FreeBSD/Linux Kernel Cross Reference
sys/contrib/zstd/lib/compress/zstd_compress_sequences.c

     /*
      * Copyright (c) Yann Collet, Facebook, Inc.
      * All rights reserved.
      *
      * This source code is licensed under both the BSD-style license (found in the
      * LICENSE file in the root directory of this source tree) and the GPLv2 (found
      * in the COPYING file in the root directory of this source tree).
      * You may select, at your option, one of the above-listed licenses.
      */
    
     /*-*************************************
     *  Dependencies
     ***************************************/
    #include "zstd_compress_sequences.h"
    
    /**
     * -log2(x / 256) lookup table for x in [0, 256).
     * If x == 0: Return 0
     * Else: Return floor(-log2(x / 256) * 256)
     */
    static unsigned const kInverseProbabilityLog256[256] = {
        0,    2048, 1792, 1642, 1536, 1453, 1386, 1329, 1280, 1236, 1197, 1162,
        1130, 1100, 1073, 1047, 1024, 1001, 980,  960,  941,  923,  906,  889,
        874,  859,  844,  830,  817,  804,  791,  779,  768,  756,  745,  734,
        724,  714,  704,  694,  685,  676,  667,  658,  650,  642,  633,  626,
        618,  610,  603,  595,  588,  581,  574,  567,  561,  554,  548,  542,
        535,  529,  523,  517,  512,  506,  500,  495,  489,  484,  478,  473,
        468,  463,  458,  453,  448,  443,  438,  434,  429,  424,  420,  415,
        411,  407,  402,  398,  394,  390,  386,  382,  377,  373,  370,  366,
        362,  358,  354,  350,  347,  343,  339,  336,  332,  329,  325,  322,
        318,  315,  311,  308,  305,  302,  298,  295,  292,  289,  286,  282,
        279,  276,  273,  270,  267,  264,  261,  258,  256,  253,  250,  247,
        244,  241,  239,  236,  233,  230,  228,  225,  222,  220,  217,  215,
        212,  209,  207,  204,  202,  199,  197,  194,  192,  190,  187,  185,
        182,  180,  178,  175,  173,  171,  168,  166,  164,  162,  159,  157,
        155,  153,  151,  149,  146,  144,  142,  140,  138,  136,  134,  132,
        130,  128,  126,  123,  121,  119,  117,  115,  114,  112,  110,  108,
        106,  104,  102,  100,  98,   96,   94,   93,   91,   89,   87,   85,
        83,   82,   80,   78,   76,   74,   73,   71,   69,   67,   66,   64,
        62,   61,   59,   57,   55,   54,   52,   50,   49,   47,   46,   44,
        42,   41,   39,   37,   36,   34,   33,   31,   30,   28,   26,   25,
        23,   22,   20,   19,   17,   16,   14,   13,   11,   10,   8,    7,
        5,    4,    2,    1,
    };
    
    static unsigned ZSTD_getFSEMaxSymbolValue(FSE_CTable const* ctable) {
      void const* ptr = ctable;
      U16 const* u16ptr = (U16 const*)ptr;
      U32 const maxSymbolValue = MEM_read16(u16ptr + 1);
      return maxSymbolValue;
    }
    
    /**
     * Returns true if we should use ncount=-1 else we should
     * use ncount=1 for low probability symbols instead.
     */
    static unsigned ZSTD_useLowProbCount(size_t const nbSeq)
    {
        /* Heuristic: This should cover most blocks <= 16K and
         * start to fade out after 16K to about 32K depending on
         * comprssibility.
         */
        return nbSeq >= 2048;
    }
    
    /**
     * Returns the cost in bytes of encoding the normalized count header.
     * Returns an error if any of the helper functions return an error.
     */
    static size_t ZSTD_NCountCost(unsigned const* count, unsigned const max,
                                  size_t const nbSeq, unsigned const FSELog)
    {
        BYTE wksp[FSE_NCOUNTBOUND];
        S16 norm[MaxSeq + 1];
        const U32 tableLog = FSE_optimalTableLog(FSELog, nbSeq, max);
        FORWARD_IF_ERROR(FSE_normalizeCount(norm, tableLog, count, nbSeq, max, ZSTD_useLowProbCount(nbSeq)), "");
        return FSE_writeNCount(wksp, sizeof(wksp), norm, max, tableLog);
    }
    
