annotate contrib/python-zstandard/zstd/compress/hist.c @ 44413:4cabeea6d214

hgext: start building a library for simple hooks

Many workflows depend on hooks to enforce certain policies, e.g. to
prevent forced pushes. The Mercurial Guide includes some cases and
Google can help finding others, but it can save users a lot of time
if hg itself has a couple of examples for further customization.

Differential Revision: https://phab.mercurial-scm.org/D6825

/* ******************************************************************
   hist : Histogram functions
   part of Finite State Entropy project
   Copyright (C) 2013-present, Yann Collet.

   BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are
   met:

       * Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
       * Redistributions in binary form must reproduce the above
   copyright notice, this list of conditions and the following disclaimer
   in the documentation and/or other materials provided with the
   distribution.

   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    You can contact the author at :
    - FSE source repository : https://github.com/Cyan4973/FiniteStateEntropy
    - Public forum : https://groups.google.com/forum/#!forum/lz4c
****************************************************************** */

/* --- dependencies --- */
#include "mem.h"             /* U32, BYTE, etc. */
#include "debug.h"           /* assert, DEBUGLOG */
#include "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;

    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` size must be a table of size >= HIST_WKSP_SIZE_U32.
 * @return : largest histogram frequency,
 *           or an error code (notably when histogram would be 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;
    unsigned maxSymbolValue = *maxSymbolValuePtr;
    unsigned max=0;
    U32* const Counting1 = workSpace;
    U32* const Counting2 = Counting1 + 256;
    U32* const Counting3 = Counting2 + 256;
    U32* const Counting4 = Counting3 + 256;

    memset(workSpace, 0, 4*256*sizeof(unsigned));

    /* safety checks */
    if (!sourceSize) {
        memset(count, 0, maxSymbolValue + 1);
        *maxSymbolValuePtr = 0;
        return 0;
    }
    if (!maxSymbolValue) maxSymbolValue = 255;            /* 0 == default */

    /* 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++]++;

    if (check) {   /* verify stats will fit into destination table */
        U32 s; for (s=255; s>maxSymbolValue; s--) {
            Counting1[s] += Counting2[s] + Counting3[s] + Counting4[s];
            if (Counting1[s]) return ERROR(maxSymbolValue_tooSmall);
    }   }

    {   U32 s;
        if (maxSymbolValue > 255) maxSymbolValue = 255;
        for (s=0; s<=maxSymbolValue; s++) {
            count[s] = Counting1[s] + Counting2[s] + Counting3[s] + Counting4[s];
            if (count[s] > max) max = count[s];
    }   }

    while (!count[maxSymbolValue]) maxSymbolValue--;
    *maxSymbolValuePtr = maxSymbolValue;
    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);
}

/* 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));
}

/* 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);
}

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));
}