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747 |
jeremybenn |
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package flate
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import (
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"io"
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"math"
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"strconv"
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)
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const (
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// The largest offset code.
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offsetCodeCount = 30
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// The special code used to mark the end of a block.
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endBlockMarker = 256
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// The first length code.
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lengthCodesStart = 257
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// The number of codegen codes.
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codegenCodeCount = 19
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badCode = 255
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)
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// The number of extra bits needed by length code X - LENGTH_CODES_START.
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var lengthExtraBits = []int8{
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/* 257 */ 0, 0, 0,
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/* 260 */ 0, 0, 0, 0, 0, 1, 1, 1, 1, 2,
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/* 270 */ 2, 2, 2, 3, 3, 3, 3, 4, 4, 4,
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/* 280 */ 4, 5, 5, 5, 5, 0,
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}
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// The length indicated by length code X - LENGTH_CODES_START.
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var lengthBase = []uint32{
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0, 1, 2, 3, 4, 5, 6, 7, 8, 10,
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12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
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64, 80, 96, 112, 128, 160, 192, 224, 255,
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}
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// offset code word extra bits.
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var offsetExtraBits = []int8{
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0, 0, 0, 0, 1, 1, 2, 2, 3, 3,
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4, 4, 5, 5, 6, 6, 7, 7, 8, 8,
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9, 9, 10, 10, 11, 11, 12, 12, 13, 13,
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/* extended window */
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14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20,
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}
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var offsetBase = []uint32{
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/* normal deflate */
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0x000000, 0x000001, 0x000002, 0x000003, 0x000004,
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0x000006, 0x000008, 0x00000c, 0x000010, 0x000018,
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0x000020, 0x000030, 0x000040, 0x000060, 0x000080,
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0x0000c0, 0x000100, 0x000180, 0x000200, 0x000300,
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0x000400, 0x000600, 0x000800, 0x000c00, 0x001000,
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0x001800, 0x002000, 0x003000, 0x004000, 0x006000,
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/* extended window */
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0x008000, 0x00c000, 0x010000, 0x018000, 0x020000,
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0x030000, 0x040000, 0x060000, 0x080000, 0x0c0000,
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0x100000, 0x180000, 0x200000, 0x300000,
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}
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// The odd order in which the codegen code sizes are written.
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var codegenOrder = []uint32{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}
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type huffmanBitWriter struct {
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w io.Writer
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// Data waiting to be written is bytes[0:nbytes]
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// and then the low nbits of bits.
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bits uint32
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nbits uint32
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bytes [64]byte
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nbytes int
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literalFreq []int32
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offsetFreq []int32
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codegen []uint8
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codegenFreq []int32
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literalEncoding *huffmanEncoder
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offsetEncoding *huffmanEncoder
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codegenEncoding *huffmanEncoder
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err error
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}
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type WrongValueError struct {
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name string
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from int32
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to int32
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value int32
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}
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func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
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return &huffmanBitWriter{
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w: w,
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literalFreq: make([]int32, maxLit),
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offsetFreq: make([]int32, offsetCodeCount),
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codegen: make([]uint8, maxLit+offsetCodeCount+1),
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codegenFreq: make([]int32, codegenCodeCount),
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literalEncoding: newHuffmanEncoder(maxLit),
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offsetEncoding: newHuffmanEncoder(offsetCodeCount),
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codegenEncoding: newHuffmanEncoder(codegenCodeCount),
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}
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}
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func (err WrongValueError) Error() string {
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return "huffmanBitWriter: " + err.name + " should belong to [" + strconv.FormatInt(int64(err.from), 10) + ";" +
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strconv.FormatInt(int64(err.to), 10) + "] but actual value is " + strconv.FormatInt(int64(err.value), 10)
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}
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func (w *huffmanBitWriter) flushBits() {
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if w.err != nil {
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w.nbits = 0
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return
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}
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bits := w.bits
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w.bits >>= 16
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w.nbits -= 16
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n := w.nbytes
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w.bytes[n] = byte(bits)
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w.bytes[n+1] = byte(bits >> 8)
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if n += 2; n >= len(w.bytes) {
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_, w.err = w.w.Write(w.bytes[0:])
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n = 0
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}
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w.nbytes = n
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}
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func (w *huffmanBitWriter) flush() {
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if w.err != nil {
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w.nbits = 0
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return
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}
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n := w.nbytes
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if w.nbits > 8 {
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w.bytes[n] = byte(w.bits)
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w.bits >>= 8
