/******************************************************************************
 *
 * Project:  CIETMap Phase 2
 * Purpose:  Use median cut algorithm to generate an near-optimal PCT for a
 *           given RGB image.  Implemented as function GDALComputeMedianCutPCT.
 * Author:   Frank Warmerdam, warmerdam@pobox.com
 *
 ******************************************************************************
 * Copyright (c) 2001, Frank Warmerdam
 * Copyright (c) 2007-2010, Even Rouault <even dot rouault at spatialys.com>
 *
 * SPDX-License-Identifier: MIT
 ******************************************************************************
 *
 * This code was based on the tiffmedian.c code from libtiff (www.libtiff.org)
 * which was based on a paper by Paul Heckbert:
 *
 *      "Color  Image Quantization for Frame Buffer Display", Paul
 *      Heckbert, SIGGRAPH proceedings, 1982, pp. 297-307.
 *
 */

#include "cpl_port.h"
#include "gdal_alg.h"
#include "gdal_alg_priv.h"

#include <climits>
#include <cstring>

#include <algorithm>
#include <limits>

#include "cpl_conv.h"
#include "cpl_error.h"
#include "cpl_progress.h"
#include "cpl_vsi.h"
#include "gdal.h"
#include "gdal_priv.h"

template <typename T> static T *HISTOGRAM(T *h, int n, int r, int g, int b)
{
    const int index = (r * n + g) * n + b;
    return &h[index];
}

#ifndef MAKE_COLOR_CODE_defined
#define MAKE_COLOR_CODE_defined

static int MAKE_COLOR_CODE(int r, int g, int b)
{
    return r | (g << 8) | (b << 16);
}
#endif

// NOTE: If changing the size of this structure, edit
// MEDIAN_CUT_AND_DITHER_BUFFER_SIZE_65536 in gdal_alg_priv.h and take into
// account ColorIndex in gdaldither.cpp.
typedef struct
{
    GUInt32 nColorCode;
    int nCount;
    GUInt32 nColorCode2;
    int nCount2;
    GUInt32 nColorCode3;
    int nCount3;
} HashHistogram;

typedef struct colorbox
{
    struct colorbox *next, *prev;
    int rmin, rmax;
    int gmin, gmax;
    int bmin, bmax;
    GUIntBig total;
} Colorbox;

template <class T>
static void splitbox(Colorbox *ptr, const T *histogram,
                     const HashHistogram *psHashHistogram, int nCLevels,
                     Colorbox **pfreeboxes, Colorbox **pusedboxes,
                     GByte *pabyRedBand, GByte *pabyGreenBand,
                     GByte *pabyBlueBand, T nPixels);

template <class T>
static void shrinkbox(Colorbox *box, const T *histogram, int nCLevels);

static Colorbox *largest_box(Colorbox *usedboxes);

/************************************************************************/
/*                      GDALComputeMedianCutPCT()                       */
/************************************************************************/

/**
 * Compute optimal PCT for RGB image.
 *
 * This function implements a median cut algorithm to compute an "optimal"
 * pseudocolor table for representing an input RGB image.  This PCT could
 * then be used with GDALDitherRGB2PCT() to convert a 24bit RGB image into
 * an eightbit pseudo-colored image.
 *
 * This code was based on the tiffmedian.c code from libtiff (www.libtiff.org)
 * which was based on a paper by Paul Heckbert:
 *
 * \verbatim
 *   "Color  Image Quantization for Frame Buffer Display", Paul
 *   Heckbert, SIGGRAPH proceedings, 1982, pp. 297-307.
 * \endverbatim
 *
 * The red, green and blue input bands do not necessarily need to come
 * from the same file, but they must be the same width and height.  They will
 * be clipped to 8bit during reading, so non-eight bit bands are generally
 * inappropriate.
 *
 * @param hRed Red input band.
 * @param hGreen Green input band.
 * @param hBlue Blue input band.
 * @param pfnIncludePixel function used to test which pixels should be included
 * in the analysis.  At this time this argument is ignored and all pixels are
 * utilized.  This should normally be NULL.
 * @param nColors the desired number of colors to be returned (2-256).
 * @param hColorTable the colors will be returned in this color table object.
 * @param pfnProgress callback for reporting algorithm progress matching the
 * GDALProgressFunc() semantics.  May be NULL.
 * @param pProgressArg callback argument passed to pfnProgress.
 *
 * @return returns CE_None on success or CE_Failure if an error occurs.
 */

extern "C" int CPL_STDCALL GDALComputeMedianCutPCT(
    GDALRasterBandH hRed, GDALRasterBandH hGreen, GDALRasterBandH hBlue,
    int (*pfnIncludePixel)(int, int, void *), int nColors,
    GDALColorTableH hColorTable, GDALProgressFunc pfnProgress,
    void *pProgressArg)

