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

     /* ******************************************************************
      * Huffman encoder, part of New Generation Entropy library
      * Copyright (c) Yann Collet, Facebook, Inc.
      *
      *  You can contact the author at :
      *  - FSE+HUF source repository : https://github.com/Cyan4973/FiniteStateEntropy
      *  - Public forum : https://groups.google.com/forum/#!forum/lz4c
      *
      * 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.
    ****************************************************************** */
    
    /* **************************************************************
    *  Compiler specifics
    ****************************************************************/
    #ifdef _MSC_VER    /* Visual Studio */
    #  pragma warning(disable : 4127)        /* disable: C4127: conditional expression is constant */
    #endif
    
    
    /* **************************************************************
    *  Includes
    ****************************************************************/
    #include "../common/zstd_deps.h"     /* ZSTD_memcpy, ZSTD_memset */
    #include "../common/compiler.h"
    #include "../common/bitstream.h"
    #include "hist.h"
    #define FSE_STATIC_LINKING_ONLY   /* FSE_optimalTableLog_internal */
    #include "../common/fse.h"        /* header compression */
    #define HUF_STATIC_LINKING_ONLY
    #include "../common/huf.h"
    #include "../common/error_private.h"
    
    
    /* **************************************************************
    *  Error Management
    ****************************************************************/
    #define HUF_isError ERR_isError
    #define HUF_STATIC_ASSERT(c) DEBUG_STATIC_ASSERT(c)   /* use only *after* variable declarations */
    
    
    /* **************************************************************
    *  Utils
    ****************************************************************/
    unsigned HUF_optimalTableLog(unsigned maxTableLog, size_t srcSize, unsigned maxSymbolValue)
    {
        return FSE_optimalTableLog_internal(maxTableLog, srcSize, maxSymbolValue, 1);
    }
    
    
    /* *******************************************************
    *  HUF : Huffman block compression
    *********************************************************/
    #define HUF_WORKSPACE_MAX_ALIGNMENT 8
    
    static void* HUF_alignUpWorkspace(void* workspace, size_t* workspaceSizePtr, size_t align)
    {
        size_t const mask = align - 1;
        size_t const rem = (size_t)workspace & mask;
        size_t const add = (align - rem) & mask;
        BYTE* const aligned = (BYTE*)workspace + add;
        assert((align & (align - 1)) == 0); /* pow 2 */
        assert(align <= HUF_WORKSPACE_MAX_ALIGNMENT);
        if (*workspaceSizePtr >= add) {
            assert(add < align);
            assert(((size_t)aligned & mask) == 0);
            *workspaceSizePtr -= add;
            return aligned;
        } else {
            *workspaceSizePtr = 0;
            return NULL;
        }
    }
    
    
    /* HUF_compressWeights() :
     * Same as FSE_compress(), but dedicated to huff0's weights compression.
     * The use case needs much less stack memory.
     * Note : all elements within weightTable are supposed to be <= HUF_TABLELOG_MAX.
     */
    #define MAX_FSE_TABLELOG_FOR_HUFF_HEADER 6
    
    typedef struct {
        FSE_CTable CTable[FSE_CTABLE_SIZE_U32(MAX_FSE_TABLELOG_FOR_HUFF_HEADER, HUF_TABLELOG_MAX)];
        U32 scratchBuffer[FSE_BUILD_CTABLE_WORKSPACE_SIZE_U32(HUF_TABLELOG_MAX, MAX_FSE_TABLELOG_FOR_HUFF_HEADER)];
        unsigned count[HUF_TABLELOG_MAX+1];
        S16 norm[HUF_TABLELOG_MAX+1];
    } HUF_CompressWeightsWksp;
    
    static size_t HUF_compressWeights(void* dst, size_t dstSize, const void* weightTable, size_t wtSize, void* workspace, size_t workspaceSize)
    {
        BYTE* const ostart = (BYTE*) dst;
        BYTE* op = ostart;
        BYTE* const oend = ostart + dstSize;
    
        unsigned maxSymbolValue = HUF_TABLELOG_MAX;
        U32 tableLog = MAX_FSE_TABLELOG_FOR_HUFF_HEADER;
       HUF_CompressWeightsWksp* wksp = (HUF_CompressWeightsWksp*)HUF_alignUpWorkspace(workspace, &workspaceSize, ZSTD_ALIGNOF(U32));
   
       if (workspaceSize < sizeof(HUF_CompressWeightsWksp)) return ERROR(GENERIC);
   
       /* init conditions */
       if (wtSize <= 1) return 0;  /* Not compressible */
   
       /* Scan input and build symbol stats */
       {   unsigned const maxCount = HIST_count_simple(wksp->count, &maxSymbolValue, weightTable, wtSize);   /* never fails */
           if (maxCount == wtSize) return 1;   /* only a single symbol in src : rle */
           if (maxCount == 1) return 0;        /* each symbol present maximum once => not compressible */
       }
   
       tableLog = FSE_optimalTableLog(tableLog, wtSize, maxSymbolValue);
       CHECK_F( FSE_normalizeCount(wksp->norm, tableLog, wksp->count, wtSize, maxSymbolValue, /* useLowProbCount */ 0) );
   
       /* Write table description header */
       {   CHECK_V_F(hSize, FSE_writeNCount(op, (size_t)(oend-op), wksp->norm, maxSymbolValue, tableLog) );
           op += hSize;
       }
   
       /* Compress */
       CHECK_F( FSE_buildCTable_wksp(wksp->CTable, wksp->norm, maxSymbolValue, tableLog, wksp->scratchBuffer, sizeof(wksp->scratchBuffer)) );
       {   CHECK_V_F(cSize, FSE_compress_usingCTable(op, (size_t)(oend - op), weightTable, wtSize, wksp->CTable) );
           if (cSize == 0) return 0;   /* not enough space for compressed data */
           op += cSize;
       }
   
       return (size_t)(op-ostart);
   }
   
   static size_t HUF_getNbBits(HUF_CElt elt)
   {
       return elt & 0xFF;
   }
   
   static size_t HUF_getNbBitsFast(HUF_CElt elt)
   {
       return elt;
   }
   
   static size_t HUF_getValue(HUF_CElt elt)
   {
       return elt & ~0xFF;
   }
   
   static size_t HUF_getValueFast(HUF_CElt elt)
   {
       return elt;
   }
   
   static void HUF_setNbBits(HUF_CElt* elt, size_t nbBits)
   {
       assert(nbBits <= HUF_TABLELOG_ABSOLUTEMAX);
       *elt = nbBits;
   }
   
   static void HUF_setValue(HUF_CElt* elt, size_t value)
   {
       size_t const nbBits = HUF_getNbBits(*elt);
       if (nbBits > 0) {
           assert((value >> nbBits) == 0);
           *elt |= value << (sizeof(HUF_CElt) * 8 - nbBits);
       }
   }
   
   typedef struct {
       HUF_CompressWeightsWksp wksp;
       BYTE bitsToWeight[HUF_TABLELOG_MAX + 1];   /* precomputed conversion table */
       BYTE huffWeight[HUF_SYMBOLVALUE_MAX];
   } HUF_WriteCTableWksp;
   
   size_t HUF_writeCTable_wksp(void* dst, size_t maxDstSize,
                               const HUF_CElt* CTable, unsigned maxSymbolValue, unsigned huffLog,
                               void* workspace, size_t workspaceSize)
   {
       HUF_CElt const* const ct = CTable + 1;
       BYTE* op = (BYTE*)dst;
       U32 n;
       HUF_WriteCTableWksp* wksp = (HUF_WriteCTableWksp*)HUF_alignUpWorkspace(workspace, &workspaceSize, ZSTD_ALIGNOF(U32));
   
       /* check conditions */
       if (workspaceSize < sizeof(HUF_WriteCTableWksp)) return ERROR(GENERIC);
       if (maxSymbolValue > HUF_SYMBOLVALUE_MAX) return ERROR(maxSymbolValue_tooLarge);
   
       /* convert to weight */
       wksp->bitsToWeight[0] = 0;
       for (n=1; n<huffLog+1; n++)
           wksp->bitsToWeight[n] = (BYTE)(huffLog + 1 - n);
       for (n=0; n<maxSymbolValue; n++)
           wksp->huffWeight[n] = wksp->bitsToWeight[HUF_getNbBits(ct[n])];
   
