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deflate.go
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deflate.go
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// Copyright 2009 The Go Authors. All rights reserved.
// Copyright (c) 2015 Klaus Post
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package flate
import (
"fmt"
"io"
"math"
)
const (
NoCompression = 0
BestSpeed = 1
fastCompression = 3
BestCompression = 9
DefaultCompression = -1
ConstantCompression = -2 // Does only Huffman encoding
logWindowSize = 15
windowSize = 1 << logWindowSize
windowMask = windowSize - 1
logMaxOffsetSize = 15 // Standard DEFLATE
minMatchLength = 4 // The smallest match that the compressor looks for
maxMatchLength = 258 // The longest match for the compressor
minOffsetSize = 1 // The shortest offset that makes any sense
// The maximum number of tokens we put into a single flat block, just too
// stop things from getting too large.
maxFlateBlockTokens = 1 << 14
maxStoreBlockSize = 65535
hashBits = 17 // After 17 performance degrades
hashSize = 1 << hashBits
hashMask = (1 << hashBits) - 1
hashShift = (hashBits + minMatchLength - 1) / minMatchLength
maxHashOffset = 1 << 24
skipNever = math.MaxInt32
)
var useSSE42 bool
type compressionLevel struct {
good, lazy, nice, chain, fastSkipHashing, level int
}
var levels = []compressionLevel{
{}, // 0
// For levels 1-3 we don't bother trying with lazy matches
{4, 0, 8, 4, 4, 1},
{4, 0, 16, 8, 5, 2},
{4, 0, 32, 32, 6, 3},
// Levels 4-9 use increasingly more lazy matching
// and increasingly stringent conditions for "good enough".
{4, 4, 16, 16, skipNever, 4},
{8, 16, 32, 32, skipNever, 5},
{8, 16, 128, 128, skipNever, 6},
{8, 32, 128, 256, skipNever, 7},
{32, 128, 258, 1024, skipNever, 8},
{32, 258, 258, 4096, skipNever, 9},
}
type hashid uint32
type compressor struct {
compressionLevel
w *huffmanBitWriter
bulkHasher func([]byte, []hash)
// compression algorithm
fill func(*compressor, []byte) int // copy data to window
step func(*compressor) // process window
sync bool // requesting flush
// Input hash chains
// hashHead[hashValue] contains the largest inputIndex with the specified hash value
// If hashHead[hashValue] is within the current window, then
// hashPrev[hashHead[hashValue] & windowMask] contains the previous index
// with the same hash value.
chainHead int
hashHead []hashid
hashPrev []hashid
hashOffset int
// input window: unprocessed data is window[index:windowEnd]
index int
window []byte
windowEnd int
blockStart int // window index where current tokens start
byteAvailable bool // if true, still need to process window[index-1].
// queued output tokens
tokens tokens
// deflate state
length int
offset int
hash hash
maxInsertIndex int
err error
ii uint16 // position of last match, intended to overflow to reset.
hashMatch [maxMatchLength + minMatchLength]hash
}
type hash int32
func (d *compressor) fillDeflate(b []byte) int {
if d.index >= 2*windowSize-(minMatchLength+maxMatchLength) {
// shift the window by windowSize
copy(d.window, d.window[windowSize:2*windowSize])
d.index -= windowSize
d.windowEnd -= windowSize
if d.blockStart >= windowSize {
d.blockStart -= windowSize
} else {
d.blockStart = math.MaxInt32
}
d.hashOffset += windowSize
if d.hashOffset > maxHashOffset {
delta := d.hashOffset - 1
d.hashOffset -= delta
d.chainHead -= delta
for i, v := range d.hashPrev {
if int(v) > delta {
d.hashPrev[i] = hashid(int(v) - delta)
} else {
d.hashPrev[i] = 0
}
}
for i, v := range d.hashHead {
if int(v) > delta {
d.hashHead[i] = hashid(int(v) - delta)
} else {
d.hashHead[i] = 0
}
}
}
}
n := copy(d.window[d.windowEnd:], b)
d.windowEnd += n
return n
}
func (d *compressor) writeBlock(tok tokens, index int, eof bool) error {
if index > 0 || eof {
var window []byte
if d.blockStart <= index {
window = d.window[d.blockStart:index]
}
d.blockStart = index
d.w.writeBlock(tok, eof, window)
return d.w.err
}
return nil
}
// fillWindow will fill the current window with the supplied
// dictionary and calculate all hashes.
