gtsocial-umbx

encode_all.go (26881B)

---

 // Copyright 2016 The Snappy-Go Authors. All rights reserved.
 // Copyright (c) 2019 Klaus Post. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 package s2
 
 import (
 	"bytes"
 	"encoding/binary"
 	"fmt"
 	"math/bits"
 )
 
 func load32(b []byte, i int) uint32 {
 	return binary.LittleEndian.Uint32(b[i:])
 }
 
 func load64(b []byte, i int) uint64 {
 	return binary.LittleEndian.Uint64(b[i:])
 }
 
 // hash6 returns the hash of the lowest 6 bytes of u to fit in a hash table with h bits.
 // Preferably h should be a constant and should always be <64.
 func hash6(u uint64, h uint8) uint32 {
 	const prime6bytes = 227718039650203
 	return uint32(((u << (64 - 48)) * prime6bytes) >> ((64 - h) & 63))
 }
 
 func encodeGo(dst, src []byte) []byte {
 	if n := MaxEncodedLen(len(src)); n < 0 {
 		panic(ErrTooLarge)
 	} else if len(dst) < n {
 		dst = make([]byte, n)
 	}
 
 	// The block starts with the varint-encoded length of the decompressed bytes.
 	d := binary.PutUvarint(dst, uint64(len(src)))
 
 	if len(src) == 0 {
 		return dst[:d]
 	}
 	if len(src) < minNonLiteralBlockSize {
 		d += emitLiteral(dst[d:], src)
 		return dst[:d]
 	}
 	n := encodeBlockGo(dst[d:], src)
 	if n > 0 {
 		d += n
 		return dst[:d]
 	}
 	// Not compressible
 	d += emitLiteral(dst[d:], src)
 	return dst[:d]
 }
 
 // encodeBlockGo encodes a non-empty src to a guaranteed-large-enough dst. It
 // assumes that the varint-encoded length of the decompressed bytes has already
 // been written.
 //
 // It also assumes that:
 //
 //	len(dst) >= MaxEncodedLen(len(src)) &&
 //	minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
 func encodeBlockGo(dst, src []byte) (d int) {
 	// Initialize the hash table.
 	const (
 		tableBits    = 14
 		maxTableSize = 1 << tableBits
 
 		debug = false
 	)
 
 	var table [maxTableSize]uint32
 
 	// 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 := len(src) - inputMargin
 
 	// Bail if we can't compress to at least this.
 	dstLimit := len(src) - len(src)>>5 - 5
 
 	// nextEmit is where in src the next emitLiteral should start from.
 	nextEmit := 0
 
 	// The encoded form must start with a literal, as there are no previous
 	// bytes to copy, so we start looking for hash matches at s == 1.
 	s := 1
 	cv := load64(src, s)
 
 	// We search for a repeat at -1, but don't output repeats when nextEmit == 0
 	repeat := 1
 
 	for {
 		candidate := 0
 		for {
 			// Next src position to check
 			nextS := s + (s-nextEmit)>>6 + 4
 			if nextS > sLimit {
 				goto emitRemainder
 			}
 			hash0 := hash6(cv, tableBits)
 			hash1 := hash6(cv>>8, tableBits)
 			candidate = int(table[hash0])
 			candidate2 := int(table[hash1])
 			table[hash0] = uint32(s)
 			table[hash1] = uint32(s + 1)
 			hash2 := hash6(cv>>16, tableBits)
 
 			// Check repeat at offset checkRep.
 			const checkRep = 1
 			if uint32(cv>>(checkRep*8)) == load32(src, s-repeat+checkRep) {
 				base := s + checkRep
 				// Extend back
 				for i := base - repeat; base > nextEmit && i > 0 && src[i-1] == src[base-1]; {
 					i--
 					base--
 				}
 				d += emitLiteral(dst[d:], src[nextEmit:base])
 
