mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2024-11-01 15:00:00 +00:00
1101 lines
26 KiB
Go
1101 lines
26 KiB
Go
// Copyright 2016 The Snappy-Go Authors. All rights reserved.
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// Copyright (c) 2019 Klaus Post. 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 s2
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import (
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"bytes"
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"fmt"
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"math/bits"
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)
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// hash4 returns the hash of the lowest 4 bytes of u to fit in a hash table with h bits.
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// Preferably h should be a constant and should always be <32.
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func hash4(u uint64, h uint8) uint32 {
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const prime4bytes = 2654435761
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return (uint32(u) * prime4bytes) >> ((32 - h) & 31)
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}
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// hash5 returns the hash of the lowest 5 bytes of u to fit in a hash table with h bits.
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// Preferably h should be a constant and should always be <64.
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func hash5(u uint64, h uint8) uint32 {
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const prime5bytes = 889523592379
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return uint32(((u << (64 - 40)) * prime5bytes) >> ((64 - h) & 63))
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}
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// hash7 returns the hash of the lowest 7 bytes of u to fit in a hash table with h bits.
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// Preferably h should be a constant and should always be <64.
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func hash7(u uint64, h uint8) uint32 {
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const prime7bytes = 58295818150454627
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return uint32(((u << (64 - 56)) * prime7bytes) >> ((64 - h) & 63))
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}
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// hash8 returns the hash of u to fit in a hash table with h bits.
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// Preferably h should be a constant and should always be <64.
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func hash8(u uint64, h uint8) uint32 {
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const prime8bytes = 0xcf1bbcdcb7a56463
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return uint32((u * prime8bytes) >> ((64 - h) & 63))
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}
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// encodeBlockBetter encodes a non-empty src to a guaranteed-large-enough dst. It
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// assumes that the varint-encoded length of the decompressed bytes has already
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// been written.
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//
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// It also assumes that:
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//
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// len(dst) >= MaxEncodedLen(len(src)) &&
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// minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
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func encodeBlockBetterGo(dst, src []byte) (d int) {
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// sLimit is when to stop looking for offset/length copies. The inputMargin
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// lets us use a fast path for emitLiteral in the main loop, while we are
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// looking for copies.
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sLimit := len(src) - inputMargin
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if len(src) < minNonLiteralBlockSize {
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return 0
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}
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// Initialize the hash tables.
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const (
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// Long hash matches.
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lTableBits = 17
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maxLTableSize = 1 << lTableBits
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// Short hash matches.
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sTableBits = 14
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maxSTableSize = 1 << sTableBits
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)
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var lTable [maxLTableSize]uint32
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var sTable [maxSTableSize]uint32
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// Bail if we can't compress to at least this.
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dstLimit := len(src) - len(src)>>5 - 6
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// nextEmit is where in src the next emitLiteral should start from.
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nextEmit := 0
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// The encoded form must start with a literal, as there are no previous
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// bytes to copy, so we start looking for hash matches at s == 1.
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s := 1
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cv := load64(src, s)
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// We initialize repeat to 0, so we never match on first attempt
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repeat := 0
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for {
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candidateL := 0
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nextS := 0
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for {
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// Next src position to check
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nextS = s + (s-nextEmit)>>7 + 1
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if nextS > sLimit {
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goto emitRemainder
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}
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hashL := hash7(cv, lTableBits)
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hashS := hash4(cv, sTableBits)
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candidateL = int(lTable[hashL])
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candidateS := int(sTable[hashS])
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lTable[hashL] = uint32(s)
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sTable[hashS] = uint32(s)
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valLong := load64(src, candidateL)
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valShort := load64(src, candidateS)
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// If long matches at least 8 bytes, use that.
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if cv == valLong {
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break
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}
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if cv == valShort {
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candidateL = candidateS
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break
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}
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// Check repeat at offset checkRep.
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const checkRep = 1
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// Minimum length of a repeat. Tested with various values.
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// While 4-5 offers improvements in some, 6 reduces
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// regressions significantly.
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const wantRepeatBytes = 6
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const repeatMask = ((1 << (wantRepeatBytes * 8)) - 1) << (8 * checkRep)
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if false && repeat > 0 && cv&repeatMask == load64(src, s-repeat)&repeatMask {
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base := s + checkRep
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// Extend back
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for i := base - repeat; base > nextEmit && i > 0 && src[i-1] == src[base-1]; {
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i--
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base--
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}
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d += emitLiteral(dst[d:], src[nextEmit:base])
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// Extend forward
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candidate := s - repeat + wantRepeatBytes + checkRep
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s += wantRepeatBytes + checkRep
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for s < len(src) {
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if len(src)-s < 8 {
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if src[s] == src[candidate] {
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s++
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candidate++
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continue
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}
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break
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}
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if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
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s += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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candidate += 8
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}
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// same as `add := emitCopy(dst[d:], repeat, s-base)` but skips storing offset.
