FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zstd/lib/compress/zstd_opt.c

     /*
      * Copyright (c) 2016-2020, Przemyslaw Skibinski, 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.
      */
    
    #include "zstd_compress_internal.h"
    #include "hist.h"
    #include "zstd_opt.h"
    
    
    #define ZSTD_LITFREQ_ADD    2   /* scaling factor for litFreq, so that frequencies adapt faster to new stats */
    #define ZSTD_FREQ_DIV       4   /* log factor when using previous stats to init next stats */
    #define ZSTD_MAX_PRICE     (1<<30)
    
    #define ZSTD_PREDEF_THRESHOLD 1024   /* if srcSize < ZSTD_PREDEF_THRESHOLD, symbols' cost is assumed static, directly determined by pre-defined distributions */
    
    
    /*-*************************************
    *  Price functions for optimal parser
    ***************************************/
    
    #if 0    /* approximation at bit level */
    #  define BITCOST_ACCURACY 0
    #  define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
    #  define WEIGHT(stat)  ((void)opt, ZSTD_bitWeight(stat))
    #elif 0  /* fractional bit accuracy */
    #  define BITCOST_ACCURACY 8
    #  define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
    #  define WEIGHT(stat,opt) ((void)opt, ZSTD_fracWeight(stat))
    #else    /* opt==approx, ultra==accurate */
    #  define BITCOST_ACCURACY 8
    #  define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
    #  define WEIGHT(stat,opt) (opt ? ZSTD_fracWeight(stat) : ZSTD_bitWeight(stat))
    #endif
    
    MEM_STATIC U32 ZSTD_bitWeight(U32 stat)
    {
        return (ZSTD_highbit32(stat+1) * BITCOST_MULTIPLIER);
    }
    
    MEM_STATIC U32 ZSTD_fracWeight(U32 rawStat)
    {
        U32 const stat = rawStat + 1;
        U32 const hb = ZSTD_highbit32(stat);
        U32 const BWeight = hb * BITCOST_MULTIPLIER;
        U32 const FWeight = (stat << BITCOST_ACCURACY) >> hb;
        U32 const weight = BWeight + FWeight;
        assert(hb + BITCOST_ACCURACY < 31);
        return weight;
    }
    
    #if (DEBUGLEVEL>=2)
    /* debugging function,
     * @return price in bytes as fractional value
     * for debug messages only */
    MEM_STATIC double ZSTD_fCost(U32 price)
    {
        return (double)price / (BITCOST_MULTIPLIER*8);
    }
    #endif
    
    static int ZSTD_compressedLiterals(optState_t const* const optPtr)
    {
        return optPtr->literalCompressionMode != ZSTD_lcm_uncompressed;
    }
    
    static void ZSTD_setBasePrices(optState_t* optPtr, int optLevel)
    {
        if (ZSTD_compressedLiterals(optPtr))
            optPtr->litSumBasePrice = WEIGHT(optPtr->litSum, optLevel);
        optPtr->litLengthSumBasePrice = WEIGHT(optPtr->litLengthSum, optLevel);
        optPtr->matchLengthSumBasePrice = WEIGHT(optPtr->matchLengthSum, optLevel);
        optPtr->offCodeSumBasePrice = WEIGHT(optPtr->offCodeSum, optLevel);
    }
    
    
    /* ZSTD_downscaleStat() :
     * reduce all elements in table by a factor 2^(ZSTD_FREQ_DIV+malus)
     * return the resulting sum of elements */
    static U32 ZSTD_downscaleStat(unsigned* table, U32 lastEltIndex, int malus)
    {
        U32 s, sum=0;
        DEBUGLOG(5, "ZSTD_downscaleStat (nbElts=%u)", (unsigned)lastEltIndex+1);
        assert(ZSTD_FREQ_DIV+malus > 0 && ZSTD_FREQ_DIV+malus < 31);
        for (s=0; s<lastEltIndex+1; s++) {
            table[s] = 1 + (table[s] >> (ZSTD_FREQ_DIV+malus));
            sum += table[s];
        }
        return sum;
    }
    
    /* ZSTD_rescaleFreqs() :
     * if first block (detected by optPtr->litLengthSum == 0) : init statistics
     *    take hints from dictionary if there is one
    *    or init from zero, using src for literals stats, or flat 1 for match symbols
    * otherwise downscale existing stats, to be used as seed for next block.
    */
   static void
   ZSTD_rescaleFreqs(optState_t* const optPtr,
               const BYTE* const src, size_t const srcSize,
                     int const optLevel)
   {
       int const compressedLiterals = ZSTD_compressedLiterals(optPtr);
       DEBUGLOG(5, "ZSTD_rescaleFreqs (srcSize=%u)", (unsigned)srcSize);
       optPtr->priceType = zop_dynamic;
   
       if (optPtr->litLengthSum == 0) {  /* first block : init */
           if (srcSize <= ZSTD_PREDEF_THRESHOLD) {  /* heuristic */
               DEBUGLOG(5, "(srcSize <= ZSTD_PREDEF_THRESHOLD) => zop_predef");
               optPtr->priceType = zop_predef;
           }
   
           assert(optPtr->symbolCosts != NULL);
           if (optPtr->symbolCosts->huf.repeatMode == HUF_repeat_valid) {
               /* huffman table presumed generated by dictionary */
               optPtr->priceType = zop_dynamic;
   
               if (compressedLiterals) {
                   unsigned lit;
                   assert(optPtr->litFreq != NULL);
                   optPtr->litSum = 0;
                   for (lit=0; lit<=MaxLit; lit++) {
                       U32 const scaleLog = 11;   /* scale to 2K */
                       U32 const bitCost = HUF_getNbBits(optPtr->symbolCosts->huf.CTable, lit);
                       assert(bitCost <= scaleLog);
                       optPtr->litFreq[lit] = bitCost ? 1 << (scaleLog-bitCost) : 1 /*minimum to calculate cost*/;
                       optPtr->litSum += optPtr->litFreq[lit];
               }   }
   
               {   unsigned ll;
                   FSE_CState_t llstate;
                   FSE_initCState(&llstate, optPtr->symbolCosts->fse.litlengthCTable);
                   optPtr->litLengthSum = 0;
                   for (ll=0; ll<=MaxLL; ll++) {
                       U32 const scaleLog = 10;   /* scale to 1K */
                       U32 const bitCost = FSE_getMaxNbBits(llstate.symbolTT, ll);
                       assert(bitCost < scaleLog);
                       optPtr->litLengthFreq[ll] = bitCost ? 1 << (scaleLog-bitCost) : 1 /*minimum to calculate cost*/;
                       optPtr->litLengthSum += optPtr->litLengthFreq[ll];
               }   }
   
               {   unsigned ml;
                   FSE_CState_t mlstate;
                   FSE_initCState(&mlstate, optPtr->symbolCosts->fse.matchlengthCTable);
                   optPtr->matchLengthSum = 0;
                   for (ml=0; ml<=MaxML; ml++) {
                       U32 const scaleLog = 10;
                       U32 const bitCost = FSE_getMaxNbBits(mlstate.symbolTT, ml);
                       assert(bitCost < scaleLog);
                       optPtr->matchLengthFreq[ml] = bitCost ? 1 << (scaleLog-bitCost) : 1 /*minimum to calculate cost*/;
                       optPtr->matchLengthSum += optPtr->matchLengthFreq[ml];
               }   }
   