{
    VALIDATE_POINTER1(hRed, "GDALComputeMedianCutPCT", CE_Failure);
    const int nXSize = GDALGetRasterBandXSize(hRed);
    const int nYSize = GDALGetRasterBandYSize(hRed);
    if (nYSize == 0)
        return CE_Failure;
    if (static_cast<GUInt32>(nXSize) <
        std::numeric_limits<GUInt32>::max() / static_cast<GUInt32>(nYSize))
    {
        return GDALComputeMedianCutPCTInternal(
            hRed, hGreen, hBlue, nullptr, nullptr, nullptr, pfnIncludePixel,
            nColors, 5, static_cast<GUInt32 *>(nullptr), hColorTable,
            pfnProgress, pProgressArg);
    }
    else
    {
        return GDALComputeMedianCutPCTInternal(
            hRed, hGreen, hBlue, nullptr, nullptr, nullptr, pfnIncludePixel,
            nColors, 5, static_cast<GUIntBig *>(nullptr), hColorTable,
            pfnProgress, pProgressArg);
    }
}

#ifndef IsColorCodeSet_defined
#define IsColorCodeSet_defined

static inline bool IsColorCodeSet(GUInt32 nColorCode)
{
    return (nColorCode >> 31) == 0;
}
#endif

static inline int FindColorCount(const HashHistogram *psHashHistogram,
                                 GUInt32 nColorCode)
{

    GUInt32 nIdx = nColorCode % PRIME_FOR_65536;
    while (true)
    {
        if (!IsColorCodeSet(psHashHistogram[nIdx].nColorCode))
        {
            return 0;
        }
        if (psHashHistogram[nIdx].nColorCode == nColorCode)
        {
            return psHashHistogram[nIdx].nCount;
        }
        if (!IsColorCodeSet(psHashHistogram[nIdx].nColorCode2))
        {
            return 0;
        }
        if (psHashHistogram[nIdx].nColorCode2 == nColorCode)
        {
            return psHashHistogram[nIdx].nCount2;
        }
        if (!IsColorCodeSet(psHashHistogram[nIdx].nColorCode3))
        {
            return 0;
        }
        if (psHashHistogram[nIdx].nColorCode3 == nColorCode)
        {
            return psHashHistogram[nIdx].nCount3;
        }

        do
        {
            nIdx += 257;
            if (nIdx >= PRIME_FOR_65536)
                nIdx -= PRIME_FOR_65536;
        } while (IsColorCodeSet(psHashHistogram[nIdx].nColorCode) &&
                 psHashHistogram[nIdx].nColorCode != nColorCode &&
                 IsColorCodeSet(psHashHistogram[nIdx].nColorCode2) &&
                 psHashHistogram[nIdx].nColorCode2 != nColorCode &&
                 IsColorCodeSet(psHashHistogram[nIdx].nColorCode3) &&
                 psHashHistogram[nIdx].nColorCode3 != nColorCode);
    }
}

static inline int *FindAndInsertColorCount(HashHistogram *psHashHistogram,
                                           GUInt32 nColorCode)
{
    GUInt32 nIdx = nColorCode % PRIME_FOR_65536;
    while (true)
    {
        if (psHashHistogram[nIdx].nColorCode == nColorCode)
        {
            return &(psHashHistogram[nIdx].nCount);
        }
        if (!IsColorCodeSet(psHashHistogram[nIdx].nColorCode))
        {
            psHashHistogram[nIdx].nColorCode = nColorCode;
            psHashHistogram[nIdx].nCount = 0;
            return &(psHashHistogram[nIdx].nCount);
        }
        if (psHashHistogram[nIdx].nColorCode2 == nColorCode)
        {
            return &(psHashHistogram[nIdx].nCount2);
        }
        if (!IsColorCodeSet(psHashHistogram[nIdx].nColorCode2))
        {
            psHashHistogram[nIdx].nColorCode2 = nColorCode;
            psHashHistogram[nIdx].nCount2 = 0;
            return &(psHashHistogram[nIdx].nCount2);
        }
        if (psHashHistogram[nIdx].nColorCode3 == nColorCode)
        {
            return &(psHashHistogram[nIdx].nCount3);
        }
        if (!IsColorCodeSet(psHashHistogram[nIdx].nColorCode3))
        {
            psHashHistogram[nIdx].nColorCode3 = nColorCode;
            psHashHistogram[nIdx].nCount3 = 0;
            return &(psHashHistogram[nIdx].nCount3);
        }

        do
        {
            nIdx += 257;
            if (nIdx >= PRIME_FOR_65536)
                nIdx -= PRIME_FOR_65536;
        } while (IsColorCodeSet(psHashHistogram[nIdx].nColorCode) &&
                 psHashHistogram[nIdx].nColorCode != nColorCode &&
                 IsColorCodeSet(psHashHistogram[nIdx].nColorCode2) &&
                 psHashHistogram[nIdx].nColorCode2 != nColorCode &&
                 IsColorCodeSet(psHashHistogram[nIdx].nColorCode3) &&
                 psHashHistogram[nIdx].nColorCode3 != nColorCode);
    }
}

template <class T>
int GDALComputeMedianCutPCTInternal(
    GDALRasterBandH hRed, GDALRasterBandH hGreen, GDALRasterBandH hBlue,
    GByte *pabyRedBand, GByte *pabyGreenBand, GByte *pabyBlueBand,
    int (*pfnIncludePixel)(int, int, void *), int nColors, int nBits,
    T *panHistogram,  // NULL, or >= size (1<<nBits)^3 * sizeof(T) bytes.
    GDALColorTableH hColorTable, GDALProgressFunc pfnProgress,
    void *pProgressArg)

