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-rw-r--r--vendor/github.com/klauspost/compress/s2/encode_best.go796
1 files changed, 796 insertions, 0 deletions
diff --git a/vendor/github.com/klauspost/compress/s2/encode_best.go b/vendor/github.com/klauspost/compress/s2/encode_best.go
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1// Copyright 2016 The Snappy-Go Authors. All rights reserved.
2// Copyright (c) 2019 Klaus Post. All rights reserved.
3// Use of this source code is governed by a BSD-style
4// license that can be found in the LICENSE file.
5
6package s2
7
8import (
9 "fmt"
10 "math"
11 "math/bits"
12)
13
14// encodeBlockBest encodes a non-empty src to a guaranteed-large-enough dst. It
15// assumes that the varint-encoded length of the decompressed bytes has already
16// been written.
17//
18// It also assumes that:
19//
20// len(dst) >= MaxEncodedLen(len(src)) &&
21// minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
22func encodeBlockBest(dst, src []byte, dict *Dict) (d int) {
23 // Initialize the hash tables.
24 const (
25 // Long hash matches.
26 lTableBits = 19
27 maxLTableSize = 1 << lTableBits
28
29 // Short hash matches.
30 sTableBits = 16
31 maxSTableSize = 1 << sTableBits
32
33 inputMargin = 8 + 2
34
35 debug = false
36 )
37
38 // sLimit is when to stop looking for offset/length copies. The inputMargin
39 // lets us use a fast path for emitLiteral in the main loop, while we are
40 // looking for copies.
41 sLimit := len(src) - inputMargin
42 if len(src) < minNonLiteralBlockSize {
43 return 0
44 }
45 sLimitDict := len(src) - inputMargin
46 if sLimitDict > MaxDictSrcOffset-inputMargin {
47 sLimitDict = MaxDictSrcOffset - inputMargin
48 }
49
50 var lTable [maxLTableSize]uint64
51 var sTable [maxSTableSize]uint64
52
53 // Bail if we can't compress to at least this.
54 dstLimit := len(src) - 5
55
56 // nextEmit is where in src the next emitLiteral should start from.
57 nextEmit := 0
58
59 // The encoded form must start with a literal, as there are no previous
60 // bytes to copy, so we start looking for hash matches at s == 1.
61 s := 1
62 repeat := 1
63 if dict != nil {
64 dict.initBest()
65 s = 0
66 repeat = len(dict.dict) - dict.repeat
67 }
68 cv := load64(src, s)
69
70 // We search for a repeat at -1, but don't output repeats when nextEmit == 0
71 const lowbitMask = 0xffffffff
72 getCur := func(x uint64) int {
73 return int(x & lowbitMask)
74 }
75 getPrev := func(x uint64) int {
76 return int(x >> 32)
77 }
78 const maxSkip = 64
79
80 for {
81 type match struct {
82 offset int
83 s int
84 length int
85 score int
86 rep, dict bool
87 }
88 var best match
89 for {
90 // Next src position to check
91 nextS := (s-nextEmit)>>8 + 1
92 if nextS > maxSkip {
93 nextS = s + maxSkip
94 } else {
95 nextS += s
96 }
97 if nextS > sLimit {
98 goto emitRemainder
99 }
100 if dict != nil && s >= MaxDictSrcOffset {
101 dict = nil
102 if repeat > s {
103 repeat = math.MinInt32
104 }
105 }
106 hashL := hash8(cv, lTableBits)
107 hashS := hash4(cv, sTableBits)
108 candidateL := lTable[hashL]
109 candidateS := sTable[hashS]
110
111 score := func(m match) int {
112 // Matches that are longer forward are penalized since we must emit it as a literal.
