kesavand | c71914f | 2022-03-25 11:19:03 +0530 | [diff] [blame] | 1 | // Copyright 2019+ Klaus Post. All rights reserved. |
| 2 | // License information can be found in the LICENSE file. |
| 3 | // Based on work by Yann Collet, released under BSD License. |
| 4 | |
| 5 | package zstd |
| 6 | |
| 7 | import ( |
| 8 | "bytes" |
| 9 | "fmt" |
| 10 | |
| 11 | "github.com/klauspost/compress" |
| 12 | ) |
| 13 | |
| 14 | const ( |
| 15 | bestLongTableBits = 22 // Bits used in the long match table |
| 16 | bestLongTableSize = 1 << bestLongTableBits // Size of the table |
| 17 | bestLongLen = 8 // Bytes used for table hash |
| 18 | |
| 19 | // Note: Increasing the short table bits or making the hash shorter |
| 20 | // can actually lead to compression degradation since it will 'steal' more from the |
| 21 | // long match table and match offsets are quite big. |
| 22 | // This greatly depends on the type of input. |
| 23 | bestShortTableBits = 18 // Bits used in the short match table |
| 24 | bestShortTableSize = 1 << bestShortTableBits // Size of the table |
| 25 | bestShortLen = 4 // Bytes used for table hash |
| 26 | |
| 27 | ) |
| 28 | |
| 29 | type match struct { |
| 30 | offset int32 |
| 31 | s int32 |
| 32 | length int32 |
| 33 | rep int32 |
| 34 | est int32 |
| 35 | } |
| 36 | |
| 37 | const highScore = 25000 |
| 38 | |
| 39 | // estBits will estimate output bits from predefined tables. |
| 40 | func (m *match) estBits(bitsPerByte int32) { |
| 41 | mlc := mlCode(uint32(m.length - zstdMinMatch)) |
| 42 | var ofc uint8 |
| 43 | if m.rep < 0 { |
| 44 | ofc = ofCode(uint32(m.s-m.offset) + 3) |
| 45 | } else { |
| 46 | ofc = ofCode(uint32(m.rep)) |
| 47 | } |
| 48 | // Cost, excluding |
| 49 | ofTT, mlTT := fsePredefEnc[tableOffsets].ct.symbolTT[ofc], fsePredefEnc[tableMatchLengths].ct.symbolTT[mlc] |
| 50 | |
| 51 | // Add cost of match encoding... |
| 52 | m.est = int32(ofTT.outBits + mlTT.outBits) |
| 53 | m.est += int32(ofTT.deltaNbBits>>16 + mlTT.deltaNbBits>>16) |
| 54 | // Subtract savings compared to literal encoding... |
| 55 | m.est -= (m.length * bitsPerByte) >> 10 |
| 56 | if m.est > 0 { |
| 57 | // Unlikely gain.. |
| 58 | m.length = 0 |
| 59 | m.est = highScore |
| 60 | } |
| 61 | } |
| 62 | |
| 63 | // bestFastEncoder uses 2 tables, one for short matches (5 bytes) and one for long matches. |
| 64 | // The long match table contains the previous entry with the same hash, |
| 65 | // effectively making it a "chain" of length 2. |
| 66 | // When we find a long match we choose between the two values and select the longest. |
| 67 | // When we find a short match, after checking the long, we check if we can find a long at n+1 |
| 68 | // and that it is longer (lazy matching). |
| 69 | type bestFastEncoder struct { |
| 70 | fastBase |
| 71 | table [bestShortTableSize]prevEntry |
| 72 | longTable [bestLongTableSize]prevEntry |
