/* ******************************************************************

 * hist : Histogram functions

 * part of Finite State Entropy project

 * Copyright (c) Meta Platforms, Inc. and affiliates.

 *

 *  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