jochen
be92762969
The live tests reached one shared bus and assert, read and remove the mesh's own objects by their fixed names, so packages run in parallel deleted what each other read and the suite passed only one package at a time; a red suite read as noise. internal/testbus starts a server per test, linked in at the nats-server release go.mod pins, and a test holds that pin to the catalogue's bus image and to the facts snapshot's bus when there is one, so the tests never run a bus the mesh does not. The waiter test read a timing (the most connections held at one look) and now reads the state it means (the fewest held across the wait). make check runs the packages in parallel under the race detector, with a timeout.
798 lines
21 KiB
Go
798 lines
21 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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"fmt"
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"math"
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"math/bits"
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)
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// encodeBlockBest 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 encodeBlockBest(dst, src []byte, dict *Dict) (d int) {
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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 = bestLongTableBits
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maxLTableSize = bestLongTableSize
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// Short hash matches.
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sTableBits = bestShortTableBits
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maxSTableSize = bestShortTableSize
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inputMargin = 8 + 2
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debug = false
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)
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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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sLimitDict := min(len(src)-inputMargin, MaxDictSrcOffset-inputMargin)
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tbl := getBestTables()
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lTable := &tbl.lTable
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sTable := &tbl.sTable
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defer bestTablePool.Put(tbl)
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// Bail if we can't compress to at least this.
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dstLimit := len(src) - 5
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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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repeat := 1
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if dict != nil {
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dict.initBest()
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s = 0
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repeat = len(dict.dict) - dict.repeat
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}
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cv := load64(src, s)
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// We search for a repeat at -1, but don't output repeats when nextEmit == 0
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const lowbitMask = 0xffffffff
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getCur := func(x uint64) int {
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return int(x & lowbitMask)
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}
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getPrev := func(x uint64) int {
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return int(x >> 32)
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}
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const maxSkip = 64
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for {
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type match struct {
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offset int
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s int
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length int
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score int
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rep, dict bool
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}
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var best match
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for {
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// Next src position to check
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nextS := (s-nextEmit)>>8 + 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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if dict != nil && s >= MaxDictSrcOffset {
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dict = nil
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if repeat > s {
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repeat = math.MinInt32
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}
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}
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hashL := hash8(cv, lTableBits)
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hashS := hash4(cv, sTableBits)
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candidateL := lTable[hashL]
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candidateS := sTable[hashS]
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score := func(m match) int {
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// Matches that are longer forward are penalized since we must emit it as a literal.
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score := m.length - m.s
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if nextEmit == m.s {
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// If we do not have to emit literals, we save 1 byte
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score++
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}
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offset := m.s - m.offset
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if m.rep {
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return score - emitRepeatSize(offset, m.length)
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}
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return score - emitCopySize(offset, m.length)
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}
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matchAt := func(offset, s int, first uint32, rep bool) match {
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if best.length != 0 && best.s-best.offset == s-offset {
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// Don't retest if we have the same offset.
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return match{offset: offset, s: s}
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}
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if load32(src, offset) != first {
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return match{offset: offset, s: s}
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}
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m := match{offset: offset, s: s, length: 4 + offset, rep: rep}
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s += 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[m.length] {
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m.length++
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s++
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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, m.length); diff != 0 {
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m.length += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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m.length += 8
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}
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m.length -= offset
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m.score = score(m)
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if m.score <= -m.s {
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// Eliminate if no savings, we might find a better one.
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m.length = 0
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}
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return m
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}
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matchDict := func(candidate, s int, first uint32, rep bool) match {
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if s >= MaxDictSrcOffset {
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return match{offset: candidate, s: s}
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}
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// Calculate offset as if in continuous array with s
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offset := -len(dict.dict) + candidate
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if best.length != 0 && best.s-best.offset == s-offset && !rep {
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// Don't retest if we have the same offset.
