vendor/github.com/klauspost/compress/flate/level5.go

package flate

import "fmt"

type fastEncL5 struct {
	fastGen
	table  [tableSize]tableEntry
	bTable [tableSize]tableEntryPrev
}

func (e *fastEncL5) 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] = tableEntryPrev{}
			}
			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]
			if v.Cur.offset <= minOff {
				v.Cur.offset = 0
				v.Prev.offset = 0
			} else {
				v.Cur.offset = v.Cur.offset - e.cur + maxMatchOffset
				if v.Prev.offset <= minOff {
					v.Prev.offset = 0
				} else {
					v.Prev.offset = v.Prev.offset - e.cur + maxMatchOffset
				}
			}
			e.bTable[i] = 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 l int32
		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
			eLong := &e.bTable[nextHashL]
			eLong.Cur, eLong.Prev = entry, eLong.Cur

			nextHashS = hashLen(next, tableBits, hashShortBytes)
			nextHashL = hash7(next, tableBits)

			t = lCandidate.Cur.offset - e.cur
			if s-t < maxMatchOffset {
				if uint32(cv) == load3232(src, t) {
					// Store the next match
					e.table[nextHashS] = tableEntry{offset: nextS + e.cur}
					eLong := &e.bTable[nextHashL]
					eLong.Cur, eLong.Prev = tableEntry{offset: nextS + e.cur}, eLong.Cur

					t2 := lCandidate.Prev.offset - e.cur
					if s-t2 < maxMatchOffset && uint32(cv) == load3232(src, t2) {
						l = e.matchlen(int(s+4), int(t+4), src) + 4
						ml1 := e.matchlen(int(s+4), int(t2+4), src) + 4
						if ml1 > l {
							t = t2
							l = ml1
							break
						}
					}
					break
				}
				t = lCandidate.Prev.offset - e.cur
				if s-t < maxMatchOffset && uint32(cv) == load3232(src, t) {
					// Store the next match
					e.table[nextHashS] = tableEntry{offset: nextS + e.cur}
					eLong := &e.bTable[nextHashL]
					eLong.Cur, eLong.Prev = tableEntry{offset: nextS + e.cur}, eLong.Cur
					break
				}
			}

			t = sCandidate.offset - e.cur
			if s-t < maxMatchOffset && uint32(cv) == load3232(src, t) {
				// Found a 4 match...
				l = e.matchlen(int(s+4), int(t+4), src) + 4
				lCandidate = e.bTable[nextHashL]
				// Store the next match

				e.table[nextHashS] = tableEntry{offset: nextS + e.cur}
				eLong := &e.bTable[nextHashL]
				eLong.Cur, eLong.Prev = tableEntry{offset: nextS + e.cur}, eLong.Cur

				// If the next long is a candidate, use that...
				t2 := lCandidate.Cur.offset - e.cur
				if nextS-t2 < maxMatchOffset {
					if load3232(src, t2) == uint32(next) {
						ml := e.matchlen(int(nextS+4), int(t2+4), src) + 4
						if ml > l {
							t = t2
							s = nextS
							l = ml
							break
						}
					}
					// If the previous long is a candidate, use that...
					t2 = lCandidate.Prev.offset - e.cur
					if nextS-t2 < maxMatchOffset && load3232(src, t2) == uint32(next) {
						ml := e.matchlen(int(nextS+4), int(t2+4), src) + 4
						if ml > l {
							t = t2
							s = nextS
							l = ml
							break
						}
					}
				}
				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.

		if l == 0 {
			// Extend the 4-byte match as long as possible.
			l = e.matchlenLong(int(s+4), int(t+4), src) + 4
		} else if l == maxMatchLength {
			l += e.matchlenLong(int(s+l), int(t+l), src)
		}