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d += emitRepeat(dst[d:], repeat, s-base)
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nextEmit = s
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if s >= sLimit {
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goto emitRemainder
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}
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// Index in-between
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index0 := base + 1
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index1 := s - 2
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cv = load64(src, s)
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for index0 < index1 {
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cv0 := load64(src, index0)
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cv1 := load64(src, index1)
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lTable[hash7(cv0, lTableBits)] = uint32(index0)
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sTable[hash4(cv0>>8, sTableBits)] = uint32(index0 + 1)
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lTable[hash7(cv1, lTableBits)] = uint32(index1)
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sTable[hash4(cv1>>8, sTableBits)] = uint32(index1 + 1)
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index0 += 2
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index1 -= 2
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}
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cv = load64(src, s)
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continue
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}
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// Long likely matches 7, so take that.
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if uint32(cv) == uint32(valLong) {
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break
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}
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// Check our short candidate
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if uint32(cv) == uint32(valShort) {
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// Try a long candidate at s+1
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hashL = hash7(cv>>8, lTableBits)
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candidateL = int(lTable[hashL])
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lTable[hashL] = uint32(s + 1)
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if uint32(cv>>8) == load32(src, candidateL) {
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s++
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break
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}
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// Use our short candidate.
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candidateL = candidateS
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break
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}
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cv = load64(src, nextS)
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s = nextS
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}
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// Extend backwards
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for candidateL > 0 && s > nextEmit && src[candidateL-1] == src[s-1] {
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candidateL--
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s--
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}
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// Bail if we exceed the maximum size.
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if d+(s-nextEmit) > dstLimit {
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return 0
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}
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base := s
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offset := base - candidateL
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// Extend the 4-byte match as long as possible.
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s += 4
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candidateL += 4
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for s < len(src) {
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if len(src)-s < 8 {
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if src[s] == src[candidateL] {
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s++
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candidateL++
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continue
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}
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break
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}
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if diff := load64(src, s) ^ load64(src, candidateL); diff != 0 {
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s += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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candidateL += 8
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}
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if offset > 65535 && s-base <= 5 && repeat != offset {
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// Bail if the match is equal or worse to the encoding.
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s = nextS + 1
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if s >= sLimit {
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goto emitRemainder
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}
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cv = load64(src, s)
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continue
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}
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d += emitLiteral(dst[d:], src[nextEmit:base])
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if repeat == offset {
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d += emitRepeat(dst[d:], offset, s-base)
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} else {
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d += emitCopy(dst[d:], offset, s-base)
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repeat = offset
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}
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nextEmit = s
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if s >= sLimit {
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goto emitRemainder
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}
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if d > dstLimit {
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// Do we have space for more, if not bail.
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return 0
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}
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// Index short & long
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index0 := base + 1
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index1 := s - 2
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cv0 := load64(src, index0)
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cv1 := load64(src, index1)
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lTable[hash7(cv0, lTableBits)] = uint32(index0)
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sTable[hash4(cv0>>8, sTableBits)] = uint32(index0 + 1)
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lTable[hash7(cv1, lTableBits)] = uint32(index1)
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sTable[hash4(cv1>>8, sTableBits)] = uint32(index1 + 1)
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index0 += 1
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index1 -= 1
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cv = load64(src, s)
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// index every second long in between.
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for index0 < index1 {
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lTable[hash7(load64(src, index0), lTableBits)] = uint32(index0)
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lTable[hash7(load64(src, index1), lTableBits)] = uint32(index1)
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index0 += 2
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index1 -= 2
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}
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}
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emitRemainder:
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if nextEmit < len(src) {
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// Bail if we exceed the maximum size.
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if d+len(src)-nextEmit > dstLimit {
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return 0
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}
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d += emitLiteral(dst[d:], src[nextEmit:])
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}
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return d
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}
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// encodeBlockBetterSnappyGo encodes a non-empty src to a guaranteed-large-enough dst. It
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// assumes that the varint-encoded length of the decompressed bytes has already
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// been written.