               {   unsigned of;
                   FSE_CState_t ofstate;
                   FSE_initCState(&ofstate, optPtr->symbolCosts->fse.offcodeCTable);
                   optPtr->offCodeSum = 0;
                   for (of=0; of<=MaxOff; of++) {
                       U32 const scaleLog = 10;
                       U32 const bitCost = FSE_getMaxNbBits(ofstate.symbolTT, of);
                       assert(bitCost < scaleLog);
                       optPtr->offCodeFreq[of] = bitCost ? 1 << (scaleLog-bitCost) : 1 /*minimum to calculate cost*/;
                       optPtr->offCodeSum += optPtr->offCodeFreq[of];
               }   }
   
           } else {  /* not a dictionary */
   
               assert(optPtr->litFreq != NULL);
               if (compressedLiterals) {
                   unsigned lit = MaxLit;
                   HIST_count_simple(optPtr->litFreq, &lit, src, srcSize);   /* use raw first block to init statistics */
                   optPtr->litSum = ZSTD_downscaleStat(optPtr->litFreq, MaxLit, 1);
               }
   
               {   unsigned ll;
                   for (ll=0; ll<=MaxLL; ll++)
                       optPtr->litLengthFreq[ll] = 1;
               }
               optPtr->litLengthSum = MaxLL+1;
   
               {   unsigned ml;
                   for (ml=0; ml<=MaxML; ml++)
                       optPtr->matchLengthFreq[ml] = 1;
               }
               optPtr->matchLengthSum = MaxML+1;
   
               {   unsigned of;
                   for (of=0; of<=MaxOff; of++)
                       optPtr->offCodeFreq[of] = 1;
               }
               optPtr->offCodeSum = MaxOff+1;
   
           }
   
       } else {   /* new block : re-use previous statistics, scaled down */
   
           if (compressedLiterals)
               optPtr->litSum = ZSTD_downscaleStat(optPtr->litFreq, MaxLit, 1);
           optPtr->litLengthSum = ZSTD_downscaleStat(optPtr->litLengthFreq, MaxLL, 0);
           optPtr->matchLengthSum = ZSTD_downscaleStat(optPtr->matchLengthFreq, MaxML, 0);
           optPtr->offCodeSum = ZSTD_downscaleStat(optPtr->offCodeFreq, MaxOff, 0);
       }
   
       ZSTD_setBasePrices(optPtr, optLevel);
   }
   
   /* ZSTD_rawLiteralsCost() :
    * price of literals (only) in specified segment (which length can be 0).
    * does not include price of literalLength symbol */
   static U32 ZSTD_rawLiteralsCost(const BYTE* const literals, U32 const litLength,
                                   const optState_t* const optPtr,
                                   int optLevel)
   {
       if (litLength == 0) return 0;
   
       if (!ZSTD_compressedLiterals(optPtr))
           return (litLength << 3) * BITCOST_MULTIPLIER;  /* Uncompressed - 8 bytes per literal. */
   
       if (optPtr->priceType == zop_predef)
           return (litLength*6) * BITCOST_MULTIPLIER;  /* 6 bit per literal - no statistic used */
   
       /* dynamic statistics */
       {   U32 price = litLength * optPtr->litSumBasePrice;
           U32 u;
           for (u=0; u < litLength; u++) {
               assert(WEIGHT(optPtr->litFreq[literals[u]], optLevel) <= optPtr->litSumBasePrice);   /* literal cost should never be negative */
               price -= WEIGHT(optPtr->litFreq[literals[u]], optLevel);
           }
           return price;
       }
   }
   
   /* ZSTD_litLengthPrice() :
    * cost of literalLength symbol */
   static U32 ZSTD_litLengthPrice(U32 const litLength, const optState_t* const optPtr, int optLevel)
   {
       if (optPtr->priceType == zop_predef) return WEIGHT(litLength, optLevel);
   
       /* dynamic statistics */
       {   U32 const llCode = ZSTD_LLcode(litLength);
           return (LL_bits[llCode] * BITCOST_MULTIPLIER)
                + optPtr->litLengthSumBasePrice
                - WEIGHT(optPtr->litLengthFreq[llCode], optLevel);
       }
   }
   
   /* ZSTD_getMatchPrice() :
    * Provides the cost of the match part (offset + matchLength) of a sequence
    * Must be combined with ZSTD_fullLiteralsCost() to get the full cost of a sequence.
    * optLevel: when <2, favors small offset for decompression speed (improved cache efficiency) */
   FORCE_INLINE_TEMPLATE U32
   ZSTD_getMatchPrice(U32 const offset,
                      U32 const matchLength,
                const optState_t* const optPtr,
                      int const optLevel)
   {
       U32 price;
       U32 const offCode = ZSTD_highbit32(offset+1);
       U32 const mlBase = matchLength - MINMATCH;
       assert(matchLength >= MINMATCH);
   
       if (optPtr->priceType == zop_predef)  /* fixed scheme, do not use statistics */
           return WEIGHT(mlBase, optLevel) + ((16 + offCode) * BITCOST_MULTIPLIER);
   
       /* dynamic statistics */
       price = (offCode * BITCOST_MULTIPLIER) + (optPtr->offCodeSumBasePrice - WEIGHT(optPtr->offCodeFreq[offCode], optLevel));
       if ((optLevel<2) /*static*/ && offCode >= 20)
           price += (offCode-19)*2 * BITCOST_MULTIPLIER; /* handicap for long distance offsets, favor decompression speed */
   
       /* match Length */
       {   U32 const mlCode = ZSTD_MLcode(mlBase);
           price += (ML_bits[mlCode] * BITCOST_MULTIPLIER) + (optPtr->matchLengthSumBasePrice - WEIGHT(optPtr->matchLengthFreq[mlCode], optLevel));
       }
   
       price += BITCOST_MULTIPLIER / 5;   /* heuristic : make matches a bit more costly to favor less sequences -> faster decompression speed */
   
       DEBUGLOG(8, "ZSTD_getMatchPrice(ml:%u) = %u", matchLength, price);
       return price;
   }
   
   /* ZSTD_updateStats() :
    * assumption : literals + litLengtn <= iend */
   static void ZSTD_updateStats(optState_t* const optPtr,
                                U32 litLength, const BYTE* literals,
                                U32 offsetCode, U32 matchLength)
   {
       /* literals */
       if (ZSTD_compressedLiterals(optPtr)) {
           U32 u;
           for (u=0; u < litLength; u++)
               optPtr->litFreq[literals[u]] += ZSTD_LITFREQ_ADD;
           optPtr->litSum += litLength*ZSTD_LITFREQ_ADD;
       }
   
       /* literal Length */
       {   U32 const llCode = ZSTD_LLcode(litLength);
           optPtr->litLengthFreq[llCode]++;
           optPtr->litLengthSum++;
       }
   
       /* match offset code (0-2=>repCode; 3+=>offset+2) */
       {   U32 const offCode = ZSTD_highbit32(offsetCode+1);
           assert(offCode <= MaxOff);
           optPtr->offCodeFreq[offCode]++;
           optPtr->offCodeSum++;
       }
   
       /* match Length */
       {   U32 const mlBase = matchLength - MINMATCH;
           U32 const mlCode = ZSTD_MLcode(mlBase);
           optPtr->matchLengthFreq[mlCode]++;
           optPtr->matchLengthSum++;
       }
   }
   
   
   /* ZSTD_readMINMATCH() :
    * function safe only for comparisons
    * assumption : memPtr must be at least 4 bytes before end of buffer */
   MEM_STATIC U32 ZSTD_readMINMATCH(const void* memPtr, U32 length)
   {
       switch (length)
       {
       default :
       case 4 : return MEM_read32(memPtr);
       case 3 : if (MEM_isLittleEndian())
                   return MEM_read32(memPtr)<<8;
                else
                   return MEM_read32(memPtr)>>8;
       }
   }
   