       /* attempt weights compression by FSE */
       if (maxDstSize < 1) return ERROR(dstSize_tooSmall);
       {   CHECK_V_F(hSize, HUF_compressWeights(op+1, maxDstSize-1, wksp->huffWeight, maxSymbolValue, &wksp->wksp, sizeof(wksp->wksp)) );
           if ((hSize>1) & (hSize < maxSymbolValue/2)) {   /* FSE compressed */
               op[0] = (BYTE)hSize;
               return hSize+1;
       }   }
   
       /* write raw values as 4-bits (max : 15) */
       if (maxSymbolValue > (256-128)) return ERROR(GENERIC);   /* should not happen : likely means source cannot be compressed */
       if (((maxSymbolValue+1)/2) + 1 > maxDstSize) return ERROR(dstSize_tooSmall);   /* not enough space within dst buffer */
       op[0] = (BYTE)(128 /*special case*/ + (maxSymbolValue-1));
       wksp->huffWeight[maxSymbolValue] = 0;   /* to be sure it doesn't cause msan issue in final combination */
       for (n=0; n<maxSymbolValue; n+=2)
           op[(n/2)+1] = (BYTE)((wksp->huffWeight[n] << 4) + wksp->huffWeight[n+1]);
       return ((maxSymbolValue+1)/2) + 1;
   }
   
   /*! HUF_writeCTable() :
       `CTable` : Huffman tree to save, using huf representation.
       @return : size of saved CTable */
   size_t HUF_writeCTable (void* dst, size_t maxDstSize,
                           const HUF_CElt* CTable, unsigned maxSymbolValue, unsigned huffLog)
   {
       HUF_WriteCTableWksp wksp;
       return HUF_writeCTable_wksp(dst, maxDstSize, CTable, maxSymbolValue, huffLog, &wksp, sizeof(wksp));
   }
   
   
   size_t HUF_readCTable (HUF_CElt* CTable, unsigned* maxSymbolValuePtr, const void* src, size_t srcSize, unsigned* hasZeroWeights)
   {
       BYTE huffWeight[HUF_SYMBOLVALUE_MAX + 1];   /* init not required, even though some static analyzer may complain */
       U32 rankVal[HUF_TABLELOG_ABSOLUTEMAX + 1];   /* large enough for values from 0 to 16 */
       U32 tableLog = 0;
       U32 nbSymbols = 0;
       HUF_CElt* const ct = CTable + 1;
   
       /* get symbol weights */
       CHECK_V_F(readSize, HUF_readStats(huffWeight, HUF_SYMBOLVALUE_MAX+1, rankVal, &nbSymbols, &tableLog, src, srcSize));
       *hasZeroWeights = (rankVal[0] > 0);
   
       /* check result */
       if (tableLog > HUF_TABLELOG_MAX) return ERROR(tableLog_tooLarge);
       if (nbSymbols > *maxSymbolValuePtr+1) return ERROR(maxSymbolValue_tooSmall);
   
       CTable[0] = tableLog;
   
       /* Prepare base value per rank */
       {   U32 n, nextRankStart = 0;
           for (n=1; n<=tableLog; n++) {
               U32 curr = nextRankStart;
               nextRankStart += (rankVal[n] << (n-1));
               rankVal[n] = curr;
       }   }
   
       /* fill nbBits */
       {   U32 n; for (n=0; n<nbSymbols; n++) {
               const U32 w = huffWeight[n];
               HUF_setNbBits(ct + n, (BYTE)(tableLog + 1 - w) & -(w != 0));
       }   }
   
       /* fill val */
       {   U16 nbPerRank[HUF_TABLELOG_MAX+2]  = {0};  /* support w=0=>n=tableLog+1 */
           U16 valPerRank[HUF_TABLELOG_MAX+2] = {0};
           { U32 n; for (n=0; n<nbSymbols; n++) nbPerRank[HUF_getNbBits(ct[n])]++; }
           /* determine stating value per rank */
           valPerRank[tableLog+1] = 0;   /* for w==0 */
           {   U16 min = 0;
               U32 n; for (n=tableLog; n>0; n--) {  /* start at n=tablelog <-> w=1 */
                   valPerRank[n] = min;     /* get starting value within each rank */
                   min += nbPerRank[n];
                   min >>= 1;
           }   }
           /* assign value within rank, symbol order */
           { U32 n; for (n=0; n<nbSymbols; n++) HUF_setValue(ct + n, valPerRank[HUF_getNbBits(ct[n])]++); }
       }
   
       *maxSymbolValuePtr = nbSymbols - 1;
       return readSize;
   }
   
   U32 HUF_getNbBitsFromCTable(HUF_CElt const* CTable, U32 symbolValue)
   {
       const HUF_CElt* ct = CTable + 1;
       assert(symbolValue <= HUF_SYMBOLVALUE_MAX);
       return (U32)HUF_getNbBits(ct[symbolValue]);
   }
   
   
   typedef struct nodeElt_s {
       U32 count;
       U16 parent;
       BYTE byte;
       BYTE nbBits;
   } nodeElt;
   
   /**
    * HUF_setMaxHeight():
    * Enforces maxNbBits on the Huffman tree described in huffNode.
    *
    * It sets all nodes with nbBits > maxNbBits to be maxNbBits. Then it adjusts
    * the tree to so that it is a valid canonical Huffman tree.
    *
    * @pre               The sum of the ranks of each symbol == 2^largestBits,
    *                    where largestBits == huffNode[lastNonNull].nbBits.
    * @post              The sum of the ranks of each symbol == 2^largestBits,
    *                    where largestBits is the return value <= maxNbBits.
    *
    * @param huffNode    The Huffman tree modified in place to enforce maxNbBits.
    * @param lastNonNull The symbol with the lowest count in the Huffman tree.
    * @param maxNbBits   The maximum allowed number of bits, which the Huffman tree
    *                    may not respect. After this function the Huffman tree will
    *                    respect maxNbBits.
    * @return            The maximum number of bits of the Huffman tree after adjustment,
    *                    necessarily no more than maxNbBits.
    */
   static U32 HUF_setMaxHeight(nodeElt* huffNode, U32 lastNonNull, U32 maxNbBits)
   {
       const U32 largestBits = huffNode[lastNonNull].nbBits;
       /* early exit : no elt > maxNbBits, so the tree is already valid. */
       if (largestBits <= maxNbBits) return largestBits;
   
       /* there are several too large elements (at least >= 2) */
       {   int totalCost = 0;
           const U32 baseCost = 1 << (largestBits - maxNbBits);
           int n = (int)lastNonNull;
   
           /* Adjust any ranks > maxNbBits to maxNbBits.
            * Compute totalCost, which is how far the sum of the ranks is
            * we are over 2^largestBits after adjust the offending ranks.
            */
           while (huffNode[n].nbBits > maxNbBits) {
               totalCost += baseCost - (1 << (largestBits - huffNode[n].nbBits));
               huffNode[n].nbBits = (BYTE)maxNbBits;
               n--;
           }
           /* n stops at huffNode[n].nbBits <= maxNbBits */
           assert(huffNode[n].nbBits <= maxNbBits);
           /* n end at index of smallest symbol using < maxNbBits */
           while (huffNode[n].nbBits == maxNbBits) --n;
   
           /* renorm totalCost from 2^largestBits to 2^maxNbBits
            * note : totalCost is necessarily a multiple of baseCost */
           assert((totalCost & (baseCost - 1)) == 0);
           totalCost >>= (largestBits - maxNbBits);
           assert(totalCost > 0);
   
           /* repay normalized cost */
           {   U32 const noSymbol = 0xF0F0F0F0;
               U32 rankLast[HUF_TABLELOG_MAX+2];
   