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//
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// It also assumes that:
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//
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// len(dst) >= MaxEncodedLen(len(src)) &&
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// minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
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func encodeBlockBetterSnappyGo(dst, src []byte) (d int) {
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// sLimit is when to stop looking for offset/length copies. The inputMargin
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// lets us use a fast path for emitLiteral in the main loop, while we are
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// looking for copies.
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sLimit := len(src) - inputMargin
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if len(src) < minNonLiteralBlockSize {
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return 0
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}
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// Initialize the hash tables.
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const (
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// Long hash matches.
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lTableBits = 16
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maxLTableSize = 1 << lTableBits
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// Short hash matches.
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sTableBits = 14
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maxSTableSize = 1 << sTableBits
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)
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var lTable [maxLTableSize]uint32
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var sTable [maxSTableSize]uint32
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// Bail if we can't compress to at least this.
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dstLimit := len(src) - len(src)>>5 - 6
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// nextEmit is where in src the next emitLiteral should start from.
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nextEmit := 0
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// The encoded form must start with a literal, as there are no previous
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// bytes to copy, so we start looking for hash matches at s == 1.
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s := 1
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cv := load64(src, s)
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// We initialize repeat to 0, so we never match on first attempt
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repeat := 0
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const maxSkip = 100
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for {
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candidateL := 0
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nextS := 0
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for {
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// Next src position to check
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nextS = (s-nextEmit)>>7 + 1
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if nextS > maxSkip {
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nextS = s + maxSkip
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} else {
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nextS += s
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}
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if nextS > sLimit {
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goto emitRemainder
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}
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hashL := hash7(cv, lTableBits)
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hashS := hash4(cv, sTableBits)
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candidateL = int(lTable[hashL])
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candidateS := int(sTable[hashS])
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lTable[hashL] = uint32(s)
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sTable[hashS] = uint32(s)
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if uint32(cv) == load32(src, candidateL) {
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break
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}
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// Check our short candidate
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if uint32(cv) == load32(src, candidateS) {
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// Try a long candidate at s+1
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hashL = hash7(cv>>8, lTableBits)
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candidateL = int(lTable[hashL])
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lTable[hashL] = uint32(s + 1)
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if uint32(cv>>8) == load32(src, candidateL) {
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s++
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break
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}
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// Use our short candidate.
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candidateL = candidateS
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break
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}
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cv = load64(src, nextS)
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s = nextS
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}
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// Extend backwards
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for candidateL > 0 && s > nextEmit && src[candidateL-1] == src[s-1] {
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candidateL--
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s--
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}
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// Bail if we exceed the maximum size.
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if d+(s-nextEmit) > dstLimit {
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return 0
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}
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base := s
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offset := base - candidateL
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// Extend the 4-byte match as long as possible.
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s += 4
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candidateL += 4
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for s < len(src) {
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if len(src)-s < 8 {
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if src[s] == src[candidateL] {
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s++
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candidateL++
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continue
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}
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break
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}
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if diff := load64(src, s) ^ load64(src, candidateL); diff != 0 {
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s += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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candidateL += 8
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}
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if offset > 65535 && s-base <= 5 && repeat != offset {
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// Bail if the match is equal or worse to the encoding.
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s = nextS + 1
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if s >= sLimit {
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goto emitRemainder
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}
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cv = load64(src, s)
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continue
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}
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d += emitLiteral(dst[d:], src[nextEmit:base])
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d += emitCopyNoRepeat(dst[d:], offset, s-base)
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repeat = offset
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nextEmit = s
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if s >= sLimit {
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goto emitRemainder
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}
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if d > dstLimit {
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// Do we have space for more, if not bail.
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return 0
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}
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// Index short & long
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index0 := base + 1
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index1 := s - 2
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cv0 := load64(src, index0)
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cv1 := load64(src, index1)
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lTable[hash7(cv0, lTableBits)] = uint32(index0)
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sTable[hash4(cv0>>8, sTableBits)] = uint32(index0 + 1)
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lTable[hash7(cv1, lTableBits)] = uint32(index1)
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sTable[hash4(cv1>>8, sTableBits)] = uint32(index1 + 1)
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index0 += 1
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index1 -= 1
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cv = load64(src, s)
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// index every second long in between.
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for index0 < index1 {
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lTable[hash7(load64(src, index0), lTableBits)] = uint32(index0)
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lTable[hash7(load64(src, index1), lTableBits)] = uint32(index1)
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index0 += 2
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index1 -= 2
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}
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}
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emitRemainder:
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if nextEmit < len(src) {
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// Bail if we exceed the maximum size.
