xref: /freebsd/sys/contrib/zstd/lib/compress/zstd_double_fast.c (revision cfd6422a5217410fbd66f7a7a8a64d9d85e61229)
1 /*
2  * Copyright (c) 2016-2020, Yann Collet, Facebook, Inc.
3  * All rights reserved.
4  *
5  * This source code is licensed under both the BSD-style license (found in the
6  * LICENSE file in the root directory of this source tree) and the GPLv2 (found
7  * in the COPYING file in the root directory of this source tree).
8  * You may select, at your option, one of the above-listed licenses.
9  */
10 
11 #include "zstd_compress_internal.h"
12 #include "zstd_double_fast.h"
13 
14 
15 void ZSTD_fillDoubleHashTable(ZSTD_matchState_t* ms,
16                               void const* end, ZSTD_dictTableLoadMethod_e dtlm)
17 {
18     const ZSTD_compressionParameters* const cParams = &ms->cParams;
19     U32* const hashLarge = ms->hashTable;
20     U32  const hBitsL = cParams->hashLog;
21     U32  const mls = cParams->minMatch;
22     U32* const hashSmall = ms->chainTable;
23     U32  const hBitsS = cParams->chainLog;
24     const BYTE* const base = ms->window.base;
25     const BYTE* ip = base + ms->nextToUpdate;
26     const BYTE* const iend = ((const BYTE*)end) - HASH_READ_SIZE;
27     const U32 fastHashFillStep = 3;
28 
29     /* Always insert every fastHashFillStep position into the hash tables.
30      * Insert the other positions into the large hash table if their entry
31      * is empty.
32      */
33     for (; ip + fastHashFillStep - 1 <= iend; ip += fastHashFillStep) {
34         U32 const curr = (U32)(ip - base);
35         U32 i;
36         for (i = 0; i < fastHashFillStep; ++i) {
37             size_t const smHash = ZSTD_hashPtr(ip + i, hBitsS, mls);
38             size_t const lgHash = ZSTD_hashPtr(ip + i, hBitsL, 8);
39             if (i == 0)
40                 hashSmall[smHash] = curr + i;
41             if (i == 0 || hashLarge[lgHash] == 0)
42                 hashLarge[lgHash] = curr + i;
43             /* Only load extra positions for ZSTD_dtlm_full */
44             if (dtlm == ZSTD_dtlm_fast)
45                 break;
46     }   }
47 }
48 
49 
50 FORCE_INLINE_TEMPLATE
51 size_t ZSTD_compressBlock_doubleFast_generic(
52         ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
53         void const* src, size_t srcSize,
54         U32 const mls /* template */, ZSTD_dictMode_e const dictMode)
55 {
56     ZSTD_compressionParameters const* cParams = &ms->cParams;
57     U32* const hashLong = ms->hashTable;
58     const U32 hBitsL = cParams->hashLog;
59     U32* const hashSmall = ms->chainTable;
60     const U32 hBitsS = cParams->chainLog;
61     const BYTE* const base = ms->window.base;
62     const BYTE* const istart = (const BYTE*)src;
63     const BYTE* ip = istart;
64     const BYTE* anchor = istart;
65     const U32 endIndex = (U32)((size_t)(istart - base) + srcSize);
66     /* presumes that, if there is a dictionary, it must be using Attach mode */
67     const U32 prefixLowestIndex = ZSTD_getLowestPrefixIndex(ms, endIndex, cParams->windowLog);
68     const BYTE* const prefixLowest = base + prefixLowestIndex;
69     const BYTE* const iend = istart + srcSize;
70     const BYTE* const ilimit = iend - HASH_READ_SIZE;
71     U32 offset_1=rep[0], offset_2=rep[1];
72     U32 offsetSaved = 0;
73 
74     const ZSTD_matchState_t* const dms = ms->dictMatchState;
75     const ZSTD_compressionParameters* const dictCParams =
76                                      dictMode == ZSTD_dictMatchState ?
77                                      &dms->cParams : NULL;
78     const U32* const dictHashLong  = dictMode == ZSTD_dictMatchState ?