 				// Extend forward
 				candidate := s - repeat + 4 + checkRep
 				s += 4 + checkRep
 				for s <= sLimit {
 					if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
 						s += bits.TrailingZeros64(diff) >> 3
 						break
 					}
 					s += 8
 					candidate += 8
 				}
 				if debug {
 					// Validate match.
 					if s <= candidate {
 						panic("s <= candidate")
 					}
 					a := src[base:s]
 					b := src[base-repeat : base-repeat+(s-base)]
 					if !bytes.Equal(a, b) {
 						panic("mismatch")
 					}
 				}
 				if nextEmit > 0 {
 					// same as `add := emitCopy(dst[d:], repeat, s-base)` but skips storing offset.
 					d += emitRepeat(dst[d:], repeat, s-base)
 				} else {
 					// First match, cannot be repeat.
 					d += emitCopy(dst[d:], repeat, s-base)
 				}
 				nextEmit = s
 				if s >= sLimit {
 					goto emitRemainder
 				}
 
 				cv = load64(src, s)
 				continue
 			}
 
 			if uint32(cv) == load32(src, candidate) {
 				break
 			}
 			candidate = int(table[hash2])
 			if uint32(cv>>8) == load32(src, candidate2) {
 				table[hash2] = uint32(s + 2)
 				candidate = candidate2
 				s++
 				break
 			}
 			table[hash2] = uint32(s + 2)
 			if uint32(cv>>16) == load32(src, candidate) {
 				s += 2
 				break
 			}
 
 			cv = load64(src, nextS)
 			s = nextS
 		}
 
 		// Extend backwards.
 		// The top bytes will be rechecked to get the full match.
 		for candidate > 0 && s > nextEmit && src[candidate-1] == src[s-1] {
 			candidate--
 			s--
 		}
 
 		// Bail if we exceed the maximum size.
 		if d+(s-nextEmit) > dstLimit {
 			return 0
 		}
 
 		// 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.
 
 		d += emitLiteral(dst[d:], src[nextEmit:s])
 
 		// Call emitCopy, and then see if another emitCopy could be our next
 		// move. Repeat until we find no match for the input immediately after
 		// what was consumed by the last emitCopy call.
 		//
 		// If we exit this loop normally then we need to call emitLiteral next,
 		// though we don't yet know how big the literal will be. We handle that
 		// by proceeding to the next iteration of the main loop. We also can
 		// exit this loop via goto if we get close to exhausting the input.
 		for {
 			// Invariant: we have a 4-byte match at s, and no need to emit any
 			// literal bytes prior to s.
 			base := s
 			repeat = base - candidate
 
 			// Extend the 4-byte match as long as possible.
 			s += 4
 			candidate += 4
 			for s <= len(src)-8 {
 				if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
 					s += bits.TrailingZeros64(diff) >> 3
 					break
 				}
 				s += 8
 				candidate += 8
 			}
 
 			d += emitCopy(dst[d:], repeat, s-base)
 			if debug {
 				// Validate match.
 				if s <= candidate {
 					panic("s <= candidate")
 				}
 				a := src[base:s]
 				b := src[base-repeat : base-repeat+(s-base)]
 				if !bytes.Equal(a, b) {
 					panic("mismatch")
 				}
 			}
 
 			nextEmit = s
 			if s >= sLimit {
 				goto emitRemainder
 			}
 
 			if d > dstLimit {
 				// Do we have space for more, if not bail.
 				return 0
 			}
 			// Check for an immediate match, otherwise start search at s+1
 			x := load64(src, s-2)
 			m2Hash := hash6(x, tableBits)
 			currHash := hash6(x>>16, tableBits)
 			candidate = int(table[currHash])
 			table[m2Hash] = uint32(s - 2)
 			table[currHash] = uint32(s)
 			if debug && s == candidate {
 				panic("s == candidate")
 			}
 			if uint32(x>>16) != load32(src, candidate) {
 				cv = load64(src, s+1)
 				s++
 				break
 			}
 		}
 	}
 
 emitRemainder:
 	if nextEmit < len(src) {
 		// Bail if we exceed the maximum size.
 		if d+len(src)-nextEmit > dstLimit {
 			return 0
 		}
 		d += emitLiteral(dst[d:], src[nextEmit:])
 	}
 	return d
 }
 
 func encodeBlockSnappyGo(dst, src []byte) (d int) {
 	// Initialize the hash table.
 	const (
 		tableBits    = 14
 		maxTableSize = 1 << tableBits
 	)
 
 	var table [maxTableSize]uint32
 
 	// 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 := len(src) - inputMargin
 
