mikktspace.c

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#include <assert.h>
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <float.h>
#include <stdlib.h>

#include "mikktspace.h"

#define TFALSE      0
#define TTRUE       1

#ifndef M_PI
#define M_PI    3.1415926535897932384626433832795
#endif

#define INTERNAL_RND_SORT_SEED      39871946

// internal structure
typedef struct
{
    float x, y, z;
} SVec3;

static tbool            veq( const SVec3 v1, const SVec3 v2 )
{
    return (v1.x == v2.x) && (v1.y == v2.y) && (v1.z == v2.z);
}

static SVec3        vadd( const SVec3 v1, const SVec3 v2 )
{
    SVec3 vRes;

    vRes.x = v1.x + v2.x;
    vRes.y = v1.y + v2.y;
    vRes.z = v1.z + v2.z;

    return vRes;
}


static SVec3        vsub( const SVec3 v1, const SVec3 v2 )
{
    SVec3 vRes;

    vRes.x = v1.x - v2.x;
    vRes.y = v1.y - v2.y;
    vRes.z = v1.z - v2.z;

    return vRes;
}

static SVec3        vscale(const float fS, const SVec3 v)
{
    SVec3 vRes;

    vRes.x = fS * v.x;
    vRes.y = fS * v.y;
    vRes.z = fS * v.z;

    return vRes;
}

static float            LengthSquared( const SVec3 v )
{
    return v.x*v.x + v.y*v.y + v.z*v.z;
}

static float            Length( const SVec3 v )
{
    return sqrtf(LengthSquared(v));
}

static SVec3        Normalize( const SVec3 v )
{
    return vscale(1 / Length(v), v);
}

static float        vdot( const SVec3 v1, const SVec3 v2)
{
    return v1.x*v2.x + v1.y*v2.y + v1.z*v2.z;
}


static tbool NotZero(const float fX)
{
    // could possibly use FLT_EPSILON instead
    return fabsf(fX) > FLT_MIN;
}

static tbool VNotZero(const SVec3 v)
{
    // might change this to an epsilon based test
    return NotZero(v.x) || NotZero(v.y) || NotZero(v.z);
}



typedef struct
{
    int iNrFaces;
    int * pTriMembers;
} SSubGroup;

typedef struct
{
    int iNrFaces;
    int * pFaceIndices;
    int iVertexRepresentitive;
    tbool bOrientPreservering;
} SGroup;

// 
#define MARK_DEGENERATE             1
#define QUAD_ONE_DEGEN_TRI          2
#define GROUP_WITH_ANY              4
#define ORIENT_PRESERVING           8



typedef struct
{
    int FaceNeighbors[3];
    SGroup * AssignedGroup[3];
    
    // normalized first order face derivatives
    SVec3 vOs, vOt;
    float fMagS, fMagT; // original magnitudes

    // determines if the current and the next triangle are a quad.
    int iOrgFaceNumber;
    int iFlag, iTSpacesOffs;
    unsigned char vert_num[4];
} STriInfo;

typedef struct
{
    SVec3 vOs;
    float fMagS;
    SVec3 vOt;
    float fMagT;
    int iCounter;   // this is to average back into quads.
    tbool bOrient;
} STSpace;

static int GenerateInitialVerticesIndexList(STriInfo pTriInfos[], int piTriList_out[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn);
static void GenerateSharedVerticesIndexList(int piTriList_in_and_out[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn);
static void InitTriInfo(STriInfo pTriInfos[], const int piTriListIn[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn);
static int Build4RuleGroups(STriInfo pTriInfos[], SGroup pGroups[], int piGroupTrianglesBuffer[], const int piTriListIn[], const int iNrTrianglesIn);
static tbool GenerateTSpaces(STSpace psTspace[], const STriInfo pTriInfos[], const SGroup pGroups[],
                             const int iNrActiveGroups, const int piTriListIn[], const float fThresCos,
                             const SMikkTSpaceContext * pContext);

static int MakeIndex(const int iFace, const int iVert)
{
    assert(iVert>=0 && iVert<4 && iFace>=0);
    return (iFace<<2) | (iVert&0x3);
}

static void IndexToData(int * piFace, int * piVert, const int iIndexIn)
{
    piVert[0] = iIndexIn&0x3;
    piFace[0] = iIndexIn>>2;
}

static STSpace AvgTSpace(const STSpace * pTS0, const STSpace * pTS1)
{
    STSpace ts_res;