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w.nbits -= 8
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n++
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}
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if w.nbits > 0 {
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w.bytes[n] = byte(w.bits)
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w.nbits = 0
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n++
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}
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w.bits = 0
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_, w.err = w.w.Write(w.bytes[0:n])
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w.nbytes = 0
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}
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func (w *huffmanBitWriter) writeBits(b, nb int32) {
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w.bits |= uint32(b) << w.nbits
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if w.nbits += uint32(nb); w.nbits >= 16 {
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w.flushBits()
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}
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}
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func (w *huffmanBitWriter) writeBytes(bytes []byte) {
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if w.err != nil {
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return
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}
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n := w.nbytes
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if w.nbits == 8 {
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w.bytes[n] = byte(w.bits)
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w.nbits = 0
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n++
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}
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if w.nbits != 0 {
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w.err = InternalError("writeBytes with unfinished bits")
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return
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}
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if n != 0 {
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_, w.err = w.w.Write(w.bytes[0:n])
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if w.err != nil {
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return
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}
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}
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w.nbytes = 0
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_, w.err = w.w.Write(bytes)
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}
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// RFC 1951 3.2.7 specifies a special run-length encoding for specifying
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// the literal and offset lengths arrays (which are concatenated into a single
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// array). This method generates that run-length encoding.
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//
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// The result is written into the codegen array, and the frequencies
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// of each code is written into the codegenFreq array.
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// Codes 0-15 are single byte codes. Codes 16-18 are followed by additional
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// information. Code badCode is an end marker
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//
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// numLiterals The number of literals in literalEncoding
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// numOffsets The number of offsets in offsetEncoding
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func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int) {
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for i := range w.codegenFreq {
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w.codegenFreq[i] = 0
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}
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// Note that we are using codegen both as a temporary variable for holding
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// a copy of the frequencies, and as the place where we put the result.
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// This is fine because the output is always shorter than the input used
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// so far.
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codegen := w.codegen // cache
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// Copy the concatenated code sizes to codegen. Put a marker at the end.
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copy(codegen[0:numLiterals], w.literalEncoding.codeBits)
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copy(codegen[numLiterals:numLiterals+numOffsets], w.offsetEncoding.codeBits)
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codegen[numLiterals+numOffsets] = badCode
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size := codegen[0]
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count := 1
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outIndex := 0
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for inIndex := 1; size != badCode; inIndex++ {
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// INVARIANT: We have seen "count" copies of size that have not yet
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// had output generated for them.
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nextSize := codegen[inIndex]
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if nextSize == size {
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count++
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continue
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}
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// We need to generate codegen indicating "count" of size.
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if size != 0 {
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codegen[outIndex] = size
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outIndex++
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w.codegenFreq[size]++
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count--
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for count >= 3 {
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n := 6
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if n > count {
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n = count
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}
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codegen[outIndex] = 16
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outIndex++
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codegen[outIndex] = uint8(n - 3)
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outIndex++
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w.codegenFreq[16]++
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count -= n
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}
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} else {
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for count >= 11 {
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n := 138
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if n > count {
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n = count
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}
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codegen[outIndex] = 18
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outIndex++
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codegen[outIndex] = uint8(n - 11)
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outIndex++
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w.codegenFreq[18]++
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count -= n
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}
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if count >= 3 {
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// count >= 3 && count <= 10
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codegen[outIndex] = 17
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outIndex++
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codegen[outIndex] = uint8(count - 3)
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outIndex++
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w.codegenFreq[17]++
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count = 0
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}
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}
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count--
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for ; count >= 0; count-- {
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codegen[outIndex] = size
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outIndex++
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w.codegenFreq[size]++
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}
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// Set up invariant for next time through the loop.