113 score := m.length - m.s
114 if nextEmit == m.s {
115 // If we do not have to emit literals, we save 1 byte
116 score++
117 }
118 offset := m.s - m.offset
119 if m.rep {
120 return score - emitRepeatSize(offset, m.length)
121 }
122 return score - emitCopySize(offset, m.length)
123 }
124
125 matchAt := func(offset, s int, first uint32, rep bool) match {
126 if best.length != 0 && best.s-best.offset == s-offset {
127 // Don't retest if we have the same offset.
128 return match{offset: offset, s: s}
129 }
130 if load32(src, offset) != first {
131 return match{offset: offset, s: s}
132 }
133 m := match{offset: offset, s: s, length: 4 + offset, rep: rep}
134 s += 4
135 for s < len(src) {
136 if len(src)-s < 8 {
137 if src[s] == src[m.length] {
138 m.length++
139 s++
140 continue
141 }
142 break
143 }
144 if diff := load64(src, s) ^ load64(src, m.length); diff != 0 {
145 m.length += bits.TrailingZeros64(diff) >> 3
146 break
147 }
148 s += 8
149 m.length += 8
150 }
151 m.length -= offset
152 m.score = score(m)
153 if m.score <= -m.s {
154 // Eliminate if no savings, we might find a better one.
155 m.length = 0
156 }
157 return m
158 }
159 matchDict := func(candidate, s int, first uint32, rep bool) match {
160 if s >= MaxDictSrcOffset {
161 return match{offset: candidate, s: s}
162 }
163 // Calculate offset as if in continuous array with s
164 offset := -len(dict.dict) + candidate
165 if best.length != 0 && best.s-best.offset == s-offset && !rep {
166 // Don't retest if we have the same offset.
167 return match{offset: offset, s: s}
168 }
169
170 if load32(dict.dict, candidate) != first {
171 return match{offset: offset, s: s}
172 }
173 m := match{offset: offset, s: s, length: 4 + candidate, rep: rep, dict: true}
174 s += 4
175 if !rep {
176 for s < sLimitDict && m.length < len(dict.dict) {
177 if len(src)-s < 8 || len(dict.dict)-m.length < 8 {
178 if src[s] == dict.dict[m.length] {
179 m.length++
180 s++
181 continue
182 }
183 break
184 }
185 if diff := load64(src, s) ^ load64(dict.dict, m.length); diff != 0 {
186 m.length += bits.TrailingZeros64(diff) >> 3
187 break
188 }
189 s += 8
190 m.length += 8
191 }
192 } else {
193 for s < len(src) && m.length < len(dict.dict) {
194 if len(src)-s < 8 || len(dict.dict)-m.length < 8 {
195 if src[s] == dict.dict[m.length] {
196 m.length++
197 s++
198 continue
199 }
200 break
201 }
202 if diff := load64(src, s) ^ load64(dict.dict, m.length); diff != 0 {
203 m.length += bits.TrailingZeros64(diff) >> 3
204 break
205 }
206 s += 8
207 m.length += 8
208 }
209 }
210 m.length -= candidate
211 m.score = score(m)
212 if m.score <= -m.s {
213 // Eliminate if no savings, we might find a better one.
