FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zstd/lib/common/entropy_common.c

     /* ******************************************************************
      * Common functions of New Generation Entropy library
      * Copyright (c) 2016-2020, 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.
    ****************************************************************** */
    
    /* *************************************
    *  Dependencies
    ***************************************/
    #include "mem.h"
    #include "error_private.h"       /* ERR_*, ERROR */
    #define FSE_STATIC_LINKING_ONLY  /* FSE_MIN_TABLELOG */
    #include "fse.h"
    #define HUF_STATIC_LINKING_ONLY  /* HUF_TABLELOG_ABSOLUTEMAX */
    #include "huf.h"
    
    
    /*===   Version   ===*/
    unsigned FSE_versionNumber(void) { return FSE_VERSION_NUMBER; }
    
    
    /*===   Error Management   ===*/
    unsigned FSE_isError(size_t code) { return ERR_isError(code); }
    const char* FSE_getErrorName(size_t code) { return ERR_getErrorName(code); }
    
    unsigned HUF_isError(size_t code) { return ERR_isError(code); }
    const char* HUF_getErrorName(size_t code) { return ERR_getErrorName(code); }
    
    
    /*-**************************************************************
    *  FSE NCount encoding-decoding
    ****************************************************************/
    size_t FSE_readNCount (short* normalizedCounter, unsigned* maxSVPtr, unsigned* tableLogPtr,
                     const void* headerBuffer, size_t hbSize)
    {
        const BYTE* const istart = (const BYTE*) headerBuffer;
        const BYTE* const iend = istart + hbSize;
        const BYTE* ip = istart;
        int nbBits;
        int remaining;
        int threshold;
        U32 bitStream;
        int bitCount;
        unsigned charnum = 0;
        int previous0 = 0;
    
        if (hbSize < 4) {
            /* This function only works when hbSize >= 4 */
            char buffer[4];
            memset(buffer, 0, sizeof(buffer));
            memcpy(buffer, headerBuffer, hbSize);
            {   size_t const countSize = FSE_readNCount(normalizedCounter, maxSVPtr, tableLogPtr,
                                                        buffer, sizeof(buffer));
                if (FSE_isError(countSize)) return countSize;
                if (countSize > hbSize) return ERROR(corruption_detected);
                return countSize;
        }   }
        assert(hbSize >= 4);
    
        /* init */
        memset(normalizedCounter, 0, (*maxSVPtr+1) * sizeof(normalizedCounter[0]));   /* all symbols not present in NCount have a frequency of 0 */
        bitStream = MEM_readLE32(ip);
        nbBits = (bitStream & 0xF) + FSE_MIN_TABLELOG;   /* extract tableLog */
        if (nbBits > FSE_TABLELOG_ABSOLUTE_MAX) return ERROR(tableLog_tooLarge);
        bitStream >>= 4;
        bitCount = 4;
        *tableLogPtr = nbBits;
        remaining = (1<<nbBits)+1;
        threshold = 1<<nbBits;
        nbBits++;
    
        while ((remaining>1) & (charnum<=*maxSVPtr)) {
            if (previous0) {
                unsigned n0 = charnum;
                while ((bitStream & 0xFFFF) == 0xFFFF) {
                    n0 += 24;
                    if (ip < iend-5) {
                        ip += 2;
                        bitStream = MEM_readLE32(ip) >> bitCount;
                    } else {
                        bitStream >>= 16;
                        bitCount   += 16;
                }   }
                while ((bitStream & 3) == 3) {
                    n0 += 3;
                    bitStream >>= 2;
                    bitCount += 2;
                }
                n0 += bitStream & 3;
                bitCount += 2;
                if (n0 > *maxSVPtr) return ERROR(maxSymbolValue_tooSmall);
               while (charnum < n0) normalizedCounter[charnum++] = 0;
               if ((ip <= iend-7) || (ip + (bitCount>>3) <= iend-4)) {
                   assert((bitCount >> 3) <= 3); /* For first condition to work */
                   ip += bitCount>>3;
                   bitCount &= 7;
                   bitStream = MEM_readLE32(ip) >> bitCount;
               } else {
                   bitStream >>= 2;
           }   }
           {   int const max = (2*threshold-1) - remaining;
               int count;
   
               if ((bitStream & (threshold-1)) < (U32)max) {
                   count = bitStream & (threshold-1);
                   bitCount += nbBits-1;
               } else {
                   count = bitStream & (2*threshold-1);
                   if (count >= threshold) count -= max;
                   bitCount += nbBits;
               }
   