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size = nextSize
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count = 1
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}
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// Marker indicating the end of the codegen.
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codegen[outIndex] = badCode
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}
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func (w *huffmanBitWriter) writeCode(code *huffmanEncoder, literal uint32) {
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if w.err != nil {
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return
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}
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w.writeBits(int32(code.code[literal]), int32(code.codeBits[literal]))
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}
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// Write the header of a dynamic Huffman block to the output stream.
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//
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// numLiterals The number of literals specified in codegen
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// numOffsets The number of offsets specified in codegen
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// numCodegens The number of codegens used in codegen
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func (w *huffmanBitWriter) writeDynamicHeader(numLiterals int, numOffsets int, numCodegens int, isEof bool) {
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if w.err != nil {
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return
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}
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| 291 |
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var firstBits int32 = 4
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| 292 |
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if isEof {
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firstBits = 5
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}
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w.writeBits(firstBits, 3)
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w.writeBits(int32(numLiterals-257), 5)
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w.writeBits(int32(numOffsets-1), 5)
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w.writeBits(int32(numCodegens-4), 4)
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for i := 0; i < numCodegens; i++ {
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value := w.codegenEncoding.codeBits[codegenOrder[i]]
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w.writeBits(int32(value), 3)
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}
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i := 0
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for {
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var codeWord int = int(w.codegen[i])
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i++
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if codeWord == badCode {
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break
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}
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// The low byte contains the actual code to generate.
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w.writeCode(w.codegenEncoding, uint32(codeWord))
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switch codeWord {
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case 16:
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w.writeBits(int32(w.codegen[i]), 2)
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i++
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break
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case 17:
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w.writeBits(int32(w.codegen[i]), 3)
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i++
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break
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case 18:
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w.writeBits(int32(w.codegen[i]), 7)
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i++
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break
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}
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}
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| 330 |
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}
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| 331 |
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func (w *huffmanBitWriter) writeStoredHeader(length int, isEof bool) {
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| 333 |
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if w.err != nil {
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| 334 |
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return
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}
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| 336 |
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var flag int32
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| 337 |
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if isEof {
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flag = 1
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| 339 |
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}
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w.writeBits(flag, 3)
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w.flush()
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| 342 |
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w.writeBits(int32(length), 16)
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w.writeBits(int32(^uint16(length)), 16)
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| 344 |
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}
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| 345 |
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| 346 |
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func (w *huffmanBitWriter) writeFixedHeader(isEof bool) {
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| 347 |
|
|
if w.err != nil {
|
| 348 |
|
|
return
|
| 349 |
|
|
}
|
| 350 |
|
|
// Indicate that we are a fixed Huffman block
|
| 351 |
|
|
var value int32 = 2
|
| 352 |
|
|
if isEof {
|
| 353 |
|
|
value = 3
|
| 354 |
|
|
}
|
| 355 |
|
|
w.writeBits(value, 3)
|
| 356 |
|
|
}
|
| 357 |
|
|
|
| 358 |
|
|
func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
|
| 359 |
|
|
if w.err != nil {
|
| 360 |
|
|
return
|
| 361 |
|
|
}
|
| 362 |
|
|
for i := range w.literalFreq {
|
| 363 |
|
|
w.literalFreq[i] = 0
|
| 364 |
|
|
}
|
| 365 |
|
|
for i := range w.offsetFreq {
|
| 366 |
|
|
w.offsetFreq[i] = 0
|
| 367 |
|
|
}
|
| 368 |
|
|
|
| 369 |
|
|
n := len(tokens)
|
| 370 |
|
|
tokens = tokens[0 : n+1]
|
| 371 |
|
|
tokens[n] = endBlockMarker
|
| 372 |
|
|
|
| 373 |
|
|
for _, t := range tokens {
|
| 374 |
|
|
switch t.typ() {
|
| 375 |
|
|
case literalType:
|
| 376 |
|
|
w.literalFreq[t.literal()]++
|
| 377 |
|
|
case matchType:
|
| 378 |
|
|
length := t.length()
|
| 379 |
|
|
offset := t.offset()
|
| 380 |
|
|
w.literalFreq[lengthCodesStart+lengthCode(length)]++
|
| 381 |
|
|
w.offsetFreq[offsetCode(offset)]++
|
| 382 |
|
|
}
|
| 383 |
|
|
}
|
| 384 |
|
|
|
| 385 |
|
|
// get the number of literals
|
| 386 |
|
|
numLiterals := len(w.literalFreq)
|
| 387 |
|
|
for w.literalFreq[numLiterals-1] == 0 {
|
| 388 |
|
|
numLiterals--
|
| 389 |
|
|
}
|
| 390 |
|
|
// get the number of offsets
|
| 391 |
|
|
numOffsets := len(w.offsetFreq)
|
| 392 |
|
|
for numOffsets > 0 && w.offsetFreq[numOffsets-1] == 0 {
|
| 393 |
|
|
numOffsets--
|
| 394 |
|
|
}
|
| 395 |
|
|
if numOffsets == 0 {
|
| 396 |
|
|
// We haven't found a single match. If we want to go with the dynamic encoding,
|
| 397 |
|
|
// we should count at least one offset to be sure that the offset huffman tree could be encoded.
