1 /*
2  * Copyright (c) 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  /*-*************************************
12  *  Dependencies
13  ***************************************/
14 #include "zstd_compress_sequences.h"
15 
16 /*
17  * -log2(x / 256) lookup table for x in [0, 256).
18  * If x == 0: Return 0
19  * Else: Return floor(-log2(x / 256) * 256)
20  */
21 static unsigned const kInverseProbabilityLog256[256] = {
22     0,    2048, 1792, 1642, 1536, 1453, 1386, 1329, 1280, 1236, 1197, 1162,
23     1130, 1100, 1073, 1047, 1024, 1001, 980,  960,  941,  923,  906,  889,
24     874,  859,  844,  830,  817,  804,  791,  779,  768,  756,  745,  734,
25     724,  714,  704,  694,  685,  676,  667,  658,  650,  642,  633,  626,
26     618,  610,  603,  595,  588,  581,  574,  567,  561,  554,  548,  542,
27     535,  529,  523,  517,  512,  506,  500,  495,  489,  484,  478,  473,
28     468,  463,  458,  453,  448,  443,  438,  434,  429,  424,  420,  415,
29     411,  407,  402,  398,  394,  390,  386,  382,  377,  373,  370,  366,
30     362,  358,  354,  350,  347,  343,  339,  336,  332,  329,  325,  322,
31     318,  315,  311,  308,  305,  302,  298,  295,  292,  289,  286,  282,
32     279,  276,  273,  270,  267,  264,  261,  258,  256,  253,  250,  247,
33     244,  241,  239,  236,  233,  230,  228,  225,  222,  220,  217,  215,
34     212,  209,  207,  204,  202,  199,  197,  194,  192,  190,  187,  185,
35     182,  180,  178,  175,  173,  171,  168,  166,  164,  162,  159,  157,
36     155,  153,  151,  149,  146,  144,  142,  140,  138,  136,  134,  132,
37     130,  128,  126,  123,  121,  119,  117,  115,  114,  112,  110,  108,
38     106,  104,  102,  100,  98,   96,   94,   93,   91,   89,   87,   85,
39     83,   82,   80,   78,   76,   74,   73,   71,   69,   67,   66,   64,
40     62,   61,   59,   57,   55,   54,   52,   50,   49,   47,   46,   44,
41     42,   41,   39,   37,   36,   34,   33,   31,   30,   28,   26,   25,
42     23,   22,   20,   19,   17,   16,   14,   13,   11,   10,   8,    7,
43     5,    4,    2,    1,
44 };
45 
46 static unsigned ZSTD_getFSEMaxSymbolValue(FSE_CTable const* ctable) {
47   void const* ptr = ctable;
48   U16 const* u16ptr = (U16 const*)ptr;
49   U32 const maxSymbolValue = MEM_read16(u16ptr + 1);
50   return maxSymbolValue;
51 }
52 
53 /*
54  * Returns true if we should use ncount=-1 else we should
55  * use ncount=1 for low probability symbols instead.
56  */
57 static unsigned ZSTD_useLowProbCount(size_t const nbSeq)
58 {
59     /* Heuristic: This should cover most blocks <= 16K and
60      * start to fade out after 16K to about 32K depending on
61      * comprssibility.
62      */
63     return nbSeq >= 2048;
64 }
65 
66 /*
67  * Returns the cost in bytes of encoding the normalized count header.
68  * Returns an error if any of the helper functions return an error.
69  */
70 static size_t ZSTD_NCountCost(unsigned const* count, unsigned const max,
71                               size_t const nbSeq, unsigned const FSELog)
72 {
73     BYTE wksp[FSE_NCOUNTBOUND];
74     S16 norm[MaxSeq + 1];
75     const U32 tableLog = FSE_optimalTableLog(FSELog, nbSeq, max);
76     FORWARD_IF_ERROR(FSE_normalizeCount(norm, tableLog, count, nbSeq, max, ZSTD_useLowProbCount(nbSeq)), "");
77     return FSE_writeNCount(wksp, sizeof(wksp), norm, max, tableLog);
78 }
79 
80 /*
81  * Returns the cost in bits of encoding the distribution described by count
82  * using the entropy bound.