    /**
     * Returns the cost in bits of encoding the distribution described by count
     * using the entropy bound.
     */
    static size_t ZSTD_entropyCost(unsigned const* count, unsigned const max, size_t const total)
    {
        unsigned cost = 0;
        unsigned s;
    
        assert(total > 0);
        for (s = 0; s <= max; ++s) {
            unsigned norm = (unsigned)((256 * count[s]) / total);
            if (count[s] != 0 && norm == 0)
                norm = 1;
            assert(count[s] < total);
            cost += count[s] * kInverseProbabilityLog256[norm];
        }
        return cost >> 8;
    }
    
   /**
    * Returns the cost in bits of encoding the distribution in count using ctable.
    * Returns an error if ctable cannot represent all the symbols in count.
    */
   size_t ZSTD_fseBitCost(
       FSE_CTable const* ctable,
       unsigned const* count,
       unsigned const max)
   {
       unsigned const kAccuracyLog = 8;
       size_t cost = 0;
       unsigned s;
       FSE_CState_t cstate;
       FSE_initCState(&cstate, ctable);
       if (ZSTD_getFSEMaxSymbolValue(ctable) < max) {
           DEBUGLOG(5, "Repeat FSE_CTable has maxSymbolValue %u < %u",
                       ZSTD_getFSEMaxSymbolValue(ctable), max);
           return ERROR(GENERIC);
       }
       for (s = 0; s <= max; ++s) {
           unsigned const tableLog = cstate.stateLog;
           unsigned const badCost = (tableLog + 1) << kAccuracyLog;
           unsigned const bitCost = FSE_bitCost(cstate.symbolTT, tableLog, s, kAccuracyLog);
           if (count[s] == 0)
               continue;
           if (bitCost >= badCost) {
               DEBUGLOG(5, "Repeat FSE_CTable has Prob[%u] == 0", s);
               return ERROR(GENERIC);
           }
           cost += (size_t)count[s] * bitCost;
       }
       return cost >> kAccuracyLog;
   }
   
   /**
    * Returns the cost in bits of encoding the distribution in count using the
    * table described by norm. The max symbol support by norm is assumed >= max.
    * norm must be valid for every symbol with non-zero probability in count.
    */
   size_t ZSTD_crossEntropyCost(short const* norm, unsigned accuracyLog,
                                unsigned const* count, unsigned const max)
   {
       unsigned const shift = 8 - accuracyLog;
       size_t cost = 0;
       unsigned s;
       assert(accuracyLog <= 8);
       for (s = 0; s <= max; ++s) {
           unsigned const normAcc = (norm[s] != -1) ? (unsigned)norm[s] : 1;
           unsigned const norm256 = normAcc << shift;
           assert(norm256 > 0);
           assert(norm256 < 256);
           cost += count[s] * kInverseProbabilityLog256[norm256];
       }
       return cost >> 8;
   }
   
   symbolEncodingType_e
   ZSTD_selectEncodingType(
           FSE_repeat* repeatMode, unsigned const* count, unsigned const max,
           size_t const mostFrequent, size_t nbSeq, unsigned const FSELog,
           FSE_CTable const* prevCTable,
           short const* defaultNorm, U32 defaultNormLog,
           ZSTD_defaultPolicy_e const isDefaultAllowed,
           ZSTD_strategy const strategy)
   {
       ZSTD_STATIC_ASSERT(ZSTD_defaultDisallowed == 0 && ZSTD_defaultAllowed != 0);
       if (mostFrequent == nbSeq) {
           *repeatMode = FSE_repeat_none;
           if (isDefaultAllowed && nbSeq <= 2) {
               /* Prefer set_basic over set_rle when there are 2 or less symbols,
                * since RLE uses 1 byte, but set_basic uses 5-6 bits per symbol.
                * If basic encoding isn't possible, always choose RLE.
                */
               DEBUGLOG(5, "Selected set_basic");
               return set_basic;
           }
           DEBUGLOG(5, "Selected set_rle");
           return set_rle;
       }
       if (strategy < ZSTD_lazy) {
           if (isDefaultAllowed) {
               size_t const staticFse_nbSeq_max = 1000;
               size_t const mult = 10 - strategy;
               size_t const baseLog = 3;
               size_t const dynamicFse_nbSeq_min = (((size_t)1 << defaultNormLog) * mult) >> baseLog;  /* 28-36 for offset, 56-72 for lengths */
               assert(defaultNormLog >= 5 && defaultNormLog <= 6);  /* xx_DEFAULTNORMLOG */
               assert(mult <= 9 && mult >= 7);
               if ( (*repeatMode == FSE_repeat_valid)
                 && (nbSeq < staticFse_nbSeq_max) ) {
                   DEBUGLOG(5, "Selected set_repeat");
                   return set_repeat;
               }
               if ( (nbSeq < dynamicFse_nbSeq_min)
                 || (mostFrequent < (nbSeq >> (defaultNormLog-1))) ) {
                   DEBUGLOG(5, "Selected set_basic");
                   /* The format allows default tables to be repeated, but it isn't useful.
                    * When using simple heuristics to select encoding type, we don't want
                    * to confuse these tables with dictionaries. When running more careful
                    * analysis, we don't need to waste time checking both repeating tables
                    * and default tables.
                    */
                   *repeatMode = FSE_repeat_none;
                   return set_basic;
               }
           }
       } else {
           size_t const basicCost = isDefaultAllowed ? ZSTD_crossEntropyCost(defaultNorm, defaultNormLog, count, max) : ERROR(GENERIC);
           size_t const repeatCost = *repeatMode != FSE_repeat_none ? ZSTD_fseBitCost(prevCTable, count, max) : ERROR(GENERIC);
           size_t const NCountCost = ZSTD_NCountCost(count, max, nbSeq, FSELog);
           size_t const compressedCost = (NCountCost << 3) + ZSTD_entropyCost(count, max, nbSeq);
   