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return match{offset: offset, s: s}
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}
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if load32(dict.dict, candidate) != first {
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return match{offset: offset, s: s}
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}
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m := match{offset: offset, s: s, length: 4 + candidate, rep: rep, dict: true}
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s += 4
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if !rep {
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for s < sLimitDict && m.length < len(dict.dict) {
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if len(src)-s < 8 || len(dict.dict)-m.length < 8 {
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if src[s] == dict.dict[m.length] {
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m.length++
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s++
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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(dict.dict, m.length); diff != 0 {
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m.length += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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m.length += 8
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}
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} else {
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for s < len(src) && m.length < len(dict.dict) {
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if len(src)-s < 8 || len(dict.dict)-m.length < 8 {
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if src[s] == dict.dict[m.length] {
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m.length++
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s++
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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(dict.dict, m.length); diff != 0 {
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m.length += bits.TrailingZeros64(diff) >> 3
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break
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}
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s += 8
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m.length += 8
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}
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}
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m.length -= candidate
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m.score = score(m)
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if m.score <= -m.s {
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// Eliminate if no savings, we might find a better one.
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m.length = 0
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}
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return m
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}
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bestOf := func(a, b match) match {
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if b.length == 0 {
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return a
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}
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if a.length == 0 {
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return b
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}
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as := a.score + b.s
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bs := b.score + a.s
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if as >= bs {
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return a
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}
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return b
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}
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if s > 0 {
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best = bestOf(matchAt(getCur(candidateL), s, uint32(cv), false), matchAt(getPrev(candidateL), s, uint32(cv), false))
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best = bestOf(best, matchAt(getCur(candidateS), s, uint32(cv), false))
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best = bestOf(best, matchAt(getPrev(candidateS), s, uint32(cv), false))
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}
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if dict != nil {
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candidateL := dict.bestTableLong[hashL]
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candidateS := dict.bestTableShort[hashS]
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best = bestOf(best, matchDict(int(candidateL&0xffff), s, uint32(cv), false))
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best = bestOf(best, matchDict(int(candidateL>>16), s, uint32(cv), false))
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best = bestOf(best, matchDict(int(candidateS&0xffff), s, uint32(cv), false))
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best = bestOf(best, matchDict(int(candidateS>>16), s, uint32(cv), false))
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}
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{
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if (dict == nil || repeat <= s) && repeat > 0 {
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best = bestOf(best, matchAt(s-repeat+1, s+1, uint32(cv>>8), true))
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} else if s-repeat < -4 && dict != nil {
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candidate := len(dict.dict) - (repeat - s)
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best = bestOf(best, matchDict(candidate, s, uint32(cv), true))
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candidate++
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best = bestOf(best, matchDict(candidate, s+1, uint32(cv>>8), true))
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}
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if best.length > 0 {
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hashS := hash4(cv>>8, sTableBits)
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// s+1
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nextShort := sTable[hashS]
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s := s + 1
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cv := load64(src, s)
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hashL := hash8(cv, lTableBits)
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nextLong := lTable[hashL]
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best = bestOf(best, matchAt(getCur(nextShort), s, uint32(cv), false))
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best = bestOf(best, matchAt(getPrev(nextShort), s, uint32(cv), false))
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best = bestOf(best, matchAt(getCur(nextLong), s, uint32(cv), false))
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best = bestOf(best, matchAt(getPrev(nextLong), s, uint32(cv), false))
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// Dict at + 1
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if dict != nil {
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candidateL := dict.bestTableLong[hashL]
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candidateS := dict.bestTableShort[hashS]
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best = bestOf(best, matchDict(int(candidateL&0xffff), s, uint32(cv), false))
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best = bestOf(best, matchDict(int(candidateS&0xffff), s, uint32(cv), false))
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}
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// s+2
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if true {
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hashS := hash4(cv>>8, sTableBits)
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nextShort = sTable[hashS]
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s++
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cv = load64(src, s)
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hashL := hash8(cv, lTableBits)
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nextLong = lTable[hashL]
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if (dict == nil || repeat <= s) && repeat > 0 {
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// Repeat at + 2
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best = bestOf(best, matchAt(s-repeat, s, uint32(cv), true))
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} else if repeat-s > 4 && dict != nil {
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candidate := len(dict.dict) - (repeat - s)
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best = bestOf(best, matchDict(candidate, s, uint32(cv), true))
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}
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best = bestOf(best, matchAt(getCur(nextShort), s, uint32(cv), false))
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best = bestOf(best, matchAt(getPrev(nextShort), s, uint32(cv), false))
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best = bestOf(best, matchAt(getCur(nextLong), s, uint32(cv), false))
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best = bestOf(best, matchAt(getPrev(nextLong), s, uint32(cv), false))
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// Dict at +2
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// Very small gain
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if dict != nil {
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candidateL := dict.bestTableLong[hashL]
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candidateS := dict.bestTableShort[hashS]
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best = bestOf(best, matchDict(int(candidateL&0xffff), s, uint32(cv), false))
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best = bestOf(best, matchDict(int(candidateS&0xffff), s, uint32(cv), false))
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}
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}
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// Search for a match at best match end, see if that is better.
