d063597e80
The package has multiple improvements and bug fixes. Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>
559 lines
16 KiB
Go
559 lines
16 KiB
Go
// 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 (
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"bytes"
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"fmt"
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"github.com/klauspost/compress"
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)
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const (
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bestLongTableBits = 22 // Bits used in the long match table
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bestLongTableSize = 1 << bestLongTableBits // Size of the table
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bestLongLen = 8 // Bytes used for table hash
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// Note: Increasing the short table bits or making the hash shorter
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// can actually lead to compression degradation since it will 'steal' more from the
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// long match table and match offsets are quite big.
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// This greatly depends on the type of input.
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bestShortTableBits = 18 // Bits used in the short match table
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bestShortTableSize = 1 << bestShortTableBits // Size of the table
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bestShortLen = 4 // Bytes used for table hash
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)
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type match struct {
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offset int32
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s int32
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length int32
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rep int32
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est int32
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}
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const highScore = 25000
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// estBits will estimate output bits from predefined tables.
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func (m *match) estBits(bitsPerByte int32) {
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mlc := mlCode(uint32(m.length - zstdMinMatch))
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var ofc uint8
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if m.rep < 0 {
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ofc = ofCode(uint32(m.s-m.offset) + 3)
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} else {
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ofc = ofCode(uint32(m.rep))
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}
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// Cost, excluding
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ofTT, mlTT := fsePredefEnc[tableOffsets].ct.symbolTT[ofc], fsePredefEnc[tableMatchLengths].ct.symbolTT[mlc]
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// Add cost of match encoding...
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m.est = int32(ofTT.outBits + mlTT.outBits)
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m.est += int32(ofTT.deltaNbBits>>16 + mlTT.deltaNbBits>>16)
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// Subtract savings compared to literal encoding...
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m.est -= (m.length * bitsPerByte) >> 10
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if m.est > 0 {
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// Unlikely gain..
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m.length = 0
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m.est = highScore
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}
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}
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// bestFastEncoder uses 2 tables, one for short matches (5 bytes) and one for long matches.
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// The long match table contains the previous entry with the same hash,
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// effectively making it a "chain" of length 2.
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// When we find a long match we choose between the two values and select the longest.
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// When we find a short match, after checking the long, we check if we can find a long at n+1
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// and that it is longer (lazy matching).
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type bestFastEncoder struct {
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fastBase
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table [bestShortTableSize]prevEntry
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longTable [bestLongTableSize]prevEntry
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dictTable []prevEntry
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dictLongTable []prevEntry
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}
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// Encode improves compression...
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func (e *bestFastEncoder) Encode(blk *blockEnc, src []byte) {
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const (
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// Input margin is the number of bytes we read (8)
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// and the maximum we will read ahead (2)
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inputMargin = 8 + 4
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minNonLiteralBlockSize = 16
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)
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// Protect against e.cur wraparound.
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for e.cur >= bufferReset {
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if len(e.hist) == 0 {
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for i := range e.table[:] {
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e.table[i] = prevEntry{}
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}
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for i := range e.longTable[:] {
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e.longTable[i] = prevEntry{}
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}
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e.cur = e.maxMatchOff
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break
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}
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// Shift down everything in the table that isn't already too far away.
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minOff := e.cur + int32(len(e.hist)) - e.maxMatchOff
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for i := range e.table[:] {
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v := e.table[i].offset
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v2 := e.table[i].prev
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if v < minOff {
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v = 0
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v2 = 0
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} else {
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v = v - e.cur + e.maxMatchOff
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if v2 < minOff {
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v2 = 0
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} else {
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v2 = v2 - e.cur + e.maxMatchOff
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}
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}
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e.table[i] = prevEntry{
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offset: v,
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prev: v2,
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}
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}
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for i := range e.longTable[:] {
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v := e.longTable[i].offset
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v2 := e.longTable[i].prev
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if v < minOff {
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v = 0
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v2 = 0
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} else {
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v = v - e.cur + e.maxMatchOff
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if v2 < minOff {
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v2 = 0
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} else {
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v2 = v2 - e.cur + e.maxMatchOff
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}
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}
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e.longTable[i] = prevEntry{
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offset: v,
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prev: v2,
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}
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}
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e.cur = e.maxMatchOff
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break
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}
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s := e.addBlock(src)
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blk.size = len(src)
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if len(src) < minNonLiteralBlockSize {
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blk.extraLits = len(src)
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blk.literals = blk.literals[:len(src)]
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copy(blk.literals, src)
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return
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}
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// Use this to estimate literal cost.