 	// Bail if we can't compress to at least this.
 	dstLimit := len(src) - len(src)>>5 - 5
 
 	// nextEmit is where in src the next emitLiteral should start from.
 	nextEmit := 0
 
 	// The encoded form must start with a literal, as there are no previous
 	// bytes to copy, so we start looking for hash matches at s == 1.
 	s := 1
 	cv := load64(src, s)
 
 	// We search for a repeat at -1, but don't output repeats when nextEmit == 0
 	repeat := 1
 
 	for {
 		candidate := 0
 		for {
 			// Next src position to check
 			nextS := s + (s-nextEmit)>>6 + 4
 			if nextS > sLimit {
 				goto emitRemainder
 			}
 			hash0 := hash6(cv, tableBits)
 			hash1 := hash6(cv>>8, tableBits)
 			candidate = int(table[hash0])
 			candidate2 := int(table[hash1])
 			table[hash0] = uint32(s)
 			table[hash1] = uint32(s + 1)
 			hash2 := hash6(cv>>16, tableBits)
 
 			// Check repeat at offset checkRep.
 			const checkRep = 1
 			if uint32(cv>>(checkRep*8)) == load32(src, s-repeat+checkRep) {
 				base := s + checkRep
 				// Extend back
 				for i := base - repeat; base > nextEmit && i > 0 && src[i-1] == src[base-1]; {
 					i--
 					base--
 				}
 				d += emitLiteral(dst[d:], src[nextEmit:base])
 
 				// Extend forward
 				candidate := s - repeat + 4 + checkRep
 				s += 4 + checkRep
 				for s <= sLimit {
 					if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
 						s += bits.TrailingZeros64(diff) >> 3
 						break
 					}
 					s += 8
 					candidate += 8
 				}
 
 				d += emitCopyNoRepeat(dst[d:], repeat, s-base)
 				nextEmit = s
 				if s >= sLimit {
 					goto emitRemainder
 				}
 
 				cv = load64(src, s)
 				continue
 			}
 
 			if uint32(cv) == load32(src, candidate) {
 				break
 			}
 			candidate = int(table[hash2])
 			if uint32(cv>>8) == load32(src, candidate2) {
 				table[hash2] = uint32(s + 2)
 				candidate = candidate2
 				s++
 				break
 			}
 			table[hash2] = uint32(s + 2)
 			if uint32(cv>>16) == load32(src, candidate) {
 				s += 2
 				break
 			}
 
 			cv = load64(src, nextS)
 			s = nextS
 		}
 
 		// Extend backwards
 		for candidate > 0 && s > nextEmit && src[candidate-1] == src[s-1] {
 			candidate--
 			s--
 		}
 
 		// Bail if we exceed the maximum size.
 		if d+(s-nextEmit) > dstLimit {
 			return 0
 		}
 
 		// 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.
 
 		d += emitLiteral(dst[d:], src[nextEmit:s])
 
 		// Call emitCopy, and then see if another emitCopy could be our next
 		// move. Repeat until we find no match for the input immediately after
 		// what was consumed by the last emitCopy call.
 		//
 		// If we exit this loop normally then we need to call emitLiteral next,
 		// though we don't yet know how big the literal will be. We handle that
 		// by proceeding to the next iteration of the main loop. We also can
 		// exit this loop via goto if we get close to exhausting the input.
 		for {
 			// Invariant: we have a 4-byte match at s, and no need to emit any
 			// literal bytes prior to s.
 			base := s
 			repeat = base - candidate
 