// This is much faster than doing a full encode.
// Should only be used after a start/reset.
func (d *compressor) fillWindow(b []byte) {
// Do not fill window if we are in store-only mode,
// use constant or Snappy compression.
if d.compressionLevel.level == 0 {
return
}
// If we are given too much, cut it.
if len(b) > windowSize {
b = b[len(b)-windowSize:]
}
// Add all to window.
n := copy(d.window[d.windowEnd:], b)
// Calculate 256 hashes at the time (more L1 cache hits)
loops := (n + 256 - minMatchLength) / 256
for j := 0; j < loops; j++ {
startindex := j * 256
end := startindex + 256 + minMatchLength - 1
if end > n {
end = n
}
tocheck := d.window[startindex:end]
dstSize := len(tocheck) - minMatchLength + 1
if dstSize <= 0 {
continue
}
dst := d.hashMatch[:dstSize]
d.bulkHasher(tocheck, dst)
var newH hash
for i, val := range dst {
di := i + startindex
newH = val & hashMask
// Get previous value with the same hash.
// Our chain should point to the previous value.
d.hashPrev[di&windowMask] = d.hashHead[newH]
// Set the head of the hash chain to us.
d.hashHead[newH] = hashid(di + d.hashOffset)
}
d.hash = newH
}
// Update window information.
d.windowEnd += n
d.index = n
}
// Try to find a match starting at index whose length is greater than prevSize.
// We only look at chainCount possibilities before giving up.
// pos = d.index, prevHead = d.chainHead-d.hashOffset, prevLength=minMatchLength-1, lookahead
func (d *compressor) findMatch(pos int, prevHead int, prevLength int, lookahead int) (length, offset int, ok bool) {
minMatchLook := maxMatchLength
if lookahead < minMatchLook {
minMatchLook = lookahead
}
win := d.window[0 : pos+minMatchLook]
// We quit when we get a match that's at least nice long
nice := len(win) - pos
if d.nice < nice {
nice = d.nice
}
// If we've got a match that's good enough, only look in 1/4 the chain.
tries := d.chain
length = prevLength
if length >= d.good {
tries >>= 2
}
wEnd := win[pos+length]
wPos := win[pos:]
minIndex := pos - windowSize
for i := prevHead; tries > 0; tries-- {
if wEnd == win[i+length] {
n := matchLen(win[i:], wPos, minMatchLook)
if n > length && (n > minMatchLength || pos-i <= 4096) {
length = n
offset = pos - i
ok = true
if n >= nice {
// The match is good enough that we don't try to find a better one.
break
}
wEnd = win[pos+n]
}
}
if i == minIndex {
// hashPrev[i & windowMask] has already been overwritten, so stop now.
break
}
i = int(d.hashPrev[i&windowMask]) - d.hashOffset
if i < minIndex || i < 0 {
break
}
}
return
}
// Try to find a match starting at index whose length is greater than prevSize.
// We only look at chainCount possibilities before giving up.