		// Try to locate a better match by checking the end of best match...
		if sAt := s + l; l < 30 && sAt < sLimit {
			// Allow some bytes at the beginning to mismatch.
			// Sweet spot is 2/3 bytes depending on input.
			// 3 is only a little better when it is but sometimes a lot worse.
			// The skipped bytes are tested in Extend backwards,
			// and still picked up as part of the match if they do.
			const skipBeginning = 2
			eLong := e.bTable[hash7(load6432(src, sAt), tableBits)].Cur.offset
			t2 := eLong - e.cur - l + skipBeginning
			s2 := s + skipBeginning
			off := s2 - t2
			if t2 >= 0 && off < maxMatchOffset && off > 0 {
				if l2 := e.matchlenLong(int(s2), int(t2), src); l2 > l {
					t = t2
					l = l2
					s = s2
				}
			}
		}

		// 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(fmt.Sprintln("s-t", s, t))
			}
			if (s - t) > maxMatchOffset {
				panic(fmt.Sprintln("mmo", s-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 {
			goto emitRemainder
		}

		// Store every 3rd hash in-between.
		if true {
			const hashEvery = 3
			i := s - l + 1
			if i < s-1 {
				cv := load6432(src, i)
				t := tableEntry{offset: i + e.cur}
				e.table[hashLen(cv, tableBits, hashShortBytes)] = t
				eLong := &e.bTable[hash7(cv, tableBits)]
				eLong.Cur, eLong.Prev = t, eLong.Cur

				// Do an long at i+1
				cv >>= 8
				t = tableEntry{offset: t.offset + 1}
				eLong = &e.bTable[hash7(cv, tableBits)]
				eLong.Cur, eLong.Prev = t, eLong.Cur

				// We only have enough bits for a short entry at i+2
				cv >>= 8
				t = tableEntry{offset: t.offset + 1}
				e.table[hashLen(cv, tableBits, hashShortBytes)] = t

				// Skip one - otherwise we risk hitting 's'
				i += 4
				for ; i < s-1; i += hashEvery {
					cv := load6432(src, i)
					t := tableEntry{offset: i + e.cur}
					t2 := tableEntry{offset: t.offset + 1}
					eLong := &e.bTable[hash7(cv, tableBits)]
					eLong.Cur, eLong.Prev = t, eLong.Cur
					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}
		eLong := &e.bTable[prevHashL]
		eLong.Cur, eLong.Prev = tableEntry{offset: o}, eLong.Cur
		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:])
	}
}

// fastEncL5Window is a level 5 encoder,
// but with a custom window size.
type fastEncL5Window struct {
	hist      []byte
	cur       int32
	maxOffset int32
	table     [tableSize]tableEntry
	bTable    [tableSize]tableEntryPrev
}

func (e *fastEncL5Window) Encode(dst *tokens, src []byte) {
	const (
		inputMargin            = 12 - 1
		minNonLiteralBlockSize = 1 + 1 + inputMargin
		hashShortBytes         = 4
	)
	maxMatchOffset := e.maxOffset
	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] = tableEntryPrev{}
			}
			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]
			if v.Cur.offset <= minOff {
				v.Cur.offset = 0
				v.Prev.offset = 0
			} else {
				v.Cur.offset = v.Cur.offset - e.cur + maxMatchOffset
				if v.Prev.offset <= minOff {
					v.Prev.offset = 0
				} else {
					v.Prev.offset = v.Prev.offset - e.cur + maxMatchOffset
				}
			}
			e.bTable[i] = 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 l int32
		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
			eLong := &e.bTable[nextHashL]
			eLong.Cur, eLong.Prev = entry, eLong.Cur

			nextHashS = hashLen(next, tableBits, hashShortBytes)
			nextHashL = hash7(next, tableBits)

			t = lCandidate.Cur.offset - e.cur
			if s-t < maxMatchOffset {
				if uint32(cv) == load3232(src, t) {
					// Store the next match
					e.table[nextHashS] = tableEntry{offset: nextS + e.cur}
					eLong := &e.bTable[nextHashL]
					eLong.Cur, eLong.Prev = tableEntry{offset: nextS + e.cur}, eLong.Cur

