mirror of https://github.com/tidwall/tile38.git
714 lines
19 KiB
Go
714 lines
19 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 "fmt"
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const (
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dFastLongTableBits = 17 // Bits used in the long match table
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dFastLongTableSize = 1 << dFastLongTableBits // Size of the table
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dFastLongTableMask = dFastLongTableSize - 1 // Mask for table indices. Redundant, but can eliminate bounds checks.
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dFastShortTableBits = tableBits // Bits used in the short match table
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dFastShortTableSize = 1 << dFastShortTableBits // Size of the table
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dFastShortTableMask = dFastShortTableSize - 1 // Mask for table indices. Redundant, but can eliminate bounds checks.
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)
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type doubleFastEncoder struct {
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fastEncoder
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longTable [dFastLongTableSize]tableEntry
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dictLongTable []tableEntry
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}
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// Encode mimmics functionality in zstd_dfast.c
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func (e *doubleFastEncoder) 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 + 2
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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] = tableEntry{}
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}
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for i := range e.longTable[:] {
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e.longTable[i] = tableEntry{}
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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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if v < minOff {
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v = 0
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} else {
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v = v - e.cur + e.maxMatchOff
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}
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e.table[i].offset = v
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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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if v < minOff {
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v = 0
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} else {
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v = v - e.cur + e.maxMatchOff
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}
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e.longTable[i].offset = v
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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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// Override src
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src = e.hist
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sLimit := int32(len(src)) - inputMargin
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// stepSize is the number of bytes to skip on every main loop iteration.
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// It should be >= 1.
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const stepSize = 1
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const kSearchStrength = 8
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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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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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if debug {
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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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var t int32
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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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for {
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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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nextHashS := hash5(cv, dFastShortTableBits)
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nextHashL := hash8(cv, dFastLongTableBits)
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candidateL := e.longTable[nextHashL]
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candidateS := e.table[nextHashS]
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const repOff = 1
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repIndex := s - offset1 + repOff
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entry := tableEntry{offset: s + e.cur, val: uint32(cv)}
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e.longTable[nextHashL] = entry
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e.table[nextHashS] = entry
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if canRepeat {
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if repIndex >= 0 && load3232(src, repIndex) == uint32(cv>>(repOff*8)) {
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// Consider history as well.
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var seq seq
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lenght := 4 + e.matchlen(s+4+repOff, repIndex+4, src)
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seq.matchLen = uint32(lenght - 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 := s + repOff
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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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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 = 1
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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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s += lenght + repOff
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nextEmit = s
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if s >= sLimit {
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if debug {
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println("repeat ended", s, lenght)
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}
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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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}
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// Find the offsets of our two matches.
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coffsetL := s - (candidateL.offset - e.cur)
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coffsetS := s - (candidateS.offset - e.cur)
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// Check if we have a long match.
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if coffsetL < e.maxMatchOff && uint32(cv) == candidateL.val {
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// Found a long match, likely at least 8 bytes.
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// Reference encoder checks all 8 bytes, we only check 4,
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// but the likelihood of both the first 4 bytes and the hash matching should be enough.
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t = candidateL.offset - e.cur
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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 && s-t > e.maxMatchOff {
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panic("s - t >e.maxMatchOff")
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}
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if debugMatches {
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println("long match")
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}
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break
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}
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// Check if we have a short match.
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if coffsetS < e.maxMatchOff && uint32(cv) == candidateS.val {
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// found a regular match
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// See if we can find a long match at s+1
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const checkAt = 1
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cv := load6432(src, s+checkAt)
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nextHashL = hash8(cv, dFastLongTableBits)
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candidateL = e.longTable[nextHashL]
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coffsetL = s - (candidateL.offset - e.cur) + checkAt
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// We can store it, since we have at least a 4 byte match.
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e.longTable[nextHashL] = tableEntry{offset: s + checkAt + e.cur, val: uint32(cv)}
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if coffsetL < e.maxMatchOff && uint32(cv) == candidateL.val {
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// Found a long match, likely at least 8 bytes.
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// Reference encoder checks all 8 bytes, we only check 4,
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// but the likelihood of both the first 4 bytes and the hash matching should be enough.