           if (isDefaultAllowed) {
               assert(!ZSTD_isError(basicCost));
               assert(!(*repeatMode == FSE_repeat_valid && ZSTD_isError(repeatCost)));
           }
           assert(!ZSTD_isError(NCountCost));
           assert(compressedCost < ERROR(maxCode));
           DEBUGLOG(5, "Estimated bit costs: basic=%u\trepeat=%u\tcompressed=%u",
                       (unsigned)basicCost, (unsigned)repeatCost, (unsigned)compressedCost);
           if (basicCost <= repeatCost && basicCost <= compressedCost) {
               DEBUGLOG(5, "Selected set_basic");
               assert(isDefaultAllowed);
               *repeatMode = FSE_repeat_none;
               return set_basic;
           }
           if (repeatCost <= compressedCost) {
               DEBUGLOG(5, "Selected set_repeat");
               assert(!ZSTD_isError(repeatCost));
               return set_repeat;
           }
           assert(compressedCost < basicCost && compressedCost < repeatCost);
       }
       DEBUGLOG(5, "Selected set_compressed");
       *repeatMode = FSE_repeat_check;
       return set_compressed;
   }
   
   typedef struct {
       S16 norm[MaxSeq + 1];
       U32 wksp[FSE_BUILD_CTABLE_WORKSPACE_SIZE_U32(MaxSeq, MaxFSELog)];
   } ZSTD_BuildCTableWksp;
   
   size_t
   ZSTD_buildCTable(void* dst, size_t dstCapacity,
                   FSE_CTable* nextCTable, U32 FSELog, symbolEncodingType_e type,
                   unsigned* count, U32 max,
                   const BYTE* codeTable, size_t nbSeq,
                   const S16* defaultNorm, U32 defaultNormLog, U32 defaultMax,
                   const FSE_CTable* prevCTable, size_t prevCTableSize,
                   void* entropyWorkspace, size_t entropyWorkspaceSize)
   {
       BYTE* op = (BYTE*)dst;
       const BYTE* const oend = op + dstCapacity;
       DEBUGLOG(6, "ZSTD_buildCTable (dstCapacity=%u)", (unsigned)dstCapacity);
   
       switch (type) {
       case set_rle:
           FORWARD_IF_ERROR(FSE_buildCTable_rle(nextCTable, (BYTE)max), "");
           RETURN_ERROR_IF(dstCapacity==0, dstSize_tooSmall, "not enough space");
           *op = codeTable[0];
           return 1;
       case set_repeat:
           ZSTD_memcpy(nextCTable, prevCTable, prevCTableSize);
           return 0;
       case set_basic:
           FORWARD_IF_ERROR(FSE_buildCTable_wksp(nextCTable, defaultNorm, defaultMax, defaultNormLog, entropyWorkspace, entropyWorkspaceSize), "");  /* note : could be pre-calculated */
           return 0;
       case set_compressed: {
           ZSTD_BuildCTableWksp* wksp = (ZSTD_BuildCTableWksp*)entropyWorkspace;
           size_t nbSeq_1 = nbSeq;
           const U32 tableLog = FSE_optimalTableLog(FSELog, nbSeq, max);
           if (count[codeTable[nbSeq-1]] > 1) {
               count[codeTable[nbSeq-1]]--;
               nbSeq_1--;
           }
           assert(nbSeq_1 > 1);
           assert(entropyWorkspaceSize >= sizeof(ZSTD_BuildCTableWksp));
           (void)entropyWorkspaceSize;
           FORWARD_IF_ERROR(FSE_normalizeCount(wksp->norm, tableLog, count, nbSeq_1, max, ZSTD_useLowProbCount(nbSeq_1)), "FSE_normalizeCount failed");
           assert(oend >= op);
           {   size_t const NCountSize = FSE_writeNCount(op, (size_t)(oend - op), wksp->norm, max, tableLog);   /* overflow protected */
               FORWARD_IF_ERROR(NCountSize, "FSE_writeNCount failed");
               FORWARD_IF_ERROR(FSE_buildCTable_wksp(nextCTable, wksp->norm, max, tableLog, wksp->wksp, sizeof(wksp->wksp)), "FSE_buildCTable_wksp failed");
               return NCountSize;
           }
       }
       default: assert(0); RETURN_ERROR(GENERIC, "impossible to reach");
       }
   }
   