214 m.length = 0
215 }
216 return m
217 }
218
219 bestOf := func(a, b match) match {
220 if b.length == 0 {
221 return a
222 }
223 if a.length == 0 {
224 return b
225 }
226 as := a.score + b.s
227 bs := b.score + a.s
228 if as >= bs {
229 return a
230 }
231 return b
232 }
233
234 if s > 0 {
235 best = bestOf(matchAt(getCur(candidateL), s, uint32(cv), false), matchAt(getPrev(candidateL), s, uint32(cv), false))
236 best = bestOf(best, matchAt(getCur(candidateS), s, uint32(cv), false))
237 best = bestOf(best, matchAt(getPrev(candidateS), s, uint32(cv), false))
238 }
239 if dict != nil {
240 candidateL := dict.bestTableLong[hashL]
241 candidateS := dict.bestTableShort[hashS]
242 best = bestOf(best, matchDict(int(candidateL&0xffff), s, uint32(cv), false))
243 best = bestOf(best, matchDict(int(candidateL>>16), s, uint32(cv), false))
244 best = bestOf(best, matchDict(int(candidateS&0xffff), s, uint32(cv), false))
245 best = bestOf(best, matchDict(int(candidateS>>16), s, uint32(cv), false))
246 }
247 {
248 if (dict == nil || repeat <= s) && repeat > 0 {
249 best = bestOf(best, matchAt(s-repeat+1, s+1, uint32(cv>>8), true))
250 } else if s-repeat < -4 && dict != nil {
251 candidate := len(dict.dict) - (repeat - s)
252 best = bestOf(best, matchDict(candidate, s, uint32(cv), true))
253 candidate++
254 best = bestOf(best, matchDict(candidate, s+1, uint32(cv>>8), true))
255 }
256
257 if best.length > 0 {
258 hashS := hash4(cv>>8, sTableBits)
259 // s+1
260 nextShort := sTable[hashS]
261 s := s + 1
262 cv := load64(src, s)
263 hashL := hash8(cv, lTableBits)
264 nextLong := lTable[hashL]
265 best = bestOf(best, matchAt(getCur(nextShort), s, uint32(cv), false))
266 best = bestOf(best, matchAt(getPrev(nextShort), s, uint32(cv), false))
267 best = bestOf(best, matchAt(getCur(nextLong), s, uint32(cv), false))
268 best = bestOf(best, matchAt(getPrev(nextLong), s, uint32(cv), false))
269
270 // Dict at + 1
271 if dict != nil {
272 candidateL := dict.bestTableLong[hashL]
273 candidateS := dict.bestTableShort[hashS]
274
275 best = bestOf(best, matchDict(int(candidateL&0xffff), s, uint32(cv), false))
276 best = bestOf(best, matchDict(int(candidateS&0xffff), s, uint32(cv), false))
277 }
278
279 // s+2
280 if true {
281 hashS := hash4(cv>>8, sTableBits)
282
283 nextShort = sTable[hashS]
284 s++
285 cv = load64(src, s)
286 hashL := hash8(cv, lTableBits)
287 nextLong = lTable[hashL]
288
289 if (dict == nil || repeat <= s) && repeat > 0 {
290 // Repeat at + 2
291 best = bestOf(best, matchAt(s-repeat, s, uint32(cv), true))
292 } else if repeat-s > 4 && dict != nil {
293 candidate := len(dict.dict) - (repeat - s)
294 best = bestOf(best, matchDict(candidate, s, uint32(cv), true))
295 }
296 best = bestOf(best, matchAt(getCur(nextShort), s, uint32(cv), false))
297 best = bestOf(best, matchAt(getPrev(nextShort), s, uint32(cv), false))
298 best = bestOf(best, matchAt(getCur(nextLong), s, uint32(cv), false))
299 best = bestOf(best, matchAt(getPrev(nextLong), s, uint32(cv), false))
300
301 // Dict at +2
302 // Very small gain
303 if dict != nil {
304 candidateL := dict.bestTableLong[hashL]
305 candidateS := dict.bestTableShort[hashS]
306
307 best = bestOf(best, matchDict(int(candidateL&0xffff), s, uint32(cv), false))
308 best = bestOf(best, matchDict(int(candidateS&0xffff), s, uint32(cv), false))
309 }
310 }
311 // Search for a match at best match end, see if that is better.
312 // Allow some bytes at the beginning to mismatch.
313 // Sweet spot is around 1-2 bytes, but depends on input.
314 // The skipped bytes are tested in Extend backwards,
315 // and still picked up as part of the match if they do.
316 const skipBeginning = 2
317 const skipEnd = 1
318 if sAt := best.s + best.length - skipEnd; sAt < sLimit {
319
320 sBack := best.s + skipBeginning - skipEnd
321 backL := best.length - skipBeginning
322 // Load initial values
323 cv = load64(src, sBack)
324
325 // Grab candidates...