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// Scaled by 10 bits.
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bitsPerByte := int32((compress.ShannonEntropyBits(src) * 1024) / len(src))
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// Huffman can never go < 1 bit/byte
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if bitsPerByte < 1024 {
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bitsPerByte = 1024
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}
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// Override src
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src = e.hist
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sLimit := int32(len(src)) - inputMargin
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const kSearchStrength = 10
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// nextEmit is where in src the next emitLiteral should start from.
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nextEmit := s
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cv := load6432(src, s)
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// Relative offsets
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offset1 := int32(blk.recentOffsets[0])
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offset2 := int32(blk.recentOffsets[1])
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offset3 := int32(blk.recentOffsets[2])
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addLiterals := func(s *seq, until int32) {
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if until == nextEmit {
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return
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}
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blk.literals = append(blk.literals, src[nextEmit:until]...)
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s.litLen = uint32(until - nextEmit)
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}
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_ = addLiterals
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if debugEncoder {
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println("recent offsets:", blk.recentOffsets)
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}
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encodeLoop:
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for {
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// We allow the encoder to optionally turn off repeat offsets across blocks
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canRepeat := len(blk.sequences) > 2
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if debugAsserts && canRepeat && offset1 == 0 {
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panic("offset0 was 0")
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}
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bestOf := func(a, b match) match {
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if a.est+(a.s-b.s)*bitsPerByte>>10 < b.est+(b.s-a.s)*bitsPerByte>>10 {
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return a
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}
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return b
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}
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const goodEnough = 100
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nextHashL := hashLen(cv, bestLongTableBits, bestLongLen)
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nextHashS := hashLen(cv, bestShortTableBits, bestShortLen)
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candidateL := e.longTable[nextHashL]
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candidateS := e.table[nextHashS]
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matchAt := func(offset int32, s int32, first uint32, rep int32) match {
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if s-offset >= e.maxMatchOff || load3232(src, offset) != first {
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return match{s: s, est: highScore}
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}
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if debugAsserts {
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if !bytes.Equal(src[s:s+4], src[offset:offset+4]) {
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panic(fmt.Sprintf("first match mismatch: %v != %v, first: %08x", src[s:s+4], src[offset:offset+4], first))
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}
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}
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m := match{offset: offset, s: s, length: 4 + e.matchlen(s+4, offset+4, src), rep: rep}
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m.estBits(bitsPerByte)
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return m
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}
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best := bestOf(matchAt(candidateL.offset-e.cur, s, uint32(cv), -1), matchAt(candidateL.prev-e.cur, s, uint32(cv), -1))
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best = bestOf(best, matchAt(candidateS.offset-e.cur, s, uint32(cv), -1))
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best = bestOf(best, matchAt(candidateS.prev-e.cur, s, uint32(cv), -1))
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if canRepeat && best.length < goodEnough {
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cv32 := uint32(cv >> 8)
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spp := s + 1
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best = bestOf(best, matchAt(spp-offset1, spp, cv32, 1))
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best = bestOf(best, matchAt(spp-offset2, spp, cv32, 2))
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best = bestOf(best, matchAt(spp-offset3, spp, cv32, 3))
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if best.length > 0 {
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cv32 = uint32(cv >> 24)
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spp += 2
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best = bestOf(best, matchAt(spp-offset1, spp, cv32, 1))
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best = bestOf(best, matchAt(spp-offset2, spp, cv32, 2))
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best = bestOf(best, matchAt(spp-offset3, spp, cv32, 3))
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}
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}
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// Load next and check...