{
    VALIDATE_POINTER1(hRed, "GDALComputeMedianCutPCT", CE_Failure);
    VALIDATE_POINTER1(hGreen, "GDALComputeMedianCutPCT", CE_Failure);
    VALIDATE_POINTER1(hBlue, "GDALComputeMedianCutPCT", CE_Failure);

    CPLErr err = CE_None;

    /* -------------------------------------------------------------------- */
    /*      Validate parameters.                                            */
    /* -------------------------------------------------------------------- */
    const int nXSize = GDALGetRasterBandXSize(hRed);
    const int nYSize = GDALGetRasterBandYSize(hRed);

    if (GDALGetRasterBandXSize(hGreen) != nXSize ||
        GDALGetRasterBandYSize(hGreen) != nYSize ||
        GDALGetRasterBandXSize(hBlue) != nXSize ||
        GDALGetRasterBandYSize(hBlue) != nYSize)
    {
        CPLError(CE_Failure, CPLE_IllegalArg,
                 "Green or blue band doesn't match size of red band.");

        return CE_Failure;
    }

    if (pfnIncludePixel != nullptr)
    {
        CPLError(CE_Failure, CPLE_IllegalArg,
                 "GDALComputeMedianCutPCT() doesn't currently support "
                 "pfnIncludePixel function.");

        return CE_Failure;
    }

    if (nColors <= 0)
    {
        CPLError(CE_Failure, CPLE_IllegalArg,
                 "GDALComputeMedianCutPCT(): "
                 "nColors must be strictly greater than 1.");

        return CE_Failure;
    }

    if (nColors > 256)
    {
        CPLError(CE_Failure, CPLE_IllegalArg,
                 "GDALComputeMedianCutPCT(): "
                 "nColors must be lesser than or equal to 256.");

        return CE_Failure;
    }

    if (pfnProgress == nullptr)
        pfnProgress = GDALDummyProgress;

    /* ==================================================================== */
    /*      STEP 1: create empty boxes.                                     */
    /* ==================================================================== */
    if (static_cast<GUInt32>(nXSize) >
        std::numeric_limits<T>::max() / static_cast<GUInt32>(nYSize))
    {
        CPLError(CE_Warning, CPLE_AppDefined,
                 "GDALComputeMedianCutPCTInternal() not called "
                 "with large enough type");
    }

    T nPixels = 0;
    if (nBits == 8 && pabyRedBand != nullptr && pabyGreenBand != nullptr &&
        pabyBlueBand != nullptr &&
        static_cast<GUInt32>(nXSize) <=
            std::numeric_limits<T>::max() / static_cast<GUInt32>(nYSize))
    {
        nPixels = static_cast<T>(nXSize) * static_cast<T>(nYSize);
    }

    const int nCLevels = 1 << nBits;
    const int nCLevelsCube = nCLevels * nCLevels * nCLevels;
    T *histogram = nullptr;
    HashHistogram *psHashHistogram = nullptr;
    if (panHistogram)
    {
        if (nBits == 8 && static_cast<GUIntBig>(nXSize) * nYSize <= 65536)
        {
            // If the image is small enough, then the number of colors
            // will be limited and using a hashmap, rather than a full table
            // will be more efficient.
            histogram = nullptr;
            psHashHistogram = reinterpret_cast<HashHistogram *>(panHistogram);
            memset(psHashHistogram, 0xFF,
                   sizeof(HashHistogram) * PRIME_FOR_65536);
        }
        else
        {
            histogram = panHistogram;
            memset(histogram, 0, nCLevelsCube * sizeof(T));
        }
    }
    else
    {
        histogram =
            static_cast<T *>(VSI_CALLOC_VERBOSE(nCLevelsCube, sizeof(T)));
        if (histogram == nullptr)
        {
            return CE_Failure;
        }
    }
    Colorbox *box_list =
        static_cast<Colorbox *>(CPLMalloc(nColors * sizeof(Colorbox)));
    Colorbox *freeboxes = box_list;
    freeboxes[0].next = &freeboxes[1];
    freeboxes[0].prev = nullptr;
    for (int i = 1; i < nColors - 1; ++i)
    {
        freeboxes[i].next = &freeboxes[i + 1];
        freeboxes[i].prev = &freeboxes[i - 1];
    }
    freeboxes[nColors - 1].next = nullptr;
    freeboxes[nColors - 1].prev = &freeboxes[nColors - 2];

    /* ==================================================================== */
    /*      Build histogram.                                                */
    /* ==================================================================== */

    /* -------------------------------------------------------------------- */
    /*      Initialize the box datastructures.                              */
    /* -------------------------------------------------------------------- */
    Colorbox *freeboxes_before = freeboxes;
    freeboxes = freeboxes_before->next;
    if (freeboxes)
        freeboxes->prev = nullptr;

    Colorbox *usedboxes = freeboxes_before;
    usedboxes->next = nullptr;
    usedboxes->rmin = 999;
    usedboxes->gmin = 999;
    usedboxes->bmin = 999;
    usedboxes->rmax = -1;
    usedboxes->gmax = -1;
    usedboxes->bmax = -1;
    usedboxes->total =
        static_cast<GUIntBig>(nXSize) * static_cast<GUIntBig>(nYSize);

    /* -------------------------------------------------------------------- */
    /*      Collect histogram.                                              */
    /* -------------------------------------------------------------------- */