 			// Extend the 4-byte match as long as possible.
 			s += 4
 			candidate += 4
 			for s <= len(src)-8 {
 				if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
 					s += bits.TrailingZeros64(diff) >> 3
 					break
 				}
 				s += 8
 				candidate += 8
 			}
 
 			d += emitCopyNoRepeat(dst[d:], repeat, s-base)
 			if false {
 				// Validate match.
 				a := src[base:s]
 				b := src[base-repeat : base-repeat+(s-base)]
 				if !bytes.Equal(a, b) {
 					panic("mismatch")
 				}
 			}
 
 			nextEmit = s
 			if s >= sLimit {
 				goto emitRemainder
 			}
 
 			if d > dstLimit {
 				// Do we have space for more, if not bail.
 				return 0
 			}
 			// Check for an immediate match, otherwise start search at s+1
 			x := load64(src, s-2)
 			m2Hash := hash6(x, tableBits)
 			currHash := hash6(x>>16, tableBits)
 			candidate = int(table[currHash])
 			table[m2Hash] = uint32(s - 2)
 			table[currHash] = uint32(s)
 			if uint32(x>>16) != load32(src, candidate) {
 				cv = load64(src, s+1)
 				s++
 				break
 			}
 		}
 	}
 
 emitRemainder:
 	if nextEmit < len(src) {
 		// Bail if we exceed the maximum size.
 		if d+len(src)-nextEmit > dstLimit {
 			return 0
 		}
 		d += emitLiteral(dst[d:], src[nextEmit:])
 	}
 	return d
 }
 
 // encodeBlockGo encodes a non-empty src to a guaranteed-large-enough dst. It
 // assumes that the varint-encoded length of the decompressed bytes has already
 // been written.
 //
 // It also assumes that:
 //
 //	len(dst) >= MaxEncodedLen(len(src)) &&
 //	minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
 func encodeBlockDictGo(dst, src []byte, dict *Dict) (d int) {
 	// Initialize the hash table.
 	const (
 		tableBits    = 14
 		maxTableSize = 1 << tableBits
 		maxAhead     = 8 // maximum bytes ahead without checking sLimit
 
 		debug = false
 	)
 	dict.initFast()
 
 	var table [maxTableSize]uint32
 
 	// 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 := len(src) - inputMargin
 	if sLimit > MaxDictSrcOffset-maxAhead {
 		sLimit = MaxDictSrcOffset - maxAhead
 	}
 
 	// Bail if we can't compress to at least this.
 	dstLimit := len(src) - len(src)>>5 - 5
 
 	// nextEmit is where in src the next emitLiteral should start from.
 	nextEmit := 0
 
 	// The encoded form can start with a dict entry (copy or repeat).
 	s := 0
 
 	// Convert dict repeat to offset
 	repeat := len(dict.dict) - dict.repeat
 	cv := load64(src, 0)
 
 	// While in dict
 searchDict:
 	for {
 		// Next src position to check
 		nextS := s + (s-nextEmit)>>6 + 4
 		hash0 := hash6(cv, tableBits)
 		hash1 := hash6(cv>>8, tableBits)
 		if nextS > sLimit {
 			if debug {
 				fmt.Println("slimit reached", s, nextS)
 			}
 			break searchDict
 		}
 		candidateDict := int(dict.fastTable[hash0])
 		candidateDict2 := int(dict.fastTable[hash1])
 		candidate2 := int(table[hash1])
 		candidate := int(table[hash0])
 		table[hash0] = uint32(s)
 		table[hash1] = uint32(s + 1)
 		hash2 := hash6(cv>>16, tableBits)
 
