mirror of
https://github.com/go-gitea/gitea.git
synced 2024-08-26 14:17:29 +02:00
211 lines
5.1 KiB
Go
211 lines
5.1 KiB
Go
package flate
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import "fmt"
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type fastEncL4 struct {
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fastGen
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table [tableSize]tableEntry
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bTable [tableSize]tableEntry
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}
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func (e *fastEncL4) 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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// 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] = tableEntry{}
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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].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.bTable[i].offset = 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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for {
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const skipLog = 6
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const doEvery = 1
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nextS := s
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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, val: uint32(cv)}
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e.table[nextHashS] = entry
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e.bTable[nextHashL] = entry
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t = lCandidate.offset - e.cur
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if s-t < maxMatchOffset && uint32(cv) == lCandidate.val {
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// We got a long match. Use that.
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break
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}
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t = sCandidate.offset - e.cur
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if s-t < maxMatchOffset && uint32(cv) == sCandidate.val {
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// Found a 4 match...
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lCandidate = e.bTable[hash7(next, tableBits)]
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// If the next long is a candidate, check if we should use that instead...
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lOff := nextS - (lCandidate.offset - e.cur)
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if lOff < maxMatchOffset && lCandidate.val == uint32(next) {
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l1, l2 := matchLen(src[s+4:], src[t+4:]), matchLen(src[nextS+4:], src[nextS-lOff+4:])
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if l2 > l1 {
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s = nextS
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t = lCandidate.offset - e.cur
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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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l := e.matchlenLong(s+4, t+4, src) + 4
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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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emitLiteral(dst, src[nextEmit:s])
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}
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if false {
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if t >= s {
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panic("s-t")
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}
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if (s - t) > maxMatchOffset {
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panic(fmt.Sprintln("mmo", 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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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 first pair after match end.
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if int(s+8) < len(src) {
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cv := load6432(src, s)
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e.table[hash4x64(cv, tableBits)] = tableEntry{offset: s + e.cur, val: uint32(cv)}
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e.bTable[hash7(cv, tableBits)] = tableEntry{offset: s + e.cur, val: uint32(cv)}
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}
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goto emitRemainder
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}
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// Store every 3rd hash in-between
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if true {
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i := nextS
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if i < s-1 {
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cv := load6432(src, i)
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t := tableEntry{offset: i + e.cur, val: uint32(cv)}
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t2 := tableEntry{val: uint32(cv >> 8), offset: t.offset + 1}
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e.bTable[hash7(cv, tableBits)] = t
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e.bTable[hash7(cv>>8, tableBits)] = t2
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e.table[hash4u(t2.val, tableBits)] = t2
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i += 3
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for ; i < s-1; i += 3 {
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cv := load6432(src, i)
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t := tableEntry{offset: i + e.cur, val: uint32(cv)}
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t2 := tableEntry{val: uint32(cv >> 8), offset: t.offset + 1}
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e.bTable[hash7(cv, tableBits)] = t
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e.bTable[hash7(cv>>8, tableBits)] = t2
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e.table[hash4u(t2.val, tableBits)] = t2
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}
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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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x := load6432(src, s-1)
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o := e.cur + s - 1
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prevHashS := hash4x64(x, tableBits)
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prevHashL := hash7(x, tableBits)
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e.table[prevHashS] = tableEntry{offset: o, val: uint32(x)}
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e.bTable[prevHashL] = tableEntry{offset: o, val: uint32(x)}
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cv = x >> 8
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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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