83  */
84 static size_t ZSTD_entropyCost(unsigned const* count, unsigned const max, size_t const total)
85 {
86     unsigned cost = 0;
87     unsigned s;
88 
89     assert(total > 0);
90     for (s = 0; s <= max; ++s) {
91         unsigned norm = (unsigned)((256 * count[s]) / total);
92         if (count[s] != 0 && norm == 0)
93             norm = 1;
94         assert(count[s] < total);
95         cost += count[s] * kInverseProbabilityLog256[norm];
96     }
97     return cost >> 8;
98 }
99 
100 /*
101  * Returns the cost in bits of encoding the distribution in count using ctable.
102  * Returns an error if ctable cannot represent all the symbols in count.
103  */
104 size_t ZSTD_fseBitCost(
105     FSE_CTable const* ctable,
106     unsigned const* count,
107     unsigned const max)
108 {
109     unsigned const kAccuracyLog = 8;
110     size_t cost = 0;
111     unsigned s;
112     FSE_CState_t cstate;
113     FSE_initCState(&cstate, ctable);
114     if (ZSTD_getFSEMaxSymbolValue(ctable) < max) {
115         DEBUGLOG(5, "Repeat FSE_CTable has maxSymbolValue %u < %u",
116                     ZSTD_getFSEMaxSymbolValue(ctable), max);
117         return ERROR(GENERIC);
118     }
119     for (s = 0; s <= max; ++s) {
120         unsigned const tableLog = cstate.stateLog;
121         unsigned const badCost = (tableLog + 1) << kAccuracyLog;
122         unsigned const bitCost = FSE_bitCost(cstate.symbolTT, tableLog, s, kAccuracyLog);
123         if (count[s] == 0)
124             continue;
125         if (bitCost >= badCost) {
126             DEBUGLOG(5, "Repeat FSE_CTable has Prob[%u] == 0", s);
127             return ERROR(GENERIC);
128         }
129         cost += (size_t)count[s] * bitCost;
130     }
131     return cost >> kAccuracyLog;
132 }
133 
134 /*
135  * Returns the cost in bits of encoding the distribution in count using the
136  * table described by norm. The max symbol support by norm is assumed >= max.
137  * norm must be valid for every symbol with non-zero probability in count.
138  */
139 size_t ZSTD_crossEntropyCost(short const* norm, unsigned accuracyLog,
140                              unsigned const* count, unsigned const max)
141 {
142     unsigned const shift = 8 - accuracyLog;
143     size_t cost = 0;
144     unsigned s;
145     assert(accuracyLog <= 8);
146     for (s = 0; s <= max; ++s) {
147         unsigned const normAcc = (norm[s] != -1) ? (unsigned)norm[s] : 1;
148         unsigned const norm256 = normAcc << shift;
149         assert(norm256 > 0);
150         assert(norm256 < 256);
151         cost += count[s] * kInverseProbabilityLog256[norm256];
152     }
153     return cost >> 8;
154 }
155 
156 symbolEncodingType_e
157 ZSTD_selectEncodingType(
158         FSE_repeat* repeatMode, unsigned const* count, unsigned const max,
159         size_t const mostFrequent, size_t nbSeq, unsigned const FSELog,
160         FSE_CTable const* prevCTable,
161         short const* defaultNorm, U32 defaultNormLog,
162         ZSTD_defaultPolicy_e const isDefaultAllowed,
163         ZSTD_strategy const strategy)
164 {
165     ZSTD_STATIC_ASSERT(ZSTD_defaultDisallowed == 0 && ZSTD_defaultAllowed != 0);
166     if (mostFrequent == nbSeq) {
167         *repeatMode = FSE_repeat_none;
168         if (isDefaultAllowed && nbSeq <= 2) {
169             /* Prefer set_basic over set_rle when there are 2 or less symbols,
170              * since RLE uses 1 byte, but set_basic uses 5-6 bits per symbol.