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if d+len(src)-nextEmit > dstLimit {
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return 0
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}
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d += emitLiteral(dst[d:], src[nextEmit:])
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}
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return d
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}
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|
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// encodeBlockBetterDict encodes a non-empty src to a guaranteed-large-enough dst. It
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// assumes that the varint-encoded length of the decompressed bytes has already
|
|
// been written.
|
|
//
|
|
// It also assumes that:
|
|
//
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|
// len(dst) >= MaxEncodedLen(len(src)) &&
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// minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
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func encodeBlockBetterDict(dst, src []byte, dict *Dict) (d int) {
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// sLimit is when to stop looking for offset/length copies. The inputMargin
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|
// lets us use a fast path for emitLiteral in the main loop, while we are
|
|
// looking for copies.
|
|
// Initialize the hash tables.
|
|
const (
|
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// Long hash matches.
|
|
lTableBits = 17
|
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maxLTableSize = 1 << lTableBits
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|
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// Short hash matches.
|
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sTableBits = 14
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maxSTableSize = 1 << sTableBits
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maxAhead = 8 // maximum bytes ahead without checking sLimit
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debug = false
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)
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sLimit := len(src) - inputMargin
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if sLimit > MaxDictSrcOffset-maxAhead {
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sLimit = MaxDictSrcOffset - maxAhead
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}
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if len(src) < minNonLiteralBlockSize {
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return 0
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}
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|
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dict.initBetter()
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|
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var lTable [maxLTableSize]uint32
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var sTable [maxSTableSize]uint32
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|
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// Bail if we can't compress to at least this.
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|
dstLimit := len(src) - len(src)>>5 - 6
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|
|
// nextEmit is where in src the next emitLiteral should start from.
|
|
nextEmit := 0
|
|
|
|
// The encoded form must start with a literal, as there are no previous
|
|
// bytes to copy, so we start looking for hash matches at s == 1.
|
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s := 0
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cv := load64(src, s)
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|
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// We initialize repeat to 0, so we never match on first attempt
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repeat := len(dict.dict) - dict.repeat
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|
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// While in dict
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|
searchDict:
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for {
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candidateL := 0
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nextS := 0
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for {
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// Next src position to check
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nextS = s + (s-nextEmit)>>7 + 1
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if nextS > sLimit {
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break searchDict
|
|
}
|
|
hashL := hash7(cv, lTableBits)
|
|
hashS := hash4(cv, sTableBits)
|
|
candidateL = int(lTable[hashL])
|
|
candidateS := int(sTable[hashS])
|
|
dictL := int(dict.betterTableLong[hashL])
|
|
dictS := int(dict.betterTableShort[hashS])
|
|
lTable[hashL] = uint32(s)
|
|
sTable[hashS] = uint32(s)
|
|
|
|
valLong := load64(src, candidateL)
|
|
valShort := load64(src, candidateS)
|
|
|
|
// If long matches at least 8 bytes, use that.
|
|
if s != 0 {
|
|
if cv == valLong {
|
|
goto emitMatch
|
|
}
|
|
if cv == valShort {
|
|
candidateL = candidateS
|
|
goto emitMatch
|
|
}
|
|
}
|
|
|
|
// Check dict repeat.
|
|
if repeat >= s+4 {
|
|
candidate := len(dict.dict) - repeat + s
|
|
if candidate > 0 && uint32(cv) == load32(dict.dict, candidate) {
|
|
// Extend back
|
|
base := s
|
|
for i := candidate; base > nextEmit && i > 0 && dict.dict[i-1] == src[base-1]; {
|
|
i--
|
|
base--
|
|
}
|
|
d += emitLiteral(dst[d:], src[nextEmit:base])
|
|
if debug && nextEmit != base {
|
|
fmt.Println("emitted ", base-nextEmit, "literals")
|
|
}
|
|
s += 4
|
|
candidate += 4
|
|
for candidate < len(dict.dict)-8 && s <= len(src)-8 {
|
|
if diff := load64(src, s) ^ load64(dict.dict, candidate); diff != 0 {
|
|
s += bits.TrailingZeros64(diff) >> 3
|
|
break
|
|
}
|
|
s += 8
|
|
candidate += 8
|
|
}
|
|
d += emitRepeat(dst[d:], repeat, s-base)
|
|
if debug {
|
|
fmt.Println("emitted dict repeat length", s-base, "offset:", repeat, "s:", s)
|
|
}
|
|
nextEmit = s
|
|
if s >= sLimit {
|
|
break searchDict
|
|
}
|
|
cv = load64(src, s)
|
|
// Index in-between
|
|
index0 := base + 1
|
|
index1 := s - 2
|
|
|
|
cv = load64(src, s)
|
|
for index0 < index1 {
|
|
cv0 := load64(src, index0)
|
|
cv1 := load64(src, index1)
|
|
lTable[hash7(cv0, lTableBits)] = uint32(index0)
|
|
sTable[hash4(cv0>>8, sTableBits)] = uint32(index0 + 1)
|
|
|
|
lTable[hash7(cv1, lTableBits)] = uint32(index1)
|
|
sTable[hash4(cv1>>8, sTableBits)] = uint32(index1 + 1)
|
|
index0 += 2
|
|
index1 -= 2
|
|
}
|
|
continue
|
|
}
|
|
}
|
|
// Don't try to find match at s==0
|
|
if s == 0 {
|
|
cv = load64(src, nextS)
|
|
s = nextS
|
|
continue
|
|
}
|
|
|
|
// Long likely matches 7, so take that.