326 next := lTable[hash8(load64(src, sAt), lTableBits)]
327
328 if checkAt := getCur(next) - backL; checkAt > 0 {
329 best = bestOf(best, matchAt(checkAt, sBack, uint32(cv), false))
330 }
331 if checkAt := getPrev(next) - backL; checkAt > 0 {
332 best = bestOf(best, matchAt(checkAt, sBack, uint32(cv), false))
333 }
334 // Disabled: Extremely small gain
335 if false {
336 next = sTable[hash4(load64(src, sAt), sTableBits)]
337 if checkAt := getCur(next) - backL; checkAt > 0 {
338 best = bestOf(best, matchAt(checkAt, sBack, uint32(cv), false))
339 }
340 if checkAt := getPrev(next) - backL; checkAt > 0 {
341 best = bestOf(best, matchAt(checkAt, sBack, uint32(cv), false))
342 }
343 }
344 }
345 }
346 }
347
348 // Update table
349 lTable[hashL] = uint64(s) | candidateL<<32
350 sTable[hashS] = uint64(s) | candidateS<<32
351
352 if best.length > 0 {
353 break
354 }
355
356 cv = load64(src, nextS)
357 s = nextS
358 }
359
360 // Extend backwards, not needed for repeats...
361 s = best.s
362 if !best.rep && !best.dict {
363 for best.offset > 0 && s > nextEmit && src[best.offset-1] == src[s-1] {
364 best.offset--
365 best.length++
366 s--
367 }
368 }
369 if false && best.offset >= s {
370 panic(fmt.Errorf("t %d >= s %d", best.offset, s))
371 }
372 // Bail if we exceed the maximum size.
373 if d+(s-nextEmit) > dstLimit {
374 return 0
375 }
376
377 base := s
378 offset := s - best.offset
379 s += best.length
380
381 if offset > 65535 && s-base <= 5 && !best.rep {
382 // Bail if the match is equal or worse to the encoding.
383 s = best.s + 1
384 if s >= sLimit {
385 goto emitRemainder
386 }
387 cv = load64(src, s)
388 continue
389 }
390 if debug && nextEmit != base {
391 fmt.Println("EMIT", base-nextEmit, "literals. base-after:", base)
392 }
393 d += emitLiteral(dst[d:], src[nextEmit:base])
394 if best.rep {
395 if nextEmit > 0 || best.dict {
396 if debug {
397 fmt.Println("REPEAT, length", best.length, "offset:", offset, "s-after:", s, "dict:", best.dict, "best:", best)
398 }
399 // same as `add := emitCopy(dst[d:], repeat, s-base)` but skips storing offset.
400 d += emitRepeat(dst[d:], offset, best.length)
401 } else {
402 // First match without dict cannot be a repeat.
403 if debug {
404 fmt.Println("COPY, length", best.length, "offset:", offset, "s-after:", s, "dict:", best.dict, "best:", best)
405 }
406 d += emitCopy(dst[d:], offset, best.length)
407 }
408 } else {
409 if debug {
410 fmt.Println("COPY, length", best.length, "offset:", offset, "s-after:", s, "dict:", best.dict, "best:", best)
411 }
412 d += emitCopy(dst[d:], offset, best.length)
413 }
414 repeat = offset
415
416 nextEmit = s
417 if s >= sLimit {
418 goto emitRemainder
419 }
420
421 if d > dstLimit {
422 // Do we have space for more, if not bail.
423 return 0
424 }
425 // Fill tables...
426 for i := best.s + 1; i < s; i++ {
427 cv0 := load64(src, i)
428 long0 := hash8(cv0, lTableBits)
429 short0 := hash4(cv0, sTableBits)
430 lTable[long0] = uint64(i) | lTable[long0]<<32
431 sTable[short0] = uint64(i) | sTable[short0]<<32
432 }
433 cv = load64(src, s)
434 }
435
436emitRemainder:
437 if nextEmit < len(src) {
438 // Bail if we exceed the maximum size.