   
   /* Update hashTable3 up to ip (excluded)
      Assumption : always within prefix (i.e. not within extDict) */
   static U32 ZSTD_insertAndFindFirstIndexHash3 (ZSTD_matchState_t* ms,
                                                 U32* nextToUpdate3,
                                                 const BYTE* const ip)
   {
       U32* const hashTable3 = ms->hashTable3;
       U32 const hashLog3 = ms->hashLog3;
       const BYTE* const base = ms->window.base;
       U32 idx = *nextToUpdate3;
       U32 const target = (U32)(ip - base);
       size_t const hash3 = ZSTD_hash3Ptr(ip, hashLog3);
       assert(hashLog3 > 0);
   
       while(idx < target) {
           hashTable3[ZSTD_hash3Ptr(base+idx, hashLog3)] = idx;
           idx++;
       }
   
       *nextToUpdate3 = target;
       return hashTable3[hash3];
   }
   
   
   /*-*************************************
   *  Binary Tree search
   ***************************************/
   /** ZSTD_insertBt1() : add one or multiple positions to tree.
    *  ip : assumed <= iend-8 .
    * @return : nb of positions added */
   static U32 ZSTD_insertBt1(
                   ZSTD_matchState_t* ms,
                   const BYTE* const ip, const BYTE* const iend,
                   U32 const mls, const int extDict)
   {
       const ZSTD_compressionParameters* const cParams = &ms->cParams;
       U32*   const hashTable = ms->hashTable;
       U32    const hashLog = cParams->hashLog;
       size_t const h  = ZSTD_hashPtr(ip, hashLog, mls);
       U32*   const bt = ms->chainTable;
       U32    const btLog  = cParams->chainLog - 1;
       U32    const btMask = (1 << btLog) - 1;
       U32 matchIndex = hashTable[h];
       size_t commonLengthSmaller=0, commonLengthLarger=0;
       const BYTE* const base = ms->window.base;
       const BYTE* const dictBase = ms->window.dictBase;
       const U32 dictLimit = ms->window.dictLimit;
       const BYTE* const dictEnd = dictBase + dictLimit;
       const BYTE* const prefixStart = base + dictLimit;
       const BYTE* match;
       const U32 current = (U32)(ip-base);
       const U32 btLow = btMask >= current ? 0 : current - btMask;
       U32* smallerPtr = bt + 2*(current&btMask);
       U32* largerPtr  = smallerPtr + 1;
       U32 dummy32;   /* to be nullified at the end */
       U32 const windowLow = ms->window.lowLimit;
       U32 matchEndIdx = current+8+1;
       size_t bestLength = 8;
       U32 nbCompares = 1U << cParams->searchLog;
   #ifdef ZSTD_C_PREDICT
       U32 predictedSmall = *(bt + 2*((current-1)&btMask) + 0);
       U32 predictedLarge = *(bt + 2*((current-1)&btMask) + 1);
       predictedSmall += (predictedSmall>0);
       predictedLarge += (predictedLarge>0);
   #endif /* ZSTD_C_PREDICT */
   
       DEBUGLOG(8, "ZSTD_insertBt1 (%u)", current);
   
       assert(ip <= iend-8);   /* required for h calculation */
       hashTable[h] = current;   /* Update Hash Table */
   
       assert(windowLow > 0);
       while (nbCompares-- && (matchIndex >= windowLow)) {
           U32* const nextPtr = bt + 2*(matchIndex & btMask);
           size_t matchLength = MIN(commonLengthSmaller, commonLengthLarger);   /* guaranteed minimum nb of common bytes */
           assert(matchIndex < current);
   
   #ifdef ZSTD_C_PREDICT   /* note : can create issues when hlog small <= 11 */
           const U32* predictPtr = bt + 2*((matchIndex-1) & btMask);   /* written this way, as bt is a roll buffer */
           if (matchIndex == predictedSmall) {
               /* no need to check length, result known */
               *smallerPtr = matchIndex;
               if (matchIndex <= btLow) { smallerPtr=&dummy32; break; }   /* beyond tree size, stop the search */
               smallerPtr = nextPtr+1;               /* new "smaller" => larger of match */
               matchIndex = nextPtr[1];              /* new matchIndex larger than previous (closer to current) */
               predictedSmall = predictPtr[1] + (predictPtr[1]>0);
               continue;
           }
           if (matchIndex == predictedLarge) {
               *largerPtr = matchIndex;
               if (matchIndex <= btLow) { largerPtr=&dummy32; break; }   /* beyond tree size, stop the search */
               largerPtr = nextPtr;
               matchIndex = nextPtr[0];
               predictedLarge = predictPtr[0] + (predictPtr[0]>0);
               continue;
           }
   #endif
   
           if (!extDict || (matchIndex+matchLength >= dictLimit)) {
               assert(matchIndex+matchLength >= dictLimit);   /* might be wrong if actually extDict */
               match = base + matchIndex;
               matchLength += ZSTD_count(ip+matchLength, match+matchLength, iend);
           } else {
               match = dictBase + matchIndex;
               matchLength += ZSTD_count_2segments(ip+matchLength, match+matchLength, iend, dictEnd, prefixStart);
               if (matchIndex+matchLength >= dictLimit)
                   match = base + matchIndex;   /* to prepare for next usage of match[matchLength] */
           }
   
           if (matchLength > bestLength) {
               bestLength = matchLength;
               if (matchLength > matchEndIdx - matchIndex)
                   matchEndIdx = matchIndex + (U32)matchLength;
           }
   
           if (ip+matchLength == iend) {   /* equal : no way to know if inf or sup */
               break;   /* drop , to guarantee consistency ; miss a bit of compression, but other solutions can corrupt tree */
           }
   
           if (match[matchLength] < ip[matchLength]) {  /* necessarily within buffer */
               /* match is smaller than current */
               *smallerPtr = matchIndex;             /* update smaller idx */
               commonLengthSmaller = matchLength;    /* all smaller will now have at least this guaranteed common length */
               if (matchIndex <= btLow) { smallerPtr=&dummy32; break; }   /* beyond tree size, stop searching */
               smallerPtr = nextPtr+1;               /* new "candidate" => larger than match, which was smaller than target */
               matchIndex = nextPtr[1];              /* new matchIndex, larger than previous and closer to current */
           } else {
               /* match is larger than current */
               *largerPtr = matchIndex;
               commonLengthLarger = matchLength;
               if (matchIndex <= btLow) { largerPtr=&dummy32; break; }   /* beyond tree size, stop searching */
               largerPtr = nextPtr;
               matchIndex = nextPtr[0];
       }   }
   
       *smallerPtr = *largerPtr = 0;
       {   U32 positions = 0;
           if (bestLength > 384) positions = MIN(192, (U32)(bestLength - 384));   /* speed optimization */
           assert(matchEndIdx > current + 8);
           return MAX(positions, matchEndIdx - (current + 8));
       }
   }
   
   FORCE_INLINE_TEMPLATE
   void ZSTD_updateTree_internal(
                   ZSTD_matchState_t* ms,
                   const BYTE* const ip, const BYTE* const iend,
                   const U32 mls, const ZSTD_dictMode_e dictMode)
   {
       const BYTE* const base = ms->window.base;
       U32 const target = (U32)(ip - base);
       U32 idx = ms->nextToUpdate;
       DEBUGLOG(6, "ZSTD_updateTree_internal, from %u to %u  (dictMode:%u)",
                   idx, target, dictMode);
   
       while(idx < target) {
           U32 const forward = ZSTD_insertBt1(ms, base+idx, iend, mls, dictMode == ZSTD_extDict);
           assert(idx < (U32)(idx + forward));
           idx += forward;
       }
       assert((size_t)(ip - base) <= (size_t)(U32)(-1));
       assert((size_t)(iend - base) <= (size_t)(U32)(-1));
       ms->nextToUpdate = target;
   }
   
   void ZSTD_updateTree(ZSTD_matchState_t* ms, const BYTE* ip, const BYTE* iend) {
       ZSTD_updateTree_internal(ms, ip, iend, ms->cParams.minMatch, ZSTD_noDict);
   }
   