    // this if is important. Due to floating point precision
    // averaging when ts0==ts1 will cause a slight difference
    // which results in tangent space splits later on
    if(pTS0->fMagS==pTS1->fMagS && pTS0->fMagT==pTS1->fMagT &&
       veq(pTS0->vOs,pTS1->vOs) && veq(pTS0->vOt, pTS1->vOt))
    {
        ts_res.fMagS = pTS0->fMagS;
        ts_res.fMagT = pTS0->fMagT;
        ts_res.vOs = pTS0->vOs;
        ts_res.vOt = pTS0->vOt;
    }
    else
    {
        ts_res.fMagS = 0.5f*(pTS0->fMagS+pTS1->fMagS);
        ts_res.fMagT = 0.5f*(pTS0->fMagT+pTS1->fMagT);
        ts_res.vOs = vadd(pTS0->vOs,pTS1->vOs);
        ts_res.vOt = vadd(pTS0->vOt,pTS1->vOt);
        if( VNotZero(ts_res.vOs) ) ts_res.vOs = Normalize(ts_res.vOs);
        if( VNotZero(ts_res.vOt) ) ts_res.vOt = Normalize(ts_res.vOt);
    }

    return ts_res;
}



static SVec3 GetPosition(const SMikkTSpaceContext * pContext, const int index);
static SVec3 GetNormal(const SMikkTSpaceContext * pContext, const int index);
static SVec3 GetTexCoord(const SMikkTSpaceContext * pContext, const int index);


// degen triangles
static void DegenPrologue(STriInfo pTriInfos[], int piTriList_out[], const int iNrTrianglesIn, const int iTotTris);
static void DegenEpilogue(STSpace psTspace[], STriInfo pTriInfos[], int piTriListIn[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn, const int iTotTris);


tbool genTangSpaceDefault(const SMikkTSpaceContext * pContext)
{
    return genTangSpace(pContext, 180.0f);
}

tbool genTangSpace(const SMikkTSpaceContext * pContext, const float fAngularThreshold)
{
    // count nr_triangles
    int * piTriListIn = NULL, * piGroupTrianglesBuffer = NULL;
    STriInfo * pTriInfos = NULL;
    SGroup * pGroups = NULL;
    STSpace * psTspace = NULL;
    int iNrTrianglesIn = 0, f=0, t=0, i=0;
    int iNrTSPaces = 0, iTotTris = 0, iDegenTriangles = 0, iNrMaxGroups = 0;
    int iNrActiveGroups = 0, index = 0;
    const int iNrFaces = pContext->m_pInterface->m_getNumFaces(pContext);
    tbool bRes = TFALSE;
    const float fThresCos = (float) cos((fAngularThreshold*(float)M_PI)/180.0f);

    // verify all call-backs have been set
    if( pContext->m_pInterface->m_getNumFaces==NULL ||
        pContext->m_pInterface->m_getNumVerticesOfFace==NULL ||
        pContext->m_pInterface->m_getPosition==NULL ||
        pContext->m_pInterface->m_getNormal==NULL ||
        pContext->m_pInterface->m_getTexCoord==NULL )
        return TFALSE;

    // count triangles on supported faces
    for(f=0; f<iNrFaces; f++)
    {
        const int verts = pContext->m_pInterface->m_getNumVerticesOfFace(pContext, f);
        if(verts==3) ++iNrTrianglesIn;
        else if(verts==4) iNrTrianglesIn += 2;
    }
    if(iNrTrianglesIn<=0) return TFALSE;