79                                      dms->hashTable : NULL;
80     const U32* const dictHashSmall = dictMode == ZSTD_dictMatchState ?
81                                      dms->chainTable : NULL;
82     const U32 dictStartIndex       = dictMode == ZSTD_dictMatchState ?
83                                      dms->window.dictLimit : 0;
84     const BYTE* const dictBase     = dictMode == ZSTD_dictMatchState ?
85                                      dms->window.base : NULL;
86     const BYTE* const dictStart    = dictMode == ZSTD_dictMatchState ?
87                                      dictBase + dictStartIndex : NULL;
88     const BYTE* const dictEnd      = dictMode == ZSTD_dictMatchState ?
89                                      dms->window.nextSrc : NULL;
90     const U32 dictIndexDelta       = dictMode == ZSTD_dictMatchState ?
91                                      prefixLowestIndex - (U32)(dictEnd - dictBase) :
92                                      0;
93     const U32 dictHBitsL           = dictMode == ZSTD_dictMatchState ?
94                                      dictCParams->hashLog : hBitsL;
95     const U32 dictHBitsS           = dictMode == ZSTD_dictMatchState ?
96                                      dictCParams->chainLog : hBitsS;
97     const U32 dictAndPrefixLength  = (U32)((ip - prefixLowest) + (dictEnd - dictStart));
98 
99     DEBUGLOG(5, "ZSTD_compressBlock_doubleFast_generic");
100 
101     assert(dictMode == ZSTD_noDict || dictMode == ZSTD_dictMatchState);
102 
103     /* if a dictionary is attached, it must be within window range */
104     if (dictMode == ZSTD_dictMatchState) {
105         assert(ms->window.dictLimit + (1U << cParams->windowLog) >= endIndex);
106     }
107 
108     /* init */
109     ip += (dictAndPrefixLength == 0);
110     if (dictMode == ZSTD_noDict) {
111         U32 const curr = (U32)(ip - base);
112         U32 const windowLow = ZSTD_getLowestPrefixIndex(ms, curr, cParams->windowLog);
113         U32 const maxRep = curr - windowLow;
114         if (offset_2 > maxRep) offsetSaved = offset_2, offset_2 = 0;
115         if (offset_1 > maxRep) offsetSaved = offset_1, offset_1 = 0;
116     }
117     if (dictMode == ZSTD_dictMatchState) {
118         /* dictMatchState repCode checks don't currently handle repCode == 0
119          * disabling. */
120         assert(offset_1 <= dictAndPrefixLength);
121         assert(offset_2 <= dictAndPrefixLength);
122     }
123 
124     /* Main Search Loop */
125     while (ip < ilimit) {   /* < instead of <=, because repcode check at (ip+1) */
126         size_t mLength;
127         U32 offset;
128         size_t const h2 = ZSTD_hashPtr(ip, hBitsL, 8);
129         size_t const h = ZSTD_hashPtr(ip, hBitsS, mls);
130         size_t const dictHL = ZSTD_hashPtr(ip, dictHBitsL, 8);
131         size_t const dictHS = ZSTD_hashPtr(ip, dictHBitsS, mls);
132         U32 const curr = (U32)(ip-base);
133         U32 const matchIndexL = hashLong[h2];
134         U32 matchIndexS = hashSmall[h];
135         const BYTE* matchLong = base + matchIndexL;
136         const BYTE* match = base + matchIndexS;
137         const U32 repIndex = curr + 1 - offset_1;
138         const BYTE* repMatch = (dictMode == ZSTD_dictMatchState
139                             && repIndex < prefixLowestIndex) ?