171              * If basic encoding isn't possible, always choose RLE.
172              */
173             DEBUGLOG(5, "Selected set_basic");
174             return set_basic;
175         }
176         DEBUGLOG(5, "Selected set_rle");
177         return set_rle;
178     }
179     if (strategy < ZSTD_lazy) {
180         if (isDefaultAllowed) {
181             size_t const staticFse_nbSeq_max = 1000;
182             size_t const mult = 10 - strategy;
183             size_t const baseLog = 3;
184             size_t const dynamicFse_nbSeq_min = (((size_t)1 << defaultNormLog) * mult) >> baseLog;  /* 28-36 for offset, 56-72 for lengths */
185             assert(defaultNormLog >= 5 && defaultNormLog <= 6);  /* xx_DEFAULTNORMLOG */
186             assert(mult <= 9 && mult >= 7);
187             if ( (*repeatMode == FSE_repeat_valid)
188               && (nbSeq < staticFse_nbSeq_max) ) {
189                 DEBUGLOG(5, "Selected set_repeat");
190                 return set_repeat;
191             }
192             if ( (nbSeq < dynamicFse_nbSeq_min)
193               || (mostFrequent < (nbSeq >> (defaultNormLog-1))) ) {
194                 DEBUGLOG(5, "Selected set_basic");
195                 /* The format allows default tables to be repeated, but it isn't useful.
196                  * When using simple heuristics to select encoding type, we don't want
197                  * to confuse these tables with dictionaries. When running more careful
198                  * analysis, we don't need to waste time checking both repeating tables
199                  * and default tables.
200                  */
201                 *repeatMode = FSE_repeat_none;
202                 return set_basic;
203             }
204         }
205     } else {
206         size_t const basicCost = isDefaultAllowed ? ZSTD_crossEntropyCost(defaultNorm, defaultNormLog, count, max) : ERROR(GENERIC);
207         size_t const repeatCost = *repeatMode != FSE_repeat_none ? ZSTD_fseBitCost(prevCTable, count, max) : ERROR(GENERIC);
208         size_t const NCountCost = ZSTD_NCountCost(count, max, nbSeq, FSELog);
209         size_t const compressedCost = (NCountCost << 3) + ZSTD_entropyCost(count, max, nbSeq);
210 
211         if (isDefaultAllowed) {
212             assert(!ZSTD_isError(basicCost));
213             assert(!(*repeatMode == FSE_repeat_valid && ZSTD_isError(repeatCost)));
214         }
215         assert(!ZSTD_isError(NCountCost));
216         assert(compressedCost < ERROR(maxCode));
217         DEBUGLOG(5, "Estimated bit costs: basic=%u\trepeat=%u\tcompressed=%u",
218                     (unsigned)basicCost, (unsigned)repeatCost, (unsigned)compressedCost);
219         if (basicCost <= repeatCost && basicCost <= compressedCost) {
220             DEBUGLOG(5, "Selected set_basic");
221             assert(isDefaultAllowed);
222             *repeatMode = FSE_repeat_none;
223             return set_basic;
224         }
225         if (repeatCost <= compressedCost) {
226             DEBUGLOG(5, "Selected set_repeat");
227             assert(!ZSTD_isError(repeatCost));
228             return set_repeat;
229         }
230         assert(compressedCost < basicCost && compressedCost < repeatCost);
231     }
232     DEBUGLOG(5, "Selected set_compressed");
233     *repeatMode = FSE_repeat_check;
234     return set_compressed;
235 }
236 
237 typedef struct {
238     S16 norm[MaxSeq + 1];
239     U32 wksp[FSE_BUILD_CTABLE_WORKSPACE_SIZE_U32(MaxSeq, MaxFSELog)];
240 } ZSTD_BuildCTableWksp;
241 
242 size_t
243 ZSTD_buildCTable(void* dst, size_t dstCapacity,