   FORCE_INLINE_TEMPLATE
   U32 ZSTD_insertBtAndGetAllMatches (
                       ZSTD_match_t* matches,   /* store result (found matches) in this table (presumed large enough) */
                       ZSTD_matchState_t* ms,
                       U32* nextToUpdate3,
                       const BYTE* const ip, const BYTE* const iLimit, const ZSTD_dictMode_e dictMode,
                       const U32 rep[ZSTD_REP_NUM],
                       U32 const ll0,   /* tells if associated literal length is 0 or not. This value must be 0 or 1 */
                       const U32 lengthToBeat,
                       U32 const mls /* template */)
   {
       const ZSTD_compressionParameters* const cParams = &ms->cParams;
       U32 const sufficient_len = MIN(cParams->targetLength, ZSTD_OPT_NUM -1);
       const BYTE* const base = ms->window.base;
       U32 const current = (U32)(ip-base);
       U32 const hashLog = cParams->hashLog;
       U32 const minMatch = (mls==3) ? 3 : 4;
       U32* const hashTable = ms->hashTable;
       size_t const h  = ZSTD_hashPtr(ip, hashLog, mls);
       U32 matchIndex  = hashTable[h];
       U32* const bt   = ms->chainTable;
       U32 const btLog = cParams->chainLog - 1;
       U32 const btMask= (1U << btLog) - 1;
       size_t commonLengthSmaller=0, commonLengthLarger=0;
       const BYTE* const dictBase = ms->window.dictBase;
       U32 const dictLimit = ms->window.dictLimit;
       const BYTE* const dictEnd = dictBase + dictLimit;
       const BYTE* const prefixStart = base + dictLimit;
       U32 const btLow = (btMask >= current) ? 0 : current - btMask;
       U32 const windowLow = ZSTD_getLowestMatchIndex(ms, current, cParams->windowLog);
       U32 const matchLow = windowLow ? windowLow : 1;
       U32* smallerPtr = bt + 2*(current&btMask);
       U32* largerPtr  = bt + 2*(current&btMask) + 1;
       U32 matchEndIdx = current+8+1;   /* farthest referenced position of any match => detects repetitive patterns */
       U32 dummy32;   /* to be nullified at the end */
       U32 mnum = 0;
       U32 nbCompares = 1U << cParams->searchLog;
   
       const ZSTD_matchState_t* dms    = dictMode == ZSTD_dictMatchState ? ms->dictMatchState : NULL;
       const ZSTD_compressionParameters* const dmsCParams =
                                         dictMode == ZSTD_dictMatchState ? &dms->cParams : NULL;
       const BYTE* const dmsBase       = dictMode == ZSTD_dictMatchState ? dms->window.base : NULL;
       const BYTE* const dmsEnd        = dictMode == ZSTD_dictMatchState ? dms->window.nextSrc : NULL;
       U32         const dmsHighLimit  = dictMode == ZSTD_dictMatchState ? (U32)(dmsEnd - dmsBase) : 0;
       U32         const dmsLowLimit   = dictMode == ZSTD_dictMatchState ? dms->window.lowLimit : 0;
       U32         const dmsIndexDelta = dictMode == ZSTD_dictMatchState ? windowLow - dmsHighLimit : 0;
       U32         const dmsHashLog    = dictMode == ZSTD_dictMatchState ? dmsCParams->hashLog : hashLog;
       U32         const dmsBtLog      = dictMode == ZSTD_dictMatchState ? dmsCParams->chainLog - 1 : btLog;
       U32         const dmsBtMask     = dictMode == ZSTD_dictMatchState ? (1U << dmsBtLog) - 1 : 0;
       U32         const dmsBtLow      = dictMode == ZSTD_dictMatchState && dmsBtMask < dmsHighLimit - dmsLowLimit ? dmsHighLimit - dmsBtMask : dmsLowLimit;
   
       size_t bestLength = lengthToBeat-1;
       DEBUGLOG(8, "ZSTD_insertBtAndGetAllMatches: current=%u", current);
   
       /* check repCode */
       assert(ll0 <= 1);   /* necessarily 1 or 0 */
       {   U32 const lastR = ZSTD_REP_NUM + ll0;
           U32 repCode;
           for (repCode = ll0; repCode < lastR; repCode++) {
               U32 const repOffset = (repCode==ZSTD_REP_NUM) ? (rep[0] - 1) : rep[repCode];
               U32 const repIndex = current - repOffset;
               U32 repLen = 0;
               assert(current >= dictLimit);
               if (repOffset-1 /* intentional overflow, discards 0 and -1 */ < current-dictLimit) {  /* equivalent to `current > repIndex >= dictLimit` */
                   /* We must validate the repcode offset because when we're using a dictionary the
                    * valid offset range shrinks when the dictionary goes out of bounds.
                    */
                   if ((repIndex >= windowLow) & (ZSTD_readMINMATCH(ip, minMatch) == ZSTD_readMINMATCH(ip - repOffset, minMatch))) {
                       repLen = (U32)ZSTD_count(ip+minMatch, ip+minMatch-repOffset, iLimit) + minMatch;
                   }
               } else {  /* repIndex < dictLimit || repIndex >= current */
                   const BYTE* const repMatch = dictMode == ZSTD_dictMatchState ?
                                                dmsBase + repIndex - dmsIndexDelta :
                                                dictBase + repIndex;
                   assert(current >= windowLow);
                   if ( dictMode == ZSTD_extDict
                     && ( ((repOffset-1) /*intentional overflow*/ < current - windowLow)  /* equivalent to `current > repIndex >= windowLow` */
                        & (((U32)((dictLimit-1) - repIndex) >= 3) ) /* intentional overflow : do not test positions overlapping 2 memory segments */)
                     && (ZSTD_readMINMATCH(ip, minMatch) == ZSTD_readMINMATCH(repMatch, minMatch)) ) {
                       repLen = (U32)ZSTD_count_2segments(ip+minMatch, repMatch+minMatch, iLimit, dictEnd, prefixStart) + minMatch;
                   }
                   if (dictMode == ZSTD_dictMatchState
                     && ( ((repOffset-1) /*intentional overflow*/ < current - (dmsLowLimit + dmsIndexDelta))  /* equivalent to `current > repIndex >= dmsLowLimit` */
                        & ((U32)((dictLimit-1) - repIndex) >= 3) ) /* intentional overflow : do not test positions overlapping 2 memory segments */
                     && (ZSTD_readMINMATCH(ip, minMatch) == ZSTD_readMINMATCH(repMatch, minMatch)) ) {
                       repLen = (U32)ZSTD_count_2segments(ip+minMatch, repMatch+minMatch, iLimit, dmsEnd, prefixStart) + minMatch;
               }   }
               /* save longer solution */
               if (repLen > bestLength) {
                   DEBUGLOG(8, "found repCode %u (ll0:%u, offset:%u) of length %u",
                               repCode, ll0, repOffset, repLen);
                   bestLength = repLen;
                   matches[mnum].off = repCode - ll0;
                   matches[mnum].len = (U32)repLen;
                   mnum++;
                   if ( (repLen > sufficient_len)
                      | (ip+repLen == iLimit) ) {  /* best possible */
                       return mnum;
       }   }   }   }
   