| 73 | dictTable []prevEntry |
| 74 | dictLongTable []prevEntry |
| 75 | } |
| 76 | |
| 77 | // Encode improves compression... |
| 78 | func (e *bestFastEncoder) Encode(blk *blockEnc, src []byte) { |
| 79 | const ( |
| 80 | // Input margin is the number of bytes we read (8) |
| 81 | // and the maximum we will read ahead (2) |
| 82 | inputMargin = 8 + 4 |
| 83 | minNonLiteralBlockSize = 16 |
| 84 | ) |
| 85 | |
| 86 | // Protect against e.cur wraparound. |
| 87 | for e.cur >= bufferReset { |
| 88 | if len(e.hist) == 0 { |
| 89 | for i := range e.table[:] { |
| 90 | e.table[i] = prevEntry{} |
| 91 | } |
| 92 | for i := range e.longTable[:] { |
| 93 | e.longTable[i] = prevEntry{} |
| 94 | } |
| 95 | e.cur = e.maxMatchOff |
| 96 | break |
| 97 | } |
| 98 | // Shift down everything in the table that isn't already too far away. |
| 99 | minOff := e.cur + int32(len(e.hist)) - e.maxMatchOff |
| 100 | for i := range e.table[:] { |
| 101 | v := e.table[i].offset |
| 102 | v2 := e.table[i].prev |
| 103 | if v < minOff { |
| 104 | v = 0 |
| 105 | v2 = 0 |
| 106 | } else { |
| 107 | v = v - e.cur + e.maxMatchOff |
| 108 | if v2 < minOff { |
| 109 | v2 = 0 |
| 110 | } else { |
| 111 | v2 = v2 - e.cur + e.maxMatchOff |
| 112 | } |
| 113 | } |
| 114 | e.table[i] = prevEntry{ |
| 115 | offset: v, |
| 116 | prev: v2, |
| 117 | } |
| 118 | } |
| 119 | for i := range e.longTable[:] { |
| 120 | v := e.longTable[i].offset |
| 121 | v2 := e.longTable[i].prev |
| 122 | if v < minOff { |
| 123 | v = 0 |
| 124 | v2 = 0 |
| 125 | } else { |
| 126 | v = v - e.cur + e.maxMatchOff |
| 127 | if v2 < minOff { |
| 128 | v2 = 0 |
| 129 | } else { |
| 130 | v2 = v2 - e.cur + e.maxMatchOff |
| 131 | } |
| 132 | } |
| 133 | e.longTable[i] = prevEntry{ |
| 134 | offset: v, |
| 135 | prev: v2, |
| 136 | } |
| 137 | } |
| 138 | e.cur = e.maxMatchOff |
| 139 | break |
| 140 | } |
| 141 | |
| 142 | s := e.addBlock(src) |
| 143 | blk.size = len(src) |
| 144 | if len(src) < minNonLiteralBlockSize { |
| 145 | blk.extraLits = len(src) |
| 146 | blk.literals = blk.literals[:len(src)] |
| 147 | copy(blk.literals, src) |
| 148 | return |
| 149 | } |
| 150 | |
| 151 | // Use this to estimate literal cost. |
| 152 | // Scaled by 10 bits. |
| 153 | bitsPerByte := int32((compress.ShannonEntropyBits(src) * 1024) / len(src)) |
| 154 | // Huffman can never go < 1 bit/byte |
| 155 | if bitsPerByte < 1024 { |
| 156 | bitsPerByte = 1024 |
| 157 | } |
| 158 | |
| 159 | // Override src |
| 160 | src = e.hist |
| 161 | sLimit := int32(len(src)) - inputMargin |
| 162 | const kSearchStrength = 10 |
| 163 | |
| 164 | // nextEmit is where in src the next emitLiteral should start from. |
| 165 | nextEmit := s |
| 166 | cv := load6432(src, s) |
| 167 | |
| 168 | // Relative offsets |
| 169 | offset1 := int32(blk.recentOffsets[0]) |
| 170 | offset2 := int32(blk.recentOffsets[1]) |
| 171 | offset3 := int32(blk.recentOffsets[2]) |