    // allocate memory for an index list
    piTriListIn = (int *) malloc(sizeof(int)*3*iNrTrianglesIn);
    pTriInfos = (STriInfo *) malloc(sizeof(STriInfo)*iNrTrianglesIn);
    if(piTriListIn==NULL || pTriInfos==NULL)
    {
        if(piTriListIn!=NULL) free(piTriListIn);
        if(pTriInfos!=NULL) free(pTriInfos);
        return TFALSE;
    }

    // make an initial triangle --> face index list
    iNrTSPaces = GenerateInitialVerticesIndexList(pTriInfos, piTriListIn, pContext, iNrTrianglesIn);

    // make a welded index list of identical positions and attributes (pos, norm, texc)
    //printf("gen welded index list begin\n");
    GenerateSharedVerticesIndexList(piTriListIn, pContext, iNrTrianglesIn);
    //printf("gen welded index list end\n");

    // Mark all degenerate triangles
    iTotTris = iNrTrianglesIn;
    iDegenTriangles = 0;
    for(t=0; t<iTotTris; t++)
    {
        const int i0 = piTriListIn[t*3+0];
        const int i1 = piTriListIn[t*3+1];
        const int i2 = piTriListIn[t*3+2];
        const SVec3 p0 = GetPosition(pContext, i0);
        const SVec3 p1 = GetPosition(pContext, i1);
        const SVec3 p2 = GetPosition(pContext, i2);
        if(veq(p0,p1) || veq(p0,p2) || veq(p1,p2))  // degenerate
        {
            pTriInfos[t].iFlag |= MARK_DEGENERATE;
            ++iDegenTriangles;
        }
    }
    iNrTrianglesIn = iTotTris - iDegenTriangles;

    // mark all triangle pairs that belong to a quad with only one
    // good triangle. These need special treatment in DegenEpilogue().
    // Additionally, move all good triangles to the start of
    // pTriInfos[] and piTriListIn[] without changing order and
    // put the degenerate triangles last.
    DegenPrologue(pTriInfos, piTriListIn, iNrTrianglesIn, iTotTris);

    
    // evaluate triangle level attributes and neighbor list
    //printf("gen neighbors list begin\n");
    InitTriInfo(pTriInfos, piTriListIn, pContext, iNrTrianglesIn);
    //printf("gen neighbors list end\n");

    
    // based on the 4 rules, identify groups based on connectivity
    iNrMaxGroups = iNrTrianglesIn*3;
    pGroups = (SGroup *) malloc(sizeof(SGroup)*iNrMaxGroups);
    piGroupTrianglesBuffer = (int *) malloc(sizeof(int)*iNrTrianglesIn*3);
    if(pGroups==NULL || piGroupTrianglesBuffer==NULL)
    {
        if(pGroups!=NULL) free(pGroups);
        if(piGroupTrianglesBuffer!=NULL) free(piGroupTrianglesBuffer);
        free(piTriListIn);
        free(pTriInfos);
        return TFALSE;
    }
    //printf("gen 4rule groups begin\n");
    iNrActiveGroups =
        Build4RuleGroups(pTriInfos, pGroups, piGroupTrianglesBuffer, piTriListIn, iNrTrianglesIn);
    //printf("gen 4rule groups end\n");

    //

    psTspace = (STSpace *) malloc(sizeof(STSpace)*iNrTSPaces);
    if(psTspace==NULL)
    {
        free(piTriListIn);
        free(pTriInfos);
        free(pGroups);
        free(piGroupTrianglesBuffer);
        return TFALSE;
    }
    memset(psTspace, 0, sizeof(STSpace)*iNrTSPaces);
    for(t=0; t<iNrTSPaces; t++)
    {
        psTspace[t].vOs.x=1.0f; psTspace[t].vOs.y=0.0f; psTspace[t].vOs.z=0.0f; psTspace[t].fMagS = 1.0f;
        psTspace[t].vOt.x=0.0f; psTspace[t].vOt.y=1.0f; psTspace[t].vOt.z=0.0f; psTspace[t].fMagT = 1.0f;
    }

    // make tspaces, each group is split up into subgroups if necessary
    // based on fAngularThreshold. Finally a tangent space is made for
    // every resulting subgroup
    //printf("gen tspaces begin\n");
    bRes = GenerateTSpaces(psTspace, pTriInfos, pGroups, iNrActiveGroups, piTriListIn, fThresCos, pContext);
    //printf("gen tspaces end\n");
    