    // TODO(schwehr): Move these closer to usage after removing gotos.
    const int nColorShift = 8 - nBits;
    int nColorCounter = 0;
    GByte anRed[256] = {};
    GByte anGreen[256] = {};
    GByte anBlue[256] = {};

    GByte *pabyRedLine = static_cast<GByte *>(VSI_MALLOC_VERBOSE(nXSize));
    GByte *pabyGreenLine = static_cast<GByte *>(VSI_MALLOC_VERBOSE(nXSize));
    GByte *pabyBlueLine = static_cast<GByte *>(VSI_MALLOC_VERBOSE(nXSize));

    if (pabyRedLine == nullptr || pabyGreenLine == nullptr ||
        pabyBlueLine == nullptr)
    {
        err = CE_Failure;
        goto end_and_cleanup;
    }

    for (int iLine = 0; iLine < nYSize; iLine++)
    {
        if (!pfnProgress(iLine / static_cast<double>(nYSize),
                         "Generating Histogram", pProgressArg))
        {
            CPLError(CE_Failure, CPLE_UserInterrupt, "User Terminated");
            err = CE_Failure;
            goto end_and_cleanup;
        }

        err = GDALRasterIO(hRed, GF_Read, 0, iLine, nXSize, 1, pabyRedLine,
                           nXSize, 1, GDT_Byte, 0, 0);
        if (err == CE_None)
            err = GDALRasterIO(hGreen, GF_Read, 0, iLine, nXSize, 1,
                               pabyGreenLine, nXSize, 1, GDT_Byte, 0, 0);
        if (err == CE_None)
            err = GDALRasterIO(hBlue, GF_Read, 0, iLine, nXSize, 1,
                               pabyBlueLine, nXSize, 1, GDT_Byte, 0, 0);
        if (err != CE_None)
            goto end_and_cleanup;

        for (int iPixel = 0; iPixel < nXSize; iPixel++)
        {
            const int nRed = pabyRedLine[iPixel] >> nColorShift;
            const int nGreen = pabyGreenLine[iPixel] >> nColorShift;
            const int nBlue = pabyBlueLine[iPixel] >> nColorShift;

            usedboxes->rmin = std::min(usedboxes->rmin, nRed);
            usedboxes->gmin = std::min(usedboxes->gmin, nGreen);
            usedboxes->bmin = std::min(usedboxes->bmin, nBlue);
            usedboxes->rmax = std::max(usedboxes->rmax, nRed);
            usedboxes->gmax = std::max(usedboxes->gmax, nGreen);
            usedboxes->bmax = std::max(usedboxes->bmax, nBlue);

            bool bFirstOccurrence;
            if (psHashHistogram)
            {
                int *pnColor = FindAndInsertColorCount(
                    psHashHistogram, MAKE_COLOR_CODE(nRed, nGreen, nBlue));
                bFirstOccurrence = (*pnColor == 0);
                (*pnColor)++;
            }
            else
            {
                T *pnColor =
                    HISTOGRAM(histogram, nCLevels, nRed, nGreen, nBlue);
                bFirstOccurrence = (*pnColor == 0);
                (*pnColor)++;
            }
            if (bFirstOccurrence)
            {
                if (nColorShift == 0 && nColorCounter < nColors)
                {
                    anRed[nColorCounter] = static_cast<GByte>(nRed);
                    anGreen[nColorCounter] = static_cast<GByte>(nGreen);
                    anBlue[nColorCounter] = static_cast<GByte>(nBlue);
                }
                nColorCounter++;
            }
        }
    }

    if (!pfnProgress(1.0, "Generating Histogram", pProgressArg))
    {
        CPLError(CE_Failure, CPLE_UserInterrupt, "User Terminated");
        err = CE_Failure;
        goto end_and_cleanup;
    }

    if (nColorShift == 0 && nColorCounter <= nColors)
    {
#if DEBUG_VERBOSE
        CPLDebug("MEDIAN_CUT", "%d colors found <= %d", nColorCounter, nColors);
#endif
        for (int iColor = 0; iColor < nColorCounter; iColor++)
        {
            const GDALColorEntry sEntry = {static_cast<GByte>(anRed[iColor]),
                                           static_cast<GByte>(anGreen[iColor]),
                                           static_cast<GByte>(anBlue[iColor]),
                                           255};
            GDALSetColorEntry(hColorTable, iColor, &sEntry);
        }
        goto end_and_cleanup;
    }

    /* ==================================================================== */
    /*      STEP 3: continually subdivide boxes until no more free          */
    /*      boxes remain or until all colors assigned.                      */
    /* ==================================================================== */
    while (freeboxes != nullptr)
    {
        auto ptr = largest_box(usedboxes);
        if (ptr != nullptr)
            splitbox(ptr, histogram, psHashHistogram, nCLevels, &freeboxes,
                     &usedboxes, pabyRedBand, pabyGreenBand, pabyBlueBand,
                     nPixels);
        else
            freeboxes = nullptr;
    }