| 172 | |
| 173 | addLiterals := func(s *seq, until int32) { |
| 174 | if until == nextEmit { |
| 175 | return |
| 176 | } |
| 177 | blk.literals = append(blk.literals, src[nextEmit:until]...) |
| 178 | s.litLen = uint32(until - nextEmit) |
| 179 | } |
| 180 | _ = addLiterals |
| 181 | |
| 182 | if debugEncoder { |
| 183 | println("recent offsets:", blk.recentOffsets) |
| 184 | } |
| 185 | |
| 186 | encodeLoop: |
| 187 | for { |
| 188 | // We allow the encoder to optionally turn off repeat offsets across blocks |
| 189 | canRepeat := len(blk.sequences) > 2 |
| 190 | |
| 191 | if debugAsserts && canRepeat && offset1 == 0 { |
| 192 | panic("offset0 was 0") |
| 193 | } |
| 194 | |
| 195 | bestOf := func(a, b match) match { |
| 196 | if a.est+(a.s-b.s)*bitsPerByte>>10 < b.est+(b.s-a.s)*bitsPerByte>>10 { |
| 197 | return a |
| 198 | } |
| 199 | return b |
| 200 | } |
| 201 | const goodEnough = 100 |
| 202 | |
| 203 | nextHashL := hashLen(cv, bestLongTableBits, bestLongLen) |
| 204 | nextHashS := hashLen(cv, bestShortTableBits, bestShortLen) |
| 205 | candidateL := e.longTable[nextHashL] |
| 206 | candidateS := e.table[nextHashS] |
| 207 | |
| 208 | matchAt := func(offset int32, s int32, first uint32, rep int32) match { |
| 209 | if s-offset >= e.maxMatchOff || load3232(src, offset) != first { |
| 210 | return match{s: s, est: highScore} |
| 211 | } |
| 212 | if debugAsserts { |
| 213 | if !bytes.Equal(src[s:s+4], src[offset:offset+4]) { |
| 214 | panic(fmt.Sprintf("first match mismatch: %v != %v, first: %08x", src[s:s+4], src[offset:offset+4], first)) |
| 215 | } |
| 216 | } |
| 217 | m := match{offset: offset, s: s, length: 4 + e.matchlen(s+4, offset+4, src), rep: rep} |
| 218 | m.estBits(bitsPerByte) |
| 219 | return m |
| 220 | } |
| 221 | |
| 222 | best := bestOf(matchAt(candidateL.offset-e.cur, s, uint32(cv), -1), matchAt(candidateL.prev-e.cur, s, uint32(cv), -1)) |
| 223 | best = bestOf(best, matchAt(candidateS.offset-e.cur, s, uint32(cv), -1)) |
| 224 | best = bestOf(best, matchAt(candidateS.prev-e.cur, s, uint32(cv), -1)) |
| 225 | |
| 226 | if canRepeat && best.length < goodEnough { |
| 227 | cv32 := uint32(cv >> 8) |
| 228 | spp := s + 1 |
| 229 | best = bestOf(best, matchAt(spp-offset1, spp, cv32, 1)) |
| 230 | best = bestOf(best, matchAt(spp-offset2, spp, cv32, 2)) |
| 231 | best = bestOf(best, matchAt(spp-offset3, spp, cv32, 3)) |
| 232 | if best.length > 0 { |
| 233 | cv32 = uint32(cv >> 24) |
| 234 | spp += 2 |
| 235 | best = bestOf(best, matchAt(spp-offset1, spp, cv32, 1)) |
| 236 | best = bestOf(best, matchAt(spp-offset2, spp, cv32, 2)) |
| 237 | best = bestOf(best, matchAt(spp-offset3, spp, cv32, 3)) |
| 238 | } |
| 239 | } |
| 240 | // Load next and check... |
| 241 | e.longTable[nextHashL] = prevEntry{offset: s + e.cur, prev: candidateL.offset} |
| 242 | e.table[nextHashS] = prevEntry{offset: s + e.cur, prev: candidateS.offset} |