       /* HC3 match finder */
       if ((mls == 3) /*static*/ && (bestLength < mls)) {
           U32 const matchIndex3 = ZSTD_insertAndFindFirstIndexHash3(ms, nextToUpdate3, ip);
           if ((matchIndex3 >= matchLow)
             & (current - matchIndex3 < (1<<18)) /*heuristic : longer distance likely too expensive*/ ) {
               size_t mlen;
               if ((dictMode == ZSTD_noDict) /*static*/ || (dictMode == ZSTD_dictMatchState) /*static*/ || (matchIndex3 >= dictLimit)) {
                   const BYTE* const match = base + matchIndex3;
                   mlen = ZSTD_count(ip, match, iLimit);
               } else {
                   const BYTE* const match = dictBase + matchIndex3;
                   mlen = ZSTD_count_2segments(ip, match, iLimit, dictEnd, prefixStart);
               }
   
               /* save best solution */
               if (mlen >= mls /* == 3 > bestLength */) {
                   DEBUGLOG(8, "found small match with hlog3, of length %u",
                               (U32)mlen);
                   bestLength = mlen;
                   assert(current > matchIndex3);
                   assert(mnum==0);  /* no prior solution */
                   matches[0].off = (current - matchIndex3) + ZSTD_REP_MOVE;
                   matches[0].len = (U32)mlen;
                   mnum = 1;
                   if ( (mlen > sufficient_len) |
                        (ip+mlen == iLimit) ) {  /* best possible length */
                       ms->nextToUpdate = current+1;  /* skip insertion */
                       return 1;
           }   }   }
           /* no dictMatchState lookup: dicts don't have a populated HC3 table */
       }
   
       hashTable[h] = current;   /* Update Hash Table */
   
       while (nbCompares-- && (matchIndex >= matchLow)) {
           U32* const nextPtr = bt + 2*(matchIndex & btMask);
           const BYTE* match;
           size_t matchLength = MIN(commonLengthSmaller, commonLengthLarger);   /* guaranteed minimum nb of common bytes */
           assert(current > matchIndex);
   
           if ((dictMode == ZSTD_noDict) || (dictMode == ZSTD_dictMatchState) || (matchIndex+matchLength >= dictLimit)) {
               assert(matchIndex+matchLength >= dictLimit);  /* ensure the condition is correct when !extDict */
               match = base + matchIndex;
               if (matchIndex >= dictLimit) assert(memcmp(match, ip, matchLength) == 0);  /* ensure early section of match is equal as expected */
               matchLength += ZSTD_count(ip+matchLength, match+matchLength, iLimit);
           } else {
               match = dictBase + matchIndex;
               assert(memcmp(match, ip, matchLength) == 0);  /* ensure early section of match is equal as expected */
               matchLength += ZSTD_count_2segments(ip+matchLength, match+matchLength, iLimit, dictEnd, prefixStart);
               if (matchIndex+matchLength >= dictLimit)
                   match = base + matchIndex;   /* prepare for match[matchLength] read */
           }
   
           if (matchLength > bestLength) {
               DEBUGLOG(8, "found match of length %u at distance %u (offCode=%u)",
                       (U32)matchLength, current - matchIndex, current - matchIndex + ZSTD_REP_MOVE);
               assert(matchEndIdx > matchIndex);
               if (matchLength > matchEndIdx - matchIndex)
                   matchEndIdx = matchIndex + (U32)matchLength;
               bestLength = matchLength;
               matches[mnum].off = (current - matchIndex) + ZSTD_REP_MOVE;
               matches[mnum].len = (U32)matchLength;
               mnum++;
               if ( (matchLength > ZSTD_OPT_NUM)
                  | (ip+matchLength == iLimit) /* equal : no way to know if inf or sup */) {
                   if (dictMode == ZSTD_dictMatchState) nbCompares = 0; /* break should also skip searching dms */
                   break; /* drop, to preserve bt consistency (miss a little bit of compression) */
               }
           }
   
           if (match[matchLength] < ip[matchLength]) {
               /* match smaller than current */
               *smallerPtr = matchIndex;             /* update smaller idx */
               commonLengthSmaller = matchLength;    /* all smaller will now have at least this guaranteed common length */
               if (matchIndex <= btLow) { smallerPtr=&dummy32; break; }   /* beyond tree size, stop the search */
               smallerPtr = nextPtr+1;               /* new candidate => larger than match, which was smaller than current */
               matchIndex = nextPtr[1];              /* new matchIndex, larger than previous, closer to current */
           } else {
               *largerPtr = matchIndex;
               commonLengthLarger = matchLength;
               if (matchIndex <= btLow) { largerPtr=&dummy32; break; }   /* beyond tree size, stop the search */
               largerPtr = nextPtr;
               matchIndex = nextPtr[0];
       }   }
   
       *smallerPtr = *largerPtr = 0;
   
       if (dictMode == ZSTD_dictMatchState && nbCompares) {
           size_t const dmsH = ZSTD_hashPtr(ip, dmsHashLog, mls);
           U32 dictMatchIndex = dms->hashTable[dmsH];
           const U32* const dmsBt = dms->chainTable;
           commonLengthSmaller = commonLengthLarger = 0;
           while (nbCompares-- && (dictMatchIndex > dmsLowLimit)) {
               const U32* const nextPtr = dmsBt + 2*(dictMatchIndex & dmsBtMask);
               size_t matchLength = MIN(commonLengthSmaller, commonLengthLarger);   /* guaranteed minimum nb of common bytes */
               const BYTE* match = dmsBase + dictMatchIndex;
               matchLength += ZSTD_count_2segments(ip+matchLength, match+matchLength, iLimit, dmsEnd, prefixStart);
               if (dictMatchIndex+matchLength >= dmsHighLimit)
                   match = base + dictMatchIndex + dmsIndexDelta;   /* to prepare for next usage of match[matchLength] */
   
               if (matchLength > bestLength) {
                   matchIndex = dictMatchIndex + dmsIndexDelta;
                   DEBUGLOG(8, "found dms match of length %u at distance %u (offCode=%u)",
                           (U32)matchLength, current - matchIndex, current - matchIndex + ZSTD_REP_MOVE);
                   if (matchLength > matchEndIdx - matchIndex)
                       matchEndIdx = matchIndex + (U32)matchLength;
                   bestLength = matchLength;
                   matches[mnum].off = (current - matchIndex) + ZSTD_REP_MOVE;
                   matches[mnum].len = (U32)matchLength;
                   mnum++;
                   if ( (matchLength > ZSTD_OPT_NUM)
                      | (ip+matchLength == iLimit) /* equal : no way to know if inf or sup */) {
                       break;   /* drop, to guarantee consistency (miss a little bit of compression) */
                   }
               }
   
               if (dictMatchIndex <= dmsBtLow) { break; }   /* beyond tree size, stop the search */
               if (match[matchLength] < ip[matchLength]) {
                   commonLengthSmaller = matchLength;    /* all smaller will now have at least this guaranteed common length */
                   dictMatchIndex = nextPtr[1];              /* new matchIndex larger than previous (closer to current) */
               } else {
                   /* match is larger than current */
                   commonLengthLarger = matchLength;
                   dictMatchIndex = nextPtr[0];
               }
           }
       }
   
       assert(matchEndIdx > current+8);
       ms->nextToUpdate = matchEndIdx - 8;  /* skip repetitive patterns */
       return mnum;
   }
   