               count--;   /* extra accuracy */
               remaining -= count < 0 ? -count : count;   /* -1 means +1 */
               normalizedCounter[charnum++] = (short)count;
               previous0 = !count;
               while (remaining < threshold) {
                   nbBits--;
                   threshold >>= 1;
               }
   
               if ((ip <= iend-7) || (ip + (bitCount>>3) <= iend-4)) {
                   ip += bitCount>>3;
                   bitCount &= 7;
               } else {
                   bitCount -= (int)(8 * (iend - 4 - ip));
                   ip = iend - 4;
               }
               bitStream = MEM_readLE32(ip) >> (bitCount & 31);
       }   }   /* while ((remaining>1) & (charnum<=*maxSVPtr)) */
       if (remaining != 1) return ERROR(corruption_detected);
       if (bitCount > 32) return ERROR(corruption_detected);
       *maxSVPtr = charnum-1;
   
       ip += (bitCount+7)>>3;
       return ip-istart;
   }
   
   
   /*! HUF_readStats() :
       Read compact Huffman tree, saved by HUF_writeCTable().
       `huffWeight` is destination buffer.
       `rankStats` is assumed to be a table of at least HUF_TABLELOG_MAX U32.
       @return : size read from `src` , or an error Code .
       Note : Needed by HUF_readCTable() and HUF_readDTableX?() .
   */
   size_t HUF_readStats(BYTE* huffWeight, size_t hwSize, U32* rankStats,
                        U32* nbSymbolsPtr, U32* tableLogPtr,
                        const void* src, size_t srcSize)
   {
       U32 weightTotal;
       const BYTE* ip = (const BYTE*) src;
       size_t iSize;
       size_t oSize;
   
       if (!srcSize) return ERROR(srcSize_wrong);
       iSize = ip[0];
       /* memset(huffWeight, 0, hwSize);   *//* is not necessary, even though some analyzer complain ... */
   
       if (iSize >= 128) {  /* special header */
           oSize = iSize - 127;
           iSize = ((oSize+1)/2);
           if (iSize+1 > srcSize) return ERROR(srcSize_wrong);
           if (oSize >= hwSize) return ERROR(corruption_detected);
           ip += 1;
           {   U32 n;
               for (n=0; n<oSize; n+=2) {
                   huffWeight[n]   = ip[n/2] >> 4;
                   huffWeight[n+1] = ip[n/2] & 15;
       }   }   }
       else  {   /* header compressed with FSE (normal case) */
           FSE_DTable fseWorkspace[FSE_DTABLE_SIZE_U32(6)];  /* 6 is max possible tableLog for HUF header (maybe even 5, to be tested) */
           if (iSize+1 > srcSize) return ERROR(srcSize_wrong);
           oSize = FSE_decompress_wksp(huffWeight, hwSize-1, ip+1, iSize, fseWorkspace, 6);   /* max (hwSize-1) values decoded, as last one is implied */
           if (FSE_isError(oSize)) return oSize;
       }
   
       /* collect weight stats */
       memset(rankStats, 0, (HUF_TABLELOG_MAX + 1) * sizeof(U32));
       weightTotal = 0;
       {   U32 n; for (n=0; n<oSize; n++) {
               if (huffWeight[n] >= HUF_TABLELOG_MAX) return ERROR(corruption_detected);
               rankStats[huffWeight[n]]++;
               weightTotal += (1 << huffWeight[n]) >> 1;
       }   }
       if (weightTotal == 0) return ERROR(corruption_detected);
   
       /* get last non-null symbol weight (implied, total must be 2^n) */
       {   U32 const tableLog = BIT_highbit32(weightTotal) + 1;
           if (tableLog > HUF_TABLELOG_MAX) return ERROR(corruption_detected);
           *tableLogPtr = tableLog;
           /* determine last weight */
           {   U32 const total = 1 << tableLog;
               U32 const rest = total - weightTotal;
               U32 const verif = 1 << BIT_highbit32(rest);
               U32 const lastWeight = BIT_highbit32(rest) + 1;
               if (verif != rest) return ERROR(corruption_detected);    /* last value must be a clean power of 2 */
               huffWeight[oSize] = (BYTE)lastWeight;
               rankStats[lastWeight]++;
       }   }
   
       /* check tree construction validity */
       if ((rankStats[1] < 2) || (rankStats[1] & 1)) return ERROR(corruption_detected);   /* by construction : at least 2 elts of rank 1, must be even */
   
       /* results */
       *nbSymbolsPtr = (U32)(oSize+1);
       return iSize+1;
   }

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