    // clean up
    free(pGroups);
    free(piGroupTrianglesBuffer);

    if(!bRes)   // if an allocation in GenerateTSpaces() failed
    {
        // clean up and return false
        free(pTriInfos); free(piTriListIn); free(psTspace);
        return TFALSE;
    }


    // degenerate quads with one good triangle will be fixed by copying a space from
    // the good triangle to the coinciding vertex.
    // all other degenerate triangles will just copy a space from any good triangle
    // with the same welded index in piTriListIn[].
    DegenEpilogue(psTspace, pTriInfos, piTriListIn, pContext, iNrTrianglesIn, iTotTris);

    free(pTriInfos); free(piTriListIn);

    index = 0;
    for(f=0; f<iNrFaces; f++)
    {
        const int verts = pContext->m_pInterface->m_getNumVerticesOfFace(pContext, f);
        if(verts!=3 && verts!=4) continue;
        

        // I've decided to let degenerate triangles and group-with-anythings
        // vary between left/right hand coordinate systems at the vertices.
        // All healthy triangles on the other hand are built to always be either or.

        /*// force the coordinate system orientation to be uniform for every face.
        // (this is already the case for good triangles but not for
        // degenerate ones and those with bGroupWithAnything==true)
        bool bOrient = psTspace[index].bOrient;
        if(psTspace[index].iCounter == 0)   // tspace was not derived from a group
        {
            // look for a space created in GenerateTSpaces() by iCounter>0
            bool bNotFound = true;
            int i=1;
            while(i<verts && bNotFound)
            {
                if(psTspace[index+i].iCounter > 0) bNotFound=false;
                else ++i;
            }
            if(!bNotFound) bOrient = psTspace[index+i].bOrient;
        }*/

        // set data
        for(i=0; i<verts; i++)
        {
            const STSpace * pTSpace = &psTspace[index];
            float tang[] = {pTSpace->vOs.x, pTSpace->vOs.y, pTSpace->vOs.z};
            float bitang[] = {pTSpace->vOt.x, pTSpace->vOt.y, pTSpace->vOt.z};
            if(pContext->m_pInterface->m_setTSpace!=NULL)
                pContext->m_pInterface->m_setTSpace(pContext, tang, bitang, pTSpace->fMagS, pTSpace->fMagT, pTSpace->bOrient, f, i);
            if(pContext->m_pInterface->m_setTSpaceBasic!=NULL)
                pContext->m_pInterface->m_setTSpaceBasic(pContext, tang, pTSpace->bOrient==TTRUE ? 1.0f : (-1.0f), f, i);

            ++index;
        }
    }

    free(psTspace);

    
    return TTRUE;
}


typedef struct
{
    float vert[3];
    int index;
} STmpVert;

const int g_iCells = 2048;

#ifdef _MSC_VER
    #define NOINLINE __declspec(noinline)
#else
    #define NOINLINE __attribute__ ((noinline))
#endif

// it is IMPORTANT that this function is called to evaluate the hash since
// inlining could potentially reorder instructions and generate different
// results for the same effective input value fVal.
NOINLINE int FindGridCell(const float fMin, const float fMax, const float fVal)
{
    const float fIndex = g_iCells * ((fVal-fMin)/(fMax-fMin));
    const int iIndex = fIndex<0?0:((int)fIndex);
    return iIndex<g_iCells?iIndex:(g_iCells-1);
}

static void MergeVertsFast(int piTriList_in_and_out[], STmpVert pTmpVert[], const SMikkTSpaceContext * pContext, const int iL_in, const int iR_in);
static void MergeVertsSlow(int piTriList_in_and_out[], const SMikkTSpaceContext * pContext, const int pTable[], const int iEntries);
static void GenerateSharedVerticesIndexListSlow(int piTriList_in_and_out[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn);

static void GenerateSharedVerticesIndexList(int piTriList_in_and_out[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn)
{