 		// Check repeat at offset checkRep.
 		const checkRep = 1
 
 		if repeat > s {
 			candidate := len(dict.dict) - repeat + s
 			if repeat-s >= 4 && uint32(cv) == load32(dict.dict, candidate) {
 				// Extend back
 				base := s
 				for i := candidate; base > nextEmit && i > 0 && dict.dict[i-1] == src[base-1]; {
 					i--
 					base--
 				}
 				d += emitLiteral(dst[d:], src[nextEmit:base])
 				if debug && nextEmit != base {
 					fmt.Println("emitted ", base-nextEmit, "literals")
 				}
 				s += 4
 				candidate += 4
 				for candidate < len(dict.dict)-8 && s <= len(src)-8 {
 					if diff := load64(src, s) ^ load64(dict.dict, candidate); diff != 0 {
 						s += bits.TrailingZeros64(diff) >> 3
 						break
 					}
 					s += 8
 					candidate += 8
 				}
 				d += emitRepeat(dst[d:], repeat, s-base)
 				if debug {
 					fmt.Println("emitted dict repeat length", s-base, "offset:", repeat, "s:", s)
 				}
 				nextEmit = s
 				if s >= sLimit {
 					break searchDict
 				}
 				cv = load64(src, s)
 				continue
 			}
 		} else if uint32(cv>>(checkRep*8)) == load32(src, s-repeat+checkRep) {
 			base := s + checkRep
 			// Extend back
 			for i := base - repeat; base > nextEmit && i > 0 && src[i-1] == src[base-1]; {
 				i--
 				base--
 			}
 			d += emitLiteral(dst[d:], src[nextEmit:base])
 			if debug && nextEmit != base {
 				fmt.Println("emitted ", base-nextEmit, "literals")
 			}
 
 			// Extend forward
 			candidate := s - repeat + 4 + checkRep
 			s += 4 + checkRep
 			for s <= sLimit {
 				if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
 					s += bits.TrailingZeros64(diff) >> 3
 					break
 				}
 				s += 8
 				candidate += 8
 			}
 			if debug {
 				// Validate match.
 				if s <= candidate {
 					panic("s <= candidate")
 				}
 				a := src[base:s]
 				b := src[base-repeat : base-repeat+(s-base)]
 				if !bytes.Equal(a, b) {
 					panic("mismatch")
 				}
 			}
 
 			if nextEmit > 0 {
 				// same as `add := emitCopy(dst[d:], repeat, s-base)` but skips storing offset.
 				d += emitRepeat(dst[d:], repeat, s-base)
 			} else {
 				// First match, cannot be repeat.
 				d += emitCopy(dst[d:], repeat, s-base)
 			}
 
 			nextEmit = s
 			if s >= sLimit {
 				break searchDict
 			}
 			if debug {
 				fmt.Println("emitted reg repeat", s-base, "s:", s)
 			}
 			cv = load64(src, s)
 			continue searchDict
 		}
 		if s == 0 {
 			cv = load64(src, nextS)
 			s = nextS
 			continue searchDict
 		}
 		// Start with table. These matches will always be closer.
 		if uint32(cv) == load32(src, candidate) {
 			goto emitMatch
 		}
 		candidate = int(table[hash2])
 		if uint32(cv>>8) == load32(src, candidate2) {
 			table[hash2] = uint32(s + 2)
 			candidate = candidate2
 			s++
 			goto emitMatch
 		}
 
 		// Check dict. Dicts have longer offsets, so we want longer matches.
 		if cv == load64(dict.dict, candidateDict) {
 			table[hash2] = uint32(s + 2)
 			goto emitDict
 		}
 
 		candidateDict = int(dict.fastTable[hash2])
 		// Check if upper 7 bytes match
 		if candidateDict2 >= 1 {
 			if cv^load64(dict.dict, candidateDict2-1) < (1 << 8) {
 				table[hash2] = uint32(s + 2)
 				candidateDict = candidateDict2
 				s++
 				goto emitDict
 			}
 		}
 
 		table[hash2] = uint32(s + 2)
 		if uint32(cv>>16) == load32(src, candidate) {
 			s += 2
 			goto emitMatch
 		}
 		if candidateDict >= 2 {
 			// Check if upper 6 bytes match
 			if cv^load64(dict.dict, candidateDict-2) < (1 << 16) {
 				s += 2
 				goto emitDict
 			}
 		}
 
 		cv = load64(src, nextS)
 		s = nextS
 		continue searchDict
 
 	emitDict:
 		{
 			if debug {
 				if load32(dict.dict, candidateDict) != load32(src, s) {
 					panic("dict emit mismatch")
 				}
 			}
 			// Extend backwards.
 			// The top bytes will be rechecked to get the full match.
 			for candidateDict > 0 && s > nextEmit && dict.dict[candidateDict-1] == src[s-1] {
 				candidateDict--
 				s--
 			}
 