    /* ==================================================================== */
    /*      STEP 4: assign colors to all boxes                              */
    /* ==================================================================== */
    {
        Colorbox *ptr = usedboxes;
        for (int i = 0; ptr != nullptr; ++i, ptr = ptr->next)
        {
            const GDALColorEntry sEntry = {
                static_cast<GByte>(((ptr->rmin + ptr->rmax) << nColorShift) /
                                   2),
                static_cast<GByte>(((ptr->gmin + ptr->gmax) << nColorShift) /
                                   2),
                static_cast<GByte>(((ptr->bmin + ptr->bmax) << nColorShift) /
                                   2),
                255};
            GDALSetColorEntry(hColorTable, i, &sEntry);
        }
    }

end_and_cleanup:
    CPLFree(pabyRedLine);
    CPLFree(pabyGreenLine);
    CPLFree(pabyBlueLine);

    // We're done with the boxes now.
    CPLFree(box_list);
    freeboxes = nullptr;
    usedboxes = nullptr;

    if (panHistogram == nullptr)
        CPLFree(histogram);

    return err;
}

/************************************************************************/
/*                            largest_box()                             */
/************************************************************************/

static Colorbox *largest_box(Colorbox *usedboxes)
{
    Colorbox *b = nullptr;

    for (Colorbox *p = usedboxes; p != nullptr; p = p->next)
    {
        if ((p->rmax > p->rmin || p->gmax > p->gmin || p->bmax > p->bmin) &&
            (b == nullptr || p->total > b->total))
        {
            b = p;
        }
    }
    return b;
}

static void shrinkboxFromBand(Colorbox *ptr, const GByte *pabyRedBand,
                              const GByte *pabyGreenBand,
                              const GByte *pabyBlueBand, GUIntBig nPixels)
{
    int rmin_new = 255;
    int rmax_new = 0;
    int gmin_new = 255;
    int gmax_new = 0;
    int bmin_new = 255;
    int bmax_new = 0;
    for (GUIntBig i = 0; i < nPixels; i++)
    {
        const int iR = pabyRedBand[i];
        const int iG = pabyGreenBand[i];
        const int iB = pabyBlueBand[i];
        if (iR >= ptr->rmin && iR <= ptr->rmax && iG >= ptr->gmin &&
            iG <= ptr->gmax && iB >= ptr->bmin && iB <= ptr->bmax)
        {
            if (iR < rmin_new)
                rmin_new = iR;
            if (iR > rmax_new)
                rmax_new = iR;
            if (iG < gmin_new)
                gmin_new = iG;
            if (iG > gmax_new)
                gmax_new = iG;
            if (iB < bmin_new)
                bmin_new = iB;
            if (iB > bmax_new)
                bmax_new = iB;
        }
    }

    CPLAssert(rmin_new >= ptr->rmin && rmin_new <= rmax_new &&
              rmax_new <= ptr->rmax);
    CPLAssert(gmin_new >= ptr->gmin && gmin_new <= gmax_new &&
              gmax_new <= ptr->gmax);
    CPLAssert(bmin_new >= ptr->bmin && bmin_new <= bmax_new &&
              bmax_new <= ptr->bmax);
    ptr->rmin = rmin_new;
    ptr->rmax = rmax_new;
    ptr->gmin = gmin_new;
    ptr->gmax = gmax_new;
    ptr->bmin = bmin_new;
    ptr->bmax = bmax_new;
}

static void shrinkboxFromHashHistogram(Colorbox *box,
                                       const HashHistogram *psHashHistogram)
{
    if (box->rmax > box->rmin)
    {
        for (int ir = box->rmin; ir <= box->rmax; ++ir)
        {
            for (int ig = box->gmin; ig <= box->gmax; ++ig)
            {
                for (int ib = box->bmin; ib <= box->bmax; ++ib)
                {
                    if (FindColorCount(psHashHistogram,
                                       MAKE_COLOR_CODE(ir, ig, ib)) != 0)
                    {
                        box->rmin = ir;
                        goto have_rmin;
                    }
                }
            }
        }
    }
have_rmin:
    if (box->rmax > box->rmin)
    {
        for (int ir = box->rmax; ir >= box->rmin; --ir)
        {
            for (int ig = box->gmin; ig <= box->gmax; ++ig)
            {
                for (int ib = box->bmin; ib <= box->bmax; ++ib)
                {
                    if (FindColorCount(psHashHistogram,
                                       MAKE_COLOR_CODE(ir, ig, ib)) != 0)
                    {
                        box->rmax = ir;
                        goto have_rmax;
                    }
                }
            }
        }
    }

have_rmax:
    if (box->gmax > box->gmin)
    {
        for (int ig = box->gmin; ig <= box->gmax; ++ig)
        {
            for (int ir = box->rmin; ir <= box->rmax; ++ir)
            {
                for (int ib = box->bmin; ib <= box->bmax; ++ib)
                {
                    if (FindColorCount(psHashHistogram,
                                       MAKE_COLOR_CODE(ir, ig, ib)) != 0)
                    {
                        box->gmin = ig;
                        goto have_gmin;
                    }
                }
            }
        }
    }

have_gmin:
    if (box->gmax > box->gmin)
    {
        for (int ig = box->gmax; ig >= box->gmin; --ig)
        {
            for (int ir = box->rmin; ir <= box->rmax; ++ir)
            {
                int ib = box->bmin;
                for (; ib <= box->bmax; ++ib)
                {
                    if (FindColorCount(psHashHistogram,
                                       MAKE_COLOR_CODE(ir, ig, ib)) != 0)
                    {
                        box->gmax = ig;
                        goto have_gmax;
                    }
                }
            }
        }
    }