   
   FORCE_INLINE_TEMPLATE U32 ZSTD_BtGetAllMatches (
                           ZSTD_match_t* matches,   /* store result (match found, increasing size) in this table */
                           ZSTD_matchState_t* ms,
                           U32* nextToUpdate3,
                           const BYTE* ip, const BYTE* const iHighLimit, const ZSTD_dictMode_e dictMode,
                           const U32 rep[ZSTD_REP_NUM],
                           U32 const ll0,
                           U32 const lengthToBeat)
   {
       const ZSTD_compressionParameters* const cParams = &ms->cParams;
       U32 const matchLengthSearch = cParams->minMatch;
       DEBUGLOG(8, "ZSTD_BtGetAllMatches");
       if (ip < ms->window.base + ms->nextToUpdate) return 0;   /* skipped area */
       ZSTD_updateTree_internal(ms, ip, iHighLimit, matchLengthSearch, dictMode);
       switch(matchLengthSearch)
       {
       case 3 : return ZSTD_insertBtAndGetAllMatches(matches, ms, nextToUpdate3, ip, iHighLimit, dictMode, rep, ll0, lengthToBeat, 3);
       default :
       case 4 : return ZSTD_insertBtAndGetAllMatches(matches, ms, nextToUpdate3, ip, iHighLimit, dictMode, rep, ll0, lengthToBeat, 4);
       case 5 : return ZSTD_insertBtAndGetAllMatches(matches, ms, nextToUpdate3, ip, iHighLimit, dictMode, rep, ll0, lengthToBeat, 5);
       case 7 :
       case 6 : return ZSTD_insertBtAndGetAllMatches(matches, ms, nextToUpdate3, ip, iHighLimit, dictMode, rep, ll0, lengthToBeat, 6);
       }
   }
   
   
   /*-*******************************
   *  Optimal parser
   *********************************/
   
   
   static U32 ZSTD_totalLen(ZSTD_optimal_t sol)
   {
       return sol.litlen + sol.mlen;
   }
   
   #if 0 /* debug */
   
   static void
   listStats(const U32* table, int lastEltID)
   {
       int const nbElts = lastEltID + 1;
       int enb;
       for (enb=0; enb < nbElts; enb++) {
           (void)table;
           /* RAWLOG(2, "%3i:%3i,  ", enb, table[enb]); */
           RAWLOG(2, "%4i,", table[enb]);
       }
       RAWLOG(2, " \n");
   }
   
   #endif
   
   FORCE_INLINE_TEMPLATE size_t
   ZSTD_compressBlock_opt_generic(ZSTD_matchState_t* ms,
                                  seqStore_t* seqStore,
                                  U32 rep[ZSTD_REP_NUM],
                            const void* src, size_t srcSize,
                            const int optLevel,
                            const ZSTD_dictMode_e dictMode)
   {
       optState_t* const optStatePtr = &ms->opt;
       const BYTE* const istart = (const BYTE*)src;
       const BYTE* ip = istart;
       const BYTE* anchor = istart;
       const BYTE* const iend = istart + srcSize;
       const BYTE* const ilimit = iend - 8;
       const BYTE* const base = ms->window.base;
       const BYTE* const prefixStart = base + ms->window.dictLimit;
       const ZSTD_compressionParameters* const cParams = &ms->cParams;
   
       U32 const sufficient_len = MIN(cParams->targetLength, ZSTD_OPT_NUM -1);
       U32 const minMatch = (cParams->minMatch == 3) ? 3 : 4;
       U32 nextToUpdate3 = ms->nextToUpdate;
   
       ZSTD_optimal_t* const opt = optStatePtr->priceTable;
       ZSTD_match_t* const matches = optStatePtr->matchTable;
       ZSTD_optimal_t lastSequence;
   
       /* init */
       DEBUGLOG(5, "ZSTD_compressBlock_opt_generic: current=%u, prefix=%u, nextToUpdate=%u",
                   (U32)(ip - base), ms->window.dictLimit, ms->nextToUpdate);
       assert(optLevel <= 2);
       ZSTD_rescaleFreqs(optStatePtr, (const BYTE*)src, srcSize, optLevel);
       ip += (ip==prefixStart);
   
       /* Match Loop */
       while (ip < ilimit) {
           U32 cur, last_pos = 0;
   
           /* find first match */
           {   U32 const litlen = (U32)(ip - anchor);
               U32 const ll0 = !litlen;
               U32 const nbMatches = ZSTD_BtGetAllMatches(matches, ms, &nextToUpdate3, ip, iend, dictMode, rep, ll0, minMatch);
               if (!nbMatches) { ip++; continue; }
   
               /* initialize opt[0] */
               { U32 i ; for (i=0; i<ZSTD_REP_NUM; i++) opt[0].rep[i] = rep[i]; }
               opt[0].mlen = 0;  /* means is_a_literal */
               opt[0].litlen = litlen;
               /* We don't need to include the actual price of the literals because
                * it is static for the duration of the forward pass, and is included
                * in every price. We include the literal length to avoid negative
                * prices when we subtract the previous literal length.
                */
               opt[0].price = ZSTD_litLengthPrice(litlen, optStatePtr, optLevel);
   
               /* large match -> immediate encoding */
               {   U32 const maxML = matches[nbMatches-1].len;
                   U32 const maxOffset = matches[nbMatches-1].off;
                   DEBUGLOG(6, "found %u matches of maxLength=%u and maxOffCode=%u at cPos=%u => start new series",
                               nbMatches, maxML, maxOffset, (U32)(ip-prefixStart));
   
                   if (maxML > sufficient_len) {
                       lastSequence.litlen = litlen;
                       lastSequence.mlen = maxML;
                       lastSequence.off = maxOffset;
                       DEBUGLOG(6, "large match (%u>%u), immediate encoding",
                                   maxML, sufficient_len);
                       cur = 0;
                       last_pos = ZSTD_totalLen(lastSequence);
                       goto _shortestPath;
               }   }
   
               /* set prices for first matches starting position == 0 */
               {   U32 const literalsPrice = opt[0].price + ZSTD_litLengthPrice(0, optStatePtr, optLevel);
                   U32 pos;
                   U32 matchNb;
                   for (pos = 1; pos < minMatch; pos++) {
                       opt[pos].price = ZSTD_MAX_PRICE;   /* mlen, litlen and price will be fixed during forward scanning */
                   }
                   for (matchNb = 0; matchNb < nbMatches; matchNb++) {
                       U32 const offset = matches[matchNb].off;
                       U32 const end = matches[matchNb].len;
                       for ( ; pos <= end ; pos++ ) {
                           U32 const matchPrice = ZSTD_getMatchPrice(offset, pos, optStatePtr, optLevel);
                           U32 const sequencePrice = literalsPrice + matchPrice;
                           DEBUGLOG(7, "rPos:%u => set initial price : %.2f",
                                       pos, ZSTD_fCost(sequencePrice));
                           opt[pos].mlen = pos;
                           opt[pos].off = offset;
                           opt[pos].litlen = litlen;
                           opt[pos].price = sequencePrice;
                   }   }
                   last_pos = pos-1;
               }
           }
   
           /* check further positions */
           for (cur = 1; cur <= last_pos; cur++) {
               const BYTE* const inr = ip + cur;
               assert(cur < ZSTD_OPT_NUM);
               DEBUGLOG(7, "cPos:%zi==rPos:%u", inr-istart, cur)
   