 			// Bail if we exceed the maximum size.
 			if d+(s-nextEmit) > dstLimit {
 				return 0
 			}
 
 			// 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.
 
 			d += emitLiteral(dst[d:], src[nextEmit:s])
 			if debug && nextEmit != s {
 				fmt.Println("emitted ", s-nextEmit, "literals")
 			}
 			{
 				// Invariant: we have a 4-byte match at s, and no need to emit any
 				// literal bytes prior to s.
 				base := s
 				repeat = s + (len(dict.dict)) - candidateDict
 
 				// Extend the 4-byte match as long as possible.
 				s += 4
 				candidateDict += 4
 				for s <= len(src)-8 && len(dict.dict)-candidateDict >= 8 {
 					if diff := load64(src, s) ^ load64(dict.dict, candidateDict); diff != 0 {
 						s += bits.TrailingZeros64(diff) >> 3
 						break
 					}
 					s += 8
 					candidateDict += 8
 				}
 
 				// Matches longer than 64 are split.
 				if s <= sLimit || s-base < 8 {
 					d += emitCopy(dst[d:], repeat, s-base)
 				} else {
 					// Split to ensure we don't start a copy within next block
 					d += emitCopy(dst[d:], repeat, 4)
 					d += emitRepeat(dst[d:], repeat, s-base-4)
 				}
 				if false {
 					// Validate match.
 					if s <= candidate {
 						panic("s <= candidate")
 					}
 					a := src[base:s]
 					b := dict.dict[base-repeat : base-repeat+(s-base)]
 					if !bytes.Equal(a, b) {
 						panic("mismatch")
 					}
 				}
 				if debug {
 					fmt.Println("emitted dict copy, length", s-base, "offset:", repeat, "s:", s)
 				}
 				nextEmit = s
 				if s >= sLimit {
 					break searchDict
 				}
 
 				if d > dstLimit {
 					// Do we have space for more, if not bail.
 					return 0
 				}
 
 				// Index and continue loop to try new candidate.
 				x := load64(src, s-2)
 				m2Hash := hash6(x, tableBits)
 				currHash := hash6(x>>8, tableBits)
 				candidate = int(table[currHash])
 				table[m2Hash] = uint32(s - 2)
 				table[currHash] = uint32(s - 1)
 				cv = load64(src, s)
 			}
 			continue
 		}
 	emitMatch:
 
 		// Extend backwards.
 		// The top bytes will be rechecked to get the full match.
 		for candidate > 0 && s > nextEmit && src[candidate-1] == src[s-1] {
 			candidate--
 			s--
 		}
 
 		// Bail if we exceed the maximum size.
 		if d+(s-nextEmit) > dstLimit {
 			return 0
 		}
 
 		// 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.
 
 		d += emitLiteral(dst[d:], src[nextEmit:s])
 		if debug && nextEmit != s {
 			fmt.Println("emitted ", s-nextEmit, "literals")
 		}
 		// Call emitCopy, and then see if another emitCopy could be our next
 		// move. Repeat until we find no match for the input immediately after
 		// what was consumed by the last emitCopy call.
 		//
 		// If we exit this loop normally then we need to call emitLiteral next,
 		// though we don't yet know how big the literal will be. We handle that
 		// by proceeding to the next iteration of the main loop. We also can
 		// exit this loop via goto if we get close to exhausting the input.
 		for {
 			// Invariant: we have a 4-byte match at s, and no need to emit any
 			// literal bytes prior to s.
 			base := s
 			repeat = base - candidate
 