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t = candidateL.offset - e.cur
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s += checkAt
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if debugMatches {
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println("long match (after short)")
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}
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break
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}
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t = candidateS.offset - e.cur
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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 && s-t > e.maxMatchOff {
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panic("s - t >e.maxMatchOff")
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}
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if debugAsserts && t < 0 {
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panic("t<0")
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}
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if debugMatches {
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println("short match")
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}
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break
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}
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// No match found, move forward in input.
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s += stepSize + ((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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}
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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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offset2 = offset1
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offset1 = s - t
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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 && canRepeat && int(offset1) > len(src) {
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panic("invalid offset")
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}
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// Extend the 4-byte match as long as possible.
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l := e.matchlen(s+4, t+4, src) + 4
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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) and start+2 (short)
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index0 := s - l + 1
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// Index match end-2 (long) and end-1 (short)
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index1 := s - 2
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cv0 := load6432(src, index0)
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cv1 := load6432(src, index1)
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te0 := tableEntry{offset: index0 + e.cur, val: uint32(cv0)}
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te1 := tableEntry{offset: index1 + e.cur, val: uint32(cv1)}
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e.longTable[hash8(cv0, dFastLongTableBits)] = te0
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e.longTable[hash8(cv1, dFastLongTableBits)] = te1
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cv0 >>= 8
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cv1 >>= 8
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te0.offset++
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te1.offset++
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te0.val = uint32(cv0)
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te1.val = uint32(cv1)
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e.table[hash5(cv0, dFastShortTableBits)] = te0
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e.table[hash5(cv1, dFastShortTableBits)] = te1
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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 := hash5(cv, dFastShortTableBits)
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nextHashL := hash8(cv, dFastLongTableBits)
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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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entry := tableEntry{offset: s + e.cur, val: uint32(cv)}
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e.longTable[nextHashL] = entry
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e.table[nextHashS] = entry
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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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if debug {
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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 *doubleFastEncoder) EncodeNoHist(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 + 2
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minNonLiteralBlockSize = 16
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)
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// Protect against e.cur wraparound.
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if e.cur >= bufferReset {
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for i := range e.table[:] {
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e.table[i] = tableEntry{}
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}
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for i := range e.longTable[:] {
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e.longTable[i] = tableEntry{}
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}
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e.cur = e.maxMatchOff
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}
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s := int32(0)
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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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// Override src
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sLimit := int32(len(src)) - inputMargin
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// stepSize is the number of bytes to skip on every main loop iteration.
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// It should be >= 1.
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const stepSize = 1
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const kSearchStrength = 8
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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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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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if debug {
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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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var t int32
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for {
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nextHashS := hash5(cv, dFastShortTableBits)
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nextHashL := hash8(cv, dFastLongTableBits)
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candidateL := e.longTable[nextHashL]
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candidateS := e.table[nextHashS]
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const repOff = 1
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repIndex := s - offset1 + repOff
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entry := tableEntry{offset: s + e.cur, val: uint32(cv)}
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e.longTable[nextHashL] = entry
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e.table[nextHashS] = entry
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if len(blk.sequences) > 2 {
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if load3232(src, repIndex) == uint32(cv>>(repOff*8)) {
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// Consider history as well.
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var seq seq
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//length := 4 + e.matchlen(s+4+repOff, repIndex+4, src)
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length := 4 + int32(matchLen(src[s+4+repOff:], src[repIndex+4:]))
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seq.matchLen = uint32(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 := s + repOff
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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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for repIndex > tMin && start > startLimit && src[repIndex-1] == src[start-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 = 1
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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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s += length + repOff
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nextEmit = s
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if s >= sLimit {
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if debug {
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println("repeat ended", s, length)
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}
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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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}
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// Find the offsets of our two matches.
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coffsetL := s - (candidateL.offset - e.cur)
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coffsetS := s - (candidateS.offset - e.cur)
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// Check if we have a long match.
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if coffsetL < e.maxMatchOff && uint32(cv) == candidateL.val {
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// Found a long match, likely at least 8 bytes.
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// Reference encoder checks all 8 bytes, we only check 4,
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// but the likelihood of both the first 4 bytes and the hash matching should be enough.
