mirror of
https://github.com/autc04/Retro68.git
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518 lines
13 KiB
Go
518 lines
13 KiB
Go
// 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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)
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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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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 (w *huffmanBitWriter) reset(writer io.Writer) {
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w.w = writer
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w.bits, w.nbits, w.nbytes, w.err = 0, 0, 0, nil
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w.bytes = [64]byte{}
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for i := range w.codegen {
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w.codegen[i] = 0
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}
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for _, s := range [...][]int32{w.literalFreq, w.offsetFreq, w.codegenFreq} {
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for i := range s {
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s[i] = 0
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}
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}
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for _, enc := range [...]*huffmanEncoder{
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w.literalEncoding,
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w.offsetEncoding,
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w.codegenEncoding} {
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for i := range enc.code {
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enc.code[i] = 0
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}
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for i := range enc.codeBits {
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enc.codeBits[i] = 0
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}
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}
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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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var firstBits int32 = 4
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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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}
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func (w *huffmanBitWriter) writeStoredHeader(length int, isEof bool) {
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if w.err != nil {
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return
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}
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var flag int32
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if isEof {
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flag = 1
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}
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w.writeBits(flag, 3)
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w.flush()
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w.writeBits(int32(length), 16)
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w.writeBits(int32(^uint16(length)), 16)
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}
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func (w *huffmanBitWriter) writeFixedHeader(isEof bool) {
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if w.err != nil {
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return
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}
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// Indicate that we are a fixed Huffman block
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var value int32 = 2
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if isEof {
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value = 3
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}
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w.writeBits(value, 3)
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}
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func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
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if w.err != nil {
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return
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}
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for i := range w.literalFreq {
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w.literalFreq[i] = 0
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}
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for i := range w.offsetFreq {
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w.offsetFreq[i] = 0
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}
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n := len(tokens)
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tokens = tokens[0 : n+1]
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tokens[n] = endBlockMarker
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for _, t := range tokens {
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switch t.typ() {
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case literalType:
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w.literalFreq[t.literal()]++
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case matchType:
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length := t.length()
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offset := t.offset()
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w.literalFreq[lengthCodesStart+lengthCode(length)]++
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w.offsetFreq[offsetCode(offset)]++
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}
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}
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// get the number of literals
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numLiterals := len(w.literalFreq)
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for w.literalFreq[numLiterals-1] == 0 {
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numLiterals--
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}
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// get the number of offsets
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numOffsets := len(w.offsetFreq)
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for numOffsets > 0 && w.offsetFreq[numOffsets-1] == 0 {
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numOffsets--
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}
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if numOffsets == 0 {
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// We haven't found a single match. If we want to go with the dynamic encoding,
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// we should count at least one offset to be sure that the offset huffman tree could be encoded.
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w.offsetFreq[0] = 1
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numOffsets = 1
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}
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w.literalEncoding.generate(w.literalFreq, 15)
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w.offsetEncoding.generate(w.offsetFreq, 15)
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storedBytes := 0
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if input != nil {
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storedBytes = len(input)
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}
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var extraBits int64
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var storedSize int64 = math.MaxInt64
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if storedBytes <= maxStoreBlockSize && input != nil {
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storedSize = int64((storedBytes + 5) * 8)
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// We only bother calculating the costs of the extra bits required by
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// the length of offset fields (which will be the same for both fixed
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// and dynamic encoding), if we need to compare those two encodings
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// against stored encoding.
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for lengthCode := lengthCodesStart + 8; lengthCode < numLiterals; lengthCode++ {
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// First eight length codes have extra size = 0.
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extraBits += int64(w.literalFreq[lengthCode]) * int64(lengthExtraBits[lengthCode-lengthCodesStart])
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}
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for offsetCode := 4; offsetCode < numOffsets; offsetCode++ {
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// First four offset codes have extra size = 0.
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extraBits += int64(w.offsetFreq[offsetCode]) * int64(offsetExtraBits[offsetCode])
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}
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}
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// Figure out smallest code.
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// Fixed Huffman baseline.
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var size = int64(3) +
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fixedLiteralEncoding.bitLength(w.literalFreq) +
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fixedOffsetEncoding.bitLength(w.offsetFreq) +
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extraBits
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var literalEncoding = fixedLiteralEncoding
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var offsetEncoding = fixedOffsetEncoding
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// Dynamic Huffman?
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var numCodegens int
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// Generate codegen and codegenFrequencies, which indicates how to encode
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// the literalEncoding and the offsetEncoding.
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w.generateCodegen(numLiterals, numOffsets)
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w.codegenEncoding.generate(w.codegenFreq, 7)
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numCodegens = len(w.codegenFreq)
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for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
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numCodegens--
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}
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dynamicHeader := int64(3+5+5+4+(3*numCodegens)) +
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w.codegenEncoding.bitLength(w.codegenFreq) +
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int64(extraBits) +
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int64(w.codegenFreq[16]*2) +
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int64(w.codegenFreq[17]*3) +
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int64(w.codegenFreq[18]*7)
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dynamicSize := dynamicHeader +
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w.literalEncoding.bitLength(w.literalFreq) +
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w.offsetEncoding.bitLength(w.offsetFreq)
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if dynamicSize < size {
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size = dynamicSize
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literalEncoding = w.literalEncoding
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offsetEncoding = w.offsetEncoding
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}
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// Stored bytes?
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if storedSize < size {
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w.writeStoredHeader(storedBytes, eof)
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w.writeBytes(input[0:storedBytes])
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return
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}
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// Huffman.
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if literalEncoding == fixedLiteralEncoding {
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w.writeFixedHeader(eof)
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} else {
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w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
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}
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for _, t := range tokens {
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switch t.typ() {
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case literalType:
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w.writeCode(literalEncoding, t.literal())
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break
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case matchType:
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// Write the length
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length := t.length()
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lengthCode := lengthCode(length)
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w.writeCode(literalEncoding, lengthCode+lengthCodesStart)
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extraLengthBits := int32(lengthExtraBits[lengthCode])
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if extraLengthBits > 0 {
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extraLength := int32(length - lengthBase[lengthCode])
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w.writeBits(extraLength, extraLengthBits)
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}
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// Write the offset
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offset := t.offset()
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offsetCode := offsetCode(offset)
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w.writeCode(offsetEncoding, offsetCode)
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extraOffsetBits := int32(offsetExtraBits[offsetCode])
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if extraOffsetBits > 0 {
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extraOffset := int32(offset - offsetBase[offsetCode])
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w.writeBits(extraOffset, extraOffsetBits)
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}
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break
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default:
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panic("unknown token type: " + string(t))
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}
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}
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}
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