|
| 398 |
|
|
w.offsetFreq[0] = 1
|
| 399 |
|
|
numOffsets = 1
|
| 400 |
|
|
}
|
| 401 |
|
|
|
| 402 |
|
|
w.literalEncoding.generate(w.literalFreq, 15)
|
| 403 |
|
|
w.offsetEncoding.generate(w.offsetFreq, 15)
|
| 404 |
|
|
|
| 405 |
|
|
storedBytes := 0
|
| 406 |
|
|
if input != nil {
|
| 407 |
|
|
storedBytes = len(input)
|
| 408 |
|
|
}
|
| 409 |
|
|
var extraBits int64
|
| 410 |
|
|
var storedSize int64 = math.MaxInt64
|
| 411 |
|
|
if storedBytes <= maxStoreBlockSize && input != nil {
|
| 412 |
|
|
storedSize = int64((storedBytes + 5) * 8)
|
| 413 |
|
|
// We only bother calculating the costs of the extra bits required by
|
| 414 |
|
|
// the length of offset fields (which will be the same for both fixed
|
| 415 |
|
|
// and dynamic encoding), if we need to compare those two encodings
|
| 416 |
|
|
// against stored encoding.
|
| 417 |
|
|
for lengthCode := lengthCodesStart + 8; lengthCode < numLiterals; lengthCode++ {
|
| 418 |
|
|
// First eight length codes have extra size = 0.
|
| 419 |
|
|
extraBits += int64(w.literalFreq[lengthCode]) * int64(lengthExtraBits[lengthCode-lengthCodesStart])
|
| 420 |
|
|
}
|
| 421 |
|
|
for offsetCode := 4; offsetCode < numOffsets; offsetCode++ {
|
| 422 |
|
|
// First four offset codes have extra size = 0.
|
| 423 |
|
|
extraBits += int64(w.offsetFreq[offsetCode]) * int64(offsetExtraBits[offsetCode])
|
| 424 |
|
|
}
|
| 425 |
|
|
}
|
| 426 |
|
|
|
| 427 |
|
|
// Figure out smallest code.
|
| 428 |
|
|
// Fixed Huffman baseline.
|
| 429 |
|
|
var size = int64(3) +
|
| 430 |
|
|
fixedLiteralEncoding.bitLength(w.literalFreq) +
|
| 431 |
|
|
fixedOffsetEncoding.bitLength(w.offsetFreq) +
|
| 432 |
|
|
extraBits
|
| 433 |
|
|
var literalEncoding = fixedLiteralEncoding
|
| 434 |
|
|
var offsetEncoding = fixedOffsetEncoding
|
| 435 |
|
|
|
| 436 |
|
|
// Dynamic Huffman?
|
| 437 |
|
|
var numCodegens int
|
| 438 |
|
|
|
| 439 |
|
|
// Generate codegen and codegenFrequencies, which indicates how to encode
|
| 440 |
|
|
// the literalEncoding and the offsetEncoding.
