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115 lines
3.2 KiB
115 lines
3.2 KiB
// Copyright 2019+ Klaus Post. All rights reserved.
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// License information can be found in the LICENSE file.
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// Based on work by Yann Collet, released under BSD License.
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package zstd
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import "math/bits"
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type seqCoders struct {
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llEnc, ofEnc, mlEnc *fseEncoder
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llPrev, ofPrev, mlPrev *fseEncoder
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}
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// swap coders with another (block).
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func (s *seqCoders) swap(other *seqCoders) {
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*s, *other = *other, *s
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}
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// setPrev will update the previous encoders to the actually used ones
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// and make sure a fresh one is in the main slot.
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func (s *seqCoders) setPrev(ll, ml, of *fseEncoder) {
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compareSwap := func(used *fseEncoder, current, prev **fseEncoder) {
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// We used the new one, more current to history and reuse the previous history
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if *current == used {
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*prev, *current = *current, *prev
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c := *current
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p := *prev
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c.reUsed = false
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p.reUsed = true
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return
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}
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if used == *prev {
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return
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}
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// Ensure we cannot reuse by accident
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prevEnc := *prev
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prevEnc.symbolLen = 0
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return
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}
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compareSwap(ll, &s.llEnc, &s.llPrev)
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compareSwap(ml, &s.mlEnc, &s.mlPrev)
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compareSwap(of, &s.ofEnc, &s.ofPrev)
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}
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func highBit(val uint32) (n uint32) {
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return uint32(bits.Len32(val) - 1)
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}
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var llCodeTable = [64]byte{0, 1, 2, 3, 4, 5, 6, 7,
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8, 9, 10, 11, 12, 13, 14, 15,
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16, 16, 17, 17, 18, 18, 19, 19,
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20, 20, 20, 20, 21, 21, 21, 21,
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22, 22, 22, 22, 22, 22, 22, 22,
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23, 23, 23, 23, 23, 23, 23, 23,
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24, 24, 24, 24, 24, 24, 24, 24,
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24, 24, 24, 24, 24, 24, 24, 24}
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// Up to 6 bits
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const maxLLCode = 35
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// llBitsTable translates from ll code to number of bits.
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var llBitsTable = [maxLLCode + 1]byte{
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0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0,
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1, 1, 1, 1, 2, 2, 3, 3,
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4, 6, 7, 8, 9, 10, 11, 12,
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13, 14, 15, 16}
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// llCode returns the code that represents the literal length requested.
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func llCode(litLength uint32) uint8 {
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const llDeltaCode = 19
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if litLength <= 63 {
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// Compiler insists on bounds check (Go 1.12)
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return llCodeTable[litLength&63]
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}
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return uint8(highBit(litLength)) + llDeltaCode
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}
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var mlCodeTable = [128]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
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16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
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32, 32, 33, 33, 34, 34, 35, 35, 36, 36, 36, 36, 37, 37, 37, 37,
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38, 38, 38, 38, 38, 38, 38, 38, 39, 39, 39, 39, 39, 39, 39, 39,
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40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
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41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
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42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
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42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42}
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// Up to 6 bits
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const maxMLCode = 52
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// mlBitsTable translates from ml code to number of bits.
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var mlBitsTable = [maxMLCode + 1]byte{
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0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0,
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1, 1, 1, 1, 2, 2, 3, 3,
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4, 4, 5, 7, 8, 9, 10, 11,
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12, 13, 14, 15, 16}
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// note : mlBase = matchLength - MINMATCH;
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// because it's the format it's stored in seqStore->sequences
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func mlCode(mlBase uint32) uint8 {
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const mlDeltaCode = 36
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if mlBase <= 127 {
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// Compiler insists on bounds check (Go 1.12)
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return mlCodeTable[mlBase&127]
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}
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return uint8(highBit(mlBase)) + mlDeltaCode
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}
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func ofCode(offset uint32) uint8 {
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// A valid offset will always be > 0.
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return uint8(bits.Len32(offset) - 1)
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}
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