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// Allow some bytes at the beginning to mismatch.
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// Sweet spot is around 1-2 bytes, but depends on input.
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// The skipped bytes are tested in Extend backwards,
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// and still picked up as part of the match if they do.
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const skipBeginning = 2
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const skipEnd = 1
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if sAt := best.s + best.length - skipEnd; sAt < sLimit {
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sBack := best.s + skipBeginning - skipEnd
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backL := best.length - skipBeginning
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// Load initial values
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cv = load64(src, sBack)
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// Grab candidates...
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next := lTable[hash8(load64(src, sAt), lTableBits)]
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if checkAt := getCur(next) - backL; checkAt > 0 {
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best = bestOf(best, matchAt(checkAt, sBack, uint32(cv), false))
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}
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if checkAt := getPrev(next) - backL; checkAt > 0 {
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best = bestOf(best, matchAt(checkAt, sBack, uint32(cv), false))
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}
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// Disabled: Extremely small gain
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if false {
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next = sTable[hash4(load64(src, sAt), sTableBits)]
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if checkAt := getCur(next) - backL; checkAt > 0 {
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best = bestOf(best, matchAt(checkAt, sBack, uint32(cv), false))
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}
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if checkAt := getPrev(next) - backL; checkAt > 0 {
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best = bestOf(best, matchAt(checkAt, sBack, uint32(cv), false))
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}
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}
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}
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}
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}
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// Update table
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lTable[hashL] = uint64(s) | candidateL<<32
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sTable[hashS] = uint64(s) | candidateS<<32
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if best.length > 0 {
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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, not needed for repeats...
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s = best.s
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if !best.rep && !best.dict {
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for best.offset > 0 && s > nextEmit && src[best.offset-1] == src[s-1] {
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best.offset--
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best.length++
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s--
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}
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}
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if false && best.offset >= s {
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panic(fmt.Errorf("t %d >= s %d", best.offset, 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 := s - best.offset
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s += best.length
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if offset > 65535 && s-base <= 5 && !best.rep {
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// Bail if the match is equal or worse to the encoding.
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s = best.s + 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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if debug && nextEmit != base {
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fmt.Println("EMIT", base-nextEmit, "literals. base-after:", base)
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}
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d += emitLiteral(dst[d:], src[nextEmit:base])
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if best.rep {
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if nextEmit > 0 || best.dict {
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if debug {
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fmt.Println("REPEAT, length", best.length, "offset:", offset, "s-after:", s, "dict:", best.dict, "best:", best)
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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:], offset, best.length)
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} else {
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// First match without dict cannot be a repeat.
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if debug {
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fmt.Println("COPY, length", best.length, "offset:", offset, "s-after:", s, "dict:", best.dict, "best:", best)
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}
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d += emitCopy(dst[d:], offset, best.length)
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}
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} else {
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if debug {
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fmt.Println("COPY, length", best.length, "offset:", offset, "s-after:", s, "dict:", best.dict, "best:", best)
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}
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d += emitCopy(dst[d:], offset, best.length)
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}
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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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// Fill tables...