    // Generate bounding box
    int * piHashTable=NULL, * piHashCount=NULL, * piHashOffsets=NULL, * piHashCount2=NULL;
    STmpVert * pTmpVert = NULL;
    int i=0, iChannel=0, k=0, e=0;
    int iMaxCount=0;
    SVec3 vMin = GetPosition(pContext, 0), vMax = vMin, vDim;
    float fMin, fMax;
    for(i=1; i<(iNrTrianglesIn*3); i++)
    {
        const int index = piTriList_in_and_out[i];

        const SVec3 vP = GetPosition(pContext, index);
        if(vMin.x > vP.x) vMin.x = vP.x;
        else if(vMax.x < vP.x) vMax.x = vP.x;
        if(vMin.y > vP.y) vMin.y = vP.y;
        else if(vMax.y < vP.y) vMax.y = vP.y;
        if(vMin.z > vP.z) vMin.z = vP.z;
        else if(vMax.z < vP.z) vMax.z = vP.z;
    }

    vDim = vsub(vMax,vMin);
    iChannel = 0;
    fMin = vMin.x; fMax=vMax.x;
    if(vDim.y>vDim.x && vDim.y>vDim.z)
    {
        iChannel=1;
        fMin = vMin.y, fMax=vMax.y;
    }
    else if(vDim.z>vDim.x)
    {
        iChannel=2;
        fMin = vMin.z, fMax=vMax.z;
    }

    // make allocations
    piHashTable = (int *) malloc(sizeof(int)*iNrTrianglesIn*3);
    piHashCount = (int *) malloc(sizeof(int)*g_iCells);
    piHashOffsets = (int *) malloc(sizeof(int)*g_iCells);
    piHashCount2 = (int *) malloc(sizeof(int)*g_iCells);

    if(piHashTable==NULL || piHashCount==NULL || piHashOffsets==NULL || piHashCount2==NULL)
    {
        if(piHashTable!=NULL) free(piHashTable);
        if(piHashCount!=NULL) free(piHashCount);
        if(piHashOffsets!=NULL) free(piHashOffsets);
        if(piHashCount2!=NULL) free(piHashCount2);
        GenerateSharedVerticesIndexListSlow(piTriList_in_and_out, pContext, iNrTrianglesIn);
        return;
    }
    memset(piHashCount, 0, sizeof(int)*g_iCells);
    memset(piHashCount2, 0, sizeof(int)*g_iCells);

    // count amount of elements in each cell unit
    for(i=0; i<(iNrTrianglesIn*3); i++)
    {
        const int index = piTriList_in_and_out[i];
        const SVec3 vP = GetPosition(pContext, index);
        const float fVal = iChannel==0 ? vP.x : (iChannel==1 ? vP.y : vP.z);
        const int iCell = FindGridCell(fMin, fMax, fVal);
        ++piHashCount[iCell];
    }

    // evaluate start index of each cell.
    piHashOffsets[0]=0;
    for(k=1; k<g_iCells; k++)
        piHashOffsets[k]=piHashOffsets[k-1]+piHashCount[k-1];

    // insert vertices
    for(i=0; i<(iNrTrianglesIn*3); i++)
    {
        const int index = piTriList_in_and_out[i];
        const SVec3 vP = GetPosition(pContext, index);
        const float fVal = iChannel==0 ? vP.x : (iChannel==1 ? vP.y : vP.z);
        const int iCell = FindGridCell(fMin, fMax, fVal);
        int * pTable = NULL;

        assert(piHashCount2[iCell]<piHashCount[iCell]);
        pTable = &piHashTable[piHashOffsets[iCell]];
        pTable[piHashCount2[iCell]] = i;    // vertex i has been inserted.
        ++piHashCount2[iCell];
    }
    for(k=0; k<g_iCells; k++)
        assert(piHashCount2[k] == piHashCount[k]);  // verify the count
    free(piHashCount2);

    // find maximum amount of entries in any hash entry
    iMaxCount = piHashCount[0];
    for(k=1; k<g_iCells; k++)
        if(iMaxCount<piHashCount[k])
            iMaxCount=piHashCount[k];
    pTmpVert = (STmpVert *) malloc(sizeof(STmpVert)*iMaxCount);
    

