mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2024-11-23 04:06:39 +00:00
316 lines
7.9 KiB
Go
316 lines
7.9 KiB
Go
package flate
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import "fmt"
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type fastEncL6 struct {
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fastGen
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table [tableSize]tableEntry
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bTable [tableSize]tableEntryPrev
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}
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func (e *fastEncL6) Encode(dst *tokens, src []byte) {
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const (
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inputMargin = 12 - 1
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minNonLiteralBlockSize = 1 + 1 + inputMargin
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)
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if debugDeflate && e.cur < 0 {
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panic(fmt.Sprint("e.cur < 0: ", e.cur))
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}
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// Protect against e.cur wraparound.
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for e.cur >= bufferReset {
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if len(e.hist) == 0 {
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for i := range e.table[:] {
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e.table[i] = tableEntry{}
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}
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for i := range e.bTable[:] {
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e.bTable[i] = tableEntryPrev{}
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}
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e.cur = maxMatchOffset
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break
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}
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// Shift down everything in the table that isn't already too far away.
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minOff := e.cur + int32(len(e.hist)) - maxMatchOffset
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for i := range e.table[:] {
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v := e.table[i].offset
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if v <= minOff {
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v = 0
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} else {
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v = v - e.cur + maxMatchOffset
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}
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e.table[i].offset = v
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}
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for i := range e.bTable[:] {
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v := e.bTable[i]
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if v.Cur.offset <= minOff {
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v.Cur.offset = 0
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v.Prev.offset = 0
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} else {
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v.Cur.offset = v.Cur.offset - e.cur + maxMatchOffset
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if v.Prev.offset <= minOff {
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v.Prev.offset = 0
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} else {
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v.Prev.offset = v.Prev.offset - e.cur + maxMatchOffset
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}
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}
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e.bTable[i] = v
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}
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e.cur = maxMatchOffset
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}
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s := e.addBlock(src)
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// This check isn't in the Snappy implementation, but there, the caller
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// instead of the callee handles this case.
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if len(src) < minNonLiteralBlockSize {
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// We do not fill the token table.
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// This will be picked up by caller.
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dst.n = uint16(len(src))
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return
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}
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// Override src
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src = e.hist
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nextEmit := s
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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 := int32(len(src) - inputMargin)
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// nextEmit is where in src the next emitLiteral should start from.
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cv := load6432(src, s)
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// Repeat MUST be > 1 and within range
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repeat := int32(1)
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for {
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const skipLog = 7
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const doEvery = 1
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nextS := s
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var l int32
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var t int32
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for {
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nextHashS := hash4x64(cv, tableBits)
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nextHashL := hash7(cv, tableBits)
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s = nextS
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nextS = s + doEvery + (s-nextEmit)>>skipLog
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if nextS > sLimit {
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goto emitRemainder
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}
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// Fetch a short+long candidate
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sCandidate := e.table[nextHashS]
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lCandidate := e.bTable[nextHashL]
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next := load6432(src, nextS)
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entry := tableEntry{offset: s + e.cur}
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e.table[nextHashS] = entry
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eLong := &e.bTable[nextHashL]
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eLong.Cur, eLong.Prev = entry, eLong.Cur
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// Calculate hashes of 'next'
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nextHashS = hash4x64(next, tableBits)
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nextHashL = hash7(next, tableBits)
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t = lCandidate.Cur.offset - e.cur
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if s-t < maxMatchOffset {
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if uint32(cv) == load3232(src, lCandidate.Cur.offset-e.cur) {
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// Long candidate matches at least 4 bytes.
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// Store the next match
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e.table[nextHashS] = tableEntry{offset: nextS + e.cur}
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eLong := &e.bTable[nextHashL]
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eLong.Cur, eLong.Prev = tableEntry{offset: nextS + e.cur}, eLong.Cur
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// Check the previous long candidate as well.
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t2 := lCandidate.Prev.offset - e.cur
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if s-t2 < maxMatchOffset && uint32(cv) == load3232(src, lCandidate.Prev.offset-e.cur) {
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l = e.matchlen(s+4, t+4, src) + 4
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ml1 := e.matchlen(s+4, t2+4, src) + 4
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if ml1 > l {
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t = t2
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l = ml1
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break
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}
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}
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break
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}
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// Current value did not match, but check if previous long value does.
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t = lCandidate.Prev.offset - e.cur
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if s-t < maxMatchOffset && uint32(cv) == load3232(src, lCandidate.Prev.offset-e.cur) {
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// Store the next match
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e.table[nextHashS] = tableEntry{offset: nextS + e.cur}
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eLong := &e.bTable[nextHashL]
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eLong.Cur, eLong.Prev = tableEntry{offset: nextS + e.cur}, eLong.Cur
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break
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}
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}
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t = sCandidate.offset - e.cur
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if s-t < maxMatchOffset && uint32(cv) == load3232(src, sCandidate.offset-e.cur) {
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// Found a 4 match...