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e.longTable[nextHashL] = prevEntry{offset: s + e.cur, prev: candidateL.offset}
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e.table[nextHashS] = prevEntry{offset: s + e.cur, prev: candidateS.offset}
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// Look far ahead, unless we have a really long match already...
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if best.length < goodEnough {
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// No match found, move forward on input, no need to check forward...
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if best.length < 4 {
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s += 1 + (s-nextEmit)>>(kSearchStrength-1)
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if s >= sLimit {
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break encodeLoop
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}
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cv = load6432(src, s)
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continue
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}
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s++
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candidateS = e.table[hashLen(cv>>8, bestShortTableBits, bestShortLen)]
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cv = load6432(src, s)
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cv2 := load6432(src, s+1)
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candidateL = e.longTable[hashLen(cv, bestLongTableBits, bestLongLen)]
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candidateL2 := e.longTable[hashLen(cv2, bestLongTableBits, bestLongLen)]
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// Short at s+1
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best = bestOf(best, matchAt(candidateS.offset-e.cur, s, uint32(cv), -1))
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// Long at s+1, s+2
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best = bestOf(best, matchAt(candidateL.offset-e.cur, s, uint32(cv), -1))
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best = bestOf(best, matchAt(candidateL.prev-e.cur, s, uint32(cv), -1))
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best = bestOf(best, matchAt(candidateL2.offset-e.cur, s+1, uint32(cv2), -1))
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best = bestOf(best, matchAt(candidateL2.prev-e.cur, s+1, uint32(cv2), -1))
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if false {
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// Short at s+3.
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// Too often worse...
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best = bestOf(best, matchAt(e.table[hashLen(cv2>>8, bestShortTableBits, bestShortLen)].offset-e.cur, s+2, uint32(cv2>>8), -1))
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}
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// See if we can find a better match by checking where the current best ends.
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// Use that offset to see if we can find a better full match.
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if sAt := best.s + best.length; sAt < sLimit {
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nextHashL := hashLen(load6432(src, sAt), bestLongTableBits, bestLongLen)
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candidateEnd := e.longTable[nextHashL]
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if pos := candidateEnd.offset - e.cur - best.length; pos >= 0 {
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bestEnd := bestOf(best, matchAt(pos, best.s, load3232(src, best.s), -1))
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if pos := candidateEnd.prev - e.cur - best.length; pos >= 0 {
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bestEnd = bestOf(bestEnd, matchAt(pos, best.s, load3232(src, best.s), -1))
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}
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best = bestEnd
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}
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}
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}
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if debugAsserts {
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if !bytes.Equal(src[best.s:best.s+best.length], src[best.offset:best.offset+best.length]) {
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panic(fmt.Sprintf("match mismatch: %v != %v", src[best.s:best.s+best.length], src[best.offset:best.offset+best.length]))
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}
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}
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// We have a match, we can store the forward value
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if best.rep > 0 {
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s = best.s
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var seq seq
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seq.matchLen = uint32(best.length - zstdMinMatch)
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// We might be able to match backwards.
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// Extend as long as we can.
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start := best.s
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// We end the search early, so we don't risk 0 literals
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// and have to do special offset treatment.
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startLimit := nextEmit + 1
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tMin := s - e.maxMatchOff
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if tMin < 0 {
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tMin = 0
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}
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repIndex := best.offset
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for repIndex > tMin && start > startLimit && src[repIndex-1] == src[start-1] && seq.matchLen < maxMatchLength-zstdMinMatch-1 {
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repIndex--
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start--
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seq.matchLen++
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}
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addLiterals(&seq, start)
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// rep 0
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seq.offset = uint32(best.rep)
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if debugSequences {
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println("repeat sequence", seq, "next s:", s)
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}
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blk.sequences = append(blk.sequences, seq)
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// Index match start+1 (long) -> s - 1
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index0 := s
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s = best.s + best.length
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nextEmit = s
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if s >= sLimit {
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if debugEncoder {
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println("repeat ended", s, best.length)
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}
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break encodeLoop
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}
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// Index skipped...