|
|
if uint32(cv) == uint32(valLong) {
|
|
goto emitMatch
|
|
}
|
|
|
|
// Long dict...
|
|
if uint32(cv) == load32(dict.dict, dictL) {
|
|
candidateL = dictL
|
|
goto emitDict
|
|
}
|
|
|
|
// Check our short candidate
|
|
if uint32(cv) == uint32(valShort) {
|
|
// Try a long candidate at s+1
|
|
hashL = hash7(cv>>8, lTableBits)
|
|
candidateL = int(lTable[hashL])
|
|
lTable[hashL] = uint32(s + 1)
|
|
if uint32(cv>>8) == load32(src, candidateL) {
|
|
s++
|
|
goto emitMatch
|
|
}
|
|
// Use our short candidate.
|
|
candidateL = candidateS
|
|
goto emitMatch
|
|
}
|
|
if uint32(cv) == load32(dict.dict, dictS) {
|
|
// Try a long candidate at s+1
|
|
hashL = hash7(cv>>8, lTableBits)
|
|
candidateL = int(lTable[hashL])
|
|
lTable[hashL] = uint32(s + 1)
|
|
if uint32(cv>>8) == load32(src, candidateL) {
|
|
s++
|
|
goto emitMatch
|
|
}
|
|
candidateL = dictS
|
|
goto emitDict
|
|
}
|
|
cv = load64(src, nextS)
|
|
s = nextS
|
|
}
|
|
emitDict:
|
|
{
|
|
if debug {
|
|
if load32(dict.dict, candidateL) != load32(src, s) {
|
|
panic("dict emit mismatch")
|
|
}
|
|
}
|
|
// Extend backwards.
|
|
// The top bytes will be rechecked to get the full match.
|
|
for candidateL > 0 && s > nextEmit && dict.dict[candidateL-1] == src[s-1] {
|
|
candidateL--
|
|
s--
|
|
}
|
|
|
|
// Bail if we exceed the maximum size.
|
|
if d+(s-nextEmit) > dstLimit {
|
|
return 0
|
|
}
|
|
|
|
// A 4-byte match has been found. We'll later see if more than 4 bytes
|
|
// match. But, prior to the match, src[nextEmit:s] are unmatched. Emit
|
|
// them as literal bytes.
|
|
|
|
d += emitLiteral(dst[d:], src[nextEmit:s])
|
|
if debug && nextEmit != s {
|
|
fmt.Println("emitted ", s-nextEmit, "literals")
|
|
}
|
|
{
|
|
// Invariant: we have a 4-byte match at s, and no need to emit any
|
|
// literal bytes prior to s.
|
|
base := s
|
|
offset := s + (len(dict.dict)) - candidateL
|
|
|
|
// Extend the 4-byte match as long as possible.
|
|
s += 4
|
|
candidateL += 4
|
|
for s <= len(src)-8 && len(dict.dict)-candidateL >= 8 {
|
|
if diff := load64(src, s) ^ load64(dict.dict, candidateL); diff != 0 {
|
|
s += bits.TrailingZeros64(diff) >> 3
|
|
break
|
|
}
|
|
s += 8
|
|
candidateL += 8
|
|
}
|
|
|
|
if repeat == offset {
|
|
if debug {
|
|
fmt.Println("emitted dict repeat, length", s-base, "offset:", offset, "s:", s, "dict offset:", candidateL)
|
|
}
|
|
d += emitRepeat(dst[d:], offset, s-base)
|
|
} else {
|
|
if debug {
|
|
fmt.Println("emitted dict copy, length", s-base, "offset:", offset, "s:", s, "dict offset:", candidateL)
|
|
}
|
|
// Matches longer than 64 are split.