140                                dictBase + (repIndex - dictIndexDelta) :
141                                base + repIndex;
142         hashLong[h2] = hashSmall[h] = curr;   /* update hash tables */
143 
144         /* check dictMatchState repcode */
145         if (dictMode == ZSTD_dictMatchState
146             && ((U32)((prefixLowestIndex-1) - repIndex) >= 3 /* intentional underflow */)
147             && (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
148             const BYTE* repMatchEnd = repIndex < prefixLowestIndex ? dictEnd : iend;
149             mLength = ZSTD_count_2segments(ip+1+4, repMatch+4, iend, repMatchEnd, prefixLowest) + 4;
150             ip++;
151             ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, 0, mLength-MINMATCH);
152             goto _match_stored;
153         }
154 
155         /* check noDict repcode */
156         if ( dictMode == ZSTD_noDict
157           && ((offset_1 > 0) & (MEM_read32(ip+1-offset_1) == MEM_read32(ip+1)))) {
158             mLength = ZSTD_count(ip+1+4, ip+1+4-offset_1, iend) + 4;
159             ip++;
160             ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, 0, mLength-MINMATCH);
161             goto _match_stored;
162         }
163 
164         if (matchIndexL > prefixLowestIndex) {
165             /* check prefix long match */
166             if (MEM_read64(matchLong) == MEM_read64(ip)) {
167                 mLength = ZSTD_count(ip+8, matchLong+8, iend) + 8;
168                 offset = (U32)(ip-matchLong);
169                 while (((ip>anchor) & (matchLong>prefixLowest)) && (ip[-1] == matchLong[-1])) { ip--; matchLong--; mLength++; } /* catch up */
170                 goto _match_found;
171             }
172         } else if (dictMode == ZSTD_dictMatchState) {
173             /* check dictMatchState long match */
174             U32 const dictMatchIndexL = dictHashLong[dictHL];
175             const BYTE* dictMatchL = dictBase + dictMatchIndexL;
176             assert(dictMatchL < dictEnd);
177 
178             if (dictMatchL > dictStart && MEM_read64(dictMatchL) == MEM_read64(ip)) {
179                 mLength = ZSTD_count_2segments(ip+8, dictMatchL+8, iend, dictEnd, prefixLowest) + 8;
180                 offset = (U32)(curr - dictMatchIndexL - dictIndexDelta);
181                 while (((ip>anchor) & (dictMatchL>dictStart)) && (ip[-1] == dictMatchL[-1])) { ip--; dictMatchL--; mLength++; } /* catch up */
182                 goto _match_found;
183         }   }
184 
185         if (matchIndexS > prefixLowestIndex) {
186             /* check prefix short match */
187             if (MEM_read32(match) == MEM_read32(ip)) {
188                 goto _search_next_long;
189             }
190         } else if (dictMode == ZSTD_dictMatchState) {
191             /* check dictMatchState short match */
192             U32 const dictMatchIndexS = dictHashSmall[dictHS];
193             match = dictBase + dictMatchIndexS;
194             matchIndexS = dictMatchIndexS + dictIndexDelta;
195 
196             if (match > dictStart && MEM_read32(match) == MEM_read32(ip)) {
197                 goto _search_next_long;
198         }   }
199 
200         ip += ((ip-anchor) >> kSearchStrength) + 1;
201 #if defined(__aarch64__)
202         PREFETCH_L1(ip+256);
203 #endif
204         continue;
205 
206 _search_next_long:
207 
208         {   size_t const hl3 = ZSTD_hashPtr(ip+1, hBitsL, 8);
209             size_t const dictHLNext = ZSTD_hashPtr(ip+1, dictHBitsL, 8);
210             U32 const matchIndexL3 = hashLong[hl3];
