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

     /* ******************************************************************
      * hist : Histogram functions
      * part of Finite State Entropy project
      * Copyright (c) Yann Collet, Facebook, Inc.
      *
      *  You can contact the author at :
      *  - FSE 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 "../common/mem.h"             /* U32, BYTE, etc. */
    #include "../common/debug.h"           /* assert, DEBUGLOG */
    #include "../common/error_private.h"   /* ERROR */
    #include "hist.h"
    
    
    /* --- Error management --- */
    unsigned HIST_isError(size_t code) { return ERR_isError(code); }
    
    /*-**************************************************************
     *  Histogram functions
     ****************************************************************/
    unsigned HIST_count_simple(unsigned* count, unsigned* maxSymbolValuePtr,
                               const void* src, size_t srcSize)
    {
        const BYTE* ip = (const BYTE*)src;
        const BYTE* const end = ip + srcSize;
        unsigned maxSymbolValue = *maxSymbolValuePtr;
        unsigned largestCount=0;
    
        ZSTD_memset(count, 0, (maxSymbolValue+1) * sizeof(*count));
        if (srcSize==0) { *maxSymbolValuePtr = 0; return 0; }
    
        while (ip<end) {
            assert(*ip <= maxSymbolValue);
            count[*ip++]++;
        }
    
        while (!count[maxSymbolValue]) maxSymbolValue--;
        *maxSymbolValuePtr = maxSymbolValue;
    
        {   U32 s;
            for (s=0; s<=maxSymbolValue; s++)
                if (count[s] > largestCount) largestCount = count[s];
        }
    
        return largestCount;
    }
    
    typedef enum { trustInput, checkMaxSymbolValue } HIST_checkInput_e;
    
    /* HIST_count_parallel_wksp() :
     * store histogram into 4 intermediate tables, recombined at the end.
     * this design makes better use of OoO cpus,
     * and is noticeably faster when some values are heavily repeated.
     * But it needs some additional workspace for intermediate tables.
     * `workSpace` must be a U32 table of size >= HIST_WKSP_SIZE_U32.
     * @return : largest histogram frequency,
     *           or an error code (notably when histogram's alphabet is larger than *maxSymbolValuePtr) */
    static size_t HIST_count_parallel_wksp(
                                    unsigned* count, unsigned* maxSymbolValuePtr,
                                    const void* source, size_t sourceSize,
                                    HIST_checkInput_e check,
                                    U32* const workSpace)
    {
        const BYTE* ip = (const BYTE*)source;
        const BYTE* const iend = ip+sourceSize;
        size_t const countSize = (*maxSymbolValuePtr + 1) * sizeof(*count);
        unsigned max=0;
        U32* const Counting1 = workSpace;
        U32* const Counting2 = Counting1 + 256;
        U32* const Counting3 = Counting2 + 256;
        U32* const Counting4 = Counting3 + 256;
    
        /* safety checks */
        assert(*maxSymbolValuePtr <= 255);
        if (!sourceSize) {
            ZSTD_memset(count, 0, countSize);
            *maxSymbolValuePtr = 0;
            return 0;
        }
        ZSTD_memset(workSpace, 0, 4*256*sizeof(unsigned));
    
        /* by stripes of 16 bytes */
        {   U32 cached = MEM_read32(ip); ip += 4;
            while (ip < iend-15) {
                U32 c = cached; cached = MEM_read32(ip); ip += 4;
                Counting1[(BYTE) c     ]++;
                Counting2[(BYTE)(c>>8) ]++;
                Counting3[(BYTE)(c>>16)]++;
                Counting4[       c>>24 ]++;
                c = cached; cached = MEM_read32(ip); ip += 4;
                Counting1[(BYTE) c     ]++;
               Counting2[(BYTE)(c>>8) ]++;
               Counting3[(BYTE)(c>>16)]++;
               Counting4[       c>>24 ]++;
               c = cached; cached = MEM_read32(ip); ip += 4;
               Counting1[(BYTE) c     ]++;
               Counting2[(BYTE)(c>>8) ]++;
               Counting3[(BYTE)(c>>16)]++;
               Counting4[       c>>24 ]++;
               c = cached; cached = MEM_read32(ip); ip += 4;
               Counting1[(BYTE) c     ]++;
               Counting2[(BYTE)(c>>8) ]++;
               Counting3[(BYTE)(c>>16)]++;
               Counting4[       c>>24 ]++;
           }
           ip-=4;
       }
   