   FORCE_INLINE_TEMPLATE size_t
   ZSTD_encodeSequences_body(
               void* dst, size_t dstCapacity,
               FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
               FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
               FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
               seqDef const* sequences, size_t nbSeq, int longOffsets)
   {
       BIT_CStream_t blockStream;
       FSE_CState_t  stateMatchLength;
       FSE_CState_t  stateOffsetBits;
       FSE_CState_t  stateLitLength;
   
       RETURN_ERROR_IF(
           ERR_isError(BIT_initCStream(&blockStream, dst, dstCapacity)),
           dstSize_tooSmall, "not enough space remaining");
       DEBUGLOG(6, "available space for bitstream : %i  (dstCapacity=%u)",
                   (int)(blockStream.endPtr - blockStream.startPtr),
                   (unsigned)dstCapacity);
   
       /* first symbols */
       FSE_initCState2(&stateMatchLength, CTable_MatchLength, mlCodeTable[nbSeq-1]);
       FSE_initCState2(&stateOffsetBits,  CTable_OffsetBits,  ofCodeTable[nbSeq-1]);
       FSE_initCState2(&stateLitLength,   CTable_LitLength,   llCodeTable[nbSeq-1]);
       BIT_addBits(&blockStream, sequences[nbSeq-1].litLength, LL_bits[llCodeTable[nbSeq-1]]);
       if (MEM_32bits()) BIT_flushBits(&blockStream);
       BIT_addBits(&blockStream, sequences[nbSeq-1].mlBase, ML_bits[mlCodeTable[nbSeq-1]]);
       if (MEM_32bits()) BIT_flushBits(&blockStream);
       if (longOffsets) {
           U32 const ofBits = ofCodeTable[nbSeq-1];
           unsigned const extraBits = ofBits - MIN(ofBits, STREAM_ACCUMULATOR_MIN-1);
           if (extraBits) {
               BIT_addBits(&blockStream, sequences[nbSeq-1].offBase, extraBits);
               BIT_flushBits(&blockStream);
           }
           BIT_addBits(&blockStream, sequences[nbSeq-1].offBase >> extraBits,
                       ofBits - extraBits);
       } else {
           BIT_addBits(&blockStream, sequences[nbSeq-1].offBase, ofCodeTable[nbSeq-1]);
       }
       BIT_flushBits(&blockStream);
   