// pos = d.index, prevHead = d.chainHead-d.hashOffset, prevLength=minMatchLength-1, lookahead
func (d *compressor) findMatchSSE(pos int, prevHead int, prevLength int, lookahead int) (length, offset int, ok bool) {
minMatchLook := maxMatchLength
if lookahead < minMatchLook {
minMatchLook = lookahead
}
win := d.window[0 : pos+minMatchLook]
// We quit when we get a match that's at least nice long
nice := len(win) - pos
if d.nice < nice {
nice = d.nice
}
// If we've got a match that's good enough, only look in 1/4 the chain.
tries := d.chain
length = prevLength
if length >= d.good {
tries >>= 2
}
wEnd := win[pos+length]
wPos := win[pos:]
minIndex := pos - windowSize
for i := prevHead; tries > 0; tries-- {
if wEnd == win[i+length] {
n := matchLenSSE4(win[i:], wPos, minMatchLook)
if n > length && (n > minMatchLength || pos-i <= 4096) {
length = n
offset = pos - i
ok = true
if n >= nice {
// The match is good enough that we don't try to find a better one.
break
}
wEnd = win[pos+n]
}
}
if i == minIndex {
// hashPrev[i & windowMask] has already been overwritten, so stop now.
break
}
i = int(d.hashPrev[i&windowMask]) - d.hashOffset
if i < minIndex || i < 0 {
break
}
}
return
}
func (d *compressor) writeStoredBlock(buf []byte) error {
if d.w.writeStoredHeader(len(buf), false); d.w.err != nil {
return d.w.err
}
d.w.writeBytes(buf)
return d.w.err
}
// oldHash is the hash function used when no native crc32 calculation
// or similar is present.
func oldHash(b []byte) hash {
return hash(b[0])<<(hashShift*3) + hash(b[1])<<(hashShift*2) + hash(b[2])<<hashShift + hash(b[3])
}
// oldBulkHash will compute hashes using the same
// algorithm as oldHash
func oldBulkHash(b []byte, dst []hash) {
if len(b) < minMatchLength {
return
}
h := oldHash(b)
dst[0] = h
i := 1
end := len(b) - minMatchLength + 1
for ; i < end; i++ {
h = (h << hashShift) + hash(b[i+3])
dst[i] = h
}
}
// matchLen returns the number of matching bytes in a and b
// up to length 'max'. Both slices must be at least 'max'
// bytes in size.
func matchLen(a, b []byte, max int) int {
a = a[:max]
for i, av := range a {
if b[i] != av {
return i
}
}
return max
}
func (d *compressor) initDeflate() {
d.hashHead = make([]hashid, hashSize)
d.hashPrev = make([]hashid, windowSize)
d.window = make([]byte, 2*windowSize)
d.hashOffset = 1
d.tokens.tokens = make([]token, maxFlateBlockTokens+1)
d.length = minMatchLength - 1
d.offset = 0
d.byteAvailable = false
d.index = 0
d.hash = 0
d.chainHead = -1
d.bulkHasher = oldBulkHash
if useSSE42 {
d.bulkHasher = crc32sseAll
}
}
// Assumes that d.fastSkipHashing != skipNever,
// otherwise use deflateNoSkip
func (d *compressor) deflate() {
// Sanity enables additional runtime tests.
// It's intended to be used during development
// to supplement the currently ad-hoc unit tests.
const sanity = false
if d.windowEnd-d.index < minMatchLength+maxMatchLength && !d.sync {
return
}
d.maxInsertIndex = d.windowEnd - (minMatchLength - 1)
if d.index < d.maxInsertIndex {
d.hash = oldHash(d.window[d.index:d.index+minMatchLength]) & hashMask
}
for {
if sanity && d.index > d.windowEnd {
panic("index > windowEnd")
}
lookahead := d.windowEnd - d.index
if lookahead < minMatchLength+maxMatchLength {
if !d.sync {
return
}
if sanity && d.index > d.windowEnd {
panic("index > windowEnd")
}
if lookahead == 0 {
if d.tokens.n > 0 {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
return
}
}
if d.index < d.maxInsertIndex {
// Update the hash
d.hash = oldHash(d.window[d.index:d.index+minMatchLength]) & hashMask
ch := d.hashHead[d.hash]
d.chainHead = int(ch)
d.hashPrev[d.index&windowMask] = ch
d.hashHead[d.hash] = hashid(d.index + d.hashOffset)
}
d.length = minMatchLength - 1
d.offset = 0
minIndex := d.index - windowSize
if minIndex < 0 {
minIndex = 0
}
if d.chainHead-d.hashOffset >= minIndex && lookahead > minMatchLength-1 {
if newLength, newOffset, ok := d.findMatch(d.index, d.chainHead-d.hashOffset, minMatchLength-1, lookahead); ok {
d.length = newLength
d.offset = newOffset
}
}
if d.length >= minMatchLength {
d.ii = 0
// There was a match at the previous step, and the current match is
// not better. Output the previous match.