    // complete the merge
    for(k=0; k<g_iCells; k++)
    {
        // extract table of cell k and amount of entries in it
        int * pTable = &piHashTable[piHashOffsets[k]];
        const int iEntries = piHashCount[k];
        if(iEntries < 2) continue;

        if(pTmpVert!=NULL)
        {
            for(e=0; e<iEntries; e++)
            {
                int i = pTable[e];
                const SVec3 vP = GetPosition(pContext, piTriList_in_and_out[i]);
                pTmpVert[e].vert[0] = vP.x; pTmpVert[e].vert[1] = vP.y;
                pTmpVert[e].vert[2] = vP.z; pTmpVert[e].index = i;
            }
            MergeVertsFast(piTriList_in_and_out, pTmpVert, pContext, 0, iEntries-1);
        }
        else
            MergeVertsSlow(piTriList_in_and_out, pContext, pTable, iEntries);
    }

    if(pTmpVert!=NULL) { free(pTmpVert); }
    free(piHashTable);
    free(piHashCount);
    free(piHashOffsets);
}

static void MergeVertsFast(int piTriList_in_and_out[], STmpVert pTmpVert[], const SMikkTSpaceContext * pContext, const int iL_in, const int iR_in)
{
    // make bbox
    int c=0, l=0, channel=0;
    float fvMin[3], fvMax[3];
    float dx=0, dy=0, dz=0, fSep=0;
    for(c=0; c<3; c++)
    {   fvMin[c]=pTmpVert[iL_in].vert[c]; fvMax[c]=fvMin[c];    }
    for(l=(iL_in+1); l<=iR_in; l++)
        for(c=0; c<3; c++)
            if(fvMin[c]>pTmpVert[l].vert[c]) fvMin[c]=pTmpVert[l].vert[c];
            else if(fvMax[c]<pTmpVert[l].vert[c]) fvMax[c]=pTmpVert[l].vert[c];

    dx = fvMax[0]-fvMin[0];
    dy = fvMax[1]-fvMin[1];
    dz = fvMax[2]-fvMin[2];

    channel = 0;
    if(dy>dx && dy>dz) channel=1;
    else if(dz>dx) channel=2;

    fSep = 0.5f*(fvMax[channel]+fvMin[channel]);

    // terminate recursion when the separation/average value
    // is no longer strictly between fMin and fMax values.
    if(fSep>=fvMax[channel] || fSep<=fvMin[channel])
    {
        // complete the weld
        for(l=iL_in; l<=iR_in; l++)
        {
            int i = pTmpVert[l].index;
            const int index = piTriList_in_and_out[i];
            const SVec3 vP = GetPosition(pContext, index);
            const SVec3 vN = GetNormal(pContext, index);
            const SVec3 vT = GetTexCoord(pContext, index);

            tbool bNotFound = TTRUE;
            int l2=iL_in, i2rec=-1;
            while(l2<l && bNotFound)
            {
                const int i2 = pTmpVert[l2].index;
                const int index2 = piTriList_in_and_out[i2];
                const SVec3 vP2 = GetPosition(pContext, index2);
                const SVec3 vN2 = GetNormal(pContext, index2);
                const SVec3 vT2 = GetTexCoord(pContext, index2);
                i2rec=i2;

                //if(vP==vP2 && vN==vN2 && vT==vT2)
                if(vP.x==vP2.x && vP.y==vP2.y && vP.z==vP2.z &&
                    vN.x==vN2.x && vN.y==vN2.y && vN.z==vN2.z &&
                    vT.x==vT2.x && vT.y==vT2.y && vT.z==vT2.z)
                    bNotFound = TFALSE;
                else
                    ++l2;
            }
            
            // merge if previously found
            if(!bNotFound)
                piTriList_in_and_out[i] = piTriList_in_and_out[i2rec];
        }
    }
    else
    {
        int iL=iL_in, iR=iR_in;
        assert((iR_in-iL_in)>0);    // at least 2 entries