|
|
if s <= sLimit || s-base < 8 {
|
|
d += emitCopy(dst[d:], offset, s-base)
|
|
} else {
|
|
// Split to ensure we don't start a copy within next block.
|
|
d += emitCopy(dst[d:], offset, 4)
|
|
d += emitRepeat(dst[d:], offset, s-base-4)
|
|
}
|
|
repeat = offset
|
|
}
|
|
if false {
|
|
// Validate match.
|
|
if s <= candidateL {
|
|
panic("s <= candidate")
|
|
}
|
|
a := src[base:s]
|
|
b := dict.dict[base-repeat : base-repeat+(s-base)]
|
|
if !bytes.Equal(a, b) {
|
|
panic("mismatch")
|
|
}
|
|
}
|
|
|
|
nextEmit = s
|
|
if s >= sLimit {
|
|
break searchDict
|
|
}
|
|
|
|
if d > dstLimit {
|
|
// Do we have space for more, if not bail.
|
|
return 0
|
|
}
|
|
|
|
// Index short & long
|
|
index0 := base + 1
|
|
index1 := s - 2
|
|
|
|
cv0 := load64(src, index0)
|
|
cv1 := load64(src, index1)
|
|
lTable[hash7(cv0, lTableBits)] = uint32(index0)
|
|
sTable[hash4(cv0>>8, sTableBits)] = uint32(index0 + 1)
|
|
|
|
lTable[hash7(cv1, lTableBits)] = uint32(index1)
|
|
sTable[hash4(cv1>>8, sTableBits)] = uint32(index1 + 1)
|
|
index0 += 1
|
|
index1 -= 1
|
|
cv = load64(src, s)
|
|
|
|
// index every second long in between.
|
|
for index0 < index1 {
|
|
lTable[hash7(load64(src, index0), lTableBits)] = uint32(index0)
|
|
lTable[hash7(load64(src, index1), lTableBits)] = uint32(index1)
|
|
index0 += 2
|
|
index1 -= 2
|
|
}
|
|
}
|
|
continue
|
|
}
|
|
emitMatch:
|
|
|
|
// Extend backwards
|
|
for candidateL > 0 && s > nextEmit && src[candidateL-1] == src[s-1] {
|
|
candidateL--
|
|
s--
|
|
}
|
|
|
|
// Bail if we exceed the maximum size.
|
|
if d+(s-nextEmit) > dstLimit {
|
|
return 0
|
|
}
|
|
|
|
base := s
|
|
offset := base - candidateL
|
|
|
|
// Extend the 4-byte match as long as possible.
|
|
s += 4
|
|
candidateL += 4
|
|
for s < len(src) {
|
|
if len(src)-s < 8 {
|
|
if src[s] == src[candidateL] {
|
|
s++
|
|
candidateL++
|
|
continue
|
|
}
|
|
break
|
|
}
|
|
if diff := load64(src, s) ^ load64(src, candidateL); diff != 0 {
|
|
s += bits.TrailingZeros64(diff) >> 3
|
|
break
|
|
}
|
|
s += 8
|
|
candidateL += 8
|
|
}
|
|
|
|
if offset > 65535 && s-base <= 5 && repeat != offset {
|
|
// Bail if the match is equal or worse to the encoding.
|
|
s = nextS + 1
|
|
if s >= sLimit {
|
|
goto emitRemainder
|
|
}
|
|
cv = load64(src, s)
|
|
continue
|
|
}
|
|
|
|
d += emitLiteral(dst[d:], src[nextEmit:base])
|
|
if debug && nextEmit != s {
|
|
fmt.Println("emitted ", s-nextEmit, "literals")
|
|
}
|
|
if repeat == offset {
|
|
if debug {
|
|
fmt.Println("emitted match repeat, length", s-base, "offset:", offset, "s:", s)
|
|
}
|
|
d += emitRepeat(dst[d:], offset, s-base)
|
|
} else {
|
|
if debug {
|
|
fmt.Println("emitted match copy, length", s-base, "offset:", offset, "s:", s)
|
|
}
|
|
d += emitCopy(dst[d:], offset, s-base)
|
|
repeat = offset
|
|
}
|
|
|
|
nextEmit = s
|
|
if s >= sLimit {
|
|
goto emitRemainder
|
|
}
|
|
|
|
if d > dstLimit {
|
|
// Do we have space for more, if not bail.