211             const BYTE* matchL3 = base + matchIndexL3;
212             hashLong[hl3] = curr + 1;
213 
214             /* check prefix long +1 match */
215             if (matchIndexL3 > prefixLowestIndex) {
216                 if (MEM_read64(matchL3) == MEM_read64(ip+1)) {
217                     mLength = ZSTD_count(ip+9, matchL3+8, iend) + 8;
218                     ip++;
219                     offset = (U32)(ip-matchL3);
220                     while (((ip>anchor) & (matchL3>prefixLowest)) && (ip[-1] == matchL3[-1])) { ip--; matchL3--; mLength++; } /* catch up */
221                     goto _match_found;
222                 }
223             } else if (dictMode == ZSTD_dictMatchState) {
224                 /* check dict long +1 match */
225                 U32 const dictMatchIndexL3 = dictHashLong[dictHLNext];
226                 const BYTE* dictMatchL3 = dictBase + dictMatchIndexL3;
227                 assert(dictMatchL3 < dictEnd);
228                 if (dictMatchL3 > dictStart && MEM_read64(dictMatchL3) == MEM_read64(ip+1)) {
229                     mLength = ZSTD_count_2segments(ip+1+8, dictMatchL3+8, iend, dictEnd, prefixLowest) + 8;
230                     ip++;
231                     offset = (U32)(curr + 1 - dictMatchIndexL3 - dictIndexDelta);
232                     while (((ip>anchor) & (dictMatchL3>dictStart)) && (ip[-1] == dictMatchL3[-1])) { ip--; dictMatchL3--; mLength++; } /* catch up */
233                     goto _match_found;
234         }   }   }
235 
236         /* if no long +1 match, explore the short match we found */
237         if (dictMode == ZSTD_dictMatchState && matchIndexS < prefixLowestIndex) {
238             mLength = ZSTD_count_2segments(ip+4, match+4, iend, dictEnd, prefixLowest) + 4;
239             offset = (U32)(curr - matchIndexS);
240             while (((ip>anchor) & (match>dictStart)) && (ip[-1] == match[-1])) { ip--; match--; mLength++; } /* catch up */
241         } else {
242             mLength = ZSTD_count(ip+4, match+4, iend) + 4;
243             offset = (U32)(ip - match);
244             while (((ip>anchor) & (match>prefixLowest)) && (ip[-1] == match[-1])) { ip--; match--; mLength++; } /* catch up */
245         }
246 
247         /* fall-through */
248 
249 _match_found:
250         offset_2 = offset_1;
251         offset_1 = offset;
252 
253         ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, offset + ZSTD_REP_MOVE, mLength-MINMATCH);
254 
255 _match_stored:
256         /* match found */
257         ip += mLength;
258         anchor = ip;
259 
260         if (ip <= ilimit) {
261             /* Complementary insertion */
262             /* done after iLimit test, as candidates could be > iend-8 */
263             {   U32 const indexToInsert = curr+2;
264                 hashLong[ZSTD_hashPtr(base+indexToInsert, hBitsL, 8)] = indexToInsert;
265                 hashLong[ZSTD_hashPtr(ip-2, hBitsL, 8)] = (U32)(ip-2-base);
266                 hashSmall[ZSTD_hashPtr(base+indexToInsert, hBitsS, mls)] = indexToInsert;
267                 hashSmall[ZSTD_hashPtr(ip-1, hBitsS, mls)] = (U32)(ip-1-base);
268             }
269 
270             /* check immediate repcode */
271             if (dictMode == ZSTD_dictMatchState) {
272                 while (ip <= ilimit) {
273                     U32 const current2 = (U32)(ip-base);
274                     U32 const repIndex2 = current2 - offset_2;
275                     const BYTE* repMatch2 = dictMode == ZSTD_dictMatchState
276                         && repIndex2 < prefixLowestIndex ?