               /* Get pos of last (smallest = lowest cum. count) symbol per rank */
               ZSTD_memset(rankLast, 0xF0, sizeof(rankLast));
               {   U32 currentNbBits = maxNbBits;
                   int pos;
                   for (pos=n ; pos >= 0; pos--) {
                       if (huffNode[pos].nbBits >= currentNbBits) continue;
                       currentNbBits = huffNode[pos].nbBits;   /* < maxNbBits */
                       rankLast[maxNbBits-currentNbBits] = (U32)pos;
               }   }
   
               while (totalCost > 0) {
                   /* Try to reduce the next power of 2 above totalCost because we
                    * gain back half the rank.
                    */
                   U32 nBitsToDecrease = BIT_highbit32((U32)totalCost) + 1;
                   for ( ; nBitsToDecrease > 1; nBitsToDecrease--) {
                       U32 const highPos = rankLast[nBitsToDecrease];
                       U32 const lowPos = rankLast[nBitsToDecrease-1];
                       if (highPos == noSymbol) continue;
                       /* Decrease highPos if no symbols of lowPos or if it is
                        * not cheaper to remove 2 lowPos than highPos.
                        */
                       if (lowPos == noSymbol) break;
                       {   U32 const highTotal = huffNode[highPos].count;
                           U32 const lowTotal = 2 * huffNode[lowPos].count;
                           if (highTotal <= lowTotal) break;
                   }   }
                   /* only triggered when no more rank 1 symbol left => find closest one (note : there is necessarily at least one !) */
                   assert(rankLast[nBitsToDecrease] != noSymbol || nBitsToDecrease == 1);
                   /* HUF_MAX_TABLELOG test just to please gcc 5+; but it should not be necessary */
                   while ((nBitsToDecrease<=HUF_TABLELOG_MAX) && (rankLast[nBitsToDecrease] == noSymbol))
                       nBitsToDecrease++;
                   assert(rankLast[nBitsToDecrease] != noSymbol);
                   /* Increase the number of bits to gain back half the rank cost. */
                   totalCost -= 1 << (nBitsToDecrease-1);
                   huffNode[rankLast[nBitsToDecrease]].nbBits++;
   
                   /* Fix up the new rank.
                    * If the new rank was empty, this symbol is now its smallest.
                    * Otherwise, this symbol will be the largest in the new rank so no adjustment.
                    */
                   if (rankLast[nBitsToDecrease-1] == noSymbol)
                       rankLast[nBitsToDecrease-1] = rankLast[nBitsToDecrease];
                   /* Fix up the old rank.
                    * If the symbol was at position 0, meaning it was the highest weight symbol in the tree,
                    * it must be the only symbol in its rank, so the old rank now has no symbols.
                    * Otherwise, since the Huffman nodes are sorted by count, the previous position is now
                    * the smallest node in the rank. If the previous position belongs to a different rank,
                    * then the rank is now empty.
                    */
                   if (rankLast[nBitsToDecrease] == 0)    /* special case, reached largest symbol */
                       rankLast[nBitsToDecrease] = noSymbol;
                   else {
                       rankLast[nBitsToDecrease]--;
                       if (huffNode[rankLast[nBitsToDecrease]].nbBits != maxNbBits-nBitsToDecrease)
                           rankLast[nBitsToDecrease] = noSymbol;   /* this rank is now empty */
                   }
               }   /* while (totalCost > 0) */
   
               /* If we've removed too much weight, then we have to add it back.
                * To avoid overshooting again, we only adjust the smallest rank.
                * We take the largest nodes from the lowest rank 0 and move them
                * to rank 1. There's guaranteed to be enough rank 0 symbols because
                * TODO.
                */
               while (totalCost < 0) {  /* Sometimes, cost correction overshoot */
                   /* special case : no rank 1 symbol (using maxNbBits-1);
                    * let's create one from largest rank 0 (using maxNbBits).
                    */
                   if (rankLast[1] == noSymbol) {
                       while (huffNode[n].nbBits == maxNbBits) n--;
                       huffNode[n+1].nbBits--;
                       assert(n >= 0);
                       rankLast[1] = (U32)(n+1);
                       totalCost++;
                       continue;
                   }
                   huffNode[ rankLast[1] + 1 ].nbBits--;
                   rankLast[1]++;
                   totalCost ++;
               }
           }   /* repay normalized cost */
       }   /* there are several too large elements (at least >= 2) */
   
       return maxNbBits;
   }
   
   typedef struct {
       U16 base;
       U16 curr;
   } rankPos;
   
   typedef nodeElt huffNodeTable[HUF_CTABLE_WORKSPACE_SIZE_U32];
   
   /* Number of buckets available for HUF_sort() */
   #define RANK_POSITION_TABLE_SIZE 192
   
   typedef struct {
     huffNodeTable huffNodeTbl;
     rankPos rankPosition[RANK_POSITION_TABLE_SIZE];
   } HUF_buildCTable_wksp_tables;
   
   /* RANK_POSITION_DISTINCT_COUNT_CUTOFF == Cutoff point in HUF_sort() buckets for which we use log2 bucketing.
    * Strategy is to use as many buckets as possible for representing distinct
    * counts while using the remainder to represent all "large" counts.
    *
    * To satisfy this requirement for 192 buckets, we can do the following:
    * Let buckets 0-166 represent distinct counts of [0, 166]
    * Let buckets 166 to 192 represent all remaining counts up to RANK_POSITION_MAX_COUNT_LOG using log2 bucketing.
    */
   #define RANK_POSITION_MAX_COUNT_LOG 32
   #define RANK_POSITION_LOG_BUCKETS_BEGIN (RANK_POSITION_TABLE_SIZE - 1) - RANK_POSITION_MAX_COUNT_LOG - 1 /* == 158 */
   #define RANK_POSITION_DISTINCT_COUNT_CUTOFF RANK_POSITION_LOG_BUCKETS_BEGIN + BIT_highbit32(RANK_POSITION_LOG_BUCKETS_BEGIN) /* == 166 */
   
   /* Return the appropriate bucket index for a given count. See definition of
    * RANK_POSITION_DISTINCT_COUNT_CUTOFF for explanation of bucketing strategy.
    */
   static U32 HUF_getIndex(U32 const count) {
       return (count < RANK_POSITION_DISTINCT_COUNT_CUTOFF)
           ? count
           : BIT_highbit32(count) + RANK_POSITION_LOG_BUCKETS_BEGIN;
   }
   
   /* Helper swap function for HUF_quickSortPartition() */
   static void HUF_swapNodes(nodeElt* a, nodeElt* b) {
           nodeElt tmp = *a;
           *a = *b;
           *b = tmp;
   }
   
   /* Returns 0 if the huffNode array is not sorted by descending count */
   MEM_STATIC int HUF_isSorted(nodeElt huffNode[], U32 const maxSymbolValue1) {
       U32 i;
       for (i = 1; i < maxSymbolValue1; ++i) {
           if (huffNode[i].count > huffNode[i-1].count) {
               return 0;
           }
       }
       return 1;
   }
   
   /* Insertion sort by descending order */
   HINT_INLINE void HUF_insertionSort(nodeElt huffNode[], int const low, int const high) {
       int i;
       int const size = high-low+1;
       huffNode += low;
       for (i = 1; i < size; ++i) {
           nodeElt const key = huffNode[i];
           int j = i - 1;
           while (j >= 0 && huffNode[j].count < key.count) {
               huffNode[j + 1] = huffNode[j];
               j--;
           }
           huffNode[j + 1] = key;
       }
   }
   
   /* Pivot helper function for quicksort. */
   static int HUF_quickSortPartition(nodeElt arr[], int const low, int const high) {
       /* Simply select rightmost element as pivot. "Better" selectors like
        * median-of-three don't experimentally appear to have any benefit.
        */
       U32 const pivot = arr[high].count;
       int i = low - 1;
       int j = low;
       for ( ; j < high; j++) {
           if (arr[j].count > pivot) {
               i++;
               HUF_swapNodes(&arr[i], &arr[j]);
           }
       }
       HUF_swapNodes(&arr[i + 1], &arr[high]);
       return i + 1;
   }
   
   /* Classic quicksort by descending with partially iterative calls
    * to reduce worst case callstack size.
    */
   static void HUF_simpleQuickSort(nodeElt arr[], int low, int high) {
       int const kInsertionSortThreshold = 8;
       if (high - low < kInsertionSortThreshold) {
           HUF_insertionSort(arr, low, high);
           return;
       }
       while (low < high) {
           int const idx = HUF_quickSortPartition(arr, low, high);
           if (idx - low < high - idx) {
               HUF_simpleQuickSort(arr, low, idx - 1);
               low = idx + 1;
           } else {
               HUF_simpleQuickSort(arr, idx + 1, high);
               high = idx - 1;
           }
       }
   }
   