| 243 | |
| 244 | // Look far ahead, unless we have a really long match already... |
| 245 | if best.length < goodEnough { |
| 246 | // No match found, move forward on input, no need to check forward... |
| 247 | if best.length < 4 { |
| 248 | s += 1 + (s-nextEmit)>>(kSearchStrength-1) |
| 249 | if s >= sLimit { |
| 250 | break encodeLoop |
| 251 | } |
| 252 | cv = load6432(src, s) |
| 253 | continue |
| 254 | } |
| 255 | |
| 256 | s++ |
| 257 | candidateS = e.table[hashLen(cv>>8, bestShortTableBits, bestShortLen)] |
| 258 | cv = load6432(src, s) |
| 259 | cv2 := load6432(src, s+1) |
| 260 | candidateL = e.longTable[hashLen(cv, bestLongTableBits, bestLongLen)] |
| 261 | candidateL2 := e.longTable[hashLen(cv2, bestLongTableBits, bestLongLen)] |
| 262 | |
| 263 | // Short at s+1 |
| 264 | best = bestOf(best, matchAt(candidateS.offset-e.cur, s, uint32(cv), -1)) |
| 265 | // Long at s+1, s+2 |
| 266 | best = bestOf(best, matchAt(candidateL.offset-e.cur, s, uint32(cv), -1)) |
| 267 | best = bestOf(best, matchAt(candidateL.prev-e.cur, s, uint32(cv), -1)) |
| 268 | best = bestOf(best, matchAt(candidateL2.offset-e.cur, s+1, uint32(cv2), -1)) |
| 269 | best = bestOf(best, matchAt(candidateL2.prev-e.cur, s+1, uint32(cv2), -1)) |
| 270 | if false { |
| 271 | // Short at s+3. |
| 272 | // Too often worse... |
| 273 | best = bestOf(best, matchAt(e.table[hashLen(cv2>>8, bestShortTableBits, bestShortLen)].offset-e.cur, s+2, uint32(cv2>>8), -1)) |
| 274 | } |
| 275 | // See if we can find a better match by checking where the current best ends. |
| 276 | // Use that offset to see if we can find a better full match. |
| 277 | if sAt := best.s + best.length; sAt < sLimit { |
| 278 | nextHashL := hashLen(load6432(src, sAt), bestLongTableBits, bestLongLen) |
| 279 | candidateEnd := e.longTable[nextHashL] |
| 280 | if pos := candidateEnd.offset - e.cur - best.length; pos >= 0 { |
| 281 | bestEnd := bestOf(best, matchAt(pos, best.s, load3232(src, best.s), -1)) |
| 282 | if pos := candidateEnd.prev - e.cur - best.length; pos >= 0 { |
| 283 | bestEnd = bestOf(bestEnd, matchAt(pos, best.s, load3232(src, best.s), -1)) |
| 284 | } |
| 285 | best = bestEnd |
| 286 | } |
| 287 | } |
| 288 | } |
| 289 | |
| 290 | if debugAsserts { |
| 291 | if !bytes.Equal(src[best.s:best.s+best.length], src[best.offset:best.offset+best.length]) { |
| 292 | panic(fmt.Sprintf("match mismatch: %v != %v", src[best.s:best.s+best.length], src[best.offset:best.offset+best.length])) |
| 293 | } |
| 294 | } |
| 295 | |
| 296 | // We have a match, we can store the forward value |
| 297 | if best.rep > 0 { |
| 298 | s = best.s |
| 299 | var seq seq |
| 300 | seq.matchLen = uint32(best.length - zstdMinMatch) |
| 301 | |
| 302 | // We might be able to match backwards. |
| 303 | // Extend as long as we can. |
| 304 | start := best.s |
| 305 | // We end the search early, so we don't risk 0 literals |