277                             dictBase + repIndex2 - dictIndexDelta :
278                             base + repIndex2;
279                     if ( ((U32)((prefixLowestIndex-1) - (U32)repIndex2) >= 3 /* intentional overflow */)
280                        && (MEM_read32(repMatch2) == MEM_read32(ip)) ) {
281                         const BYTE* const repEnd2 = repIndex2 < prefixLowestIndex ? dictEnd : iend;
282                         size_t const repLength2 = ZSTD_count_2segments(ip+4, repMatch2+4, iend, repEnd2, prefixLowest) + 4;
283                         U32 tmpOffset = offset_2; offset_2 = offset_1; offset_1 = tmpOffset;   /* swap offset_2 <=> offset_1 */
284                         ZSTD_storeSeq(seqStore, 0, anchor, iend, 0, repLength2-MINMATCH);
285                         hashSmall[ZSTD_hashPtr(ip, hBitsS, mls)] = current2;
286                         hashLong[ZSTD_hashPtr(ip, hBitsL, 8)] = current2;
287                         ip += repLength2;
288                         anchor = ip;
289                         continue;
290                     }
291                     break;
292             }   }
293 
294             if (dictMode == ZSTD_noDict) {
295                 while ( (ip <= ilimit)
296                      && ( (offset_2>0)
297                         & (MEM_read32(ip) == MEM_read32(ip - offset_2)) )) {
298                     /* store sequence */
299                     size_t const rLength = ZSTD_count(ip+4, ip+4-offset_2, iend) + 4;
300                     U32 const tmpOff = offset_2; offset_2 = offset_1; offset_1 = tmpOff;  /* swap offset_2 <=> offset_1 */
301                     hashSmall[ZSTD_hashPtr(ip, hBitsS, mls)] = (U32)(ip-base);
302                     hashLong[ZSTD_hashPtr(ip, hBitsL, 8)] = (U32)(ip-base);
303                     ZSTD_storeSeq(seqStore, 0, anchor, iend, 0, rLength-MINMATCH);
304                     ip += rLength;
305                     anchor = ip;
306                     continue;   /* faster when present ... (?) */
307         }   }   }
308     }   /* while (ip < ilimit) */
309 
310     /* save reps for next block */
311     rep[0] = offset_1 ? offset_1 : offsetSaved;
312     rep[1] = offset_2 ? offset_2 : offsetSaved;
313 
314     /* Return the last literals size */
315     return (size_t)(iend - anchor);
316 }
317 
318 
319 size_t ZSTD_compressBlock_doubleFast(
320         ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
321         void const* src, size_t srcSize)
322 {
323     const U32 mls = ms->cParams.minMatch;
324     switch(mls)
325     {
326     default: /* includes case 3 */
327     case 4 :
328         return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 4, ZSTD_noDict);
329     case 5 :
330         return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 5, ZSTD_noDict);
331     case 6 :
332         return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 6, ZSTD_noDict);
333     case 7 :
334         return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 7, ZSTD_noDict);
335     }
336 }
337 
338 
339 size_t ZSTD_compressBlock_doubleFast_dictMatchState(
340         ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
341         void const* src, size_t srcSize)
342 {
343     const U32 mls = ms->cParams.minMatch;
344     switch(mls)
345     {
346     default: /* includes case 3 */
347     case 4 :
348         return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 4, ZSTD_dictMatchState);
349     case 5 :
350         return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 5, ZSTD_dictMatchState);
351     case 6 :
352         return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 6, ZSTD_dictMatchState);
353     case 7 :
354         return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 7, ZSTD_dictMatchState);
355     }
356 }
357 
358 
359 static size_t ZSTD_compressBlock_doubleFast_extDict_generic(
360         ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
361         void const* src, size_t srcSize,
362         U32 const mls /* template */)
363 {
364     ZSTD_compressionParameters const* cParams = &ms->cParams;
365     U32* const hashLong = ms->hashTable;
366     U32  const hBitsL = cParams->hashLog;
367     U32* const hashSmall = ms->chainTable;
368     U32  const hBitsS = cParams->chainLog;
369     const BYTE* const istart = (const BYTE*)src;
370     const BYTE* ip = istart;