 			// Extend the 4-byte match as long as possible.
 			s += 4
 			candidate += 4
 			for s <= len(src)-8 {
 				if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
 					s += bits.TrailingZeros64(diff) >> 3
 					break
 				}
 				s += 8
 				candidate += 8
 			}
 
 			d += emitCopy(dst[d:], repeat, s-base)
 			if debug {
 				// Validate match.
 				if s <= candidate {
 					panic("s <= candidate")
 				}
 				a := src[base:s]
 				b := src[base-repeat : base-repeat+(s-base)]
 				if !bytes.Equal(a, b) {
 					panic("mismatch")
 				}
 			}
 			if debug {
 				fmt.Println("emitted src copy, length", s-base, "offset:", repeat, "s:", s)
 			}
 			nextEmit = s
 			if s >= sLimit {
 				break searchDict
 			}
 
 			if d > dstLimit {
 				// Do we have space for more, if not bail.
 				return 0
 			}
 			// Check for an immediate match, otherwise start search at s+1
 			x := load64(src, s-2)
 			m2Hash := hash6(x, tableBits)
 			currHash := hash6(x>>16, tableBits)
 			candidate = int(table[currHash])
 			table[m2Hash] = uint32(s - 2)
 			table[currHash] = uint32(s)
 			if debug && s == candidate {
 				panic("s == candidate")
 			}
 			if uint32(x>>16) != load32(src, candidate) {
 				cv = load64(src, s+1)
 				s++
 				break
 			}
 		}
 	}
 
 	// Search without dict:
 	if repeat > s {
 		repeat = 0
 	}
 
 	// No more dict
 	sLimit = len(src) - inputMargin
 	if s >= sLimit {
 		goto emitRemainder
 	}
 	if debug {
 		fmt.Println("non-dict matching at", s, "repeat:", repeat)
 	}
 	cv = load64(src, s)
 	if debug {
 		fmt.Println("now", s, "->", sLimit, "out:", d, "left:", len(src)-s, "nextemit:", nextEmit, "dstLimit:", dstLimit, "s:", s)
 	}
 	for {
 		candidate := 0
 		for {
 			// Next src position to check
 			nextS := s + (s-nextEmit)>>6 + 4
 			if nextS > sLimit {
 				goto emitRemainder
 			}
 			hash0 := hash6(cv, tableBits)
 			hash1 := hash6(cv>>8, tableBits)
 			candidate = int(table[hash0])
 			candidate2 := int(table[hash1])
 			table[hash0] = uint32(s)
 			table[hash1] = uint32(s + 1)
 			hash2 := hash6(cv>>16, tableBits)
 
 			// Check repeat at offset checkRep.
 			const checkRep = 1
 			if repeat > 0 && uint32(cv>>(checkRep*8)) == load32(src, s-repeat+checkRep) {
 				base := s + checkRep
 				// Extend back
 				for i := base - repeat; base > nextEmit && i > 0 && src[i-1] == src[base-1]; {
 					i--
 					base--
 				}
 				d += emitLiteral(dst[d:], src[nextEmit:base])
 				if debug && nextEmit != base {
 					fmt.Println("emitted ", base-nextEmit, "literals")
 				}
 				// Extend forward
 				candidate := s - repeat + 4 + checkRep
 				s += 4 + checkRep
 				for s <= sLimit {
 					if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
 						s += bits.TrailingZeros64(diff) >> 3
 						break
 					}
 					s += 8
 					candidate += 8
 				}
 				if debug {
 					// Validate match.
 					if s <= candidate {
 						panic("s <= candidate")
 					}
 					a := src[base:s]
 					b := src[base-repeat : base-repeat+(s-base)]
 					if !bytes.Equal(a, b) {
 						panic("mismatch")
 					}
 				}
 				if nextEmit > 0 {
 					// same as `add := emitCopy(dst[d:], repeat, s-base)` but skips storing offset.
 					d += emitRepeat(dst[d:], repeat, s-base)
 				} else {
 					// First match, cannot be repeat.
 					d += emitCopy(dst[d:], repeat, s-base)
 				}
 				if debug {
 					fmt.Println("emitted src repeat length", s-base, "offset:", repeat, "s:", s)
 				}
 				nextEmit = s
 				if s >= sLimit {
 					goto emitRemainder
 				}
 