|
|
return 0
|
|
}
|
|
|
|
// Index short & long
|
|
index0 := base + 1
|
|
index1 := s - 2
|
|
|
|
cv0 := load64(src, index0)
|
|
cv1 := load64(src, index1)
|
|
lTable[hash7(cv0, lTableBits)] = uint32(index0)
|
|
sTable[hash4(cv0>>8, sTableBits)] = uint32(index0 + 1)
|
|
|
|
lTable[hash7(cv1, lTableBits)] = uint32(index1)
|
|
sTable[hash4(cv1>>8, sTableBits)] = uint32(index1 + 1)
|
|
index0 += 1
|
|
index1 -= 1
|
|
cv = load64(src, s)
|
|
|
|
// index every second long in between.
|
|
for index0 < index1 {
|
|
lTable[hash7(load64(src, index0), lTableBits)] = uint32(index0)
|
|
lTable[hash7(load64(src, index1), lTableBits)] = uint32(index1)
|
|
index0 += 2
|
|
index1 -= 2
|
|
}
|
|
}
|
|
|
|
// Search without dict:
|
|
if repeat > s {
|
|
repeat = 0
|
|
}
|
|
|
|
// No more dict
|
|
sLimit = len(src) - inputMargin
|
|
if s >= sLimit {
|
|
goto emitRemainder
|
|
}
|
|
cv = load64(src, s)
|
|
if debug {
|
|
fmt.Println("now", s, "->", sLimit, "out:", d, "left:", len(src)-s, "nextemit:", nextEmit, "dstLimit:", dstLimit, "s:", s)
|
|
}
|
|
for {
|
|
candidateL := 0
|
|
nextS := 0
|
|
for {
|
|
// Next src position to check
|
|
nextS = s + (s-nextEmit)>>7 + 1
|
|
if nextS > sLimit {
|
|
goto emitRemainder
|
|
}
|
|
hashL := hash7(cv, lTableBits)
|
|
hashS := hash4(cv, sTableBits)
|
|
candidateL = int(lTable[hashL])
|
|
candidateS := int(sTable[hashS])
|
|
lTable[hashL] = uint32(s)
|
|
sTable[hashS] = uint32(s)
|
|
|
|
valLong := load64(src, candidateL)
|
|
valShort := load64(src, candidateS)
|
|
|
|
// If long matches at least 8 bytes, use that.
|
|
if cv == valLong {
|
|
break
|
|
}
|
|
if cv == valShort {
|
|
candidateL = candidateS
|
|
break
|
|
}
|
|
|
|
// Check repeat at offset checkRep.
|
|
const checkRep = 1
|
|
// Minimum length of a repeat. Tested with various values.
|
|
// While 4-5 offers improvements in some, 6 reduces
|
|
// regressions significantly.
|
|
const wantRepeatBytes = 6
|
|
const repeatMask = ((1 << (wantRepeatBytes * 8)) - 1) << (8 * checkRep)
|
|
if false && repeat > 0 && cv&repeatMask == load64(src, s-repeat)&repeatMask {
|
|
base := s + checkRep
|
|
// Extend back
|
|
for i := base - repeat; base > nextEmit && i > 0 && src[i-1] == src[base-1]; {
|
|
i--
|
|
base--
|
|
}
|
|
d += emitLiteral(dst[d:], src[nextEmit:base])
|
|
|
|
// Extend forward
|
|
candidate := s - repeat + wantRepeatBytes + checkRep
|
|
s += wantRepeatBytes + checkRep
|
|
for s < len(src) {
|
|
if len(src)-s < 8 {
|
|
if src[s] == src[candidate] {
|
|
s++
|
|
candidate++
|
|
continue
|
|
}
|
|
break
|
|
}
|
|
if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
|
|
s += bits.TrailingZeros64(diff) >> 3
|
|
break
|
|
}
|
|
s += 8
|
|
candidate += 8
|
|
}
|
|
// same as `add := emitCopy(dst[d:], repeat, s-base)` but skips storing offset.
|
|
d += emitRepeat(dst[d:], repeat, s-base)
|
|
nextEmit = s
|
|
if s >= sLimit {
|
|
goto emitRemainder
|
|
}
|
|
// Index in-between
|
|
index0 := base + 1
|
|
index1 := s - 2
|
|
|
|
cv = load64(src, s)
|
|
for index0 < index1 {
|
|
cv0 := load64(src, index0)
|
|
cv1 := load64(src, index1)
|
|
lTable[hash7(cv0, lTableBits)] = uint32(index0)
|
|
sTable[hash4(cv0>>8, sTableBits)] = uint32(index0 + 1)
|
|
|
|
lTable[hash7(cv1, lTableBits)] = uint32(index1)
|
|
sTable[hash4(cv1>>8, sTableBits)] = uint32(index1 + 1)
|
|
index0 += 2
|
|
index1 -= 2
|
|
}
|
|
|
|
cv = load64(src, s)
|
|
continue
|
|
}
|
|
|
|
// Long likely matches 7, so take that.