| 306 | // and have to do special offset treatment. |
| 307 | startLimit := nextEmit + 1 |
| 308 | |
| 309 | tMin := s - e.maxMatchOff |
| 310 | if tMin < 0 { |
| 311 | tMin = 0 |
| 312 | } |
| 313 | repIndex := best.offset |
| 314 | for repIndex > tMin && start > startLimit && src[repIndex-1] == src[start-1] && seq.matchLen < maxMatchLength-zstdMinMatch-1 { |
| 315 | repIndex-- |
| 316 | start-- |
| 317 | seq.matchLen++ |
| 318 | } |
| 319 | addLiterals(&seq, start) |
| 320 | |
| 321 | // rep 0 |
| 322 | seq.offset = uint32(best.rep) |
| 323 | if debugSequences { |
| 324 | println("repeat sequence", seq, "next s:", s) |
| 325 | } |
| 326 | blk.sequences = append(blk.sequences, seq) |
| 327 | |
| 328 | // Index match start+1 (long) -> s - 1 |
| 329 | index0 := s |
| 330 | s = best.s + best.length |
| 331 | |
| 332 | nextEmit = s |
| 333 | if s >= sLimit { |
| 334 | if debugEncoder { |
| 335 | println("repeat ended", s, best.length) |
| 336 | |
| 337 | } |
| 338 | break encodeLoop |
| 339 | } |
| 340 | // Index skipped... |
| 341 | off := index0 + e.cur |
| 342 | for index0 < s-1 { |
| 343 | cv0 := load6432(src, index0) |
| 344 | h0 := hashLen(cv0, bestLongTableBits, bestLongLen) |
| 345 | h1 := hashLen(cv0, bestShortTableBits, bestShortLen) |
| 346 | e.longTable[h0] = prevEntry{offset: off, prev: e.longTable[h0].offset} |
| 347 | e.table[h1] = prevEntry{offset: off, prev: e.table[h1].offset} |
| 348 | off++ |
| 349 | index0++ |
| 350 | } |
| 351 | switch best.rep { |
| 352 | case 2: |
| 353 | offset1, offset2 = offset2, offset1 |
| 354 | case 3: |
| 355 | offset1, offset2, offset3 = offset3, offset1, offset2 |
| 356 | } |
| 357 | cv = load6432(src, s) |
| 358 | continue |
| 359 | } |
| 360 | |
| 361 | // A 4-byte match has been found. Update recent offsets. |
| 362 | // We'll later see if more than 4 bytes. |
| 363 | s = best.s |
| 364 | t := best.offset |
| 365 | offset1, offset2, offset3 = s-t, offset1, offset2 |
| 366 | |
| 367 | if debugAsserts && s <= t { |
| 368 | panic(fmt.Sprintf("s (%d) <= t (%d)", s, t)) |
| 369 | } |
| 370 | |
| 371 | if debugAsserts && int(offset1) > len(src) { |
| 372 | panic("invalid offset") |
| 373 | } |
| 374 | |
| 375 | // Extend the n-byte match as long as possible. |
| 376 | l := best.length |
| 377 | |
| 378 | // Extend backwards |
| 379 | tMin := s - e.maxMatchOff |
| 380 | if tMin < 0 { |
| 381 | tMin = 0 |
| 382 | } |
| 383 | for t > tMin && s > nextEmit && src[t-1] == src[s-1] && l < maxMatchLength { |
| 384 | s-- |
| 385 | t-- |
| 386 | l++ |
| 387 | } |
| 388 | |
| 389 | // Write our sequence |
| 390 | var seq seq |
| 391 | seq.litLen = uint32(s - nextEmit) |
| 392 | seq.matchLen = uint32(l - zstdMinMatch) |
| 393 | if seq.litLen > 0 { |
| 394 | blk.literals = append(blk.literals, src[nextEmit:s]...) |
| 395 | } |
| 396 | seq.offset = uint32(s-t) + 3 |
| 397 | s += l |
| 398 | if debugSequences { |