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for i := best.s + 1; i < s; i++ {
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cv0 := load64(src, i)
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long0 := hash8(cv0, lTableBits)
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short0 := hash4(cv0, sTableBits)
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lTable[long0] = uint64(i) | lTable[long0]<<32
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sTable[short0] = uint64(i) | sTable[short0]<<32
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}
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cv = load64(src, s)
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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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if debug && nextEmit != s {
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fmt.Println("emitted ", len(src)-nextEmit, "literals")
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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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}
|
|
|
|
// encodeBlockBestSnappy encodes a non-empty src to a guaranteed-large-enough dst. It
|
|
// assumes that the varint-encoded length of the decompressed bytes has already
|
|
// been written.
|
|
//
|
|
// It also assumes that:
|
|
//
|
|
// len(dst) >= MaxEncodedLen(len(src)) &&
|
|
// minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
|
|
func encodeBlockBestSnappy(dst, src []byte) (d int) {
|
|
// Initialize the hash tables.
|
|
const (
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|
// Long hash matches.
|
|
lTableBits = bestLongTableBits
|
|
maxLTableSize = bestLongTableSize
|
|
|
|
// Short hash matches.
|
|
sTableBits = bestShortTableBits
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|
maxSTableSize = bestShortTableSize
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|
|
|
inputMargin = 8 + 2
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)
|
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|
|
// sLimit is when to stop looking for offset/length copies. The inputMargin
|
|
// lets us use a fast path for emitLiteral in the main loop, while we are
|
|
// looking for copies.
|
|
sLimit := len(src) - inputMargin
|
|
if len(src) < minNonLiteralBlockSize {
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|
return 0
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|
}
|
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|
|
tbl := getBestTables()
|
|
lTable := &tbl.lTable
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|
sTable := &tbl.sTable
|
|
defer bestTablePool.Put(tbl)
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|
|
// Bail if we can't compress to at least this.
|
|
dstLimit := len(src) - 5
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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.
|
|
s := 1
|
|
cv := load64(src, s)
|
|
|
|
// We search for a repeat at -1, but don't output repeats when nextEmit == 0
|
|
repeat := 1
|
|
const lowbitMask = 0xffffffff
|
|
getCur := func(x uint64) int {
|
|
return int(x & lowbitMask)
|
|
}
|
|
getPrev := func(x uint64) int {
|
|
return int(x >> 32)
|
|
}
|
|
const maxSkip = 64
|
|
|
|
for {
|
|
type match struct {
|
|
offset int
|
|
s int
|
|
length int
|
|
score int
|
|
}
|
|
var best match
|
|
for {
|
|
// Next src position to check
|
|
nextS := (s-nextEmit)>>8 + 1
|
|
if nextS > maxSkip {
|
|
nextS = s + maxSkip
|
|
} else {
|
|
nextS += s
|
|
}
|
|
if nextS > sLimit {
|
|
goto emitRemainder
|
|
}
|
|
hashL := hash8(cv, lTableBits)
|
|
hashS := hash4(cv, sTableBits)
|
|
candidateL := lTable[hashL]
|
|
candidateS := sTable[hashS]
|
|
|
|
score := func(m match) int {
|
|
// Matches that are longer forward are penalized since we must emit it as a literal.
|
|
score := m.length - m.s
|
|
if nextEmit == m.s {
|
|
// If we do not have to emit literals, we save 1 byte
|
|
score++
|
|
}
|
|
offset := m.s - m.offset
|
|
|
|
return score - emitCopyNoRepeatSize(offset, m.length)
|
|
}
|
|
|
|
matchAt := func(offset, s int, first uint32) match {
|
|
if best.length != 0 && best.s-best.offset == s-offset {
|
|
// Don't retest if we have the same offset.
|
|
return match{offset: offset, s: s}
|
|
}
|
|
if load32(src, offset) != first {
|
|
return match{offset: offset, s: s}
|
|
}
|
|
m := match{offset: offset, s: s, length: 4 + offset}
|
|
s += 4
|
|
for s <= sLimit {
|
|
if diff := load64(src, s) ^ load64(src, m.length); diff != 0 {
|
|
m.length += bits.TrailingZeros64(diff) >> 3
|
|
break
|
|
}
|
|
s += 8
|
|
m.length += 8
|
|
}
|
|
m.length -= offset
|
|
m.score = score(m)
|
|
if m.score <= -m.s {
|
|
// Eliminate if no savings, we might find a better one.