244                 FSE_CTable* nextCTable, U32 FSELog, symbolEncodingType_e type,
245                 unsigned* count, U32 max,
246                 const BYTE* codeTable, size_t nbSeq,
247                 const S16* defaultNorm, U32 defaultNormLog, U32 defaultMax,
248                 const FSE_CTable* prevCTable, size_t prevCTableSize,
249                 void* entropyWorkspace, size_t entropyWorkspaceSize)
250 {
251     BYTE* op = (BYTE*)dst;
252     const BYTE* const oend = op + dstCapacity;
253     DEBUGLOG(6, "ZSTD_buildCTable (dstCapacity=%u)", (unsigned)dstCapacity);
254 
255     switch (type) {
256     case set_rle:
257         FORWARD_IF_ERROR(FSE_buildCTable_rle(nextCTable, (BYTE)max), "");
258         RETURN_ERROR_IF(dstCapacity==0, dstSize_tooSmall, "not enough space");
259         *op = codeTable[0];
260         return 1;
261     case set_repeat:
262         ZSTD_memcpy(nextCTable, prevCTable, prevCTableSize);
263         return 0;
264     case set_basic:
265         FORWARD_IF_ERROR(FSE_buildCTable_wksp(nextCTable, defaultNorm, defaultMax, defaultNormLog, entropyWorkspace, entropyWorkspaceSize), "");  /* note : could be pre-calculated */
266         return 0;
267     case set_compressed: {
268         ZSTD_BuildCTableWksp* wksp = (ZSTD_BuildCTableWksp*)entropyWorkspace;
269         size_t nbSeq_1 = nbSeq;
270         const U32 tableLog = FSE_optimalTableLog(FSELog, nbSeq, max);
271         if (count[codeTable[nbSeq-1]] > 1) {
272             count[codeTable[nbSeq-1]]--;
273             nbSeq_1--;
274         }
275         assert(nbSeq_1 > 1);
276         assert(entropyWorkspaceSize >= sizeof(ZSTD_BuildCTableWksp));
277         (void)entropyWorkspaceSize;
278         FORWARD_IF_ERROR(FSE_normalizeCount(wksp->norm, tableLog, count, nbSeq_1, max, ZSTD_useLowProbCount(nbSeq_1)), "FSE_normalizeCount failed");
279         assert(oend >= op);
280         {   size_t const NCountSize = FSE_writeNCount(op, (size_t)(oend - op), wksp->norm, max, tableLog);   /* overflow protected */
281             FORWARD_IF_ERROR(NCountSize, "FSE_writeNCount failed");
282             FORWARD_IF_ERROR(FSE_buildCTable_wksp(nextCTable, wksp->norm, max, tableLog, wksp->wksp, sizeof(wksp->wksp)), "FSE_buildCTable_wksp failed");
283             return NCountSize;
284         }
285     }
286     default: assert(0); RETURN_ERROR(GENERIC, "impossible to reach");
287     }
288 }
289 
290 FORCE_INLINE_TEMPLATE size_t
291 ZSTD_encodeSequences_body(
292             void* dst, size_t dstCapacity,
293             FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
294             FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
295             FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
296             seqDef const* sequences, size_t nbSeq, int longOffsets)
297 {
298     BIT_CStream_t blockStream;
299     FSE_CState_t  stateMatchLength;
300     FSE_CState_t  stateOffsetBits;
301     FSE_CState_t  stateLitLength;
302 
303     RETURN_ERROR_IF(
304         ERR_isError(BIT_initCStream(&blockStream, dst, dstCapacity)),
305         dstSize_tooSmall, "not enough space remaining");
306     DEBUGLOG(6, "available space for bitstream : %i  (dstCapacity=%u)",
307                 (int)(blockStream.endPtr - blockStream.startPtr),
308                 (unsigned)dstCapacity);
309 
310     /* first symbols */
311     FSE_initCState2(&stateMatchLength, CTable_MatchLength, mlCodeTable[nbSeq-1]);
312     FSE_initCState2(&stateOffsetBits,  CTable_OffsetBits,  ofCodeTable[nbSeq-1]);
313     FSE_initCState2(&stateLitLength,   CTable_LitLength,   llCodeTable[nbSeq-1]);