   /**
    * HUF_sort():
    * Sorts the symbols [0, maxSymbolValue] by count[symbol] in decreasing order.
    * This is a typical bucket sorting strategy that uses either quicksort or insertion sort to sort each bucket.
    *
    * @param[out] huffNode       Sorted symbols by decreasing count. Only members `.count` and `.byte` are filled.
    *                            Must have (maxSymbolValue + 1) entries.
    * @param[in]  count          Histogram of the symbols.
    * @param[in]  maxSymbolValue Maximum symbol value.
    * @param      rankPosition   This is a scratch workspace. Must have RANK_POSITION_TABLE_SIZE entries.
    */
   static void HUF_sort(nodeElt huffNode[], const unsigned count[], U32 const maxSymbolValue, rankPos rankPosition[]) {
       U32 n;
       U32 const maxSymbolValue1 = maxSymbolValue+1;
   
       /* Compute base and set curr to base.
        * For symbol s let lowerRank = HUF_getIndex(count[n]) and rank = lowerRank + 1.
        * See HUF_getIndex to see bucketing strategy.
        * We attribute each symbol to lowerRank's base value, because we want to know where
        * each rank begins in the output, so for rank R we want to count ranks R+1 and above.
        */
       ZSTD_memset(rankPosition, 0, sizeof(*rankPosition) * RANK_POSITION_TABLE_SIZE);
       for (n = 0; n < maxSymbolValue1; ++n) {
           U32 lowerRank = HUF_getIndex(count[n]);
           assert(lowerRank < RANK_POSITION_TABLE_SIZE - 1);
           rankPosition[lowerRank].base++;
       }
   
       assert(rankPosition[RANK_POSITION_TABLE_SIZE - 1].base == 0);
       /* Set up the rankPosition table */
       for (n = RANK_POSITION_TABLE_SIZE - 1; n > 0; --n) {
           rankPosition[n-1].base += rankPosition[n].base;
           rankPosition[n-1].curr = rankPosition[n-1].base;
       }
   
       /* Insert each symbol into their appropriate bucket, setting up rankPosition table. */
       for (n = 0; n < maxSymbolValue1; ++n) {
           U32 const c = count[n];
           U32 const r = HUF_getIndex(c) + 1;
           U32 const pos = rankPosition[r].curr++;
           assert(pos < maxSymbolValue1);
           huffNode[pos].count = c;
           huffNode[pos].byte  = (BYTE)n;
       }
   
       /* Sort each bucket. */
       for (n = RANK_POSITION_DISTINCT_COUNT_CUTOFF; n < RANK_POSITION_TABLE_SIZE - 1; ++n) {
           U32 const bucketSize = rankPosition[n].curr-rankPosition[n].base;
           U32 const bucketStartIdx = rankPosition[n].base;
           if (bucketSize > 1) {
               assert(bucketStartIdx < maxSymbolValue1);
               HUF_simpleQuickSort(huffNode + bucketStartIdx, 0, bucketSize-1);
           }
       }
   
       assert(HUF_isSorted(huffNode, maxSymbolValue1));
   }
   
   /** HUF_buildCTable_wksp() :
    *  Same as HUF_buildCTable(), but using externally allocated scratch buffer.
    *  `workSpace` must be aligned on 4-bytes boundaries, and be at least as large as sizeof(HUF_buildCTable_wksp_tables).
    */
   #define STARTNODE (HUF_SYMBOLVALUE_MAX+1)
   
   /* HUF_buildTree():
    * Takes the huffNode array sorted by HUF_sort() and builds an unlimited-depth Huffman tree.
    *
    * @param huffNode        The array sorted by HUF_sort(). Builds the Huffman tree in this array.
    * @param maxSymbolValue  The maximum symbol value.
    * @return                The smallest node in the Huffman tree (by count).
    */
   static int HUF_buildTree(nodeElt* huffNode, U32 maxSymbolValue)
   {
       nodeElt* const huffNode0 = huffNode - 1;
       int nonNullRank;
       int lowS, lowN;
       int nodeNb = STARTNODE;
       int n, nodeRoot;
       /* init for parents */
       nonNullRank = (int)maxSymbolValue;
       while(huffNode[nonNullRank].count == 0) nonNullRank--;
       lowS = nonNullRank; nodeRoot = nodeNb + lowS - 1; lowN = nodeNb;
       huffNode[nodeNb].count = huffNode[lowS].count + huffNode[lowS-1].count;
       huffNode[lowS].parent = huffNode[lowS-1].parent = (U16)nodeNb;
       nodeNb++; lowS-=2;
       for (n=nodeNb; n<=nodeRoot; n++) huffNode[n].count = (U32)(1U<<30);
       huffNode0[0].count = (U32)(1U<<31);  /* fake entry, strong barrier */
   
       /* create parents */
       while (nodeNb <= nodeRoot) {
           int const n1 = (huffNode[lowS].count < huffNode[lowN].count) ? lowS-- : lowN++;
           int const n2 = (huffNode[lowS].count < huffNode[lowN].count) ? lowS-- : lowN++;
           huffNode[nodeNb].count = huffNode[n1].count + huffNode[n2].count;
           huffNode[n1].parent = huffNode[n2].parent = (U16)nodeNb;
           nodeNb++;
       }
   
       /* distribute weights (unlimited tree height) */
       huffNode[nodeRoot].nbBits = 0;
       for (n=nodeRoot-1; n>=STARTNODE; n--)
           huffNode[n].nbBits = huffNode[ huffNode[n].parent ].nbBits + 1;
       for (n=0; n<=nonNullRank; n++)
           huffNode[n].nbBits = huffNode[ huffNode[n].parent ].nbBits + 1;
   
       return nonNullRank;
   }
   
   /**
    * HUF_buildCTableFromTree():
    * Build the CTable given the Huffman tree in huffNode.
    *
    * @param[out] CTable         The output Huffman CTable.
    * @param      huffNode       The Huffman tree.
    * @param      nonNullRank    The last and smallest node in the Huffman tree.
    * @param      maxSymbolValue The maximum symbol value.
    * @param      maxNbBits      The exact maximum number of bits used in the Huffman tree.
    */
   static void HUF_buildCTableFromTree(HUF_CElt* CTable, nodeElt const* huffNode, int nonNullRank, U32 maxSymbolValue, U32 maxNbBits)
   {
       HUF_CElt* const ct = CTable + 1;
       /* fill result into ctable (val, nbBits) */
       int n;
       U16 nbPerRank[HUF_TABLELOG_MAX+1] = {0};
       U16 valPerRank[HUF_TABLELOG_MAX+1] = {0};
       int const alphabetSize = (int)(maxSymbolValue + 1);
       for (n=0; n<=nonNullRank; n++)
           nbPerRank[huffNode[n].nbBits]++;
       /* determine starting value per rank */
       {   U16 min = 0;
           for (n=(int)maxNbBits; n>0; n--) {
               valPerRank[n] = min;      /* get starting value within each rank */
               min += nbPerRank[n];
               min >>= 1;
       }   }
       for (n=0; n<alphabetSize; n++)
           HUF_setNbBits(ct + huffNode[n].byte, huffNode[n].nbBits);   /* push nbBits per symbol, symbol order */
       for (n=0; n<alphabetSize; n++)
           HUF_setValue(ct + n, valPerRank[HUF_getNbBits(ct[n])]++);   /* assign value within rank, symbol order */
       CTable[0] = maxNbBits;
   }
   
   size_t HUF_buildCTable_wksp (HUF_CElt* CTable, const unsigned* count, U32 maxSymbolValue, U32 maxNbBits, void* workSpace, size_t wkspSize)
   {
       HUF_buildCTable_wksp_tables* const wksp_tables = (HUF_buildCTable_wksp_tables*)HUF_alignUpWorkspace(workSpace, &wkspSize, ZSTD_ALIGNOF(U32));
       nodeElt* const huffNode0 = wksp_tables->huffNodeTbl;
       nodeElt* const huffNode = huffNode0+1;
       int nonNullRank;
   