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off := index0 + e.cur
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for index0 < s-1 {
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cv0 := load6432(src, index0)
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h0 := hashLen(cv0, bestLongTableBits, bestLongLen)
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h1 := hashLen(cv0, bestShortTableBits, bestShortLen)
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e.longTable[h0] = prevEntry{offset: off, prev: e.longTable[h0].offset}
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e.table[h1] = prevEntry{offset: off, prev: e.table[h1].offset}
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off++
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index0++
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}
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switch best.rep {
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case 2:
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offset1, offset2 = offset2, offset1
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case 3:
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offset1, offset2, offset3 = offset3, offset1, offset2
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}
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cv = load6432(src, s)
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continue
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}
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// A 4-byte match has been found. Update recent offsets.
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// We'll later see if more than 4 bytes.
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s = best.s
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t := best.offset
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offset1, offset2, offset3 = s-t, offset1, offset2
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if debugAsserts && s <= t {
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panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
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}
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if debugAsserts && int(offset1) > len(src) {
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panic("invalid offset")
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}
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// Extend the n-byte match as long as possible.
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l := best.length
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// Extend backwards
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tMin := s - e.maxMatchOff
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if tMin < 0 {
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tMin = 0
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}
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for t > tMin && s > nextEmit && src[t-1] == src[s-1] && l < maxMatchLength {
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s--
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t--
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l++
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}
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// Write our sequence
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var seq seq
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seq.litLen = uint32(s - nextEmit)
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seq.matchLen = uint32(l - zstdMinMatch)
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if seq.litLen > 0 {
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blk.literals = append(blk.literals, src[nextEmit:s]...)
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}
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seq.offset = uint32(s-t) + 3
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s += l
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if debugSequences {
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println("sequence", seq, "next s:", s)
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}
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blk.sequences = append(blk.sequences, seq)
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nextEmit = s
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if s >= sLimit {
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break encodeLoop
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}
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// Index match start+1 (long) -> s - 1
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index0 := s - l + 1
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// every entry
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for index0 < s-1 {
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cv0 := load6432(src, index0)
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h0 := hashLen(cv0, bestLongTableBits, bestLongLen)
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h1 := hashLen(cv0, bestShortTableBits, bestShortLen)
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off := index0 + e.cur
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e.longTable[h0] = prevEntry{offset: off, prev: e.longTable[h0].offset}
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e.table[h1] = prevEntry{offset: off, prev: e.table[h1].offset}
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index0++
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}
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cv = load6432(src, s)
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if !canRepeat {
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continue
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}
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// Check offset 2
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for {
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o2 := s - offset2
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if load3232(src, o2) != uint32(cv) {
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// Do regular search
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break
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}
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// Store this, since we have it.
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nextHashS := hashLen(cv, bestShortTableBits, bestShortLen)
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nextHashL := hashLen(cv, bestLongTableBits, bestLongLen)
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// We have at least 4 byte match.
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// No need to check backwards. We come straight from a match
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l := 4 + e.matchlen(s+4, o2+4, src)
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e.longTable[nextHashL] = prevEntry{offset: s + e.cur, prev: e.longTable[nextHashL].offset}
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e.table[nextHashS] = prevEntry{offset: s + e.cur, prev: e.table[nextHashS].offset}
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seq.matchLen = uint32(l) - zstdMinMatch
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seq.litLen = 0
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// Since litlen is always 0, this is offset 1.
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seq.offset = 1
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s += l
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nextEmit = s
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if debugSequences {
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println("sequence", seq, "next s:", s)
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}
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blk.sequences = append(blk.sequences, seq)
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// Swap offset 1 and 2.
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offset1, offset2 = offset2, offset1
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if s >= sLimit {
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// Finished
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break encodeLoop
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}
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cv = load6432(src, s)
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}
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}
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if int(nextEmit) < len(src) {
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blk.literals = append(blk.literals, src[nextEmit:]...)