have_gmax:
    if (box->bmax > box->bmin)
    {
        for (int ib = box->bmin; ib <= box->bmax; ++ib)
        {
            for (int ir = box->rmin; ir <= box->rmax; ++ir)
            {
                for (int ig = box->gmin; ig <= box->gmax; ++ig)
                {
                    if (FindColorCount(psHashHistogram,
                                       MAKE_COLOR_CODE(ir, ig, ib)) != 0)
                    {
                        box->bmin = ib;
                        goto have_bmin;
                    }
                }
            }
        }
    }

have_bmin:
    if (box->bmax > box->bmin)
    {
        for (int ib = box->bmax; ib >= box->bmin; --ib)
        {
            for (int ir = box->rmin; ir <= box->rmax; ++ir)
            {
                for (int ig = box->gmin; ig <= box->gmax; ++ig)
                {
                    if (FindColorCount(psHashHistogram,
                                       MAKE_COLOR_CODE(ir, ig, ib)) != 0)
                    {
                        box->bmax = ib;
                        goto have_bmax;
                    }
                }
            }
        }
    }

have_bmax:;
}

/************************************************************************/
/*                              splitbox()                              */
/************************************************************************/
template <class T>
static void splitbox(Colorbox *ptr, const T *histogram,
                     const HashHistogram *psHashHistogram, int nCLevels,
                     Colorbox **pfreeboxes, Colorbox **pusedboxes,
                     GByte *pabyRedBand, GByte *pabyGreenBand,
                     GByte *pabyBlueBand, T nPixels)
{
    T hist2[256] = {};
    int first = 0;
    int last = 0;

    enum
    {
        RED,
        GREEN,
        BLUE
    } axis;

    // See which axis is the largest, do a histogram along that axis.  Split at
    // median point.  Contract both new boxes to fit points and return.
    {
        int i = ptr->rmax - ptr->rmin;
        if (i >= ptr->gmax - ptr->gmin && i >= ptr->bmax - ptr->bmin)
            axis = RED;
        else if (ptr->gmax - ptr->gmin >= ptr->bmax - ptr->bmin)
            axis = GREEN;
        else
            axis = BLUE;
    }
    // Get histogram along longest axis.
    const GUInt32 nIters = (ptr->rmax - ptr->rmin + 1) *
                           (ptr->gmax - ptr->gmin + 1) *
                           (ptr->bmax - ptr->bmin + 1);