       /* safety checks */
       if (wkspSize < sizeof(HUF_buildCTable_wksp_tables))
         return ERROR(workSpace_tooSmall);
       if (maxNbBits == 0) maxNbBits = HUF_TABLELOG_DEFAULT;
       if (maxSymbolValue > HUF_SYMBOLVALUE_MAX)
         return ERROR(maxSymbolValue_tooLarge);
       ZSTD_memset(huffNode0, 0, sizeof(huffNodeTable));
   
       /* sort, decreasing order */
       HUF_sort(huffNode, count, maxSymbolValue, wksp_tables->rankPosition);
   
       /* build tree */
       nonNullRank = HUF_buildTree(huffNode, maxSymbolValue);
   
       /* enforce maxTableLog */
       maxNbBits = HUF_setMaxHeight(huffNode, (U32)nonNullRank, maxNbBits);
       if (maxNbBits > HUF_TABLELOG_MAX) return ERROR(GENERIC);   /* check fit into table */
   
       HUF_buildCTableFromTree(CTable, huffNode, nonNullRank, maxSymbolValue, maxNbBits);
   
       return maxNbBits;
   }
   
   size_t HUF_estimateCompressedSize(const HUF_CElt* CTable, const unsigned* count, unsigned maxSymbolValue)
   {
       HUF_CElt const* ct = CTable + 1;
       size_t nbBits = 0;
       int s;
       for (s = 0; s <= (int)maxSymbolValue; ++s) {
           nbBits += HUF_getNbBits(ct[s]) * count[s];
       }
       return nbBits >> 3;
   }
   
   int HUF_validateCTable(const HUF_CElt* CTable, const unsigned* count, unsigned maxSymbolValue) {
     HUF_CElt const* ct = CTable + 1;
     int bad = 0;
     int s;
     for (s = 0; s <= (int)maxSymbolValue; ++s) {
       bad |= (count[s] != 0) & (HUF_getNbBits(ct[s]) == 0);
     }
     return !bad;
   }
   
   size_t HUF_compressBound(size_t size) { return HUF_COMPRESSBOUND(size); }
   
   /** HUF_CStream_t:
    * Huffman uses its own BIT_CStream_t implementation.
    * There are three major differences from BIT_CStream_t:
    *   1. HUF_addBits() takes a HUF_CElt (size_t) which is
    *      the pair (nbBits, value) in the format:
    *      format:
    *        - Bits [0, 4)            = nbBits
    *        - Bits [4, 64 - nbBits)  = 0
    *        - Bits [64 - nbBits, 64) = value
    *   2. The bitContainer is built from the upper bits and
    *      right shifted. E.g. to add a new value of N bits
    *      you right shift the bitContainer by N, then or in
    *      the new value into the N upper bits.
    *   3. The bitstream has two bit containers. You can add
    *      bits to the second container and merge them into
    *      the first container.
    */
   
   #define HUF_BITS_IN_CONTAINER (sizeof(size_t) * 8)
   
   typedef struct {
       size_t bitContainer[2];
       size_t bitPos[2];
   
       BYTE* startPtr;
       BYTE* ptr;
       BYTE* endPtr;
   } HUF_CStream_t;
   
   /**! HUF_initCStream():
    * Initializes the bitstream.
    * @returns 0 or an error code.
    */
   static size_t HUF_initCStream(HUF_CStream_t* bitC,
                                     void* startPtr, size_t dstCapacity)
   {
       ZSTD_memset(bitC, 0, sizeof(*bitC));
       bitC->startPtr = (BYTE*)startPtr;
       bitC->ptr = bitC->startPtr;
       bitC->endPtr = bitC->startPtr + dstCapacity - sizeof(bitC->bitContainer[0]);
       if (dstCapacity <= sizeof(bitC->bitContainer[0])) return ERROR(dstSize_tooSmall);
       return 0;
   }
   
   /*! HUF_addBits():
    * Adds the symbol stored in HUF_CElt elt to the bitstream.
    *
    * @param elt   The element we're adding. This is a (nbBits, value) pair.
    *              See the HUF_CStream_t docs for the format.
    * @param idx   Insert into the bitstream at this idx.
    * @param kFast This is a template parameter. If the bitstream is guaranteed
    *              to have at least 4 unused bits after this call it may be 1,
    *              otherwise it must be 0. HUF_addBits() is faster when fast is set.
    */
   FORCE_INLINE_TEMPLATE void HUF_addBits(HUF_CStream_t* bitC, HUF_CElt elt, int idx, int kFast)
   {
       assert(idx <= 1);
       assert(HUF_getNbBits(elt) <= HUF_TABLELOG_ABSOLUTEMAX);
       /* This is efficient on x86-64 with BMI2 because shrx
        * only reads the low 6 bits of the register. The compiler
        * knows this and elides the mask. When fast is set,
        * every operation can use the same value loaded from elt.
        */
       bitC->bitContainer[idx] >>= HUF_getNbBits(elt);
       bitC->bitContainer[idx] |= kFast ? HUF_getValueFast(elt) : HUF_getValue(elt);
       /* We only read the low 8 bits of bitC->bitPos[idx] so it
        * doesn't matter that the high bits have noise from the value.
        */
       bitC->bitPos[idx] += HUF_getNbBitsFast(elt);
       assert((bitC->bitPos[idx] & 0xFF) <= HUF_BITS_IN_CONTAINER);
       /* The last 4-bits of elt are dirty if fast is set,
        * so we must not be overwriting bits that have already been
        * inserted into the bit container.
        */
   #if DEBUGLEVEL >= 1
       {
           size_t const nbBits = HUF_getNbBits(elt);
           size_t const dirtyBits = nbBits == 0 ? 0 : BIT_highbit32((U32)nbBits) + 1;
           (void)dirtyBits;
           /* Middle bits are 0. */
           assert(((elt >> dirtyBits) << (dirtyBits + nbBits)) == 0);
           /* We didn't overwrite any bits in the bit container. */
           assert(!kFast || (bitC->bitPos[idx] & 0xFF) <= HUF_BITS_IN_CONTAINER);
           (void)dirtyBits;
       }
   #endif
   }
   
   FORCE_INLINE_TEMPLATE void HUF_zeroIndex1(HUF_CStream_t* bitC)
   {
       bitC->bitContainer[1] = 0;
       bitC->bitPos[1] = 0;
   }
   
   /*! HUF_mergeIndex1() :
    * Merges the bit container @ index 1 into the bit container @ index 0
    * and zeros the bit container @ index 1.
    */
   FORCE_INLINE_TEMPLATE void HUF_mergeIndex1(HUF_CStream_t* bitC)
   {
       assert((bitC->bitPos[1] & 0xFF) < HUF_BITS_IN_CONTAINER);
       bitC->bitContainer[0] >>= (bitC->bitPos[1] & 0xFF);
       bitC->bitContainer[0] |= bitC->bitContainer[1];
       bitC->bitPos[0] += bitC->bitPos[1];
       assert((bitC->bitPos[0] & 0xFF) <= HUF_BITS_IN_CONTAINER);
   }
   
   /*! HUF_flushBits() :
   * Flushes the bits in the bit container @ index 0.
   *
   * @post bitPos will be < 8.
   * @param kFast If kFast is set then we must know a-priori that
   *              the bit container will not overflow.
   */
   FORCE_INLINE_TEMPLATE void HUF_flushBits(HUF_CStream_t* bitC, int kFast)
   {
       /* The upper bits of bitPos are noisy, so we must mask by 0xFF. */
       size_t const nbBits = bitC->bitPos[0] & 0xFF;
       size_t const nbBytes = nbBits >> 3;
       /* The top nbBits bits of bitContainer are the ones we need. */
       size_t const bitContainer = bitC->bitContainer[0] >> (HUF_BITS_IN_CONTAINER - nbBits);
       /* Mask bitPos to account for the bytes we consumed. */
       bitC->bitPos[0] &= 7;
       assert(nbBits > 0);
       assert(nbBits <= sizeof(bitC->bitContainer[0]) * 8);
       assert(bitC->ptr <= bitC->endPtr);
       MEM_writeLEST(bitC->ptr, bitContainer);
       bitC->ptr += nbBytes;
       assert(!kFast || bitC->ptr <= bitC->endPtr);
       if (!kFast && bitC->ptr > bitC->endPtr) bitC->ptr = bitC->endPtr;
       /* bitContainer doesn't need to be modified because the leftover
        * bits are already the top bitPos bits. And we don't care about
        * noise in the lower values.
        */
   }
   