371     const BYTE* anchor = istart;
372     const BYTE* const iend = istart + srcSize;
373     const BYTE* const ilimit = iend - 8;
374     const BYTE* const base = ms->window.base;
375     const U32   endIndex = (U32)((size_t)(istart - base) + srcSize);
376     const U32   lowLimit = ZSTD_getLowestMatchIndex(ms, endIndex, cParams->windowLog);
377     const U32   dictStartIndex = lowLimit;
378     const U32   dictLimit = ms->window.dictLimit;
379     const U32   prefixStartIndex = (dictLimit > lowLimit) ? dictLimit : lowLimit;
380     const BYTE* const prefixStart = base + prefixStartIndex;
381     const BYTE* const dictBase = ms->window.dictBase;
382     const BYTE* const dictStart = dictBase + dictStartIndex;
383     const BYTE* const dictEnd = dictBase + prefixStartIndex;
384     U32 offset_1=rep[0], offset_2=rep[1];
385 
386     DEBUGLOG(5, "ZSTD_compressBlock_doubleFast_extDict_generic (srcSize=%zu)", srcSize);
387 
388     /* if extDict is invalidated due to maxDistance, switch to "regular" variant */
389     if (prefixStartIndex == dictStartIndex)
390         return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, mls, ZSTD_noDict);
391 
392     /* Search Loop */
393     while (ip < ilimit) {  /* < instead of <=, because (ip+1) */
394         const size_t hSmall = ZSTD_hashPtr(ip, hBitsS, mls);
395         const U32 matchIndex = hashSmall[hSmall];
396         const BYTE* const matchBase = matchIndex < prefixStartIndex ? dictBase : base;
397         const BYTE* match = matchBase + matchIndex;
398 
399         const size_t hLong = ZSTD_hashPtr(ip, hBitsL, 8);
400         const U32 matchLongIndex = hashLong[hLong];
401         const BYTE* const matchLongBase = matchLongIndex < prefixStartIndex ? dictBase : base;
402         const BYTE* matchLong = matchLongBase + matchLongIndex;
403 
404         const U32 curr = (U32)(ip-base);
405         const U32 repIndex = curr + 1 - offset_1;   /* offset_1 expected <= curr +1 */
406         const BYTE* const repBase = repIndex < prefixStartIndex ? dictBase : base;
407         const BYTE* const repMatch = repBase + repIndex;
408         size_t mLength;
409         hashSmall[hSmall] = hashLong[hLong] = curr;   /* update hash table */
410 
411         if ((((U32)((prefixStartIndex-1) - repIndex) >= 3) /* intentional underflow : ensure repIndex doesn't overlap dict + prefix */
412             & (repIndex > dictStartIndex))
413           && (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
414             const BYTE* repMatchEnd = repIndex < prefixStartIndex ? dictEnd : iend;
415             mLength = ZSTD_count_2segments(ip+1+4, repMatch+4, iend, repMatchEnd, prefixStart) + 4;
416             ip++;
417             ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, 0, mLength-MINMATCH);
418         } else {
419             if ((matchLongIndex > dictStartIndex) && (MEM_read64(matchLong) == MEM_read64(ip))) {
420                 const BYTE* const matchEnd = matchLongIndex < prefixStartIndex ? dictEnd : iend;
421                 const BYTE* const lowMatchPtr = matchLongIndex < prefixStartIndex ? dictStart : prefixStart;
422                 U32 offset;
423                 mLength = ZSTD_count_2segments(ip+8, matchLong+8, iend, matchEnd, prefixStart) + 8;
424                 offset = curr - matchLongIndex;
425                 while (((ip>anchor) & (matchLong>lowMatchPtr)) && (ip[-1] == matchLong[-1])) { ip--; matchLong--; mLength++; }   /* catch up */
426                 offset_2 = offset_1;
427                 offset_1 = offset;
428                 ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, offset + ZSTD_REP_MOVE, mLength-MINMATCH);
429 
430             } else if ((matchIndex > dictStartIndex) && (MEM_read32(match) == MEM_read32(ip))) {
431                 size_t const h3 = ZSTD_hashPtr(ip+1, hBitsL, 8);
432                 U32 const matchIndex3 = hashLong[h3];
433                 const BYTE* const match3Base = matchIndex3 < prefixStartIndex ? dictBase : base;
434                 const BYTE* match3 = match3Base + matchIndex3;
435                 U32 offset;
436                 hashLong[h3] = curr + 1;
437                 if ( (matchIndex3 > dictStartIndex) && (MEM_read64(match3) == MEM_read64(ip+1)) ) {
438                     const BYTE* const matchEnd = matchIndex3 < prefixStartIndex ? dictEnd : iend;