|
|
m.length = 0
|
|
}
|
|
return m
|
|
}
|
|
|
|
bestOf := func(a, b match) match {
|
|
if b.length == 0 {
|
|
return a
|
|
}
|
|
if a.length == 0 {
|
|
return b
|
|
}
|
|
as := a.score + b.s
|
|
bs := b.score + a.s
|
|
if as >= bs {
|
|
return a
|
|
}
|
|
return b
|
|
}
|
|
|
|
best = bestOf(matchAt(getCur(candidateL), s, uint32(cv)), matchAt(getPrev(candidateL), s, uint32(cv)))
|
|
best = bestOf(best, matchAt(getCur(candidateS), s, uint32(cv)))
|
|
best = bestOf(best, matchAt(getPrev(candidateS), s, uint32(cv)))
|
|
|
|
{
|
|
best = bestOf(best, matchAt(s-repeat+1, s+1, uint32(cv>>8)))
|
|
if best.length > 0 {
|
|
// s+1
|
|
nextShort := sTable[hash4(cv>>8, sTableBits)]
|
|
s := s + 1
|
|
cv := load64(src, s)
|
|
nextLong := lTable[hash8(cv, lTableBits)]
|
|
best = bestOf(best, matchAt(getCur(nextShort), s, uint32(cv)))
|
|
best = bestOf(best, matchAt(getPrev(nextShort), s, uint32(cv)))
|
|
best = bestOf(best, matchAt(getCur(nextLong), s, uint32(cv)))
|
|
best = bestOf(best, matchAt(getPrev(nextLong), s, uint32(cv)))
|
|
// Repeat at + 2
|
|
best = bestOf(best, matchAt(s-repeat+1, s+1, uint32(cv>>8)))
|
|
|
|
// s+2
|
|
if true {
|
|
nextShort = sTable[hash4(cv>>8, sTableBits)]
|
|
s++
|
|
cv = load64(src, s)
|
|
nextLong = lTable[hash8(cv, lTableBits)]
|
|
best = bestOf(best, matchAt(getCur(nextShort), s, uint32(cv)))
|
|
best = bestOf(best, matchAt(getPrev(nextShort), s, uint32(cv)))
|
|
best = bestOf(best, matchAt(getCur(nextLong), s, uint32(cv)))
|
|
best = bestOf(best, matchAt(getPrev(nextLong), s, uint32(cv)))
|
|
}
|
|
// Search for a match at best match end, see if that is better.
|
|
if sAt := best.s + best.length; sAt < sLimit {
|
|
sBack := best.s
|
|
backL := best.length
|
|
// Load initial values
|
|
cv = load64(src, sBack)
|
|
// Search for mismatch
|
|
next := lTable[hash8(load64(src, sAt), lTableBits)]
|
|
//next := sTable[hash4(load64(src, sAt), sTableBits)]
|
|
|
|
if checkAt := getCur(next) - backL; checkAt > 0 {
|
|
best = bestOf(best, matchAt(checkAt, sBack, uint32(cv)))
|
|
}
|
|
if checkAt := getPrev(next) - backL; checkAt > 0 {
|
|
best = bestOf(best, matchAt(checkAt, sBack, uint32(cv)))
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Update table
|
|
lTable[hashL] = uint64(s) | candidateL<<32
|
|
sTable[hashS] = uint64(s) | candidateS<<32
|
|
|
|
if best.length > 0 {
|
|
break
|
|
}
|
|
|
|
cv = load64(src, nextS)
|
|
s = nextS
|
|
}
|
|
|
|
// Extend backwards, not needed for repeats...
|
|
s = best.s
|
|
if true {
|
|
for best.offset > 0 && s > nextEmit && src[best.offset-1] == src[s-1] {
|
|
best.offset--
|
|
best.length++
|
|
s--
|
|
}
|
|
}
|
|
if false && best.offset >= s {
|
|
panic(fmt.Errorf("t %d >= s %d", best.offset, s))
|
|
}
|
|
// Bail if we exceed the maximum size.
|
|
if d+(s-nextEmit) > dstLimit {
|
|
return 0
|
|
}
|
|
|
|
base := s
|
|
offset := s - best.offset
|
|
|
|
s += best.length
|
|
|
|
if offset > 65535 && s-base <= 5 {
|
|
// Bail if the match is equal or worse to the encoding.