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t = candidateL.offset - e.cur
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if debugAsserts && s <= t {
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panic(fmt.Sprintf("s (%d) <= t (%d). cur: %d", s, t, e.cur))
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}
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if debugAsserts && s-t > e.maxMatchOff {
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panic("s - t >e.maxMatchOff")
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}
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if debugMatches {
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println("long match")
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}
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break
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}
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// Check if we have a short match.
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if coffsetS < e.maxMatchOff && uint32(cv) == candidateS.val {
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// found a regular match
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// See if we can find a long match at s+1
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const checkAt = 1
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cv := load6432(src, s+checkAt)
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nextHashL = hash8(cv, dFastLongTableBits)
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candidateL = e.longTable[nextHashL]
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coffsetL = s - (candidateL.offset - e.cur) + checkAt
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// We can store it, since we have at least a 4 byte match.
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e.longTable[nextHashL] = tableEntry{offset: s + checkAt + e.cur, val: uint32(cv)}
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if coffsetL < e.maxMatchOff && uint32(cv) == candidateL.val {
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// Found a long match, likely at least 8 bytes.
|
|
// Reference encoder checks all 8 bytes, we only check 4,
|
|
// but the likelihood of both the first 4 bytes and the hash matching should be enough.
|
|
t = candidateL.offset - e.cur
|
|
s += checkAt
|
|
if debugMatches {
|
|
println("long match (after short)")
|
|
}
|
|
break
|
|
}
|
|
|
|
t = candidateS.offset - e.cur
|
|
if debugAsserts && s <= t {
|
|
panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
|
|
}
|
|
if debugAsserts && s-t > e.maxMatchOff {
|
|
panic("s - t >e.maxMatchOff")
|
|
}
|
|
if debugAsserts && t < 0 {
|
|
panic("t<0")
|
|
}
|
|
if debugMatches {
|
|
println("short match")
|
|
}
|
|
break
|
|
}
|
|
|
|
// No match found, move forward in input.
|
|
s += stepSize + ((s - nextEmit) >> (kSearchStrength - 1))
|
|
if s >= sLimit {
|
|
break encodeLoop
|
|
}
|
|
cv = load6432(src, s)
|
|
}
|
|
|
|
// A 4-byte match has been found. Update recent offsets.
|
|
// We'll later see if more than 4 bytes.
|
|
offset2 = offset1
|
|
offset1 = s - t
|
|
|
|
if debugAsserts && s <= t {
|
|
panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
|
|
}
|
|
|
|
// Extend the 4-byte match as long as possible.
|
|
//l := e.matchlen(s+4, t+4, src) + 4
|
|
l := int32(matchLen(src[s+4:], src[t+4:])) + 4
|
|
|
|
// Extend backwards
|
|
tMin := s - e.maxMatchOff
|
|
if tMin < 0 {
|
|
tMin = 0
|
|
}
|
|
for t > tMin && s > nextEmit && src[t-1] == src[s-1] {
|
|
s--
|
|
t--
|
|
l++
|
|
}
|
|
|
|
// Write our sequence
|
|
var seq seq
|
|
seq.litLen = uint32(s - nextEmit)
|
|
seq.matchLen = uint32(l - zstdMinMatch)
|
|
if seq.litLen > 0 {
|
|
blk.literals = append(blk.literals, src[nextEmit:s]...)