| 399 | println("sequence", seq, "next s:", s) |
| 400 | } |
| 401 | blk.sequences = append(blk.sequences, seq) |
| 402 | nextEmit = s |
| 403 | if s >= sLimit { |
| 404 | break encodeLoop |
| 405 | } |
| 406 | |
| 407 | // Index match start+1 (long) -> s - 1 |
| 408 | index0 := s - l + 1 |
| 409 | // every entry |
| 410 | for index0 < s-1 { |
| 411 | cv0 := load6432(src, index0) |
| 412 | h0 := hashLen(cv0, bestLongTableBits, bestLongLen) |
| 413 | h1 := hashLen(cv0, bestShortTableBits, bestShortLen) |
| 414 | off := index0 + e.cur |
| 415 | e.longTable[h0] = prevEntry{offset: off, prev: e.longTable[h0].offset} |
| 416 | e.table[h1] = prevEntry{offset: off, prev: e.table[h1].offset} |
| 417 | index0++ |
| 418 | } |
| 419 | |
| 420 | cv = load6432(src, s) |
| 421 | if !canRepeat { |
| 422 | continue |
| 423 | } |
| 424 | |
| 425 | // Check offset 2 |
| 426 | for { |
| 427 | o2 := s - offset2 |
| 428 | if load3232(src, o2) != uint32(cv) { |
| 429 | // Do regular search |
| 430 | break |
| 431 | } |
| 432 | |
| 433 | // Store this, since we have it. |
| 434 | nextHashS := hashLen(cv, bestShortTableBits, bestShortLen) |
| 435 | nextHashL := hashLen(cv, bestLongTableBits, bestLongLen) |
| 436 | |
| 437 | // We have at least 4 byte match. |
| 438 | // No need to check backwards. We come straight from a match |
| 439 | l := 4 + e.matchlen(s+4, o2+4, src) |
| 440 | |
| 441 | e.longTable[nextHashL] = prevEntry{offset: s + e.cur, prev: e.longTable[nextHashL].offset} |
| 442 | e.table[nextHashS] = prevEntry{offset: s + e.cur, prev: e.table[nextHashS].offset} |
| 443 | seq.matchLen = uint32(l) - zstdMinMatch |
| 444 | seq.litLen = 0 |
| 445 | |
| 446 | // Since litlen is always 0, this is offset 1. |
| 447 | seq.offset = 1 |
| 448 | s += l |
| 449 | nextEmit = s |
| 450 | if debugSequences { |
| 451 | println("sequence", seq, "next s:", s) |
| 452 | } |
| 453 | blk.sequences = append(blk.sequences, seq) |
| 454 | |
| 455 | // Swap offset 1 and 2. |
| 456 | offset1, offset2 = offset2, offset1 |
| 457 | if s >= sLimit { |
| 458 | // Finished |
| 459 | break encodeLoop |
| 460 | } |
| 461 | cv = load6432(src, s) |
| 462 | } |
| 463 | } |
| 464 | |
| 465 | if int(nextEmit) < len(src) { |
| 466 | blk.literals = append(blk.literals, src[nextEmit:]...) |
| 467 | blk.extraLits = len(src) - int(nextEmit) |
| 468 | } |
| 469 | blk.recentOffsets[0] = uint32(offset1) |
| 470 | blk.recentOffsets[1] = uint32(offset2) |
| 471 | blk.recentOffsets[2] = uint32(offset3) |
| 472 | if debugEncoder { |
| 473 | println("returning, recent offsets:", blk.recentOffsets, "extra literals:", blk.extraLits) |
| 474 | } |
| 475 | } |
| 476 | |
| 477 | // EncodeNoHist will encode a block with no history and no following blocks. |
| 478 | // Most notable difference is that src will not be copied for history and |
| 479 | // we do not need to check for max match length. |