   /*! HUF_endMark()
    * @returns The Huffman stream end mark: A 1-bit value = 1.
    */
   static HUF_CElt HUF_endMark(void)
   {
       HUF_CElt endMark;
       HUF_setNbBits(&endMark, 1);
       HUF_setValue(&endMark, 1);
       return endMark;
   }
   
   /*! HUF_closeCStream() :
    *  @return Size of CStream, in bytes,
    *          or 0 if it could not fit into dstBuffer */
   static size_t HUF_closeCStream(HUF_CStream_t* bitC)
   {
       HUF_addBits(bitC, HUF_endMark(), /* idx */ 0, /* kFast */ 0);
       HUF_flushBits(bitC, /* kFast */ 0);
       {
           size_t const nbBits = bitC->bitPos[0] & 0xFF;
           if (bitC->ptr >= bitC->endPtr) return 0; /* overflow detected */
           return (bitC->ptr - bitC->startPtr) + (nbBits > 0);
       }
   }
   
   FORCE_INLINE_TEMPLATE void
   HUF_encodeSymbol(HUF_CStream_t* bitCPtr, U32 symbol, const HUF_CElt* CTable, int idx, int fast)
   {
       HUF_addBits(bitCPtr, CTable[symbol], idx, fast);
   }
   
   FORCE_INLINE_TEMPLATE void
   HUF_compress1X_usingCTable_internal_body_loop(HUF_CStream_t* bitC,
                                      const BYTE* ip, size_t srcSize,
                                      const HUF_CElt* ct,
                                      int kUnroll, int kFastFlush, int kLastFast)
   {
       /* Join to kUnroll */
       int n = (int)srcSize;
       int rem = n % kUnroll;
       if (rem > 0) {
           for (; rem > 0; --rem) {
               HUF_encodeSymbol(bitC, ip[--n], ct, 0, /* fast */ 0);
           }
           HUF_flushBits(bitC, kFastFlush);
       }
       assert(n % kUnroll == 0);
   
       /* Join to 2 * kUnroll */
       if (n % (2 * kUnroll)) {
           int u;
           for (u = 1; u < kUnroll; ++u) {
               HUF_encodeSymbol(bitC, ip[n - u], ct, 0, 1);
           }
           HUF_encodeSymbol(bitC, ip[n - kUnroll], ct, 0, kLastFast);
           HUF_flushBits(bitC, kFastFlush);
           n -= kUnroll;
       }
       assert(n % (2 * kUnroll) == 0);
   
       for (; n>0; n-= 2 * kUnroll) {
           /* Encode kUnroll symbols into the bitstream @ index 0. */
           int u;
           for (u = 1; u < kUnroll; ++u) {
               HUF_encodeSymbol(bitC, ip[n - u], ct, /* idx */ 0, /* fast */ 1);
           }
           HUF_encodeSymbol(bitC, ip[n - kUnroll], ct, /* idx */ 0, /* fast */ kLastFast);
           HUF_flushBits(bitC, kFastFlush);
           /* Encode kUnroll symbols into the bitstream @ index 1.
            * This allows us to start filling the bit container
            * without any data dependencies.
            */
           HUF_zeroIndex1(bitC);
           for (u = 1; u < kUnroll; ++u) {
               HUF_encodeSymbol(bitC, ip[n - kUnroll - u], ct, /* idx */ 1, /* fast */ 1);
           }
           HUF_encodeSymbol(bitC, ip[n - kUnroll - kUnroll], ct, /* idx */ 1, /* fast */ kLastFast);
           /* Merge bitstream @ index 1 into the bitstream @ index 0 */
           HUF_mergeIndex1(bitC);
           HUF_flushBits(bitC, kFastFlush);
       }
       assert(n == 0);
   
   }
   
   /**
    * Returns a tight upper bound on the output space needed by Huffman
    * with 8 bytes buffer to handle over-writes. If the output is at least
    * this large we don't need to do bounds checks during Huffman encoding.
    */
   static size_t HUF_tightCompressBound(size_t srcSize, size_t tableLog)
   {
       return ((srcSize * tableLog) >> 3) + 8;
   }
   
   
   FORCE_INLINE_TEMPLATE size_t
   HUF_compress1X_usingCTable_internal_body(void* dst, size_t dstSize,
                                      const void* src, size_t srcSize,
                                      const HUF_CElt* CTable)
   {
       U32 const tableLog = (U32)CTable[0];
       HUF_CElt const* ct = CTable + 1;
       const BYTE* ip = (const BYTE*) src;
       BYTE* const ostart = (BYTE*)dst;
       BYTE* const oend = ostart + dstSize;
       BYTE* op = ostart;
       HUF_CStream_t bitC;
   
       /* init */
       if (dstSize < 8) return 0;   /* not enough space to compress */
       { size_t const initErr = HUF_initCStream(&bitC, op, (size_t)(oend-op));
         if (HUF_isError(initErr)) return 0; }
   
       if (dstSize < HUF_tightCompressBound(srcSize, (size_t)tableLog) || tableLog > 11)
           HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ MEM_32bits() ? 2 : 4, /* kFast */ 0, /* kLastFast */ 0);
       else {
           if (MEM_32bits()) {
               switch (tableLog) {
               case 11:
                   HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ 2, /* kFastFlush */ 1, /* kLastFast */ 0);
                   break;
               case 10: ZSTD_FALLTHROUGH;
               case 9: ZSTD_FALLTHROUGH;
               case 8:
                   HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ 2, /* kFastFlush */ 1, /* kLastFast */ 1);
                   break;
               case 7: ZSTD_FALLTHROUGH;
               default:
                   HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ 3, /* kFastFlush */ 1, /* kLastFast */ 1);
                   break;
              }
          } else {
              switch (tableLog) {
              case 11:
                  HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ 5, /* kFastFlush */ 1, /* kLastFast */ 0);
                  break;
              case 10:
                  HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ 5, /* kFastFlush */ 1, /* kLastFast */ 1);
                  break;
              case 9:
                  HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ 6, /* kFastFlush */ 1, /* kLastFast */ 0);
                  break;
              case 8:
                  HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ 7, /* kFastFlush */ 1, /* kLastFast */ 0);
                  break;
              case 7:
                  HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ 8, /* kFastFlush */ 1, /* kLastFast */ 0);
                  break;
              case 6: ZSTD_FALLTHROUGH;
              default:
                  HUF_compress1X_usingCTable_internal_body_loop(&bitC, ip, srcSize, ct, /* kUnroll */ 9, /* kFastFlush */ 1, /* kLastFast */ 1);
                  break;
              }
          }
      }
      assert(bitC.ptr <= bitC.endPtr);
  
      return HUF_closeCStream(&bitC);
  }
  
  #if DYNAMIC_BMI2
  
  static BMI2_TARGET_ATTRIBUTE size_t
  HUF_compress1X_usingCTable_internal_bmi2(void* dst, size_t dstSize,
                                     const void* src, size_t srcSize,
                                     const HUF_CElt* CTable)
  {
      return HUF_compress1X_usingCTable_internal_body(dst, dstSize, src, srcSize, CTable);
  }
  
  static size_t
  HUF_compress1X_usingCTable_internal_default(void* dst, size_t dstSize,
                                        const void* src, size_t srcSize,
                                        const HUF_CElt* CTable)
  {
      return HUF_compress1X_usingCTable_internal_body(dst, dstSize, src, srcSize, CTable);
  }
  
  static size_t
  HUF_compress1X_usingCTable_internal(void* dst, size_t dstSize,
                                const void* src, size_t srcSize,
                                const HUF_CElt* CTable, const int bmi2)
  {
      if (bmi2) {
          return HUF_compress1X_usingCTable_internal_bmi2(dst, dstSize, src, srcSize, CTable);
      }
      return HUF_compress1X_usingCTable_internal_default(dst, dstSize, src, srcSize, CTable);
  }
  