    switch (axis)
    {
        case RED:
        {
            if (nPixels != 0 && nIters > nPixels)
            {
                const int rmin = ptr->rmin;
                const int rmax = ptr->rmax;
                const int gmin = ptr->gmin;
                const int gmax = ptr->gmax;
                const int bmin = ptr->bmin;
                const int bmax = ptr->bmax;
                for (T iPixel = 0; iPixel < nPixels; iPixel++)
                {
                    int iR = pabyRedBand[iPixel];
                    int iG = pabyGreenBand[iPixel];
                    int iB = pabyBlueBand[iPixel];
                    if (iR >= rmin && iR <= rmax && iG >= gmin && iG <= gmax &&
                        iB >= bmin && iB <= bmax)
                    {
                        hist2[iR]++;
                    }
                }
            }
            else if (psHashHistogram)
            {
                T *histp = &hist2[ptr->rmin];
                for (int ir = ptr->rmin; ir <= ptr->rmax; ++ir)
                {
                    *histp = 0;
                    for (int ig = ptr->gmin; ig <= ptr->gmax; ++ig)
                    {
                        for (int ib = ptr->bmin; ib <= ptr->bmax; ++ib)
                        {
                            *histp += FindColorCount(
                                psHashHistogram, MAKE_COLOR_CODE(ir, ig, ib));
                        }
                    }
                    histp++;
                }
            }
            else
            {
                T *histp = &hist2[ptr->rmin];
                for (int ir = ptr->rmin; ir <= ptr->rmax; ++ir)
                {
                    *histp = 0;
                    for (int ig = ptr->gmin; ig <= ptr->gmax; ++ig)
                    {
                        const T *iptr =
                            HISTOGRAM(histogram, nCLevels, ir, ig, ptr->bmin);
                        for (int ib = ptr->bmin; ib <= ptr->bmax; ++ib)
                            *histp += *iptr++;
                    }
                    histp++;
                }
            }
            first = ptr->rmin;
            last = ptr->rmax;
            break;
        }
        case GREEN:
        {
            if (nPixels != 0 && nIters > nPixels)
            {
                const int rmin = ptr->rmin;
                const int rmax = ptr->rmax;
                const int gmin = ptr->gmin;
                const int gmax = ptr->gmax;
                const int bmin = ptr->bmin;
                const int bmax = ptr->bmax;
                for (T iPixel = 0; iPixel < nPixels; iPixel++)
                {
                    const int iR = pabyRedBand[iPixel];
                    const int iG = pabyGreenBand[iPixel];
                    const int iB = pabyBlueBand[iPixel];
                    if (iR >= rmin && iR <= rmax && iG >= gmin && iG <= gmax &&
                        iB >= bmin && iB <= bmax)
                    {
                        hist2[iG]++;
                    }
                }
            }
            else if (psHashHistogram)
            {
                T *histp = &hist2[ptr->gmin];
                for (int ig = ptr->gmin; ig <= ptr->gmax; ++ig)
                {
                    *histp = 0;
                    for (int ir = ptr->rmin; ir <= ptr->rmax; ++ir)
                    {
                        for (int ib = ptr->bmin; ib <= ptr->bmax; ++ib)
                        {
                            *histp += FindColorCount(
                                psHashHistogram, MAKE_COLOR_CODE(ir, ig, ib));
                        }
                    }
                    histp++;
                }
            }
            else
            {
                T *histp = &hist2[ptr->gmin];
                for (int ig = ptr->gmin; ig <= ptr->gmax; ++ig)
                {
                    *histp = 0;
                    for (int ir = ptr->rmin; ir <= ptr->rmax; ++ir)
                    {
                        const T *iptr =
                            HISTOGRAM(histogram, nCLevels, ir, ig, ptr->bmin);
                        for (int ib = ptr->bmin; ib <= ptr->bmax; ++ib)
                            *histp += *iptr++;
                    }
                    histp++;
                }
            }
            first = ptr->gmin;
            last = ptr->gmax;
            break;
        }
        case BLUE:
        {
            if (nPixels != 0 && nIters > nPixels)
            {
                const int rmin = ptr->rmin;
                const int rmax = ptr->rmax;
                const int gmin = ptr->gmin;
                const int gmax = ptr->gmax;
                const int bmin = ptr->bmin;
                const int bmax = ptr->bmax;
                for (T iPixel = 0; iPixel < nPixels; iPixel++)
                {
                    const int iR = pabyRedBand[iPixel];
                    const int iG = pabyGreenBand[iPixel];
                    const int iB = pabyBlueBand[iPixel];
                    if (iR >= rmin && iR <= rmax && iG >= gmin && iG <= gmax &&
                        iB >= bmin && iB <= bmax)
                    {
                        hist2[iB]++;
                    }
                }
            }
            else if (psHashHistogram)
            {
                T *histp = &hist2[ptr->bmin];
                for (int ib = ptr->bmin; ib <= ptr->bmax; ++ib)
                {
                    *histp = 0;
                    for (int ir = ptr->rmin; ir <= ptr->rmax; ++ir)
                    {
                        for (int ig = ptr->gmin; ig <= ptr->gmax; ++ig)
                        {
                            *histp += FindColorCount(
                                psHashHistogram, MAKE_COLOR_CODE(ir, ig, ib));
                        }
                    }
                    histp++;
                }
            }
            else
            {
                T *histp = &hist2[ptr->bmin];
                for (int ib = ptr->bmin; ib <= ptr->bmax; ++ib)
                {
                    *histp = 0;
                    for (int ir = ptr->rmin; ir <= ptr->rmax; ++ir)
                    {
                        const T *iptr =
                            HISTOGRAM(histogram, nCLevels, ir, ptr->gmin, ib);
                        for (int ig = ptr->gmin; ig <= ptr->gmax; ++ig)
                        {
                            *histp += *iptr;
                            iptr += nCLevels;
                        }
                    }
                    histp++;
                }
            }
            first = ptr->bmin;
            last = ptr->bmax;
            break;
        }
    }
    // Find median point.
    T *histp = &hist2[first];
    int i = first;  // TODO(schwehr): Rename i.
    {
        T sum = 0;
        T sum2 = static_cast<T>(ptr->total / 2);
        for (; i <= last && (sum += *histp++) < sum2; ++i)
        {
        }
    }
    if (i == first)
        i++;

    // Create new box, re-allocate points.
    Colorbox *new_cb = *pfreeboxes;
    *pfreeboxes = new_cb->next;
    if (*pfreeboxes)
        (*pfreeboxes)->prev = nullptr;
    if (*pusedboxes)
        (*pusedboxes)->prev = new_cb;
    new_cb->next = *pusedboxes;
    *pusedboxes = new_cb;

    histp = &hist2[first];
    {
        T sum1 = 0;
        for (int j = first; j < i; j++)
            sum1 += *histp++;
        T sum2 = 0;
        for (int j = i; j <= last; j++)
            sum2 += *histp++;
        new_cb->total = sum1;
        ptr->total = sum2;
    }
    new_cb->rmin = ptr->rmin;
    new_cb->rmax = ptr->rmax;
    new_cb->gmin = ptr->gmin;
    new_cb->gmax = ptr->gmax;
    new_cb->bmin = ptr->bmin;
    new_cb->bmax = ptr->bmax;
    switch (axis)
    {
        case RED:
            new_cb->rmax = i - 1;
            ptr->rmin = i;
            break;
        case GREEN:
            new_cb->gmax = i - 1;
            ptr->gmin = i;
            break;
        case BLUE:
            new_cb->bmax = i - 1;
            ptr->bmin = i;
            break;
    }

    if (nPixels != 0 &&
        static_cast<T>(new_cb->rmax - new_cb->rmin + 1) *
                static_cast<T>(new_cb->gmax - new_cb->gmin + 1) *
                static_cast<T>(new_cb->bmax - new_cb->bmin + 1) >
            nPixels)
    {
        shrinkboxFromBand(new_cb, pabyRedBand, pabyGreenBand, pabyBlueBand,
                          nPixels);
    }
    else if (psHashHistogram != nullptr)
    {
        shrinkboxFromHashHistogram(new_cb, psHashHistogram);
    }
    else
    {
        shrinkbox(new_cb, histogram, nCLevels);
    }

    if (nPixels != 0 && static_cast<T>(ptr->rmax - ptr->rmin + 1) *
                                static_cast<T>(ptr->gmax - ptr->gmin + 1) *
                                static_cast<T>(ptr->bmax - ptr->bmin + 1) >
                            nPixels)
    {
        shrinkboxFromBand(ptr, pabyRedBand, pabyGreenBand, pabyBlueBand,
                          nPixels);
    }
    else if (psHashHistogram != nullptr)
    {
        shrinkboxFromHashHistogram(ptr, psHashHistogram);
    }
    else
    {
        shrinkbox(ptr, histogram, nCLevels);
    }
}