					t2 := lCandidate.Prev.offset - e.cur
					if s-t2 < maxMatchOffset && uint32(cv) == load3232(src, t2) {
						l = e.matchlen(s+4, t+4, src) + 4
						ml1 := e.matchlen(s+4, t2+4, src) + 4
						if ml1 > l {
							t = t2
							l = ml1
							break
						}
					}
					break
				}
				t = lCandidate.Prev.offset - e.cur
				if s-t < maxMatchOffset && uint32(cv) == load3232(src, t) {
					// Store the next match
					e.table[nextHashS] = tableEntry{offset: nextS + e.cur}
					eLong := &e.bTable[nextHashL]
					eLong.Cur, eLong.Prev = tableEntry{offset: nextS + e.cur}, eLong.Cur
					break
				}
			}

			t = sCandidate.offset - e.cur
			if s-t < maxMatchOffset && uint32(cv) == load3232(src, t) {
				// Found a 4 match...
				l = e.matchlen(s+4, t+4, src) + 4
				lCandidate = e.bTable[nextHashL]
				// Store the next match

				e.table[nextHashS] = tableEntry{offset: nextS + e.cur}
				eLong := &e.bTable[nextHashL]
				eLong.Cur, eLong.Prev = tableEntry{offset: nextS + e.cur}, eLong.Cur

				// If the next long is a candidate, use that...
				t2 := lCandidate.Cur.offset - e.cur
				if nextS-t2 < maxMatchOffset {
					if load3232(src, t2) == uint32(next) {
						ml := e.matchlen(nextS+4, t2+4, src) + 4
						if ml > l {
							t = t2
							s = nextS
							l = ml
							break
						}
					}
					// If the previous long is a candidate, use that...
					t2 = lCandidate.Prev.offset - e.cur
					if nextS-t2 < maxMatchOffset && load3232(src, t2) == uint32(next) {
						ml := e.matchlen(nextS+4, t2+4, src) + 4
						if ml > l {
							t = t2
							s = nextS
							l = ml
							break
						}
					}
				}
				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.

		if l == 0 {
			// Extend the 4-byte match as long as possible.
			l = e.matchlenLong(s+4, t+4, src) + 4
		} else if l == maxMatchLength {
			l += e.matchlenLong(s+l, t+l, src)
		}

		// Try to locate a better match by checking the end of best match...
		if sAt := s + l; l < 30 && sAt < sLimit {
			// Allow some bytes at the beginning to mismatch.
			// Sweet spot is 2/3 bytes depending on input.
			// 3 is only a little better when it is but sometimes a lot worse.
			// The skipped bytes are tested in Extend backwards,
			// and still picked up as part of the match if they do.
			const skipBeginning = 2
			eLong := e.bTable[hash7(load6432(src, sAt), tableBits)].Cur.offset
			t2 := eLong - e.cur - l + skipBeginning
			s2 := s + skipBeginning
			off := s2 - t2
			if t2 >= 0 && off < maxMatchOffset && off > 0 {
				if l2 := e.matchlenLong(s2, t2, src); l2 > l {
					t = t2
					l = l2
					s = s2
				}
			}
		}

		// 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(fmt.Sprintln("s-t", s, t))
			}
			if (s - t) > maxMatchOffset {
				panic(fmt.Sprintln("mmo", s-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 {
			goto emitRemainder
		}

		// Store every 3rd hash in-between.
		if true {
			const hashEvery = 3
			i := s - l + 1
			if i < s-1 {
				cv := load6432(src, i)
				t := tableEntry{offset: i + e.cur}
				e.table[hashLen(cv, tableBits, hashShortBytes)] = t
				eLong := &e.bTable[hash7(cv, tableBits)]
				eLong.Cur, eLong.Prev = t, eLong.Cur

				// Do an long at i+1
				cv >>= 8
				t = tableEntry{offset: t.offset + 1}
				eLong = &e.bTable[hash7(cv, tableBits)]
				eLong.Cur, eLong.Prev = t, eLong.Cur