|
| 441 |
|
|
w.generateCodegen(numLiterals, numOffsets)
|
| 442 |
|
|
w.codegenEncoding.generate(w.codegenFreq, 7)
|
| 443 |
|
|
numCodegens = len(w.codegenFreq)
|
| 444 |
|
|
for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
|
| 445 |
|
|
numCodegens--
|
| 446 |
|
|
}
|
| 447 |
|
|
dynamicHeader := int64(3+5+5+4+(3*numCodegens)) +
|
| 448 |
|
|
w.codegenEncoding.bitLength(w.codegenFreq) +
|
| 449 |
|
|
int64(extraBits) +
|
| 450 |
|
|
int64(w.codegenFreq[16]*2) +
|
| 451 |
|
|
int64(w.codegenFreq[17]*3) +
|
| 452 |
|
|
int64(w.codegenFreq[18]*7)
|
| 453 |
|
|
dynamicSize := dynamicHeader +
|
| 454 |
|
|
w.literalEncoding.bitLength(w.literalFreq) +
|
| 455 |
|
|
w.offsetEncoding.bitLength(w.offsetFreq)
|
| 456 |
|
|
|
| 457 |
|
|
if dynamicSize < size {
|
| 458 |
|
|
size = dynamicSize
|
| 459 |
|
|
literalEncoding = w.literalEncoding
|
| 460 |
|
|
offsetEncoding = w.offsetEncoding
|
| 461 |
|
|
}
|
| 462 |
|
|
|
| 463 |
|
|
// Stored bytes?
|
| 464 |
|
|
if storedSize < size {
|
| 465 |
|
|
w.writeStoredHeader(storedBytes, eof)
|
| 466 |
|
|
w.writeBytes(input[0:storedBytes])
|
| 467 |
|
|
return
|
| 468 |
|
|
}
|
| 469 |
|
|
|
| 470 |
|
|
// Huffman.
|
| 471 |
|
|
if literalEncoding == fixedLiteralEncoding {
|
| 472 |
|
|
w.writeFixedHeader(eof)
|
| 473 |
|
|
} else {
|
| 474 |
|
|
w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
|
| 475 |
|
|
}
|
| 476 |
|
|
for _, t := range tokens {
|
| 477 |
|
|
switch t.typ() {
|
| 478 |
|
|
case literalType:
|
| 479 |
|
|
w.writeCode(literalEncoding, t.literal())
|
| 480 |
|
|
break
|
| 481 |
|
|
case matchType:
|
| 482 |
|
|
// Write the length
|
| 483 |
|
|
length := t.length()
|
| 484 |
|
|
lengthCode := lengthCode(length)
|
| 485 |
|
|
w.writeCode(literalEncoding, lengthCode+lengthCodesStart)
|
| 486 |
|
|
extraLengthBits := int32(lengthExtraBits[lengthCode])
|
| 487 |
|
|
if extraLengthBits > 0 {
|
| 488 |
|
|
extraLength := int32(length - lengthBase[lengthCode])
|
| 489 |
|
|
w.writeBits(extraLength, extraLengthBits)
|
| 490 |
|
|
}
|
| 491 |
|
|
// Write the offset
|
| 492 |
|
|
offset := t.offset()
|
| 493 |
|
|
offsetCode := offsetCode(offset)
|
| 494 |
|
|
w.writeCode(offsetEncoding, offsetCode)
|
| 495 |
|
|
extraOffsetBits := int32(offsetExtraBits[offsetCode])
|
| 496 |
|
|
if extraOffsetBits > 0 {
|
| 497 |
|
|
extraOffset := int32(offset - offsetBase[offsetCode])
|
| 498 |
|
|
w.writeBits(extraOffset, extraOffsetBits)
|
| 499 |
|
|
}
|
| 500 |
|
|
break
|
| 501 |
|
|
default:
|
| 502 |
|
|
panic("unknown token type: " + string(t))
|
| 503 |
|
|
}
|
| 504 |
|
|
}
|
| 505 |
|
|
}
|