               /* Fix current position with one literal if cheaper */
               {   U32 const litlen = (opt[cur-1].mlen == 0) ? opt[cur-1].litlen + 1 : 1;
                   int const price = opt[cur-1].price
                                   + ZSTD_rawLiteralsCost(ip+cur-1, 1, optStatePtr, optLevel)
                                   + ZSTD_litLengthPrice(litlen, optStatePtr, optLevel)
                                   - ZSTD_litLengthPrice(litlen-1, optStatePtr, optLevel);
                   assert(price < 1000000000); /* overflow check */
                   if (price <= opt[cur].price) {
                       DEBUGLOG(7, "cPos:%zi==rPos:%u : better price (%.2f<=%.2f) using literal (ll==%u) (hist:%u,%u,%u)",
                                   inr-istart, cur, ZSTD_fCost(price), ZSTD_fCost(opt[cur].price), litlen,
                                   opt[cur-1].rep[0], opt[cur-1].rep[1], opt[cur-1].rep[2]);
                       opt[cur].mlen = 0;
                       opt[cur].off = 0;
                       opt[cur].litlen = litlen;
                       opt[cur].price = price;
                   } else {
                       DEBUGLOG(7, "cPos:%zi==rPos:%u : literal would cost more (%.2f>%.2f) (hist:%u,%u,%u)",
                                   inr-istart, cur, ZSTD_fCost(price), ZSTD_fCost(opt[cur].price),
                                   opt[cur].rep[0], opt[cur].rep[1], opt[cur].rep[2]);
                   }
               }
   
               /* Set the repcodes of the current position. We must do it here
                * because we rely on the repcodes of the 2nd to last sequence being
                * correct to set the next chunks repcodes during the backward
                * traversal.
                */
               ZSTD_STATIC_ASSERT(sizeof(opt[cur].rep) == sizeof(repcodes_t));
               assert(cur >= opt[cur].mlen);
               if (opt[cur].mlen != 0) {
                   U32 const prev = cur - opt[cur].mlen;
                   repcodes_t newReps = ZSTD_updateRep(opt[prev].rep, opt[cur].off, opt[cur].litlen==0);
                   memcpy(opt[cur].rep, &newReps, sizeof(repcodes_t));
               } else {
                   memcpy(opt[cur].rep, opt[cur - 1].rep, sizeof(repcodes_t));
               }
   
               /* last match must start at a minimum distance of 8 from oend */
               if (inr > ilimit) continue;
   
               if (cur == last_pos) break;
   
               if ( (optLevel==0) /*static_test*/
                 && (opt[cur+1].price <= opt[cur].price + (BITCOST_MULTIPLIER/2)) ) {
                   DEBUGLOG(7, "move to next rPos:%u : price is <=", cur+1);
                   continue;  /* skip unpromising positions; about ~+6% speed, -0.01 ratio */
               }
   
               {   U32 const ll0 = (opt[cur].mlen != 0);
                   U32 const litlen = (opt[cur].mlen == 0) ? opt[cur].litlen : 0;
                   U32 const previousPrice = opt[cur].price;
                   U32 const basePrice = previousPrice + ZSTD_litLengthPrice(0, optStatePtr, optLevel);
                   U32 const nbMatches = ZSTD_BtGetAllMatches(matches, ms, &nextToUpdate3, inr, iend, dictMode, opt[cur].rep, ll0, minMatch);
                   U32 matchNb;
                   if (!nbMatches) {
                       DEBUGLOG(7, "rPos:%u : no match found", cur);
                       continue;
                   }
   
                   {   U32 const maxML = matches[nbMatches-1].len;
                       DEBUGLOG(7, "cPos:%zi==rPos:%u, found %u matches, of maxLength=%u",
                                   inr-istart, cur, nbMatches, maxML);
   
                       if ( (maxML > sufficient_len)
                         || (cur + maxML >= ZSTD_OPT_NUM) ) {
                           lastSequence.mlen = maxML;
                           lastSequence.off = matches[nbMatches-1].off;
                           lastSequence.litlen = litlen;
                           cur -= (opt[cur].mlen==0) ? opt[cur].litlen : 0;  /* last sequence is actually only literals, fix cur to last match - note : may underflow, in which case, it's first sequence, and it's okay */
                           last_pos = cur + ZSTD_totalLen(lastSequence);
                           if (cur > ZSTD_OPT_NUM) cur = 0;   /* underflow => first match */
                           goto _shortestPath;
                   }   }
   
                   /* set prices using matches found at position == cur */
                   for (matchNb = 0; matchNb < nbMatches; matchNb++) {
                       U32 const offset = matches[matchNb].off;
                       U32 const lastML = matches[matchNb].len;
                       U32 const startML = (matchNb>0) ? matches[matchNb-1].len+1 : minMatch;
                       U32 mlen;
   
                       DEBUGLOG(7, "testing match %u => offCode=%4u, mlen=%2u, llen=%2u",
                                   matchNb, matches[matchNb].off, lastML, litlen);
   
                       for (mlen = lastML; mlen >= startML; mlen--) {  /* scan downward */
                           U32 const pos = cur + mlen;
                           int const price = basePrice + ZSTD_getMatchPrice(offset, mlen, optStatePtr, optLevel);
   
                           if ((pos > last_pos) || (price < opt[pos].price)) {
                               DEBUGLOG(7, "rPos:%u (ml=%2u) => new better price (%.2f<%.2f)",
                                           pos, mlen, ZSTD_fCost(price), ZSTD_fCost(opt[pos].price));
                               while (last_pos < pos) { opt[last_pos+1].price = ZSTD_MAX_PRICE; last_pos++; }   /* fill empty positions */
                               opt[pos].mlen = mlen;
                               opt[pos].off = offset;
                               opt[pos].litlen = litlen;
                               opt[pos].price = price;
                           } else {
                               DEBUGLOG(7, "rPos:%u (ml=%2u) => new price is worse (%.2f>=%.2f)",
                                           pos, mlen, ZSTD_fCost(price), ZSTD_fCost(opt[pos].price));
                               if (optLevel==0) break;  /* early update abort; gets ~+10% speed for about -0.01 ratio loss */
                           }
               }   }   }
           }  /* for (cur = 1; cur <= last_pos; cur++) */
   
          lastSequence = opt[last_pos];
          cur = last_pos > ZSTD_totalLen(lastSequence) ? last_pos - ZSTD_totalLen(lastSequence) : 0;  /* single sequence, and it starts before `ip` */
          assert(cur < ZSTD_OPT_NUM);  /* control overflow*/
  
  _shortestPath:   /* cur, last_pos, best_mlen, best_off have to be set */
          assert(opt[0].mlen == 0);
  
          /* Set the next chunk's repcodes based on the repcodes of the beginning
           * of the last match, and the last sequence. This avoids us having to
           * update them while traversing the sequences.
           */
          if (lastSequence.mlen != 0) {
              repcodes_t reps = ZSTD_updateRep(opt[cur].rep, lastSequence.off, lastSequence.litlen==0);
              memcpy(rep, &reps, sizeof(reps));
          } else {
              memcpy(rep, opt[cur].rep, sizeof(repcodes_t));
          }
  
          {   U32 const storeEnd = cur + 1;
              U32 storeStart = storeEnd;
              U32 seqPos = cur;
  
              DEBUGLOG(6, "start reverse traversal (last_pos:%u, cur:%u)",
                          last_pos, cur); (void)last_pos;
              assert(storeEnd < ZSTD_OPT_NUM);
              DEBUGLOG(6, "last sequence copied into pos=%u (llen=%u,mlen=%u,ofc=%u)",
                          storeEnd, lastSequence.litlen, lastSequence.mlen, lastSequence.off);
              opt[storeEnd] = lastSequence;
              while (seqPos > 0) {
                  U32 const backDist = ZSTD_totalLen(opt[seqPos]);
                  storeStart--;
                  DEBUGLOG(6, "sequence from rPos=%u copied into pos=%u (llen=%u,mlen=%u,ofc=%u)",
                              seqPos, storeStart, opt[seqPos].litlen, opt[seqPos].mlen, opt[seqPos].off);
                  opt[storeStart] = opt[seqPos];
                  seqPos = (seqPos > backDist) ? seqPos - backDist : 0;
              }
  
