368 lines
10 KiB
Go
368 lines
10 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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"bytes"
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"encoding/binary"
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"fmt"
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"io"
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"math"
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)
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const (
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// 2 bits: type 0 = literal 1=EOF 2=Match 3=Unused
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// 8 bits: xlength = length - MIN_MATCH_LENGTH
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// 22 bits xoffset = offset - MIN_OFFSET_SIZE, or literal
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lengthShift = 22
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offsetMask = 1<<lengthShift - 1
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typeMask = 3 << 30
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literalType = 0 << 30
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matchType = 1 << 30
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)
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// The length code for length X (MIN_MATCH_LENGTH <= X <= MAX_MATCH_LENGTH)
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// is lengthCodes[length - MIN_MATCH_LENGTH]
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var lengthCodes = [256]uint8{
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0, 1, 2, 3, 4, 5, 6, 7, 8, 8,
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9, 9, 10, 10, 11, 11, 12, 12, 12, 12,
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13, 13, 13, 13, 14, 14, 14, 14, 15, 15,
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15, 15, 16, 16, 16, 16, 16, 16, 16, 16,
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17, 17, 17, 17, 17, 17, 17, 17, 18, 18,
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18, 18, 18, 18, 18, 18, 19, 19, 19, 19,
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19, 19, 19, 19, 20, 20, 20, 20, 20, 20,
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20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
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21, 21, 21, 21, 21, 21, 21, 21, 21, 21,
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21, 21, 21, 21, 21, 21, 22, 22, 22, 22,
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22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
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22, 22, 23, 23, 23, 23, 23, 23, 23, 23,
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23, 23, 23, 23, 23, 23, 23, 23, 24, 24,
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24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
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24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
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24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
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25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
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25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
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25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
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25, 25, 26, 26, 26, 26, 26, 26, 26, 26,
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26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
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26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
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26, 26, 26, 26, 27, 27, 27, 27, 27, 27,
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27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
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27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
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27, 27, 27, 27, 27, 28,
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}
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// lengthCodes1 is length codes, but starting at 1.
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var lengthCodes1 = [256]uint8{
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1, 2, 3, 4, 5, 6, 7, 8, 9, 9,
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10, 10, 11, 11, 12, 12, 13, 13, 13, 13,
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14, 14, 14, 14, 15, 15, 15, 15, 16, 16,
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16, 16, 17, 17, 17, 17, 17, 17, 17, 17,
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18, 18, 18, 18, 18, 18, 18, 18, 19, 19,
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19, 19, 19, 19, 19, 19, 20, 20, 20, 20,
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20, 20, 20, 20, 21, 21, 21, 21, 21, 21,
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21, 21, 21, 21, 21, 21, 21, 21, 21, 21,
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22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
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22, 22, 22, 22, 22, 22, 23, 23, 23, 23,
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23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
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23, 23, 24, 24, 24, 24, 24, 24, 24, 24,
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24, 24, 24, 24, 24, 24, 24, 24, 25, 25,
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25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
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25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
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25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
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26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
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26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
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26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
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26, 26, 27, 27, 27, 27, 27, 27, 27, 27,
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27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
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27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
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27, 27, 27, 27, 28, 28, 28, 28, 28, 28,
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28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
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28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
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28, 28, 28, 28, 28, 29,
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}
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var offsetCodes = [256]uint32{
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0, 1, 2, 3, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7,
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8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9,
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10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
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11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
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12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
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12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
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13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
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13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
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14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
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14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
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14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
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14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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}
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// offsetCodes14 are offsetCodes, but with 14 added.
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var offsetCodes14 = [256]uint32{
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14, 15, 16, 17, 18, 18, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21,
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22, 22, 22, 22, 22, 22, 22, 22, 23, 23, 23, 23, 23, 23, 23, 23,
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24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
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25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
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26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
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26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
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27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
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27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
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28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
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28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
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28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
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28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
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29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
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29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
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29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
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29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
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}
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type token uint32
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type tokens struct {
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nLits int
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extraHist [32]uint16 // codes 256->maxnumlit
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offHist [32]uint16 // offset codes
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litHist [256]uint16 // codes 0->255
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n uint16 // Must be able to contain maxStoreBlockSize
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tokens [maxStoreBlockSize + 1]token
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}
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func (t *tokens) Reset() {
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if t.n == 0 {
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return
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}
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t.n = 0
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t.nLits = 0
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for i := range t.litHist[:] {
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t.litHist[i] = 0
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}
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for i := range t.extraHist[:] {
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t.extraHist[i] = 0
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}
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for i := range t.offHist[:] {
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t.offHist[i] = 0
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}
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}
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func (t *tokens) Fill() {
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if t.n == 0 {
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return
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}
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for i, v := range t.litHist[:] {
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if v == 0 {
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t.litHist[i] = 1
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t.nLits++
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}
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}
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for i, v := range t.extraHist[:literalCount-256] {
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if v == 0 {
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t.nLits++
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t.extraHist[i] = 1
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}
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}
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for i, v := range t.offHist[:offsetCodeCount] {
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if v == 0 {
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t.offHist[i] = 1
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}
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}
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}
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func indexTokens(in []token) tokens {
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var t tokens
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t.indexTokens(in)
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return t
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}
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func (t *tokens) indexTokens(in []token) {
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t.Reset()
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for _, tok := range in {
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if tok < matchType {
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t.tokens[t.n] = tok
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t.litHist[tok]++
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t.n++
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continue
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}
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t.AddMatch(uint32(tok.length()), tok.offset())
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}
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}
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// emitLiteral writes a literal chunk and returns the number of bytes written.