        // separate (by fSep) all points between iL_in and iR_in in pTmpVert[]
        while(iL < iR)
        {
            tbool bReadyLeftSwap = TFALSE, bReadyRightSwap = TFALSE;
            while((!bReadyLeftSwap) && iL<iR)
            {
                assert(iL>=iL_in && iL<=iR_in);
                bReadyLeftSwap = !(pTmpVert[iL].vert[channel]<fSep);
                if(!bReadyLeftSwap) ++iL;
            }
            while((!bReadyRightSwap) && iL<iR)
            {
                assert(iR>=iL_in && iR<=iR_in);
                bReadyRightSwap = pTmpVert[iR].vert[channel]<fSep;
                if(!bReadyRightSwap) --iR;
            }
            assert( (iL<iR) || !(bReadyLeftSwap && bReadyRightSwap) );

            if(bReadyLeftSwap && bReadyRightSwap)
            {
                const STmpVert sTmp = pTmpVert[iL];
                assert(iL<iR);
                pTmpVert[iL] = pTmpVert[iR];
                pTmpVert[iR] = sTmp;
                ++iL; --iR;
            }
        }

        assert(iL==(iR+1) || (iL==iR));
        if(iL==iR)
        {
            const tbool bReadyRightSwap = pTmpVert[iR].vert[channel]<fSep;
            if(bReadyRightSwap) ++iL;
            else --iR;
        }

        // only need to weld when there is more than 1 instance of the (x,y,z)
        if(iL_in < iR)
            MergeVertsFast(piTriList_in_and_out, pTmpVert, pContext, iL_in, iR);    // weld all left of fSep
        if(iL < iR_in)
            MergeVertsFast(piTriList_in_and_out, pTmpVert, pContext, iL, iR_in);    // weld all right of (or equal to) fSep
    }
}

static void MergeVertsSlow(int piTriList_in_and_out[], const SMikkTSpaceContext * pContext, const int pTable[], const int iEntries)
{
    // this can be optimized further using a tree structure or more hashing.
    int e=0;
    for(e=0; e<iEntries; e++)
    {
        int i = pTable[e];
        const int index = piTriList_in_and_out[i];
        const SVec3 vP = GetPosition(pContext, index);
        const SVec3 vN = GetNormal(pContext, index);
        const SVec3 vT = GetTexCoord(pContext, index);

        tbool bNotFound = TTRUE;
        int e2=0, i2rec=-1;
        while(e2<e && bNotFound)
        {
            const int i2 = pTable[e2];
            const int index2 = piTriList_in_and_out[i2];
            const SVec3 vP2 = GetPosition(pContext, index2);
            const SVec3 vN2 = GetNormal(pContext, index2);
            const SVec3 vT2 = GetTexCoord(pContext, index2);
            i2rec = i2;

            if(veq(vP,vP2) && veq(vN,vN2) && veq(vT,vT2))
                bNotFound = TFALSE;
            else
                ++e2;
        }
        
        // merge if previously found
        if(!bNotFound)
            piTriList_in_and_out[i] = piTriList_in_and_out[i2rec];
    }
}

static void GenerateSharedVerticesIndexListSlow(int piTriList_in_and_out[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn)
{
    int iNumUniqueVerts = 0, t=0, i=0;
    for(t=0; t<iNrTrianglesIn; t++)
    {
        for(i=0; i<3; i++)
        {
            const int offs = t*3 + i;
            const int index = piTriList_in_and_out[offs];

            const SVec3 vP = GetPosition(pContext, index);
            const SVec3 vN = GetNormal(pContext, index);
            const SVec3 vT = GetTexCoord(pContext, index);

            tbool bFound = TFALSE;
            int t2=0, index2rec=-1;
            while(!bFound && t2<=t)
            {
                int j=0;
                while(!bFound && j<3)
                {
                    const int index2 = piTriList_in_and_out[t2*3 + j];
                    const SVec3 vP2 = GetPosition(pContext, index2);
                    const SVec3 vN2 = GetNormal(pContext, index2);
                    const SVec3 vT2 = GetTexCoord(pContext, index2);
                    