       {   size_t n;
           for (n=nbSeq-2 ; n<nbSeq ; n--) {      /* intentional underflow */
               BYTE const llCode = llCodeTable[n];
               BYTE const ofCode = ofCodeTable[n];
               BYTE const mlCode = mlCodeTable[n];
               U32  const llBits = LL_bits[llCode];
               U32  const ofBits = ofCode;
               U32  const mlBits = ML_bits[mlCode];
               DEBUGLOG(6, "encoding: litlen:%2u - matchlen:%2u - offCode:%7u",
                           (unsigned)sequences[n].litLength,
                           (unsigned)sequences[n].mlBase + MINMATCH,
                           (unsigned)sequences[n].offBase);
                                                                               /* 32b*/  /* 64b*/
                                                                               /* (7)*/  /* (7)*/
               FSE_encodeSymbol(&blockStream, &stateOffsetBits, ofCode);       /* 15 */  /* 15 */
               FSE_encodeSymbol(&blockStream, &stateMatchLength, mlCode);      /* 24 */  /* 24 */
               if (MEM_32bits()) BIT_flushBits(&blockStream);                  /* (7)*/
               FSE_encodeSymbol(&blockStream, &stateLitLength, llCode);        /* 16 */  /* 33 */
               if (MEM_32bits() || (ofBits+mlBits+llBits >= 64-7-(LLFSELog+MLFSELog+OffFSELog)))
                   BIT_flushBits(&blockStream);                                /* (7)*/
               BIT_addBits(&blockStream, sequences[n].litLength, llBits);
               if (MEM_32bits() && ((llBits+mlBits)>24)) BIT_flushBits(&blockStream);
               BIT_addBits(&blockStream, sequences[n].mlBase, mlBits);
               if (MEM_32bits() || (ofBits+mlBits+llBits > 56)) BIT_flushBits(&blockStream);
               if (longOffsets) {
                   unsigned const extraBits = ofBits - MIN(ofBits, STREAM_ACCUMULATOR_MIN-1);
                   if (extraBits) {
                       BIT_addBits(&blockStream, sequences[n].offBase, extraBits);
                       BIT_flushBits(&blockStream);                            /* (7)*/
                   }
                   BIT_addBits(&blockStream, sequences[n].offBase >> extraBits,
                               ofBits - extraBits);                            /* 31 */
               } else {
                   BIT_addBits(&blockStream, sequences[n].offBase, ofBits);     /* 31 */
               }
               BIT_flushBits(&blockStream);                                    /* (7)*/
               DEBUGLOG(7, "remaining space : %i", (int)(blockStream.endPtr - blockStream.ptr));
       }   }
   
       DEBUGLOG(6, "ZSTD_encodeSequences: flushing ML state with %u bits", stateMatchLength.stateLog);
       FSE_flushCState(&blockStream, &stateMatchLength);
       DEBUGLOG(6, "ZSTD_encodeSequences: flushing Off state with %u bits", stateOffsetBits.stateLog);
       FSE_flushCState(&blockStream, &stateOffsetBits);
       DEBUGLOG(6, "ZSTD_encodeSequences: flushing LL state with %u bits", stateLitLength.stateLog);
       FSE_flushCState(&blockStream, &stateLitLength);
   
       {   size_t const streamSize = BIT_closeCStream(&blockStream);
           RETURN_ERROR_IF(streamSize==0, dstSize_tooSmall, "not enough space");
           return streamSize;
       }
   }
   
   static size_t
   ZSTD_encodeSequences_default(
               void* dst, size_t dstCapacity,
               FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
               FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
               FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
               seqDef const* sequences, size_t nbSeq, int longOffsets)
   {
       return ZSTD_encodeSequences_body(dst, dstCapacity,
                                       CTable_MatchLength, mlCodeTable,
                                       CTable_OffsetBits, ofCodeTable,
                                       CTable_LitLength, llCodeTable,
                                       sequences, nbSeq, longOffsets);
   }
   
   
   #if DYNAMIC_BMI2
   
   static BMI2_TARGET_ATTRIBUTE size_t
   ZSTD_encodeSequences_bmi2(
               void* dst, size_t dstCapacity,
               FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
               FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
               FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
               seqDef const* sequences, size_t nbSeq, int longOffsets)
   {
       return ZSTD_encodeSequences_body(dst, dstCapacity,
                                       CTable_MatchLength, mlCodeTable,
                                       CTable_OffsetBits, ofCodeTable,
                                       CTable_LitLength, llCodeTable,
                                       sequences, nbSeq, longOffsets);
   }
   
   #endif
   
   size_t ZSTD_encodeSequences(
               void* dst, size_t dstCapacity,
               FSE_CTable const* CTable_MatchLength, BYTE const* mlCodeTable,
               FSE_CTable const* CTable_OffsetBits, BYTE const* ofCodeTable,
               FSE_CTable const* CTable_LitLength, BYTE const* llCodeTable,
               seqDef const* sequences, size_t nbSeq, int longOffsets, int bmi2)
   {
       DEBUGLOG(5, "ZSTD_encodeSequences: dstCapacity = %u", (unsigned)dstCapacity);
   #if DYNAMIC_BMI2
       if (bmi2) {
           return ZSTD_encodeSequences_bmi2(dst, dstCapacity,
                                            CTable_MatchLength, mlCodeTable,
                                            CTable_OffsetBits, ofCodeTable,
                                            CTable_LitLength, llCodeTable,
                                            sequences, nbSeq, longOffsets);
       }
   #endif
       (void)bmi2;
       return ZSTD_encodeSequences_default(dst, dstCapacity,
                                           CTable_MatchLength, mlCodeTable,
                                           CTable_OffsetBits, ofCodeTable,
                                           CTable_LitLength, llCodeTable,
                                           sequences, nbSeq, longOffsets);
   }

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