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blk.extraLits = len(src) - int(nextEmit)
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}
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blk.recentOffsets[0] = uint32(offset1)
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blk.recentOffsets[1] = uint32(offset2)
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blk.recentOffsets[2] = uint32(offset3)
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if debugEncoder {
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println("returning, recent offsets:", blk.recentOffsets, "extra literals:", blk.extraLits)
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}
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}
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// EncodeNoHist will encode a block with no history and no following blocks.
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// Most notable difference is that src will not be copied for history and
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// we do not need to check for max match length.
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func (e *bestFastEncoder) EncodeNoHist(blk *blockEnc, src []byte) {
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e.ensureHist(len(src))
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e.Encode(blk, src)
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}
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// Reset will reset and set a dictionary if not nil
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func (e *bestFastEncoder) Reset(d *dict, singleBlock bool) {
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e.resetBase(d, singleBlock)
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if d == nil {
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return
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}
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// Init or copy dict table
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if len(e.dictTable) != len(e.table) || d.id != e.lastDictID {
|
|
if len(e.dictTable) != len(e.table) {
|
|
e.dictTable = make([]prevEntry, len(e.table))
|
|
}
|
|
end := int32(len(d.content)) - 8 + e.maxMatchOff
|
|
for i := e.maxMatchOff; i < end; i += 4 {
|
|
const hashLog = bestShortTableBits
|
|
|
|
cv := load6432(d.content, i-e.maxMatchOff)
|
|
nextHash := hashLen(cv, hashLog, bestShortLen) // 0 -> 4
|
|
nextHash1 := hashLen(cv>>8, hashLog, bestShortLen) // 1 -> 5
|
|
nextHash2 := hashLen(cv>>16, hashLog, bestShortLen) // 2 -> 6
|
|
nextHash3 := hashLen(cv>>24, hashLog, bestShortLen) // 3 -> 7
|
|
e.dictTable[nextHash] = prevEntry{
|
|
prev: e.dictTable[nextHash].offset,
|
|
offset: i,
|
|
}
|
|
e.dictTable[nextHash1] = prevEntry{
|
|
prev: e.dictTable[nextHash1].offset,
|
|
offset: i + 1,
|
|
}
|
|
e.dictTable[nextHash2] = prevEntry{
|
|
prev: e.dictTable[nextHash2].offset,
|
|
offset: i + 2,
|
|
}
|
|
e.dictTable[nextHash3] = prevEntry{
|
|
prev: e.dictTable[nextHash3].offset,
|
|
offset: i + 3,
|
|
}
|
|
}
|
|
e.lastDictID = d.id
|
|
}
|
|
|
|
// Init or copy dict table
|
|
if len(e.dictLongTable) != len(e.longTable) || d.id != e.lastDictID {
|
|
if len(e.dictLongTable) != len(e.longTable) {
|
|
e.dictLongTable = make([]prevEntry, len(e.longTable))
|
|
}
|
|
if len(d.content) >= 8 {
|
|
cv := load6432(d.content, 0)
|
|
h := hashLen(cv, bestLongTableBits, bestLongLen)
|
|
e.dictLongTable[h] = prevEntry{
|
|
offset: e.maxMatchOff,
|
|
prev: e.dictLongTable[h].offset,
|
|
}
|
|
|
|
end := int32(len(d.content)) - 8 + e.maxMatchOff
|
|
off := 8 // First to read
|
|
for i := e.maxMatchOff + 1; i < end; i++ {
|
|
cv = cv>>8 | (uint64(d.content[off]) << 56)
|
|
h := hashLen(cv, bestLongTableBits, bestLongLen)
|
|
e.dictLongTable[h] = prevEntry{
|
|
offset: i,
|
|
prev: e.dictLongTable[h].offset,
|
|
}
|
|
off++
|
|
}
|
|
}
|
|
e.lastDictID = d.id
|
|
}
|
|
// Reset table to initial state
|
|
copy(e.longTable[:], e.dictLongTable)
|
|
|
|
e.cur = e.maxMatchOff
|
|
// Reset table to initial state
|
|
copy(e.table[:], e.dictTable)
|
|
}
|