|
|
}
|
|
seq.offset = uint32(s-t) + 3
|
|
s += l
|
|
if debugSequences {
|
|
println("sequence", seq, "next s:", s)
|
|
}
|
|
blk.sequences = append(blk.sequences, seq)
|
|
nextEmit = s
|
|
if s >= sLimit {
|
|
break encodeLoop
|
|
}
|
|
|
|
// Index match start+1 (long) and start+2 (short)
|
|
index0 := s - l + 1
|
|
// Index match end-2 (long) and end-1 (short)
|
|
index1 := s - 2
|
|
|
|
cv0 := load6432(src, index0)
|
|
cv1 := load6432(src, index1)
|
|
te0 := tableEntry{offset: index0 + e.cur, val: uint32(cv0)}
|
|
te1 := tableEntry{offset: index1 + e.cur, val: uint32(cv1)}
|
|
e.longTable[hash8(cv0, dFastLongTableBits)] = te0
|
|
e.longTable[hash8(cv1, dFastLongTableBits)] = te1
|
|
cv0 >>= 8
|
|
cv1 >>= 8
|
|
te0.offset++
|
|
te1.offset++
|
|
te0.val = uint32(cv0)
|
|
te1.val = uint32(cv1)
|
|
e.table[hash5(cv0, dFastShortTableBits)] = te0
|
|
e.table[hash5(cv1, dFastShortTableBits)] = te1
|
|
|
|
cv = load6432(src, s)
|
|
|
|
if len(blk.sequences) <= 2 {
|
|
continue
|
|
}
|
|
|
|
// Check offset 2
|
|
for {
|
|
o2 := s - offset2
|
|
if load3232(src, o2) != uint32(cv) {
|
|
// Do regular search
|
|
break
|
|
}
|
|
|
|
// Store this, since we have it.
|
|
nextHashS := hash5(cv1>>8, dFastShortTableBits)
|
|
nextHashL := hash8(cv, dFastLongTableBits)
|
|
|
|
// We have at least 4 byte match.
|
|
// No need to check backwards. We come straight from a match
|
|
//l := 4 + e.matchlen(s+4, o2+4, src)
|
|
l := 4 + int32(matchLen(src[s+4:], src[o2+4:]))
|
|
|
|
entry := tableEntry{offset: s + e.cur, val: uint32(cv)}
|
|
e.longTable[nextHashL] = entry
|
|
e.table[nextHashS] = entry
|
|
seq.matchLen = uint32(l) - zstdMinMatch
|
|
seq.litLen = 0
|
|
|
|
// Since litlen is always 0, this is offset 1.
|
|
seq.offset = 1
|
|
s += l
|
|
nextEmit = s
|
|
if debugSequences {
|
|
println("sequence", seq, "next s:", s)
|
|
}
|
|
blk.sequences = append(blk.sequences, seq)
|
|
|
|
// Swap offset 1 and 2.
|
|
offset1, offset2 = offset2, offset1
|
|
if s >= sLimit {
|
|
// Finished
|
|
break encodeLoop
|
|
}
|
|
cv = load6432(src, s)
|
|
}
|
|
}
|
|
|
|
if int(nextEmit) < len(src) {
|
|
blk.literals = append(blk.literals, src[nextEmit:]...)
|
|
blk.extraLits = len(src) - int(nextEmit)
|
|
}
|
|
if debug {
|
|
println("returning, recent offsets:", blk.recentOffsets, "extra literals:", blk.extraLits)
|
|
}
|
|
|
|
// We do not store history, so we must offset e.cur to avoid false matches for next user.
|
|
if e.cur < bufferReset {
|
|
e.cur += int32(len(src))
|
|
}
|
|
}
|
|
|
|
// ResetDict will reset and set a dictionary if not nil
|
|
func (e *doubleFastEncoder) Reset(d *dict, singleBlock bool) {
|
|
e.fastEncoder.Reset(d, singleBlock)
|
|
if d == nil {
|
|
return
|
|
}
|
|
|
|
// 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([]tableEntry, len(e.longTable))
|
|
}
|
|
if len(d.content) >= 8 {
|
|
cv := load6432(d.content, 0)
|
|
e.dictLongTable[hash8(cv, dFastLongTableBits)] = tableEntry{
|
|
val: uint32(cv),
|
|
offset: e.maxMatchOff,
|
|
}
|
|
end := int32(len(d.content)) - 8 + e.maxMatchOff
|
|
for i := e.maxMatchOff + 1; i < end; i++ {
|
|
cv = cv>>8 | (uint64(d.content[i-e.maxMatchOff+7]) << 56)
|
|
e.dictLongTable[hash8(cv, dFastLongTableBits)] = tableEntry{
|
|
val: uint32(cv),
|
|
offset: i,
|
|
}
|
|
}
|
|
}
|
|
e.lastDictID = d.id
|
|
}
|
|
// Reset table to initial state
|
|
e.cur = e.maxMatchOff
|
|
copy(e.longTable[:], e.dictLongTable)
|
|
}
|