314     BIT_addBits(&blockStream, sequences[nbSeq-1].litLength, LL_bits[llCodeTable[nbSeq-1]]);
315     if (MEM_32bits()) BIT_flushBits(&blockStream);
316     BIT_addBits(&blockStream, sequences[nbSeq-1].mlBase, ML_bits[mlCodeTable[nbSeq-1]]);
317     if (MEM_32bits()) BIT_flushBits(&blockStream);
318     if (longOffsets) {
319         U32 const ofBits = ofCodeTable[nbSeq-1];
320         unsigned const extraBits = ofBits - MIN(ofBits, STREAM_ACCUMULATOR_MIN-1);
321         if (extraBits) {
322             BIT_addBits(&blockStream, sequences[nbSeq-1].offBase, extraBits);
323             BIT_flushBits(&blockStream);
324         }
325         BIT_addBits(&blockStream, sequences[nbSeq-1].offBase >> extraBits,
326                     ofBits - extraBits);
327     } else {
328         BIT_addBits(&blockStream, sequences[nbSeq-1].offBase, ofCodeTable[nbSeq-1]);
329     }
330     BIT_flushBits(&blockStream);
331 
332     {   size_t n;
333         for (n=nbSeq-2 ; n<nbSeq ; n--) {      /* intentional underflow */
334             BYTE const llCode = llCodeTable[n];
335             BYTE const ofCode = ofCodeTable[n];
336             BYTE const mlCode = mlCodeTable[n];
337             U32  const llBits = LL_bits[llCode];
338             U32  const ofBits = ofCode;
339             U32  const mlBits = ML_bits[mlCode];
340             DEBUGLOG(6, "encoding: litlen:%2u - matchlen:%2u - offCode:%7u",
341                         (unsigned)sequences[n].litLength,
342                         (unsigned)sequences[n].mlBase + MINMATCH,
343                         (unsigned)sequences[n].offBase);
344                                                                             /* 32b*/  /* 64b*/
345                                                                             /* (7)*/  /* (7)*/
346             FSE_encodeSymbol(&blockStream, &stateOffsetBits, ofCode);       /* 15 */  /* 15 */
347             FSE_encodeSymbol(&blockStream, &stateMatchLength, mlCode);      /* 24 */  /* 24 */
348             if (MEM_32bits()) BIT_flushBits(&blockStream);                  /* (7)*/
349             FSE_encodeSymbol(&blockStream, &stateLitLength, llCode);        /* 16 */  /* 33 */
350             if (MEM_32bits() || (ofBits+mlBits+llBits >= 64-7-(LLFSELog+MLFSELog+OffFSELog)))
351                 BIT_flushBits(&blockStream);                                /* (7)*/
352             BIT_addBits(&blockStream, sequences[n].litLength, llBits);
353             if (MEM_32bits() && ((llBits+mlBits)>24)) BIT_flushBits(&blockStream);
354             BIT_addBits(&blockStream, sequences[n].mlBase, mlBits);
355             if (MEM_32bits() || (ofBits+mlBits+llBits > 56)) BIT_flushBits(&blockStream);
356             if (longOffsets) {
357                 unsigned const extraBits = ofBits - MIN(ofBits, STREAM_ACCUMULATOR_MIN-1);
358                 if (extraBits) {
359                     BIT_addBits(&blockStream, sequences[n].offBase, extraBits);
360                     BIT_flushBits(&blockStream);                            /* (7)*/
361                 }
362                 BIT_addBits(&blockStream, sequences[n].offBase >> extraBits,
363                             ofBits - extraBits);                            /* 31 */
364             } else {
365                 BIT_addBits(&blockStream, sequences[n].offBase, ofBits);     /* 31 */
366             }
367             BIT_flushBits(&blockStream);                                    /* (7)*/
368             DEBUGLOG(7, "remaining space : %i", (int)(blockStream.endPtr - blockStream.ptr));