// "d.length-3" should NOT be "d.length-minMatchLength", since the format always assume 3
d.tokens.tokens[d.tokens.n] = matchToken(uint32(d.length-3), uint32(d.offset-minOffsetSize))
d.tokens.n++
// Insert in the hash table all strings up to the end of the match.
// index and index-1 are already inserted. If there is not enough
// lookahead, the last two strings are not inserted into the hash
// table.
if d.length <= d.fastSkipHashing {
var newIndex int
newIndex = d.index + d.length
// Calculate missing hashes
end := newIndex
if end > d.maxInsertIndex {
end = d.maxInsertIndex
}
end += minMatchLength - 1
startindex := d.index + 1
if startindex > d.maxInsertIndex {
startindex = d.maxInsertIndex
}
tocheck := d.window[startindex:end]
dstSize := len(tocheck) - minMatchLength + 1
if dstSize > 0 {
dst := d.hashMatch[:dstSize]
oldBulkHash(tocheck, dst)
var newH hash
for i, val := range dst {
di := i + startindex
newH = val & hashMask
// Get previous value with the same hash.
// Our chain should point to the previous value.
d.hashPrev[di&windowMask] = d.hashHead[newH]
// Set the head of the hash chain to us.
d.hashHead[newH] = hashid(di + d.hashOffset)
}
d.hash = newH
}
d.index = newIndex
} else {
// For matches this long, we don't bother inserting each individual
// item into the table.
d.index += d.length
if d.index < d.maxInsertIndex {
d.hash = oldHash(d.window[d.index:d.index+minMatchLength]) & hashMask
}
}
if d.tokens.n == maxFlateBlockTokens {
// The block includes the current character
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
} else {
d.ii++
end := d.index + int(d.ii>>uint(d.fastSkipHashing)) + 1
if end > d.windowEnd {
end = d.windowEnd
}
for i := d.index; i < end; i++ {
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[i]))
d.tokens.n++
if d.tokens.n == maxFlateBlockTokens {
if d.err = d.writeBlock(d.tokens, i+1, false); d.err != nil {
return
}
d.tokens.n = 0
}
}
d.index = end
}
}
}
// deflateLazy is the same as deflate, but with d.fastSkipHashing == skipNever,
// meaning it always has lazy matching on.
func (d *compressor) deflateLazy() {
// Sanity enables additional runtime tests.
// It's intended to be used during development
// to supplement the currently ad-hoc unit tests.
const sanity = false
if d.windowEnd-d.index < minMatchLength+maxMatchLength && !d.sync {
return
}
d.maxInsertIndex = d.windowEnd - (minMatchLength - 1)
if d.index < d.maxInsertIndex {
d.hash = oldHash(d.window[d.index:d.index+minMatchLength]) & hashMask
}
for {
if sanity && d.index > d.windowEnd {
panic("index > windowEnd")
}
lookahead := d.windowEnd - d.index
if lookahead < minMatchLength+maxMatchLength {
if !d.sync {
return
}
if sanity && d.index > d.windowEnd {
panic("index > windowEnd")
}
if lookahead == 0 {
// Flush current output block if any.