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l = e.matchlen(s+4, t+4, src) + 4
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// Look up next long candidate (at nextS)
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lCandidate = e.bTable[nextHashL]
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// Store the next match
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e.table[nextHashS] = tableEntry{offset: nextS + e.cur}
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eLong := &e.bTable[nextHashL]
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eLong.Cur, eLong.Prev = tableEntry{offset: nextS + e.cur}, eLong.Cur
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// Check repeat at s + repOff
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const repOff = 1
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t2 := s - repeat + repOff
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if load3232(src, t2) == uint32(cv>>(8*repOff)) {
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ml := e.matchlen(s+4+repOff, t2+4, src) + 4
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if ml > l {
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t = t2
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l = ml
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s += repOff
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// Not worth checking more.
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break
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}
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}
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// If the next long is a candidate, use that...
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t2 = lCandidate.Cur.offset - e.cur
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if nextS-t2 < maxMatchOffset {
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if load3232(src, lCandidate.Cur.offset-e.cur) == uint32(next) {
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ml := e.matchlen(nextS+4, t2+4, src) + 4
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if ml > l {
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t = t2
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s = nextS
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l = ml
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// This is ok, but check previous as well.
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}
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}
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// If the previous long is a candidate, use that...
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t2 = lCandidate.Prev.offset - e.cur
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if nextS-t2 < maxMatchOffset && load3232(src, lCandidate.Prev.offset-e.cur) == uint32(next) {
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ml := e.matchlen(nextS+4, t2+4, src) + 4
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if ml > l {
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t = t2
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s = nextS
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l = ml
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break
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}
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}
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}
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break
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}
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cv = next
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}
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// A 4-byte match has been found. We'll later see if more than 4 bytes
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// match. But, prior to the match, src[nextEmit:s] are unmatched. Emit
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// them as literal bytes.
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// Extend the 4-byte match as long as possible.
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if l == 0 {
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l = e.matchlenLong(s+4, t+4, src) + 4
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} else if l == maxMatchLength {
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l += e.matchlenLong(s+l, t+l, src)
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}
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// Try to locate a better match by checking the end-of-match...
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if sAt := s + l; sAt < sLimit {
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eLong := &e.bTable[hash7(load6432(src, sAt), tableBits)]
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// Test current
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t2 := eLong.Cur.offset - e.cur - l
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off := s - t2
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if off < maxMatchOffset {
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if off > 0 && t2 >= 0 {
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if l2 := e.matchlenLong(s, t2, src); l2 > l {
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t = t2
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l = l2
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}
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}
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// Test next:
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t2 = eLong.Prev.offset - e.cur - l
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off := s - t2
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if off > 0 && off < maxMatchOffset && t2 >= 0 {
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if l2 := e.matchlenLong(s, t2, src); l2 > l {
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t = t2
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l = l2
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}
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}
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}
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}
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// Extend backwards
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for t > 0 && s > nextEmit && src[t-1] == src[s-1] {
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s--
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t--
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l++
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}
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if nextEmit < s {
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if false {
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emitLiteral(dst, src[nextEmit:s])
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} else {
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for _, v := range src[nextEmit:s] {
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dst.tokens[dst.n] = token(v)
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dst.litHist[v]++
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dst.n++
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}
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}
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}
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if false {
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if t >= s {
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panic(fmt.Sprintln("s-t", s, t))
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}
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if (s - t) > maxMatchOffset {
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panic(fmt.Sprintln("mmo", s-t))
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}
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if l < baseMatchLength {
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panic("bml")
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}
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}
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dst.AddMatchLong(l, uint32(s-t-baseMatchOffset))
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repeat = s - t
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s += l
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nextEmit = s
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if nextS >= s {
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s = nextS + 1
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}
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if s >= sLimit {
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// Index after match end.
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for i := nextS + 1; i < int32(len(src))-8; i += 2 {
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cv := load6432(src, i)
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e.table[hash4x64(cv, tableBits)] = tableEntry{offset: i + e.cur}
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eLong := &e.bTable[hash7(cv, tableBits)]
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eLong.Cur, eLong.Prev = tableEntry{offset: i + e.cur}, eLong.Cur
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}
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goto emitRemainder
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}
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// Store every long hash in-between and every second short.
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if true {
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for i := nextS + 1; i < s-1; i += 2 {
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cv := load6432(src, i)
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t := tableEntry{offset: i + e.cur}
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t2 := tableEntry{offset: t.offset + 1}
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eLong := &e.bTable[hash7(cv, tableBits)]
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eLong2 := &e.bTable[hash7(cv>>8, tableBits)]
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e.table[hash4x64(cv, tableBits)] = t
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eLong.Cur, eLong.Prev = t, eLong.Cur
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eLong2.Cur, eLong2.Prev = t2, eLong2.Cur
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}
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}
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// We could immediately start working at s now, but to improve
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// compression we first update the hash table at s-1 and at s.
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cv = load6432(src, s)
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}
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emitRemainder:
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if int(nextEmit) < len(src) {
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// If nothing was added, don't encode literals.
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if dst.n == 0 {
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return
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}
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emitLiteral(dst, src[nextEmit:])
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}
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}
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