|
|
s = best.s + 1
|
|
if s >= sLimit {
|
|
goto emitRemainder
|
|
}
|
|
cv = load64(src, s)
|
|
continue
|
|
}
|
|
d += emitLiteral(dst[d:], src[nextEmit:base])
|
|
d += emitCopyNoRepeat(dst[d:], offset, best.length)
|
|
repeat = offset
|
|
|
|
nextEmit = s
|
|
if s >= sLimit {
|
|
goto emitRemainder
|
|
}
|
|
|
|
if d > dstLimit {
|
|
// Do we have space for more, if not bail.
|
|
return 0
|
|
}
|
|
// Fill tables...
|
|
for i := best.s + 1; i < s; i++ {
|
|
cv0 := load64(src, i)
|
|
long0 := hash8(cv0, lTableBits)
|
|
short0 := hash4(cv0, sTableBits)
|
|
lTable[long0] = uint64(i) | lTable[long0]<<32
|
|
sTable[short0] = uint64(i) | sTable[short0]<<32
|
|
}
|
|
cv = load64(src, s)
|
|
}
|
|
|
|
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
|
|
}
|
|
|
|
// emitCopySize returns the size to encode the offset+length
|
|
//
|
|
// It assumes that:
|
|
//
|
|
// 1 <= offset && offset <= math.MaxUint32
|
|
// 4 <= length && length <= 1 << 24
|
|
func emitCopySize(offset, length int) int {
|
|
if offset >= 65536 {
|
|
i := 0
|
|
if length > 64 {
|
|
length -= 64
|
|
if length >= 4 {
|
|
// Emit remaining as repeats
|
|
return 5 + emitRepeatSize(offset, length)
|
|
}
|
|
i = 5
|
|
}
|
|
if length == 0 {
|
|
return i
|
|
}
|
|
return i + 5
|
|
}
|
|
|
|
// Offset no more than 2 bytes.
|
|
if length > 64 {
|
|
if offset < 2048 {
|
|
// Emit 8 bytes, then rest as repeats...
|
|
return 2 + emitRepeatSize(offset, length-8)
|
|
}
|
|
// Emit remaining as repeats, at least 4 bytes remain.
|
|
return 3 + emitRepeatSize(offset, length-60)
|
|
}
|
|
if length >= 12 || offset >= 2048 {
|
|
return 3
|
|
}
|
|
// Emit the remaining copy, encoded as 2 bytes.
|
|
return 2
|
|
}
|
|
|
|
// emitCopyNoRepeatSize returns the size to encode the offset+length
|
|
//
|
|
// It assumes that:
|
|
//
|
|
// 1 <= offset && offset <= math.MaxUint32
|
|
// 4 <= length && length <= 1 << 24
|
|
func emitCopyNoRepeatSize(offset, length int) int {
|
|
if offset >= 65536 {
|
|
return 5 + 5*(length/64)
|
|
}
|
|
|
|
// Offset no more than 2 bytes.
|
|
if length > 64 {
|
|
// Emit remaining as repeats, at least 4 bytes remain.
|
|
return 3 + 3*(length/60)
|
|
}
|
|
if length >= 12 || offset >= 2048 {
|
|
return 3
|
|
}
|
|
// Emit the remaining copy, encoded as 2 bytes.
|
|
return 2
|
|
}
|
|
|
|
// emitRepeatSize returns the number of bytes required to encode a repeat.
|
|
// Length must be at least 4 and < 1<<24
|
|
func emitRepeatSize(offset, length int) int {
|
|
// Repeat offset, make length cheaper
|
|
if length <= 4+4 || (length < 8+4 && offset < 2048) {
|
|
return 2
|
|
}
|
|
if length < (1<<8)+4+4 {
|
|
return 3
|
|
}
|
|
if length < (1<<16)+(1<<8)+4 {
|
|
return 4
|
|
}
|
|
const maxRepeat = (1 << 24) - 1
|
|
length -= (1 << 16) - 4
|
|
left := 0
|
|
if length > maxRepeat {
|
|
left = length - maxRepeat + 4
|
|
}
|
|
if left > 0 {
|
|
return 5 + emitRepeatSize(offset, left)
|
|
}
|
|
return 5
|
|
}
|