if d.byteAvailable {
// There is still one pending token that needs to be flushed
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[d.index-1]))
d.tokens.n++
d.byteAvailable = false
}
if d.tokens.n > 0 {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
return
}
}
if d.index < d.maxInsertIndex {
// Update the hash
d.hash = oldHash(d.window[d.index:d.index+minMatchLength]) & hashMask
ch := d.hashHead[d.hash]
d.chainHead = int(ch)
d.hashPrev[d.index&windowMask] = ch
d.hashHead[d.hash] = hashid(d.index + d.hashOffset)
}
prevLength := d.length
prevOffset := d.offset
d.length = minMatchLength - 1
d.offset = 0
minIndex := d.index - windowSize
if minIndex < 0 {
minIndex = 0
}
if d.chainHead-d.hashOffset >= minIndex && lookahead > prevLength && prevLength < d.lazy {
if newLength, newOffset, ok := d.findMatch(d.index, d.chainHead-d.hashOffset, minMatchLength-1, lookahead); ok {
d.length = newLength
d.offset = newOffset
}
}
if prevLength >= minMatchLength && d.length <= prevLength {
// There was a match at the previous step, and the current match is
// not better. Output the previous match.
d.tokens.tokens[d.tokens.n] = matchToken(uint32(prevLength-3), uint32(prevOffset-minOffsetSize))
d.tokens.n++
// Insert in the hash table all strings up to the end of the match.
// index and index-1 are already inserted. If there is not enough
// lookahead, the last two strings are not inserted into the hash
// table.
var newIndex int
newIndex = d.index + prevLength - 1
// Calculate missing hashes
end := newIndex
if end > d.maxInsertIndex {
end = d.maxInsertIndex
}
end += minMatchLength - 1
startindex := d.index + 1
if startindex > d.maxInsertIndex {
startindex = d.maxInsertIndex
}
tocheck := d.window[startindex:end]
dstSize := len(tocheck) - minMatchLength + 1
if dstSize > 0 {
dst := d.hashMatch[:dstSize]
oldBulkHash(tocheck, dst)
var newH hash
for i, val := range dst {
di := i + startindex
newH = val & hashMask
// Get previous value with the same hash.
// Our chain should point to the previous value.
d.hashPrev[di&windowMask] = d.hashHead[newH]
// Set the head of the hash chain to us.
d.hashHead[newH] = hashid(di + d.hashOffset)
}
d.hash = newH
}
d.index = newIndex
d.byteAvailable = false
d.length = minMatchLength - 1
if d.tokens.n == maxFlateBlockTokens {
// The block includes the current character
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
} else {
// Reset, if we got a match this run.
if d.length >= minMatchLength {
d.ii = 0
}
// We have a byte waiting. Emit it.
if d.byteAvailable {
d.ii++
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[d.index-1]))
d.tokens.n++
if d.tokens.n == maxFlateBlockTokens {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
d.index++
// If we have a long run of no matches, skip additional bytes
// Resets when d.ii overflows after 64KB.
if d.ii > 31 {
n := int(d.ii >> 6)
for j := 0; j < n; j++ {
if d.index >= d.windowEnd-1 {
break
}
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[d.index-1]))
d.tokens.n++
if d.tokens.n == maxFlateBlockTokens {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
d.index++
}
// Flush last byte
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[d.index-1]))
d.tokens.n++
d.byteAvailable = false
// d.length = minMatchLength - 1 // not needed, since d.ii is reset above, so it should never be > minMatchLength
if d.tokens.n == maxFlateBlockTokens {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
}
} else {
d.index++
d.byteAvailable = true
}
}
}
}
// Assumes that d.fastSkipHashing != skipNever,
// otherwise use deflateNoSkip
func (d *compressor) deflateSSE() {
// Sanity enables additional runtime tests.