  #else
  
  static size_t
  HUF_compress1X_usingCTable_internal(void* dst, size_t dstSize,
                                const void* src, size_t srcSize,
                                const HUF_CElt* CTable, const int bmi2)
  {
      (void)bmi2;
      return HUF_compress1X_usingCTable_internal_body(dst, dstSize, src, srcSize, CTable);
  }
  
  #endif
  
  size_t HUF_compress1X_usingCTable(void* dst, size_t dstSize, const void* src, size_t srcSize, const HUF_CElt* CTable)
  {
      return HUF_compress1X_usingCTable_bmi2(dst, dstSize, src, srcSize, CTable, /* bmi2 */ 0);
  }
  
  size_t HUF_compress1X_usingCTable_bmi2(void* dst, size_t dstSize, const void* src, size_t srcSize, const HUF_CElt* CTable, int bmi2)
  {
      return HUF_compress1X_usingCTable_internal(dst, dstSize, src, srcSize, CTable, bmi2);
  }
  
  static size_t
  HUF_compress4X_usingCTable_internal(void* dst, size_t dstSize,
                                const void* src, size_t srcSize,
                                const HUF_CElt* CTable, int bmi2)
  {
      size_t const segmentSize = (srcSize+3)/4;   /* first 3 segments */
      const BYTE* ip = (const BYTE*) src;
      const BYTE* const iend = ip + srcSize;
      BYTE* const ostart = (BYTE*) dst;
      BYTE* const oend = ostart + dstSize;
      BYTE* op = ostart;
  
      if (dstSize < 6 + 1 + 1 + 1 + 8) return 0;   /* minimum space to compress successfully */
      if (srcSize < 12) return 0;   /* no saving possible : too small input */
      op += 6;   /* jumpTable */
  
      assert(op <= oend);
      {   CHECK_V_F(cSize, HUF_compress1X_usingCTable_internal(op, (size_t)(oend-op), ip, segmentSize, CTable, bmi2) );
          if (cSize == 0 || cSize > 65535) return 0;
          MEM_writeLE16(ostart, (U16)cSize);
          op += cSize;
      }
  
      ip += segmentSize;
      assert(op <= oend);
      {   CHECK_V_F(cSize, HUF_compress1X_usingCTable_internal(op, (size_t)(oend-op), ip, segmentSize, CTable, bmi2) );
          if (cSize == 0 || cSize > 65535) return 0;
          MEM_writeLE16(ostart+2, (U16)cSize);
          op += cSize;
      }
  
      ip += segmentSize;
      assert(op <= oend);
      {   CHECK_V_F(cSize, HUF_compress1X_usingCTable_internal(op, (size_t)(oend-op), ip, segmentSize, CTable, bmi2) );
          if (cSize == 0 || cSize > 65535) return 0;
          MEM_writeLE16(ostart+4, (U16)cSize);
          op += cSize;
      }
  
      ip += segmentSize;
      assert(op <= oend);
      assert(ip <= iend);
      {   CHECK_V_F(cSize, HUF_compress1X_usingCTable_internal(op, (size_t)(oend-op), ip, (size_t)(iend-ip), CTable, bmi2) );
          if (cSize == 0 || cSize > 65535) return 0;
          op += cSize;
      }
  
      return (size_t)(op-ostart);
  }
  
  size_t HUF_compress4X_usingCTable(void* dst, size_t dstSize, const void* src, size_t srcSize, const HUF_CElt* CTable)
  {
      return HUF_compress4X_usingCTable_bmi2(dst, dstSize, src, srcSize, CTable, /* bmi2 */ 0);
  }
  
  size_t HUF_compress4X_usingCTable_bmi2(void* dst, size_t dstSize, const void* src, size_t srcSize, const HUF_CElt* CTable, int bmi2)
  {
      return HUF_compress4X_usingCTable_internal(dst, dstSize, src, srcSize, CTable, bmi2);
  }
  
  typedef enum { HUF_singleStream, HUF_fourStreams } HUF_nbStreams_e;
  
  static size_t HUF_compressCTable_internal(
                  BYTE* const ostart, BYTE* op, BYTE* const oend,
                  const void* src, size_t srcSize,
                  HUF_nbStreams_e nbStreams, const HUF_CElt* CTable, const int bmi2)
  {
      size_t const cSize = (nbStreams==HUF_singleStream) ?
                           HUF_compress1X_usingCTable_internal(op, (size_t)(oend - op), src, srcSize, CTable, bmi2) :
                           HUF_compress4X_usingCTable_internal(op, (size_t)(oend - op), src, srcSize, CTable, bmi2);
      if (HUF_isError(cSize)) { return cSize; }
      if (cSize==0) { return 0; }   /* uncompressible */
      op += cSize;
      /* check compressibility */
      assert(op >= ostart);
      if ((size_t)(op-ostart) >= srcSize-1) { return 0; }
      return (size_t)(op-ostart);
  }
  
  typedef struct {
      unsigned count[HUF_SYMBOLVALUE_MAX + 1];
      HUF_CElt CTable[HUF_CTABLE_SIZE_ST(HUF_SYMBOLVALUE_MAX)];
      union {
          HUF_buildCTable_wksp_tables buildCTable_wksp;
          HUF_WriteCTableWksp writeCTable_wksp;
          U32 hist_wksp[HIST_WKSP_SIZE_U32];
      } wksps;
  } HUF_compress_tables_t;
  
  #define SUSPECT_INCOMPRESSIBLE_SAMPLE_SIZE 4096
  #define SUSPECT_INCOMPRESSIBLE_SAMPLE_RATIO 10  /* Must be >= 2 */
  
  /* HUF_compress_internal() :
   * `workSpace_align4` must be aligned on 4-bytes boundaries,
   * and occupies the same space as a table of HUF_WORKSPACE_SIZE_U64 unsigned */
  static size_t
  HUF_compress_internal (void* dst, size_t dstSize,
                   const void* src, size_t srcSize,
                         unsigned maxSymbolValue, unsigned huffLog,
                         HUF_nbStreams_e nbStreams,
                         void* workSpace, size_t wkspSize,
                         HUF_CElt* oldHufTable, HUF_repeat* repeat, int preferRepeat,
                   const int bmi2, unsigned suspectUncompressible)
  {
      HUF_compress_tables_t* const table = (HUF_compress_tables_t*)HUF_alignUpWorkspace(workSpace, &wkspSize, ZSTD_ALIGNOF(size_t));
      BYTE* const ostart = (BYTE*)dst;
      BYTE* const oend = ostart + dstSize;
      BYTE* op = ostart;
  
      HUF_STATIC_ASSERT(sizeof(*table) + HUF_WORKSPACE_MAX_ALIGNMENT <= HUF_WORKSPACE_SIZE);
  
      /* checks & inits */
      if (wkspSize < sizeof(*table)) return ERROR(workSpace_tooSmall);
      if (!srcSize) return 0;  /* Uncompressed */
      if (!dstSize) return 0;  /* cannot fit anything within dst budget */
      if (srcSize > HUF_BLOCKSIZE_MAX) return ERROR(srcSize_wrong);   /* current block size limit */
      if (huffLog > HUF_TABLELOG_MAX) return ERROR(tableLog_tooLarge);
      if (maxSymbolValue > HUF_SYMBOLVALUE_MAX) return ERROR(maxSymbolValue_tooLarge);
      if (!maxSymbolValue) maxSymbolValue = HUF_SYMBOLVALUE_MAX;
      if (!huffLog) huffLog = HUF_TABLELOG_DEFAULT;
  
      /* Heuristic : If old table is valid, use it for small inputs */
      if (preferRepeat && repeat && *repeat == HUF_repeat_valid) {
          return HUF_compressCTable_internal(ostart, op, oend,
                                             src, srcSize,
                                             nbStreams, oldHufTable, bmi2);
      }
  