              /* save sequences */
              DEBUGLOG(6, "sending selected sequences into seqStore")
              {   U32 storePos;
                  for (storePos=storeStart; storePos <= storeEnd; storePos++) {
                      U32 const llen = opt[storePos].litlen;
                      U32 const mlen = opt[storePos].mlen;
                      U32 const offCode = opt[storePos].off;
                      U32 const advance = llen + mlen;
                      DEBUGLOG(6, "considering seq starting at %zi, llen=%u, mlen=%u",
                                  anchor - istart, (unsigned)llen, (unsigned)mlen);
  
                      if (mlen==0) {  /* only literals => must be last "sequence", actually starting a new stream of sequences */
                          assert(storePos == storeEnd);   /* must be last sequence */
                          ip = anchor + llen;     /* last "sequence" is a bunch of literals => don't progress anchor */
                          continue;   /* will finish */
                      }
  
                      assert(anchor + llen <= iend);
                      ZSTD_updateStats(optStatePtr, llen, anchor, offCode, mlen);
                      ZSTD_storeSeq(seqStore, llen, anchor, iend, offCode, mlen-MINMATCH);
                      anchor += advance;
                      ip = anchor;
              }   }
              ZSTD_setBasePrices(optStatePtr, optLevel);
          }
      }   /* while (ip < ilimit) */
  
      /* Return the last literals size */
      return (size_t)(iend - anchor);
  }
  
  
  size_t ZSTD_compressBlock_btopt(
          ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
          const void* src, size_t srcSize)
  {
      DEBUGLOG(5, "ZSTD_compressBlock_btopt");
      return ZSTD_compressBlock_opt_generic(ms, seqStore, rep, src, srcSize, 0 /*optLevel*/, ZSTD_noDict);
  }
  
  
  /* used in 2-pass strategy */
  static U32 ZSTD_upscaleStat(unsigned* table, U32 lastEltIndex, int bonus)
  {
      U32 s, sum=0;
      assert(ZSTD_FREQ_DIV+bonus >= 0);
      for (s=0; s<lastEltIndex+1; s++) {
          table[s] <<= ZSTD_FREQ_DIV+bonus;
          table[s]--;
          sum += table[s];
      }
      return sum;
  }
  
  /* used in 2-pass strategy */
  MEM_STATIC void ZSTD_upscaleStats(optState_t* optPtr)
  {
      if (ZSTD_compressedLiterals(optPtr))
          optPtr->litSum = ZSTD_upscaleStat(optPtr->litFreq, MaxLit, 0);
      optPtr->litLengthSum = ZSTD_upscaleStat(optPtr->litLengthFreq, MaxLL, 0);
      optPtr->matchLengthSum = ZSTD_upscaleStat(optPtr->matchLengthFreq, MaxML, 0);
      optPtr->offCodeSum = ZSTD_upscaleStat(optPtr->offCodeFreq, MaxOff, 0);
  }
  
  /* ZSTD_initStats_ultra():
   * make a first compression pass, just to seed stats with more accurate starting values.
   * only works on first block, with no dictionary and no ldm.
   * this function cannot error, hence its contract must be respected.
   */
  static void
  ZSTD_initStats_ultra(ZSTD_matchState_t* ms,
                       seqStore_t* seqStore,
                       U32 rep[ZSTD_REP_NUM],
                 const void* src, size_t srcSize)
  {
      U32 tmpRep[ZSTD_REP_NUM];  /* updated rep codes will sink here */
      memcpy(tmpRep, rep, sizeof(tmpRep));
  
      DEBUGLOG(4, "ZSTD_initStats_ultra (srcSize=%zu)", srcSize);
      assert(ms->opt.litLengthSum == 0);    /* first block */
      assert(seqStore->sequences == seqStore->sequencesStart);   /* no ldm */
      assert(ms->window.dictLimit == ms->window.lowLimit);   /* no dictionary */
      assert(ms->window.dictLimit - ms->nextToUpdate <= 1);  /* no prefix (note: intentional overflow, defined as 2-complement) */
  
      ZSTD_compressBlock_opt_generic(ms, seqStore, tmpRep, src, srcSize, 2 /*optLevel*/, ZSTD_noDict);   /* generate stats into ms->opt*/
  
      /* invalidate first scan from history */
      ZSTD_resetSeqStore(seqStore);
      ms->window.base -= srcSize;
      ms->window.dictLimit += (U32)srcSize;
      ms->window.lowLimit = ms->window.dictLimit;
      ms->nextToUpdate = ms->window.dictLimit;
  
      /* re-inforce weight of collected statistics */
      ZSTD_upscaleStats(&ms->opt);
  }
  
  size_t ZSTD_compressBlock_btultra(
          ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
          const void* src, size_t srcSize)
  {
      DEBUGLOG(5, "ZSTD_compressBlock_btultra (srcSize=%zu)", srcSize);
      return ZSTD_compressBlock_opt_generic(ms, seqStore, rep, src, srcSize, 2 /*optLevel*/, ZSTD_noDict);
  }
  
  size_t ZSTD_compressBlock_btultra2(
          ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
          const void* src, size_t srcSize)
  {
      U32 const current = (U32)((const BYTE*)src - ms->window.base);
      DEBUGLOG(5, "ZSTD_compressBlock_btultra2 (srcSize=%zu)", srcSize);
  
      /* 2-pass strategy:
       * this strategy makes a first pass over first block to collect statistics
       * and seed next round's statistics with it.
       * After 1st pass, function forgets everything, and starts a new block.
       * Consequently, this can only work if no data has been previously loaded in tables,
       * aka, no dictionary, no prefix, no ldm preprocessing.
       * The compression ratio gain is generally small (~0.5% on first block),
       * the cost is 2x cpu time on first block. */
      assert(srcSize <= ZSTD_BLOCKSIZE_MAX);
      if ( (ms->opt.litLengthSum==0)   /* first block */
        && (seqStore->sequences == seqStore->sequencesStart)  /* no ldm */
        && (ms->window.dictLimit == ms->window.lowLimit)   /* no dictionary */
        && (current == ms->window.dictLimit)   /* start of frame, nothing already loaded nor skipped */
        && (srcSize > ZSTD_PREDEF_THRESHOLD)
        ) {
          ZSTD_initStats_ultra(ms, seqStore, rep, src, srcSize);
      }
  
      return ZSTD_compressBlock_opt_generic(ms, seqStore, rep, src, srcSize, 2 /*optLevel*/, ZSTD_noDict);
  }
  
  size_t ZSTD_compressBlock_btopt_dictMatchState(
          ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
          const void* src, size_t srcSize)
  {
      return ZSTD_compressBlock_opt_generic(ms, seqStore, rep, src, srcSize, 0 /*optLevel*/, ZSTD_dictMatchState);
  }
  
  size_t ZSTD_compressBlock_btultra_dictMatchState(
          ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
          const void* src, size_t srcSize)
  {
      return ZSTD_compressBlock_opt_generic(ms, seqStore, rep, src, srcSize, 2 /*optLevel*/, ZSTD_dictMatchState);
  }
  
  size_t ZSTD_compressBlock_btopt_extDict(
          ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
          const void* src, size_t srcSize)
  {
      return ZSTD_compressBlock_opt_generic(ms, seqStore, rep, src, srcSize, 0 /*optLevel*/, ZSTD_extDict);
  }
  
  size_t ZSTD_compressBlock_btultra_extDict(
          ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
          const void* src, size_t srcSize)
  {
      return ZSTD_compressBlock_opt_generic(ms, seqStore, rep, src, srcSize, 2 /*optLevel*/, ZSTD_extDict);
  }
  
  /* note : no btultra2 variant for extDict nor dictMatchState,
   * because btultra2 is not meant to work with dictionaries
   * and is only specific for the first block (no prefix) */

Cache object: 3a63e824934a771f7fbd3dce6488665b