439                     const BYTE* const lowMatchPtr = matchIndex3 < prefixStartIndex ? dictStart : prefixStart;
440                     mLength = ZSTD_count_2segments(ip+9, match3+8, iend, matchEnd, prefixStart) + 8;
441                     ip++;
442                     offset = curr+1 - matchIndex3;
443                     while (((ip>anchor) & (match3>lowMatchPtr)) && (ip[-1] == match3[-1])) { ip--; match3--; mLength++; } /* catch up */
444                 } else {
445                     const BYTE* const matchEnd = matchIndex < prefixStartIndex ? dictEnd : iend;
446                     const BYTE* const lowMatchPtr = matchIndex < prefixStartIndex ? dictStart : prefixStart;
447                     mLength = ZSTD_count_2segments(ip+4, match+4, iend, matchEnd, prefixStart) + 4;
448                     offset = curr - matchIndex;
449                     while (((ip>anchor) & (match>lowMatchPtr)) && (ip[-1] == match[-1])) { ip--; match--; mLength++; }   /* catch up */
450                 }
451                 offset_2 = offset_1;
452                 offset_1 = offset;
453                 ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, offset + ZSTD_REP_MOVE, mLength-MINMATCH);
454 
455             } else {
456                 ip += ((ip-anchor) >> kSearchStrength) + 1;
457                 continue;
458         }   }
459 
460         /* move to next sequence start */
461         ip += mLength;
462         anchor = ip;
463 
464         if (ip <= ilimit) {
465             /* Complementary insertion */
466             /* done after iLimit test, as candidates could be > iend-8 */
467             {   U32 const indexToInsert = curr+2;
468                 hashLong[ZSTD_hashPtr(base+indexToInsert, hBitsL, 8)] = indexToInsert;
469                 hashLong[ZSTD_hashPtr(ip-2, hBitsL, 8)] = (U32)(ip-2-base);
470                 hashSmall[ZSTD_hashPtr(base+indexToInsert, hBitsS, mls)] = indexToInsert;
471                 hashSmall[ZSTD_hashPtr(ip-1, hBitsS, mls)] = (U32)(ip-1-base);
472             }
473 
474             /* check immediate repcode */
475             while (ip <= ilimit) {
476                 U32 const current2 = (U32)(ip-base);
477                 U32 const repIndex2 = current2 - offset_2;
478                 const BYTE* repMatch2 = repIndex2 < prefixStartIndex ? dictBase + repIndex2 : base + repIndex2;
479                 if ( (((U32)((prefixStartIndex-1) - repIndex2) >= 3)   /* intentional overflow : ensure repIndex2 doesn't overlap dict + prefix */
480                     & (repIndex2 > dictStartIndex))
481                   && (MEM_read32(repMatch2) == MEM_read32(ip)) ) {
482                     const BYTE* const repEnd2 = repIndex2 < prefixStartIndex ? dictEnd : iend;
483                     size_t const repLength2 = ZSTD_count_2segments(ip+4, repMatch2+4, iend, repEnd2, prefixStart) + 4;
484                     U32 const tmpOffset = offset_2; offset_2 = offset_1; offset_1 = tmpOffset;   /* swap offset_2 <=> offset_1 */
485                     ZSTD_storeSeq(seqStore, 0, anchor, iend, 0, repLength2-MINMATCH);
486                     hashSmall[ZSTD_hashPtr(ip, hBitsS, mls)] = current2;
487                     hashLong[ZSTD_hashPtr(ip, hBitsL, 8)] = current2;
488                     ip += repLength2;
489                     anchor = ip;
490                     continue;
491                 }
492                 break;
493     }   }   }
494 
495     /* save reps for next block */
496     rep[0] = offset_1;
497     rep[1] = offset_2;
498 
499     /* Return the last literals size */
500     return (size_t)(iend - anchor);
501 }
502 
503 
504 size_t ZSTD_compressBlock_doubleFast_extDict(
505         ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
506         void const* src, size_t srcSize)
507 {
508     U32 const mls = ms->cParams.minMatch;
509     switch(mls)
510     {
511     default: /* includes case 3 */
512     case 4 :
513         return ZSTD_compressBlock_doubleFast_extDict_generic(ms, seqStore, rep, src, srcSize, 4);
514     case 5 :
515         return ZSTD_compressBlock_doubleFast_extDict_generic(ms, seqStore, rep, src, srcSize, 5);
516     case 6 :
517         return ZSTD_compressBlock_doubleFast_extDict_generic(ms, seqStore, rep, src, srcSize, 6);
518     case 7 :
519         return ZSTD_compressBlock_doubleFast_extDict_generic(ms, seqStore, rep, src, srcSize, 7);
520     }
521 }
522