      /* If uncompressible data is suspected, do a smaller sampling first */
      DEBUG_STATIC_ASSERT(SUSPECT_INCOMPRESSIBLE_SAMPLE_RATIO >= 2);
      if (suspectUncompressible && srcSize >= (SUSPECT_INCOMPRESSIBLE_SAMPLE_SIZE * SUSPECT_INCOMPRESSIBLE_SAMPLE_RATIO)) {
          size_t largestTotal = 0;
          {   unsigned maxSymbolValueBegin = maxSymbolValue;
              CHECK_V_F(largestBegin, HIST_count_simple (table->count, &maxSymbolValueBegin, (const BYTE*)src, SUSPECT_INCOMPRESSIBLE_SAMPLE_SIZE) );
              largestTotal += largestBegin;
          }
          {   unsigned maxSymbolValueEnd = maxSymbolValue;
              CHECK_V_F(largestEnd, HIST_count_simple (table->count, &maxSymbolValueEnd, (const BYTE*)src + srcSize - SUSPECT_INCOMPRESSIBLE_SAMPLE_SIZE, SUSPECT_INCOMPRESSIBLE_SAMPLE_SIZE) );
              largestTotal += largestEnd;
          }
          if (largestTotal <= ((2 * SUSPECT_INCOMPRESSIBLE_SAMPLE_SIZE) >> 7)+4) return 0;   /* heuristic : probably not compressible enough */
      }
  
      /* Scan input and build symbol stats */
      {   CHECK_V_F(largest, HIST_count_wksp (table->count, &maxSymbolValue, (const BYTE*)src, srcSize, table->wksps.hist_wksp, sizeof(table->wksps.hist_wksp)) );
          if (largest == srcSize) { *ostart = ((const BYTE*)src)[0]; return 1; }   /* single symbol, rle */
          if (largest <= (srcSize >> 7)+4) return 0;   /* heuristic : probably not compressible enough */
      }
  
      /* Check validity of previous table */
      if ( repeat
        && *repeat == HUF_repeat_check
        && !HUF_validateCTable(oldHufTable, table->count, maxSymbolValue)) {
          *repeat = HUF_repeat_none;
      }
      /* Heuristic : use existing table for small inputs */
      if (preferRepeat && repeat && *repeat != HUF_repeat_none) {
          return HUF_compressCTable_internal(ostart, op, oend,
                                             src, srcSize,
                                             nbStreams, oldHufTable, bmi2);
      }
  
      /* Build Huffman Tree */
      huffLog = HUF_optimalTableLog(huffLog, srcSize, maxSymbolValue);
      {   size_t const maxBits = HUF_buildCTable_wksp(table->CTable, table->count,
                                              maxSymbolValue, huffLog,
                                              &table->wksps.buildCTable_wksp, sizeof(table->wksps.buildCTable_wksp));
          CHECK_F(maxBits);
          huffLog = (U32)maxBits;
      }
      /* Zero unused symbols in CTable, so we can check it for validity */
      {
          size_t const ctableSize = HUF_CTABLE_SIZE_ST(maxSymbolValue);
          size_t const unusedSize = sizeof(table->CTable) - ctableSize * sizeof(HUF_CElt);
          ZSTD_memset(table->CTable + ctableSize, 0, unusedSize);
      }
  
      /* Write table description header */
      {   CHECK_V_F(hSize, HUF_writeCTable_wksp(op, dstSize, table->CTable, maxSymbolValue, huffLog,
                                                &table->wksps.writeCTable_wksp, sizeof(table->wksps.writeCTable_wksp)) );
          /* Check if using previous huffman table is beneficial */
          if (repeat && *repeat != HUF_repeat_none) {
              size_t const oldSize = HUF_estimateCompressedSize(oldHufTable, table->count, maxSymbolValue);
              size_t const newSize = HUF_estimateCompressedSize(table->CTable, table->count, maxSymbolValue);
              if (oldSize <= hSize + newSize || hSize + 12 >= srcSize) {
                  return HUF_compressCTable_internal(ostart, op, oend,
                                                     src, srcSize,
                                                     nbStreams, oldHufTable, bmi2);
          }   }
  
          /* Use the new huffman table */
          if (hSize + 12ul >= srcSize) { return 0; }
          op += hSize;
          if (repeat) { *repeat = HUF_repeat_none; }
          if (oldHufTable)
              ZSTD_memcpy(oldHufTable, table->CTable, sizeof(table->CTable));  /* Save new table */
      }
      return HUF_compressCTable_internal(ostart, op, oend,
                                         src, srcSize,
                                         nbStreams, table->CTable, bmi2);
  }
  
  
  size_t HUF_compress1X_wksp (void* dst, size_t dstSize,
                        const void* src, size_t srcSize,
                        unsigned maxSymbolValue, unsigned huffLog,
                        void* workSpace, size_t wkspSize)
  {
      return HUF_compress_internal(dst, dstSize, src, srcSize,
                                   maxSymbolValue, huffLog, HUF_singleStream,
                                   workSpace, wkspSize,
                                   NULL, NULL, 0, 0 /*bmi2*/, 0);
  }
  
  size_t HUF_compress1X_repeat (void* dst, size_t dstSize,
                        const void* src, size_t srcSize,
                        unsigned maxSymbolValue, unsigned huffLog,
                        void* workSpace, size_t wkspSize,
                        HUF_CElt* hufTable, HUF_repeat* repeat, int preferRepeat,
                        int bmi2, unsigned suspectUncompressible)
  {
      return HUF_compress_internal(dst, dstSize, src, srcSize,
                                   maxSymbolValue, huffLog, HUF_singleStream,
                                   workSpace, wkspSize, hufTable,
                                   repeat, preferRepeat, bmi2, suspectUncompressible);
  }
  
  /* HUF_compress4X_repeat():
   * compress input using 4 streams.
   * provide workspace to generate compression tables */
  size_t HUF_compress4X_wksp (void* dst, size_t dstSize,
                        const void* src, size_t srcSize,
                        unsigned maxSymbolValue, unsigned huffLog,
                        void* workSpace, size_t wkspSize)
  {
      return HUF_compress_internal(dst, dstSize, src, srcSize,
                                   maxSymbolValue, huffLog, HUF_fourStreams,
                                   workSpace, wkspSize,
                                   NULL, NULL, 0, 0 /*bmi2*/, 0);
  }
  
  /* HUF_compress4X_repeat():
   * compress input using 4 streams.
   * consider skipping quickly
   * re-use an existing huffman compression table */
  size_t HUF_compress4X_repeat (void* dst, size_t dstSize,
                        const void* src, size_t srcSize,
                        unsigned maxSymbolValue, unsigned huffLog,
                        void* workSpace, size_t wkspSize,
                        HUF_CElt* hufTable, HUF_repeat* repeat, int preferRepeat, int bmi2, unsigned suspectUncompressible)
  {
      return HUF_compress_internal(dst, dstSize, src, srcSize,
                                   maxSymbolValue, huffLog, HUF_fourStreams,
                                   workSpace, wkspSize,
                                   hufTable, repeat, preferRepeat, bmi2, suspectUncompressible);
  }
  
  #ifndef ZSTD_NO_UNUSED_FUNCTIONS
  /** HUF_buildCTable() :
   * @return : maxNbBits
   *  Note : count is used before tree is written, so they can safely overlap
   */
  size_t HUF_buildCTable (HUF_CElt* tree, const unsigned* count, unsigned maxSymbolValue, unsigned maxNbBits)
  {
      HUF_buildCTable_wksp_tables workspace;
      return HUF_buildCTable_wksp(tree, count, maxSymbolValue, maxNbBits, &workspace, sizeof(workspace));
  }
  
  size_t HUF_compress1X (void* dst, size_t dstSize,
                   const void* src, size_t srcSize,
                   unsigned maxSymbolValue, unsigned huffLog)
  {
      U64 workSpace[HUF_WORKSPACE_SIZE_U64];
      return HUF_compress1X_wksp(dst, dstSize, src, srcSize, maxSymbolValue, huffLog, workSpace, sizeof(workSpace));
  }
  
  size_t HUF_compress2 (void* dst, size_t dstSize,
                  const void* src, size_t srcSize,
                  unsigned maxSymbolValue, unsigned huffLog)
  {
      U64 workSpace[HUF_WORKSPACE_SIZE_U64];
      return HUF_compress4X_wksp(dst, dstSize, src, srcSize, maxSymbolValue, huffLog, workSpace, sizeof(workSpace));
  }
  
  size_t HUF_compress (void* dst, size_t maxDstSize, const void* src, size_t srcSize)
  {
      return HUF_compress2(dst, maxDstSize, src, srcSize, 255, HUF_TABLELOG_DEFAULT);
  }
  #endif

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