439 if d+len(src)-nextEmit > dstLimit {
440 return 0
441 }
442 if debug && nextEmit != s {
443 fmt.Println("emitted ", len(src)-nextEmit, "literals")
444 }
445 d += emitLiteral(dst[d:], src[nextEmit:])
446 }
447 return d
448}
449
450// encodeBlockBestSnappy encodes a non-empty src to a guaranteed-large-enough dst. It
451// assumes that the varint-encoded length of the decompressed bytes has already
452// been written.
453//
454// It also assumes that:
455//
456// len(dst) >= MaxEncodedLen(len(src)) &&
457// minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
458func encodeBlockBestSnappy(dst, src []byte) (d int) {
459 // Initialize the hash tables.
460 const (
461 // Long hash matches.
462 lTableBits = 19
463 maxLTableSize = 1 << lTableBits
464
465 // Short hash matches.
466 sTableBits = 16
467 maxSTableSize = 1 << sTableBits
468
469 inputMargin = 8 + 2
470 )
471
472 // sLimit is when to stop looking for offset/length copies. The inputMargin
473 // lets us use a fast path for emitLiteral in the main loop, while we are
474 // looking for copies.
475 sLimit := len(src) - inputMargin
476 if len(src) < minNonLiteralBlockSize {
477 return 0
478 }
479
480 var lTable [maxLTableSize]uint64
481 var sTable [maxSTableSize]uint64
482
483 // Bail if we can't compress to at least this.
484 dstLimit := len(src) - 5
485
486 // nextEmit is where in src the next emitLiteral should start from.
487 nextEmit := 0
488
489 // The encoded form must start with a literal, as there are no previous
490 // bytes to copy, so we start looking for hash matches at s == 1.
491 s := 1
492 cv := load64(src, s)
493
494 // We search for a repeat at -1, but don't output repeats when nextEmit == 0
495 repeat := 1
496 const lowbitMask = 0xffffffff
497 getCur := func(x uint64) int {
498 return int(x & lowbitMask)
499 }
500 getPrev := func(x uint64) int {
501 return int(x >> 32)
502 }
503 const maxSkip = 64
504
505 for {
506 type match struct {
507 offset int
508 s int
509 length int
510 score int
511 }
512 var best match
513 for {
514 // Next src position to check
515 nextS := (s-nextEmit)>>8 + 1
516 if nextS > maxSkip {
517 nextS = s + maxSkip
518 } else {
519 nextS += s
520 }
521 if nextS > sLimit {
522 goto emitRemainder
523 }
524 hashL := hash8(cv, lTableBits)
525 hashS := hash4(cv, sTableBits)
526 candidateL := lTable[hashL]
527 candidateS := sTable[hashS]
528
529 score := func(m match) int {
530 // Matches that are longer forward are penalized since we must emit it as a literal.
531 score := m.length - m.s
532 if nextEmit == m.s {
533 // If we do not have to emit literals, we save 1 byte
534 score++
535 }
536 offset := m.s - m.offset
537
538 return score - emitCopyNoRepeatSize(offset, m.length)
539 }
540
541 matchAt := func(offset, s int, first uint32) match {
542 if best.length != 0 && best.s-best.offset == s-offset {
543 // Don't retest if we have the same offset.
544 return match{offset: offset, s: s}
545 }
546 if load32(src, offset) != first {
547 return match{offset: offset, s: s}
548 }
549 m := match{offset: offset, s: s, length: 4 + offset}
550 s += 4
551 for s <= sLimit {
552 if diff := load64(src, s) ^ load64(src, m.length); diff != 0 {
553 m.length += bits.TrailingZeros64(diff) >> 3
554 break
555 }
556 s += 8
557 m.length += 8
558 }
559 m.length -= offset
560 m.score = score(m)
561 if m.score <= -m.s {
562 // Eliminate if no savings, we might find a better one.