// It's intended to be used during development
// to supplement the currently ad-hoc unit tests.
const sanity = false
if d.windowEnd-d.index < minMatchLength+maxMatchLength && !d.sync {
return
}
d.maxInsertIndex = d.windowEnd - (minMatchLength - 1)
if d.index < d.maxInsertIndex {
d.hash = oldHash(d.window[d.index:d.index+minMatchLength]) & hashMask
}
for {
if sanity && d.index > d.windowEnd {
panic("index > windowEnd")
}
lookahead := d.windowEnd - d.index
if lookahead < minMatchLength+maxMatchLength {
if !d.sync {
return
}
if sanity && d.index > d.windowEnd {
panic("index > windowEnd")
}
if lookahead == 0 {
if d.tokens.n > 0 {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
return
}
}
if d.index < d.maxInsertIndex {
// Update the hash
d.hash = crc32sse(d.window[d.index:d.index+minMatchLength]) & hashMask
ch := d.hashHead[d.hash]
d.chainHead = int(ch)
d.hashPrev[d.index&windowMask] = ch
d.hashHead[d.hash] = hashid(d.index + d.hashOffset)
}
d.length = minMatchLength - 1
d.offset = 0
minIndex := d.index - windowSize
if minIndex < 0 {
minIndex = 0
}
if d.chainHead-d.hashOffset >= minIndex && lookahead > minMatchLength-1 {
if newLength, newOffset, ok := d.findMatchSSE(d.index, d.chainHead-d.hashOffset, minMatchLength-1, lookahead); ok {
d.length = newLength
d.offset = newOffset
}
}
if d.length >= minMatchLength {
d.ii = 0
// There was a match at the previous step, and the current match is
// not better. Output the previous match.
// "d.length-3" should NOT be "d.length-minMatchLength", since the format always assume 3
d.tokens.tokens[d.tokens.n] = matchToken(uint32(d.length-3), uint32(d.offset-minOffsetSize))
d.tokens.n++
// Insert in the hash table all strings up to the end of the match.
// index and index-1 are already inserted. If there is not enough
// lookahead, the last two strings are not inserted into the hash
// table.
if d.length <= d.fastSkipHashing {
var newIndex int
newIndex = d.index + d.length
// Calculate missing hashes
end := newIndex
if end > d.maxInsertIndex {
end = d.maxInsertIndex
}
end += minMatchLength - 1
startindex := d.index + 1
if startindex > d.maxInsertIndex {
startindex = d.maxInsertIndex
}
tocheck := d.window[startindex:end]
dstSize := len(tocheck) - minMatchLength + 1
if dstSize > 0 {
dst := d.hashMatch[:dstSize]
crc32sseAll(tocheck, dst)
var newH hash
for i, val := range dst {
di := i + startindex
newH = val & hashMask
// Get previous value with the same hash.
// Our chain should point to the previous value.
d.hashPrev[di&windowMask] = d.hashHead[newH]
// Set the head of the hash chain to us.
d.hashHead[newH] = hashid(di + d.hashOffset)
}
d.hash = newH
}
d.index = newIndex
} else {
// For matches this long, we don't bother inserting each individual
// item into the table.
d.index += d.length
if d.index < d.maxInsertIndex {
d.hash = crc32sse(d.window[d.index:d.index+minMatchLength]) & hashMask
}
}
if d.tokens.n == maxFlateBlockTokens {
// The block includes the current character
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
} else {
d.ii++
end := d.index + int(d.ii>>uint(d.fastSkipHashing)) + 1
if end > d.windowEnd {
end = d.windowEnd
}
for i := d.index; i < end; i++ {
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[i]))
d.tokens.n++
if d.tokens.n == maxFlateBlockTokens {
if d.err = d.writeBlock(d.tokens, i+1, false); d.err != nil {
return
}
d.tokens.n = 0
}
}
d.index = end
}
}
}
// deflateLazy is the same as deflate, but with d.fastSkipHashing == skipNever,
// meaning it always has lazy matching on.
func (d *compressor) deflateLazySSE() {
// Sanity enables additional runtime tests.