 				cv = load64(src, s)
 				continue
 			}
 
 			if uint32(cv) == load32(src, candidate) {
 				break
 			}
 			candidate = int(table[hash2])
 			if uint32(cv>>8) == load32(src, candidate2) {
 				table[hash2] = uint32(s + 2)
 				candidate = candidate2
 				s++
 				break
 			}
 			table[hash2] = uint32(s + 2)
 			if uint32(cv>>16) == load32(src, candidate) {
 				s += 2
 				break
 			}
 
 			cv = load64(src, nextS)
 			s = nextS
 		}
 
 		// Extend backwards.
 		// The top bytes will be rechecked to get the full match.
 		for candidate > 0 && s > nextEmit && src[candidate-1] == src[s-1] {
 			candidate--
 			s--
 		}
 
 		// Bail if we exceed the maximum size.
 		if d+(s-nextEmit) > dstLimit {
 			return 0
 		}
 
 		// 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.
 
 		d += emitLiteral(dst[d:], src[nextEmit:s])
 		if debug && nextEmit != s {
 			fmt.Println("emitted ", s-nextEmit, "literals")
 		}
 		// Call emitCopy, and then see if another emitCopy could be our next
 		// move. Repeat until we find no match for the input immediately after
 		// what was consumed by the last emitCopy call.
 		//
 		// If we exit this loop normally then we need to call emitLiteral next,
 		// though we don't yet know how big the literal will be. We handle that
 		// by proceeding to the next iteration of the main loop. We also can
 		// exit this loop via goto if we get close to exhausting the input.
 		for {
 			// Invariant: we have a 4-byte match at s, and no need to emit any
 			// literal bytes prior to s.
 			base := s
 			repeat = base - candidate
 
 			// Extend the 4-byte match as long as possible.
 			s += 4
 			candidate += 4
 			for s <= len(src)-8 {
 				if diff := load64(src, s) ^ load64(src, candidate); diff != 0 {
 					s += bits.TrailingZeros64(diff) >> 3
 					break
 				}
 				s += 8
 				candidate += 8
 			}
 
 			d += emitCopy(dst[d:], repeat, s-base)
 			if debug {
 				// Validate match.
 				if s <= candidate {
 					panic("s <= candidate")
 				}
 				a := src[base:s]
 				b := src[base-repeat : base-repeat+(s-base)]
 				if !bytes.Equal(a, b) {
 					panic("mismatch")
 				}
 			}
 			if debug {
 				fmt.Println("emitted src copy, length", s-base, "offset:", repeat, "s:", s)
 			}
 			nextEmit = s
 			if s >= sLimit {
 				goto emitRemainder
 			}
 
 			if d > dstLimit {
 				// Do we have space for more, if not bail.
 				return 0
 			}
 			// Check for an immediate match, otherwise start search at s+1
 			x := load64(src, s-2)
 			m2Hash := hash6(x, tableBits)
 			currHash := hash6(x>>16, tableBits)
 			candidate = int(table[currHash])
 			table[m2Hash] = uint32(s - 2)
 			table[currHash] = uint32(s)
 			if debug && s == candidate {
 				panic("s == candidate")
 			}
 			if uint32(x>>16) != load32(src, candidate) {
 				cv = load64(src, s+1)
 				s++
 				break
 			}
 		}
 	}
 
 emitRemainder:
 	if nextEmit < len(src) {
 		// Bail if we exceed the maximum size.
 		if d+len(src)-nextEmit > dstLimit {
 			return 0
 		}
 		d += emitLiteral(dst[d:], src[nextEmit:])
 		if debug && nextEmit != s {
 			fmt.Println("emitted ", len(src)-nextEmit, "literals")
 		}
 	}
 	return d
 }