aboutsummaryrefslogtreecommitdiff
path: root/vendor/github.com/klauspost/compress/flate/level4.go
blob: c689ac771b823c383948b1844eee0f68aeaeac54 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
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
	)

	// 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 := hash4x64(cv, tableBits)
			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, val: uint32(cv)}
			e.table[nextHashS] = entry
			e.bTable[nextHashL] = entry

			t = lCandidate.offset - e.cur
			if s-t < maxMatchOffset && uint32(cv) == lCandidate.val {
				// We got a long match. Use that.
				break
			}

			t = sCandidate.offset - e.cur
			if s-t < maxMatchOffset && uint32(cv) == sCandidate.val {
				// 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 && lCandidate.val == 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 {
			emitLiteral(dst, src[nextEmit:s])
		}
		if false {
			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[hash4x64(cv, tableBits)] = tableEntry{offset: s + e.cur, val: uint32(cv)}
				e.bTable[hash7(cv, tableBits)] = tableEntry{offset: s + e.cur, val: uint32(cv)}
			}
			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, val: uint32(cv)}
				t2 := tableEntry{val: uint32(cv >> 8), offset: t.offset + 1}
				e.bTable[hash7(cv, tableBits)] = t
				e.bTable[hash7(cv>>8, tableBits)] = t2
				e.table[hash4u(t2.val, tableBits)] = t2

				i += 3
				for ; i < s-1; i += 3 {
					cv := load6432(src, i)
					t := tableEntry{offset: i + e.cur, val: uint32(cv)}
					t2 := tableEntry{val: uint32(cv >> 8), offset: t.offset + 1}
					e.bTable[hash7(cv, tableBits)] = t
					e.bTable[hash7(cv>>8, tableBits)] = t2
					e.table[hash4u(t2.val, tableBits)] = 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 := hash4x64(x, tableBits)
		prevHashL := hash7(x, tableBits)
		e.table[prevHashS] = tableEntry{offset: o, val: uint32(x)}
		e.bTable[prevHashL] = tableEntry{offset: o, val: uint32(x)}
		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:])
	}
}