563 m.length = 0
564 }
565 return m
566 }
567
568 bestOf := func(a, b match) match {
569 if b.length == 0 {
570 return a
571 }
572 if a.length == 0 {
573 return b
574 }
575 as := a.score + b.s
576 bs := b.score + a.s
577 if as >= bs {
578 return a
579 }
580 return b
581 }
582
583 best = bestOf(matchAt(getCur(candidateL), s, uint32(cv)), matchAt(getPrev(candidateL), s, uint32(cv)))
584 best = bestOf(best, matchAt(getCur(candidateS), s, uint32(cv)))
585 best = bestOf(best, matchAt(getPrev(candidateS), s, uint32(cv)))
586
587 {
588 best = bestOf(best, matchAt(s-repeat+1, s+1, uint32(cv>>8)))
589 if best.length > 0 {
590 // s+1
591 nextShort := sTable[hash4(cv>>8, sTableBits)]
592 s := s + 1
593 cv := load64(src, s)
594 nextLong := lTable[hash8(cv, lTableBits)]
595 best = bestOf(best, matchAt(getCur(nextShort), s, uint32(cv)))
596 best = bestOf(best, matchAt(getPrev(nextShort), s, uint32(cv)))
597 best = bestOf(best, matchAt(getCur(nextLong), s, uint32(cv)))
598 best = bestOf(best, matchAt(getPrev(nextLong), s, uint32(cv)))
599 // Repeat at + 2
600 best = bestOf(best, matchAt(s-repeat+1, s+1, uint32(cv>>8)))
601
602 // s+2
603 if true {
604 nextShort = sTable[hash4(cv>>8, sTableBits)]
605 s++
606 cv = load64(src, s)
607 nextLong = lTable[hash8(cv, lTableBits)]
608 best = bestOf(best, matchAt(getCur(nextShort), s, uint32(cv)))
609 best = bestOf(best, matchAt(getPrev(nextShort), s, uint32(cv)))
610 best = bestOf(best, matchAt(getCur(nextLong), s, uint32(cv)))
611 best = bestOf(best, matchAt(getPrev(nextLong), s, uint32(cv)))
612 }
613 // Search for a match at best match end, see if that is better.
614 if sAt := best.s + best.length; sAt < sLimit {
615 sBack := best.s
616 backL := best.length
617 // Load initial values
618 cv = load64(src, sBack)
619 // Search for mismatch
620 next := lTable[hash8(load64(src, sAt), lTableBits)]
621 //next := sTable[hash4(load64(src, sAt), sTableBits)]
622
623 if checkAt := getCur(next) - backL; checkAt > 0 {
624 best = bestOf(best, matchAt(checkAt, sBack, uint32(cv)))
625 }
626 if checkAt := getPrev(next) - backL; checkAt > 0 {
627 best = bestOf(best, matchAt(checkAt, sBack, uint32(cv)))
628 }
629 }
630 }
631 }
632
633 // Update table
634 lTable[hashL] = uint64(s) | candidateL<<32
635 sTable[hashS] = uint64(s) | candidateS<<32
636
637 if best.length > 0 {
638 break
639 }
640
641 cv = load64(src, nextS)
642 s = nextS
643 }
644
645 // Extend backwards, not needed for repeats...
646 s = best.s
647 if true {
648 for best.offset > 0 && s > nextEmit && src[best.offset-1] == src[s-1] {
649 best.offset--
650 best.length++
651 s--
652 }
653 }
654 if false && best.offset >= s {
655 panic(fmt.Errorf("t %d >= s %d", best.offset, s))
656 }
657 // Bail if we exceed the maximum size.
658 if d+(s-nextEmit) > dstLimit {
659 return 0
660 }
661
662 base := s
663 offset := s - best.offset
664
665 s += best.length
666
667 if offset > 65535 && s-base <= 5 {
668 // Bail if the match is equal or worse to the encoding.