       /* finish last symbols */
       while (ip<iend) Counting1[*ip++]++;
   
       {   U32 s;
           for (s=0; s<256; s++) {
               Counting1[s] += Counting2[s] + Counting3[s] + Counting4[s];
               if (Counting1[s] > max) max = Counting1[s];
       }   }
   
       {   unsigned maxSymbolValue = 255;
           while (!Counting1[maxSymbolValue]) maxSymbolValue--;
           if (check && maxSymbolValue > *maxSymbolValuePtr) return ERROR(maxSymbolValue_tooSmall);
           *maxSymbolValuePtr = maxSymbolValue;
           ZSTD_memmove(count, Counting1, countSize);   /* in case count & Counting1 are overlapping */
       }
       return (size_t)max;
   }
   
   /* HIST_countFast_wksp() :
    * Same as HIST_countFast(), but using an externally provided scratch buffer.
    * `workSpace` is a writable buffer which must be 4-bytes aligned,
    * `workSpaceSize` must be >= HIST_WKSP_SIZE
    */
   size_t HIST_countFast_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
                             const void* source, size_t sourceSize,
                             void* workSpace, size_t workSpaceSize)
   {
       if (sourceSize < 1500) /* heuristic threshold */
           return HIST_count_simple(count, maxSymbolValuePtr, source, sourceSize);
       if ((size_t)workSpace & 3) return ERROR(GENERIC);  /* must be aligned on 4-bytes boundaries */
       if (workSpaceSize < HIST_WKSP_SIZE) return ERROR(workSpace_tooSmall);
       return HIST_count_parallel_wksp(count, maxSymbolValuePtr, source, sourceSize, trustInput, (U32*)workSpace);
   }
   
   /* HIST_count_wksp() :
    * Same as HIST_count(), but using an externally provided scratch buffer.
    * `workSpace` size must be table of >= HIST_WKSP_SIZE_U32 unsigned */
   size_t HIST_count_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
                          const void* source, size_t sourceSize,
                          void* workSpace, size_t workSpaceSize)
   {
       if ((size_t)workSpace & 3) return ERROR(GENERIC);  /* must be aligned on 4-bytes boundaries */
       if (workSpaceSize < HIST_WKSP_SIZE) return ERROR(workSpace_tooSmall);
       if (*maxSymbolValuePtr < 255)
           return HIST_count_parallel_wksp(count, maxSymbolValuePtr, source, sourceSize, checkMaxSymbolValue, (U32*)workSpace);
       *maxSymbolValuePtr = 255;
       return HIST_countFast_wksp(count, maxSymbolValuePtr, source, sourceSize, workSpace, workSpaceSize);
   }
   
   #ifndef ZSTD_NO_UNUSED_FUNCTIONS
   /* fast variant (unsafe : won't check if src contains values beyond count[] limit) */
   size_t HIST_countFast(unsigned* count, unsigned* maxSymbolValuePtr,
                        const void* source, size_t sourceSize)
   {
       unsigned tmpCounters[HIST_WKSP_SIZE_U32];
       return HIST_countFast_wksp(count, maxSymbolValuePtr, source, sourceSize, tmpCounters, sizeof(tmpCounters));
   }
   
   size_t HIST_count(unsigned* count, unsigned* maxSymbolValuePtr,
                    const void* src, size_t srcSize)
   {
       unsigned tmpCounters[HIST_WKSP_SIZE_U32];
       return HIST_count_wksp(count, maxSymbolValuePtr, src, srcSize, tmpCounters, sizeof(tmpCounters));
   }
   #endif

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