// It's intended to be used during development
// to supplement the currently ad-hoc unit tests.
const sanity = false
if d.windowEnd-d.index < minMatchLength+maxMatchLength && !d.sync {
return
}
d.maxInsertIndex = d.windowEnd - (minMatchLength - 1)
if d.index < d.maxInsertIndex {
d.hash = crc32sse(d.window[d.index:d.index+minMatchLength]) & hashMask
}
for {
if sanity && d.index > d.windowEnd {
panic("index > windowEnd")
}
lookahead := d.windowEnd - d.index
if lookahead < minMatchLength+maxMatchLength {
if !d.sync {
return
}
if sanity && d.index > d.windowEnd {
panic("index > windowEnd")
}
if lookahead == 0 {
// Flush current output block if any.
if d.byteAvailable {
// There is still one pending token that needs to be flushed
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[d.index-1]))
d.tokens.n++
d.byteAvailable = false
}
if d.tokens.n > 0 {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
return
}
}
if d.index < d.maxInsertIndex {
// Update the hash
d.hash = crc32sse(d.window[d.index:d.index+minMatchLength]) & hashMask
ch := d.hashHead[d.hash]
d.chainHead = int(ch)
d.hashPrev[d.index&windowMask] = ch
d.hashHead[d.hash] = hashid(d.index + d.hashOffset)
}
prevLength := d.length
prevOffset := d.offset
d.length = minMatchLength - 1
d.offset = 0
minIndex := d.index - windowSize
if minIndex < 0 {
minIndex = 0
}
if d.chainHead-d.hashOffset >= minIndex && lookahead > prevLength && prevLength < d.lazy {
if newLength, newOffset, ok := d.findMatchSSE(d.index, d.chainHead-d.hashOffset, minMatchLength-1, lookahead); ok {
d.length = newLength
d.offset = newOffset
}
}
if prevLength >= minMatchLength && d.length <= prevLength {
// There was a match at the previous step, and the current match is
// not better. Output the previous match.
d.tokens.tokens[d.tokens.n] = matchToken(uint32(prevLength-3), uint32(prevOffset-minOffsetSize))
d.tokens.n++
// Insert in the hash table all strings up to the end of the match.
// index and index-1 are already inserted. If there is not enough
// lookahead, the last two strings are not inserted into the hash
// table.
var newIndex int
newIndex = d.index + prevLength - 1
// Calculate missing hashes
end := newIndex
if end > d.maxInsertIndex {
end = d.maxInsertIndex
}
end += minMatchLength - 1
startindex := d.index + 1
if startindex > d.maxInsertIndex {
startindex = d.maxInsertIndex
}
tocheck := d.window[startindex:end]
dstSize := len(tocheck) - minMatchLength + 1
if dstSize > 0 {
dst := d.hashMatch[:dstSize]
crc32sseAll(tocheck, dst)
var newH hash
for i, val := range dst {
di := i + startindex
newH = val & hashMask
// Get previous value with the same hash.
// Our chain should point to the previous value.
d.hashPrev[di&windowMask] = d.hashHead[newH]
// Set the head of the hash chain to us.
d.hashHead[newH] = hashid(di + d.hashOffset)
}
d.hash = newH
}
d.index = newIndex
d.byteAvailable = false
d.length = minMatchLength - 1
if d.tokens.n == maxFlateBlockTokens {
// The block includes the current character
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
} else {
// Reset, if we got a match this run.
if d.length >= minMatchLength {
d.ii = 0
}
// We have a byte waiting. Emit it.
if d.byteAvailable {
d.ii++
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[d.index-1]))
d.tokens.n++
if d.tokens.n == maxFlateBlockTokens {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
d.index++
// If we have a long run of no matches, skip additional bytes
// Resets when d.ii overflows after 64KB.
if d.ii > 31 {
n := int(d.ii >> 6)
for j := 0; j < n; j++ {
if d.index >= d.windowEnd-1 {
break
}
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[d.index-1]))
d.tokens.n++
if d.tokens.n == maxFlateBlockTokens {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return
}
d.tokens.n = 0
}
d.index++
}
// Flush last byte
d.tokens.tokens[d.tokens.n] = literalToken(uint32(d.window[d.index-1]))
d.tokens.n++
d.byteAvailable = false
// d.length = minMatchLength - 1 // not needed, since d.ii is reset above, so it should never be > minMatchLength
if d.tokens.n == maxFlateBlockTokens {
if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
return