				// We only have enough bits for a short entry at i+2
				cv >>= 8
				t = tableEntry{offset: t.offset + 1}
				e.table[hashLen(cv, tableBits, hashShortBytes)] = t

				// Skip one - otherwise we risk hitting 's'
				i += 4
				for ; i < s-1; i += hashEvery {
					cv := load6432(src, i)
					t := tableEntry{offset: i + e.cur}
					t2 := tableEntry{offset: t.offset + 1}
					eLong := &e.bTable[hash7(cv, tableBits)]
					eLong.Cur, eLong.Prev = t, eLong.Cur
					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}
		eLong := &e.bTable[prevHashL]
		eLong.Cur, eLong.Prev = tableEntry{offset: o}, eLong.Cur
		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:])
	}
}

// Reset the encoding table.
func (e *fastEncL5Window) Reset() {
	// We keep the same allocs, since we are compressing the same block sizes.
	if cap(e.hist) < allocHistory {
		e.hist = make([]byte, 0, allocHistory)
	}

	// We offset current position so everything will be out of reach.
	// If we are above the buffer reset it will be cleared anyway since len(hist) == 0.
	if e.cur <= int32(bufferReset) {
		e.cur += e.maxOffset + int32(len(e.hist))
	}
	e.hist = e.hist[:0]
}

func (e *fastEncL5Window) addBlock(src []byte) int32 {
	// check if we have space already
	maxMatchOffset := e.maxOffset

	if len(e.hist)+len(src) > cap(e.hist) {
		if cap(e.hist) == 0 {
			e.hist = make([]byte, 0, allocHistory)
		} else {
			if cap(e.hist) < int(maxMatchOffset*2) {
				panic("unexpected buffer size")
			}
			// Move down
			offset := int32(len(e.hist)) - maxMatchOffset
			copy(e.hist[0:maxMatchOffset], e.hist[offset:])
			e.cur += offset
			e.hist = e.hist[:maxMatchOffset]
		}
	}
	s := int32(len(e.hist))
	e.hist = append(e.hist, src...)
	return s
}

// matchlen will return the match length between offsets and t in src.
// The maximum length returned is maxMatchLength - 4.
// It is assumed that s > t, that t >=0 and s < len(src).
func (e *fastEncL5Window) matchlen(s, t int32, src []byte) int32 {
	if debugDecode {
		if t >= s {
			panic(fmt.Sprint("t >=s:", t, s))
		}
		if int(s) >= len(src) {
			panic(fmt.Sprint("s >= len(src):", s, len(src)))
		}
		if t < 0 {
			panic(fmt.Sprint("t < 0:", t))
		}
		if s-t > e.maxOffset {
			panic(fmt.Sprint(s, "-", t, "(", s-t, ") > maxMatchLength (", maxMatchOffset, ")"))
		}
	}
	s1 := int(s) + maxMatchLength - 4
	if s1 > len(src) {
		s1 = len(src)
	}

	// Extend the match to be as long as possible.
	return int32(matchLen(src[s:s1], src[t:]))
}

// matchlenLong will return the match length between offsets and t in src.
// It is assumed that s > t, that t >=0 and s < len(src).
func (e *fastEncL5Window) matchlenLong(s, t int32, src []byte) int32 {
	if debugDeflate {
		if t >= s {
			panic(fmt.Sprint("t >=s:", t, s))
		}
		if int(s) >= len(src) {
			panic(fmt.Sprint("s >= len(src):", s, len(src)))
		}
		if t < 0 {
			panic(fmt.Sprint("t < 0:", t))
		}
		if s-t > e.maxOffset {
			panic(fmt.Sprint(s, "-", t, "(", s-t, ") > maxMatchLength (", maxMatchOffset, ")"))
		}
	}
	// Extend the match to be as long as possible.
	return int32(matchLen(src[s:], src[t:]))
}