/************************************************************************/
/*                             shrinkbox()                              */
/************************************************************************/
template <class T>
static void shrinkbox(Colorbox *box, const T *histogram, int nCLevels)
{
    if (box->rmax > box->rmin)
    {
        for (int ir = box->rmin; ir <= box->rmax; ++ir)
        {
            for (int ig = box->gmin; ig <= box->gmax; ++ig)
            {
                const T *histp =
                    HISTOGRAM(histogram, nCLevels, ir, ig, box->bmin);
                for (int ib = box->bmin; ib <= box->bmax; ++ib)
                {
                    if (*histp++ != 0)
                    {
                        box->rmin = ir;
                        goto have_rmin;
                    }
                }
            }
        }
    }
have_rmin:
    if (box->rmax > box->rmin)
    {
        for (int ir = box->rmax; ir >= box->rmin; --ir)
        {
            for (int ig = box->gmin; ig <= box->gmax; ++ig)
            {
                const T *histp =
                    HISTOGRAM(histogram, nCLevels, ir, ig, box->bmin);
                for (int ib = box->bmin; ib <= box->bmax; ++ib)
                {
                    if (*histp++ != 0)
                    {
                        box->rmax = ir;
                        goto have_rmax;
                    }
                }
            }
        }
    }

have_rmax:
    if (box->gmax > box->gmin)
    {
        for (int ig = box->gmin; ig <= box->gmax; ++ig)
        {
            for (int ir = box->rmin; ir <= box->rmax; ++ir)
            {
                const T *histp =
                    HISTOGRAM(histogram, nCLevels, ir, ig, box->bmin);
                for (int ib = box->bmin; ib <= box->bmax; ++ib)
                {
                    if (*histp++ != 0)
                    {
                        box->gmin = ig;
                        goto have_gmin;
                    }
                }
            }
        }
    }

have_gmin:
    if (box->gmax > box->gmin)
    {
        for (int ig = box->gmax; ig >= box->gmin; --ig)
        {
            for (int ir = box->rmin; ir <= box->rmax; ++ir)
            {
                const T *histp =
                    HISTOGRAM(histogram, nCLevels, ir, ig, box->bmin);
                for (int ib = box->bmin; ib <= box->bmax; ++ib)
                {
                    if (*histp++ != 0)
                    {
                        box->gmax = ig;
                        goto have_gmax;
                    }
                }
            }
        }
    }

have_gmax:
    if (box->bmax > box->bmin)
    {
        for (int ib = box->bmin; ib <= box->bmax; ++ib)
        {
            for (int ir = box->rmin; ir <= box->rmax; ++ir)
            {
                const T *histp =
                    HISTOGRAM(histogram, nCLevels, ir, box->gmin, ib);
                for (int ig = box->gmin; ig <= box->gmax; ++ig)
                {
                    if (*histp != 0)
                    {
                        box->bmin = ib;
                        goto have_bmin;
                    }
                    histp += nCLevels;
                }
            }
        }
    }

have_bmin:
    if (box->bmax > box->bmin)
    {
        for (int ib = box->bmax; ib >= box->bmin; --ib)
        {
            for (int ir = box->rmin; ir <= box->rmax; ++ir)
            {
                const T *histp =
                    HISTOGRAM(histogram, nCLevels, ir, box->gmin, ib);
                for (int ig = box->gmin; ig <= box->gmax; ++ig)
                {
                    if (*histp != 0)
                    {
                        box->bmax = ib;
                        goto have_bmax;
                    }
                    histp += nCLevels;
                }
            }
        }
    }

have_bmax:;
}

// Explicitly instantiate template functions.
template int GDALComputeMedianCutPCTInternal<GUInt32>(
    GDALRasterBandH hRed, GDALRasterBandH hGreen, GDALRasterBandH hBlue,
    GByte *pabyRedBand, GByte *pabyGreenBand, GByte *pabyBlueBand,
    int (*pfnIncludePixel)(int, int, void *), int nColors, int nBits,
    GUInt32 *panHistogram, GDALColorTableH hColorTable,
    GDALProgressFunc pfnProgress, void *pProgressArg);

template int GDALComputeMedianCutPCTInternal<GUIntBig>(
    GDALRasterBandH hRed, GDALRasterBandH hGreen, GDALRasterBandH hBlue,
    GByte *pabyRedBand, GByte *pabyGreenBand, GByte *pabyBlueBand,
    int (*pfnIncludePixel)(int, int, void *), int nColors, int nBits,
    GUIntBig *panHistogram, GDALColorTableH hColorTable,
    GDALProgressFunc pfnProgress, void *pProgressArg);
