gtsocial-umbx

level4.go (5470B)

---

 package flate
 
 import "fmt"
 
 type fastEncL4 struct {
 	fastGen
 	table  [tableSize]tableEntry
 	bTable [tableSize]tableEntry
 }
 
 func (e *fastEncL4) Encode(dst *tokens, src []byte) {
 	const (
 		inputMargin            = 12 - 1
 		minNonLiteralBlockSize = 1 + 1 + inputMargin
 		hashShortBytes         = 4
 	)
 	if debugDeflate && e.cur < 0 {
 		panic(fmt.Sprint("e.cur < 0: ", e.cur))
 	}
 	// Protect against e.cur wraparound.
 	for e.cur >= bufferReset {
 		if len(e.hist) == 0 {
 			for i := range e.table[:] {
 				e.table[i] = tableEntry{}
 			}
 			for i := range e.bTable[:] {
 				e.bTable[i] = tableEntry{}
 			}
 			e.cur = maxMatchOffset
 			break
 		}
 		// Shift down everything in the table that isn't already too far away.
 		minOff := e.cur + int32(len(e.hist)) - maxMatchOffset
 		for i := range e.table[:] {
 			v := e.table[i].offset
 			if v <= minOff {
 				v = 0
 			} else {
 				v = v - e.cur + maxMatchOffset
 			}
 			e.table[i].offset = v
 		}
 		for i := range e.bTable[:] {
 			v := e.bTable[i].offset
 			if v <= minOff {
 				v = 0
 			} else {
 				v = v - e.cur + maxMatchOffset
 			}
 			e.bTable[i].offset = v
 		}
 		e.cur = maxMatchOffset
 	}
 
 	s := e.addBlock(src)
 
 	// This check isn't in the Snappy implementation, but there, the caller
 	// instead of the callee handles this case.
 	if len(src) < minNonLiteralBlockSize {
 		// We do not fill the token table.
 		// This will be picked up by caller.
 		dst.n = uint16(len(src))
 		return
 	}
 
 	// Override src
 	src = e.hist
 	nextEmit := s
 
 	// 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 := int32(len(src) - inputMargin)
 
 	// nextEmit is where in src the next emitLiteral should start from.
 	cv := load6432(src, s)
 	for {
 		const skipLog = 6
 		const doEvery = 1
 
 		nextS := s
 		var t int32
 		for {
 			nextHashS := hashLen(cv, tableBits, hashShortBytes)
 			nextHashL := hash7(cv, tableBits)
 
 			s = nextS
 			nextS = s + doEvery + (s-nextEmit)>>skipLog
 			if nextS > sLimit {
 				goto emitRemainder
 			}
 			// Fetch a short+long candidate
 			sCandidate := e.table[nextHashS]
 			lCandidate := e.bTable[nextHashL]
 			next := load6432(src, nextS)
 			entry := tableEntry{offset: s + e.cur}
 			e.table[nextHashS] = entry
 			e.bTable[nextHashL] = entry
 
 			t = lCandidate.offset - e.cur
 			if s-t < maxMatchOffset && uint32(cv) == load3232(src, lCandidate.offset-e.cur) {
 				// We got a long match. Use that.
 				break
 			}
 
 			t = sCandidate.offset - e.cur
 			if s-t < maxMatchOffset && uint32(cv) == load3232(src, sCandidate.offset-e.cur) {
 				// Found a 4 match...
 				lCandidate = e.bTable[hash7(next, tableBits)]
 
 				// If the next long is a candidate, check if we should use that instead...
 				lOff := nextS - (lCandidate.offset - e.cur)
 				if lOff < maxMatchOffset && load3232(src, lCandidate.offset-e.cur) == uint32(next) {
 					l1, l2 := matchLen(src[s+4:], src[t+4:]), matchLen(src[nextS+4:], src[nextS-lOff+4:])
 					if l2 > l1 {
 						s = nextS
 						t = lCandidate.offset - e.cur
 					}
 				}
 				break
 			}
 			cv = next
 		}
 
 		// A 4-byte match has been found. We'll later see if more than 4 bytes
 		// match. But, prior to the match, src[nextEmit:s] are unmatched. Emit
 		// them as literal bytes.
 
 		// Extend the 4-byte match as long as possible.
 		l := e.matchlenLong(s+4, t+4, src) + 4
 
 		// Extend backwards
 		for t > 0 && s > nextEmit && src[t-1] == src[s-1] {
 			s--
 			t--
 			l++
 		}
 		if nextEmit < s {
 			if false {
 				emitLiteral(dst, src[nextEmit:s])
 			} else {
 				for _, v := range src[nextEmit:s] {
 					dst.tokens[dst.n] = token(v)
 					dst.litHist[v]++
 					dst.n++
 				}
 			}
 		}
 		if debugDeflate {
 			if t >= s {
 				panic("s-t")
 			}
 			if (s - t) > maxMatchOffset {
 				panic(fmt.Sprintln("mmo", t))
 			}
 			if l < baseMatchLength {
 				panic("bml")
 			}
 		}
 
 		dst.AddMatchLong(l, uint32(s-t-baseMatchOffset))
 		s += l
 		nextEmit = s
 		if nextS >= s {
 			s = nextS + 1
 		}
 
 		if s >= sLimit {
 			// Index first pair after match end.
 			if int(s+8) < len(src) {
 				cv := load6432(src, s)
 				e.table[hashLen(cv, tableBits, hashShortBytes)] = tableEntry{offset: s + e.cur}
 				e.bTable[hash7(cv, tableBits)] = tableEntry{offset: s + e.cur}
 			}
 			goto emitRemainder
 		}
 
 		// Store every 3rd hash in-between
 		if true {
 			i := nextS
 			if i < s-1 {
 				cv := load6432(src, i)
 				t := tableEntry{offset: i + e.cur}
 				t2 := tableEntry{offset: t.offset + 1}
 				e.bTable[hash7(cv, tableBits)] = t
 				e.bTable[hash7(cv>>8, tableBits)] = t2
 				e.table[hashLen(cv>>8, tableBits, hashShortBytes)] = t2
 
 				i += 3
 				for ; i < s-1; i += 3 {
 					cv := load6432(src, i)
 					t := tableEntry{offset: i + e.cur}
 					t2 := tableEntry{offset: t.offset + 1}
 					e.bTable[hash7(cv, tableBits)] = t
 					e.bTable[hash7(cv>>8, tableBits)] = t2
 					e.table[hashLen(cv>>8, tableBits, hashShortBytes)] = t2
 				}
 			}
 		}
 
 		// We could immediately start working at s now, but to improve
 		// compression we first update the hash table at s-1 and at s.
 		x := load6432(src, s-1)
 		o := e.cur + s - 1
 		prevHashS := hashLen(x, tableBits, hashShortBytes)
 		prevHashL := hash7(x, tableBits)
 		e.table[prevHashS] = tableEntry{offset: o}
 		e.bTable[prevHashL] = tableEntry{offset: o}
 		cv = x >> 8
 	}
 
 emitRemainder:
 	if int(nextEmit) < len(src) {
 		// If nothing was added, don't encode literals.
 		if dst.n == 0 {
 			return
 		}
 
 		emitLiteral(dst, src[nextEmit:])
 	}
 }