669 s = best.s + 1
670 if s >= sLimit {
671 goto emitRemainder
672 }
673 cv = load64(src, s)
674 continue
675 }
676 d += emitLiteral(dst[d:], src[nextEmit:base])
677 d += emitCopyNoRepeat(dst[d:], offset, best.length)
678 repeat = offset
679
680 nextEmit = s
681 if s >= sLimit {
682 goto emitRemainder
683 }
684
685 if d > dstLimit {
686 // Do we have space for more, if not bail.
687 return 0
688 }
689 // Fill tables...
690 for i := best.s + 1; i < s; i++ {
691 cv0 := load64(src, i)
692 long0 := hash8(cv0, lTableBits)
693 short0 := hash4(cv0, sTableBits)
694 lTable[long0] = uint64(i) | lTable[long0]<<32
695 sTable[short0] = uint64(i) | sTable[short0]<<32
696 }
697 cv = load64(src, s)
698 }
699
700emitRemainder:
701 if nextEmit < len(src) {
702 // Bail if we exceed the maximum size.
703 if d+len(src)-nextEmit > dstLimit {
704 return 0
705 }
706 d += emitLiteral(dst[d:], src[nextEmit:])
707 }
708 return d
709}
710
711// emitCopySize returns the size to encode the offset+length
712//
713// It assumes that:
714//
715// 1 <= offset && offset <= math.MaxUint32
716// 4 <= length && length <= 1 << 24
717func emitCopySize(offset, length int) int {
718 if offset >= 65536 {
719 i := 0
720 if length > 64 {
721 length -= 64
722 if length >= 4 {
723 // Emit remaining as repeats
724 return 5 + emitRepeatSize(offset, length)
725 }
726 i = 5
727 }
728 if length == 0 {
729 return i
730 }
731 return i + 5
732 }
733
734 // Offset no more than 2 bytes.
735 if length > 64 {
736 if offset < 2048 {
737 // Emit 8 bytes, then rest as repeats...
738 return 2 + emitRepeatSize(offset, length-8)
739 }
740 // Emit remaining as repeats, at least 4 bytes remain.
741 return 3 + emitRepeatSize(offset, length-60)
742 }
743 if length >= 12 || offset >= 2048 {
744 return 3
745 }
746 // Emit the remaining copy, encoded as 2 bytes.
747 return 2
748}
749
750// emitCopyNoRepeatSize returns the size to encode the offset+length
751//
752// It assumes that:
753//
754// 1 <= offset && offset <= math.MaxUint32
755// 4 <= length && length <= 1 << 24
756func emitCopyNoRepeatSize(offset, length int) int {
757 if offset >= 65536 {
758 return 5 + 5*(length/64)
759 }
760
761 // Offset no more than 2 bytes.
762 if length > 64 {
763 // Emit remaining as repeats, at least 4 bytes remain.
764 return 3 + 3*(length/60)
765 }
766 if length >= 12 || offset >= 2048 {
767 return 3
768 }
769 // Emit the remaining copy, encoded as 2 bytes.
770 return 2
771}
772
773// emitRepeatSize returns the number of bytes required to encode a repeat.
774// Length must be at least 4 and < 1<<24
775func emitRepeatSize(offset, length int) int {
776 // Repeat offset, make length cheaper
777 if length <= 4+4 || (length < 8+4 && offset < 2048) {
778 return 2
779 }
780 if length < (1<<8)+4+4 {
781 return 3
782 }
783 if length < (1<<16)+(1<<8)+4 {
784 return 4
785 }
786 const maxRepeat = (1 << 24) - 1
787 length -= (1 << 16) - 4
788 left := 0
789 if length > maxRepeat {
790 left = length - maxRepeat + 4
791 }
792 if left > 0 {
793 return 5 + emitRepeatSize(offset, left)
794 }
795 return 5
796}
generated by cgit v1.2.3 (git 2.45.2) at 2024-11-05 19:15:58 +0000