|
|
if uint32(cv) == uint32(valLong) {
|
|
break
|
|
}
|
|
|
|
// Check our short candidate
|
|
if uint32(cv) == uint32(valShort) {
|
|
// Try a long candidate at s+1
|
|
hashL = hash7(cv>>8, lTableBits)
|
|
candidateL = int(lTable[hashL])
|
|
lTable[hashL] = uint32(s + 1)
|
|
if uint32(cv>>8) == load32(src, candidateL) {
|
|
s++
|
|
break
|
|
}
|
|
// Use our short candidate.
|
|
candidateL = candidateS
|
|
break
|
|
}
|
|
|
|
cv = load64(src, nextS)
|
|
s = nextS
|
|
}
|
|
|
|
// Extend backwards
|
|
for candidateL > 0 && s > nextEmit && src[candidateL-1] == src[s-1] {
|
|
candidateL--
|
|
s--
|
|
}
|
|
|
|
// Bail if we exceed the maximum size.
|
|
if d+(s-nextEmit) > dstLimit {
|
|
return 0
|
|
}
|
|
|
|
base := s
|
|
offset := base - candidateL
|
|
|
|
// Extend the 4-byte match as long as possible.
|
|
s += 4
|
|
candidateL += 4
|
|
for s < len(src) {
|
|
if len(src)-s < 8 {
|
|
if src[s] == src[candidateL] {
|
|
s++
|
|
candidateL++
|
|
continue
|
|
}
|
|
break
|
|
}
|
|
if diff := load64(src, s) ^ load64(src, candidateL); diff != 0 {
|
|
s += bits.TrailingZeros64(diff) >> 3
|
|
break
|
|
}
|
|
s += 8
|
|
candidateL += 8
|
|
}
|
|
|
|
if offset > 65535 && s-base <= 5 && repeat != offset {
|
|
// Bail if the match is equal or worse to the encoding.
|
|
s = nextS + 1
|
|
if s >= sLimit {
|
|
goto emitRemainder
|
|
}
|
|
cv = load64(src, s)
|
|
continue
|
|
}
|
|
|
|
d += emitLiteral(dst[d:], src[nextEmit:base])
|
|
if repeat == offset {
|
|
d += emitRepeat(dst[d:], offset, s-base)
|
|
} else {
|
|
d += emitCopy(dst[d:], offset, s-base)
|
|
repeat = offset
|
|
}
|
|
|
|
nextEmit = s
|
|
if s >= sLimit {
|
|
goto emitRemainder
|
|
}
|
|
|
|
if d > dstLimit {
|
|
// Do we have space for more, if not bail.
|
|
return 0
|
|
}
|
|
|
|
// Index short & long
|
|
index0 := base + 1
|
|
index1 := s - 2
|
|
|
|
cv0 := load64(src, index0)
|
|
cv1 := load64(src, index1)
|
|
lTable[hash7(cv0, lTableBits)] = uint32(index0)
|
|
sTable[hash4(cv0>>8, sTableBits)] = uint32(index0 + 1)
|
|
|
|
lTable[hash7(cv1, lTableBits)] = uint32(index1)
|
|
sTable[hash4(cv1>>8, sTableBits)] = uint32(index1 + 1)
|
|
index0 += 1
|
|
index1 -= 1
|
|
cv = load64(src, s)
|
|
|
|
// index every second long in between.
|
|
for index0 < index1 {
|
|
lTable[hash7(load64(src, index0), lTableBits)] = uint32(index0)
|
|
lTable[hash7(load64(src, index1), lTableBits)] = uint32(index1)
|
|
index0 += 2
|
|
index1 -= 2
|
|
}
|
|
}
|
|
|
|
emitRemainder:
|
|
if nextEmit < len(src) {
|
|
// Bail if we exceed the maximum size.
|
|
if d+len(src)-nextEmit > dstLimit {
|
|
return 0
|
|
}
|
|
d += emitLiteral(dst[d:], src[nextEmit:])
|
|
}
|
|
return d
|
|
}
|