369     }   }
370 
371     DEBUGLOG(6, "ZSTD_encodeSequences: flushing ML state with %u bits", stateMatchLength.stateLog);
372     FSE_flushCState(&blockStream, &stateMatchLength);
373     DEBUGLOG(6, "ZSTD_encodeSequences: flushing Off state with %u bits", stateOffsetBits.stateLog);
374     FSE_flushCState(&blockStream, &stateOffsetBits);
375     DEBUGLOG(6, "ZSTD_encodeSequences: flushing LL state with %u bits", stateLitLength.stateLog);
376     FSE_flushCState(&blockStream, &stateLitLength);
377 
378     {   size_t const streamSize = BIT_closeCStream(&blockStream);
379         RETURN_ERROR_IF(streamSize==0, dstSize_tooSmall, "not enough space");
380         return streamSize;
381     }
382 }
383 
384 static size_t
385 ZSTD_encodeSequences_default(
386             void* dst, size_t dstCapacity,
387             FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
388             FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
389             FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
390             seqDef const* sequences, size_t nbSeq, int longOffsets)
391 {
392     return ZSTD_encodeSequences_body(dst, dstCapacity,
393                                     CTable_MatchLength, mlCodeTable,
394                                     CTable_OffsetBits, ofCodeTable,
395                                     CTable_LitLength, llCodeTable,
396                                     sequences, nbSeq, longOffsets);
397 }
398 
399 
400 #if DYNAMIC_BMI2
401 
402 static BMI2_TARGET_ATTRIBUTE size_t
403 ZSTD_encodeSequences_bmi2(
404             void* dst, size_t dstCapacity,
405             FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
406             FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
407             FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
408             seqDef const* sequences, size_t nbSeq, int longOffsets)
409 {
410     return ZSTD_encodeSequences_body(dst, dstCapacity,
411                                     CTable_MatchLength, mlCodeTable,
412                                     CTable_OffsetBits, ofCodeTable,
413                                     CTable_LitLength, llCodeTable,
414                                     sequences, nbSeq, longOffsets);
415 }
416 
417 #endif
418 
419 size_t ZSTD_encodeSequences(
420             void* dst, size_t dstCapacity,
421             FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
422             FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
423             FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
424             seqDef const* sequences, size_t nbSeq, int longOffsets, int bmi2)
425 {
426     DEBUGLOG(5, "ZSTD_encodeSequences: dstCapacity = %u", (unsigned)dstCapacity);
427 #if DYNAMIC_BMI2
428     if (bmi2) {
429         return ZSTD_encodeSequences_bmi2(dst, dstCapacity,
430                                          CTable_MatchLength, mlCodeTable,
431                                          CTable_OffsetBits, ofCodeTable,
432                                          CTable_LitLength, llCodeTable,
433                                          sequences, nbSeq, longOffsets);
434     }
435 #endif
436     (void)bmi2;
437     return ZSTD_encodeSequences_default(dst, dstCapacity,
438                                         CTable_MatchLength, mlCodeTable,
439                                         CTable_OffsetBits, ofCodeTable,
440                                         CTable_LitLength, llCodeTable,
441                                         sequences, nbSeq, longOffsets);
442 }
443