|
|
// Store bytes, if we don't get a reasonable improvement.
|
|
ssize, storable := w.storedSize(input)
|
|
if storable && ssize < estBits {
|
|
w.writeStoredHeader(len(input), eof)
|
|
w.writeBytes(input)
|
|
return
|
|
}
|
|
|
|
if w.lastHeader > 0 {
|
|
reuseSize := w.literalEncoding.bitLength(w.literalFreq[:256])
|
|
estBits += estExtra
|
|
|
|
if estBits < reuseSize {
|
|
// We owe an EOB
|
|
w.writeCode(w.literalEncoding.codes[endBlockMarker])
|
|
w.lastHeader = 0
|
|
}
|
|
}
|
|
|
|
const numLiterals = endBlockMarker + 1
|
|
const numOffsets = 1
|
|
if w.lastHeader == 0 {
|
|
w.literalFreq[endBlockMarker] = 1
|
|
w.literalEncoding.generate(w.literalFreq[:numLiterals], 15)
|
|
|
|
// 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)
|
|
numCodegens := w.codegens()
|
|
|
|
// Huffman.
|
|
w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
|
|
w.lastHuffMan = true
|
|
w.lastHeader, _ = w.headerSize()
|
|
}
|
|
|
|
encoding := w.literalEncoding.codes[:257]
|
|
for _, t := range input {
|
|
// Bitwriting inlined, ~30% speedup
|
|
c := encoding[t]
|
|
w.bits |= uint64(c.code) << ((w.nbits) & 63)
|
|
w.nbits += c.len
|
|
if w.nbits >= 48 {
|
|
bits := w.bits
|
|
w.bits >>= 48
|
|
w.nbits -= 48
|
|
n := w.nbytes
|
|
w.bytes[n] = byte(bits)
|
|
w.bytes[n+1] = byte(bits >> 8)
|
|
w.bytes[n+2] = byte(bits >> 16)
|
|
w.bytes[n+3] = byte(bits >> 24)
|
|
w.bytes[n+4] = byte(bits >> 32)
|
|
w.bytes[n+5] = byte(bits >> 40)
|
|
n += 6
|
|
if n >= bufferFlushSize {
|
|
if w.err != nil {
|
|
n = 0
|
|
return
|
|
}
|
|
w.write(w.bytes[:n])
|
|
n = 0
|
|
}
|
|
w.nbytes = n
|
|
}
|
|
}
|
|
if eof || sync {
|
|
w.writeCode(encoding[endBlockMarker])
|
|
w.lastHeader = 0
|
|
w.lastHuffMan = false
|
|
}
|
|
}
|