| 480 | func (e *bestFastEncoder) EncodeNoHist(blk *blockEnc, src []byte) { |
| 481 | e.ensureHist(len(src)) |
| 482 | e.Encode(blk, src) |
| 483 | } |
| 484 | |
| 485 | // Reset will reset and set a dictionary if not nil |
| 486 | func (e *bestFastEncoder) Reset(d *dict, singleBlock bool) { |
| 487 | e.resetBase(d, singleBlock) |
| 488 | if d == nil { |
| 489 | return |
| 490 | } |
| 491 | // Init or copy dict table |
| 492 | if len(e.dictTable) != len(e.table) || d.id != e.lastDictID { |
| 493 | if len(e.dictTable) != len(e.table) { |
| 494 | e.dictTable = make([]prevEntry, len(e.table)) |
| 495 | } |
| 496 | end := int32(len(d.content)) - 8 + e.maxMatchOff |
| 497 | for i := e.maxMatchOff; i < end; i += 4 { |
| 498 | const hashLog = bestShortTableBits |
| 499 | |
| 500 | cv := load6432(d.content, i-e.maxMatchOff) |
| 501 | nextHash := hashLen(cv, hashLog, bestShortLen) // 0 -> 4 |
| 502 | nextHash1 := hashLen(cv>>8, hashLog, bestShortLen) // 1 -> 5 |
| 503 | nextHash2 := hashLen(cv>>16, hashLog, bestShortLen) // 2 -> 6 |
| 504 | nextHash3 := hashLen(cv>>24, hashLog, bestShortLen) // 3 -> 7 |
| 505 | e.dictTable[nextHash] = prevEntry{ |
| 506 | prev: e.dictTable[nextHash].offset, |
| 507 | offset: i, |
| 508 | } |
| 509 | e.dictTable[nextHash1] = prevEntry{ |
| 510 | prev: e.dictTable[nextHash1].offset, |
| 511 | offset: i + 1, |
| 512 | } |
| 513 | e.dictTable[nextHash2] = prevEntry{ |
| 514 | prev: e.dictTable[nextHash2].offset, |
| 515 | offset: i + 2, |
| 516 | } |
| 517 | e.dictTable[nextHash3] = prevEntry{ |
| 518 | prev: e.dictTable[nextHash3].offset, |
| 519 | offset: i + 3, |
| 520 | } |
| 521 | } |
| 522 | e.lastDictID = d.id |
| 523 | } |
| 524 | |
| 525 | // Init or copy dict table |
| 526 | if len(e.dictLongTable) != len(e.longTable) || d.id != e.lastDictID { |
| 527 | if len(e.dictLongTable) != len(e.longTable) { |
| 528 | e.dictLongTable = make([]prevEntry, len(e.longTable)) |
| 529 | } |
| 530 | if len(d.content) >= 8 { |
| 531 | cv := load6432(d.content, 0) |
| 532 | h := hashLen(cv, bestLongTableBits, bestLongLen) |
| 533 | e.dictLongTable[h] = prevEntry{ |
| 534 | offset: e.maxMatchOff, |
| 535 | prev: e.dictLongTable[h].offset, |
| 536 | } |
| 537 | |
| 538 | end := int32(len(d.content)) - 8 + e.maxMatchOff |
| 539 | off := 8 // First to read |
| 540 | for i := e.maxMatchOff + 1; i < end; i++ { |
| 541 | cv = cv>>8 | (uint64(d.content[off]) << 56) |
| 542 | h := hashLen(cv, bestLongTableBits, bestLongLen) |
| 543 | e.dictLongTable[h] = prevEntry{ |
| 544 | offset: i, |
| 545 | prev: e.dictLongTable[h].offset, |
| 546 | } |
| 547 | off++ |
| 548 | } |
| 549 | } |
| 550 | e.lastDictID = d.id |
| 551 | } |
| 552 | // Reset table to initial state |
| 553 | copy(e.longTable[:], e.dictLongTable) |
| 554 | |
| 555 | e.cur = e.maxMatchOff |
| 556 | // Reset table to initial state |
| 557 | copy(e.table[:], e.dictTable) |
| 558 | } |