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func emitLiteral(dst *tokens, lit []byte) {
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ol := int(dst.n)
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for i, v := range lit {
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dst.tokens[(i+ol)&maxStoreBlockSize] = token(v)
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dst.litHist[v]++
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}
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dst.n += uint16(len(lit))
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dst.nLits += len(lit)
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}
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func (t *tokens) AddLiteral(lit byte) {
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t.tokens[t.n] = token(lit)
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t.litHist[lit]++
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t.n++
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t.nLits++
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}
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// EstimatedBits will return an minimum size estimated by an *optimal*
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// compression of the block.
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// The size of the block
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func (t *tokens) EstimatedBits() int {
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shannon := float64(0)
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bits := int(0)
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nMatches := 0
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if t.nLits > 0 {
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invTotal := 1.0 / float64(t.nLits)
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for _, v := range t.litHist[:] {
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if v > 0 {
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n := float64(v)
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shannon += math.Ceil(-math.Log2(n*invTotal) * n)
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}
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}
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// Just add 15 for EOB
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shannon += 15
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for _, v := range t.extraHist[1 : literalCount-256] {
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if v > 0 {
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n := float64(v)
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shannon += math.Ceil(-math.Log2(n*invTotal) * n)
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bits += int(lengthExtraBits[v&31]) * int(v)
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nMatches += int(v)
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}
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}
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}
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if nMatches > 0 {
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invTotal := 1.0 / float64(nMatches)
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for _, v := range t.offHist[:offsetCodeCount] {
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if v > 0 {
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n := float64(v)
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shannon += math.Ceil(-math.Log2(n*invTotal) * n)
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bits += int(offsetExtraBits[v&31]) * int(n)
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}
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}
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}
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return int(shannon) + bits
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}
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// AddMatch adds a match to the tokens.
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// This function is very sensitive to inlining and right on the border.
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func (t *tokens) AddMatch(xlength uint32, xoffset uint32) {
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if debugDecode {
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if xlength >= maxMatchLength+baseMatchLength {
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panic(fmt.Errorf("invalid length: %v", xlength))
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}
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if xoffset >= maxMatchOffset+baseMatchOffset {
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panic(fmt.Errorf("invalid offset: %v", xoffset))
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}
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}
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t.nLits++
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lengthCode := lengthCodes1[uint8(xlength)] & 31
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t.tokens[t.n] = token(matchType | xlength<<lengthShift | xoffset)
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t.extraHist[lengthCode]++
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t.offHist[offsetCode(xoffset)&31]++
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t.n++
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}
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// AddMatchLong adds a match to the tokens, potentially longer than max match length.
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// Length should NOT have the base subtracted, only offset should.
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func (t *tokens) AddMatchLong(xlength int32, xoffset uint32) {
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if debugDecode {
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if xoffset >= maxMatchOffset+baseMatchOffset {
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panic(fmt.Errorf("invalid offset: %v", xoffset))
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}
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}
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oc := offsetCode(xoffset) & 31
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for xlength > 0 {
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xl := xlength
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if xl > 258 {
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// We need to have at least baseMatchLength left over for next loop.
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xl = 258 - baseMatchLength
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}
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xlength -= xl
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xl -= 3
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t.nLits++
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lengthCode := lengthCodes1[uint8(xl)] & 31
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t.tokens[t.n] = token(matchType | uint32(xl)<<lengthShift | xoffset)
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t.extraHist[lengthCode]++
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t.offHist[oc]++
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t.n++
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}
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}
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func (t *tokens) AddEOB() {
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t.tokens[t.n] = token(endBlockMarker)
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t.extraHist[0]++
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t.n++
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}
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func (t *tokens) Slice() []token {
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return t.tokens[:t.n]
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}
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// VarInt returns the tokens as varint encoded bytes.
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func (t *tokens) VarInt() []byte {
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var b = make([]byte, binary.MaxVarintLen32*int(t.n))
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var off int
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for _, v := range t.tokens[:t.n] {
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off += binary.PutUvarint(b[off:], uint64(v))
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}
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return b[:off]
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}
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// FromVarInt restores t to the varint encoded tokens provided.
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// Any data in t is removed.
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func (t *tokens) FromVarInt(b []byte) error {
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var buf = bytes.NewReader(b)
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var toks []token
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for {
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r, err := binary.ReadUvarint(buf)
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if err == io.EOF {
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break
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}
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if err != nil {
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return err
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}
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toks = append(toks, token(r))
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}
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t.indexTokens(toks)
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return nil
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}
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// Returns the type of a token
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func (t token) typ() uint32 { return uint32(t) & typeMask }
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// Returns the literal of a literal token
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func (t token) literal() uint8 { return uint8(t) }
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// Returns the extra offset of a match token
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func (t token) offset() uint32 { return uint32(t) & offsetMask }
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func (t token) length() uint8 { return uint8(t >> lengthShift) }
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// The code is never more than 8 bits, but is returned as uint32 for convenience.
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func lengthCode(len uint8) uint32 { return uint32(lengthCodes[len]) }
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// Returns the offset code corresponding to a specific offset
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func offsetCode(off uint32) uint32 {
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if false {
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if off < uint32(len(offsetCodes)) {
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return offsetCodes[off&255]
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} else if off>>7 < uint32(len(offsetCodes)) {
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return offsetCodes[(off>>7)&255] + 14
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} else {
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return offsetCodes[(off>>14)&255] + 28
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}
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}
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if off < uint32(len(offsetCodes)) {
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return offsetCodes[uint8(off)]
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}
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return offsetCodes14[uint8(off>>7)]
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}
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