                    if(veq(vP,vP2) && veq(vN,vN2) && veq(vT,vT2))
                        bFound = TTRUE;
                    else
                        ++j;
                }
                if(!bFound) ++t2;
            }

            assert(bFound);
            // if we found our own
            if(index2rec == index) { ++iNumUniqueVerts; }

            piTriList_in_and_out[offs] = index2rec;
        }
    }
}

static int GenerateInitialVerticesIndexList(STriInfo pTriInfos[], int piTriList_out[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn)
{
    int iTSpacesOffs = 0, f=0, t=0;
    int iDstTriIndex = 0;
    for(f=0; f<pContext->m_pInterface->m_getNumFaces(pContext); f++)
    {
        const int verts = pContext->m_pInterface->m_getNumVerticesOfFace(pContext, f);
        if(verts!=3 && verts!=4) continue;

        pTriInfos[iDstTriIndex].iOrgFaceNumber = f;
        pTriInfos[iDstTriIndex].iTSpacesOffs = iTSpacesOffs;

        if(verts==3)
        {
            unsigned char * pVerts = pTriInfos[iDstTriIndex].vert_num;
            pVerts[0]=0; pVerts[1]=1; pVerts[2]=2;
            piTriList_out[iDstTriIndex*3+0] = MakeIndex(f, 0);
            piTriList_out[iDstTriIndex*3+1] = MakeIndex(f, 1);
            piTriList_out[iDstTriIndex*3+2] = MakeIndex(f, 2);
            ++iDstTriIndex; // next
        }
        else
        {
            {
                pTriInfos[iDstTriIndex+1].iOrgFaceNumber = f;
                pTriInfos[iDstTriIndex+1].iTSpacesOffs = iTSpacesOffs;
            }

            {
                // need an order independent way to evaluate
                // tspace on quads. This is done by splitting
                // along the shortest diagonal.
                const int i0 = MakeIndex(f, 0);
                const int i1 = MakeIndex(f, 1);
                const int i2 = MakeIndex(f, 2);
                const int i3 = MakeIndex(f, 3);
                const SVec3 T0 = GetTexCoord(pContext, i0);
                const SVec3 T1 = GetTexCoord(pContext, i1);
                const SVec3 T2 = GetTexCoord(pContext, i2);
                const SVec3 T3 = GetTexCoord(pContext, i3);
                const float distSQ_02 = LengthSquared(vsub(T2,T0));
                const float distSQ_13 = LengthSquared(vsub(T3,T1));
                tbool bQuadDiagIs_02;
                if(distSQ_02<distSQ_13)
                    bQuadDiagIs_02 = TTRUE;
                else if(distSQ_13<distSQ_02)
                    bQuadDiagIs_02 = TFALSE;
                else
                {
                    const SVec3 P0 = GetPosition(pContext, i0);
                    const SVec3 P1 = GetPosition(pContext, i1);
                    const SVec3 P2 = GetPosition(pContext, i2);
                    const SVec3 P3 = GetPosition(pContext, i3);
                    const float distSQ_02 = LengthSquared(vsub(P2,P0));
                    const float distSQ_13 = LengthSquared(vsub(P3,P1));

                    bQuadDiagIs_02 = distSQ_13<distSQ_02 ? TFALSE : TTRUE;
                }

                if(bQuadDiagIs_02)
                {
                    {
                        unsigned char * pVerts_A = pTriInfos[iDstTriIndex].vert_num;
                        pVerts_A[0]=0; pVerts_A[1]=1; pVerts_A[2]=2;
                    }
                    piTriList_out[iDstTriIndex*3+0] = i0;
                    piTriList_out[iDstTriIndex*3+1] = i1;
                    piTriList_out[iDstTriIndex*3+2] = i2;
                    ++iDstTriIndex; // next
                    {
                        unsigned char * pVerts_B = pTriInfos[iDstTriIndex].vert_num;
                        pVerts_B[0]=0; pVerts_B[1]=2; pVerts_B[2]=3;
                    }
                    piTriList_out[iDstTriIndex*3+0] = i0;
                    piTriList_out[iDstTriIndex*3+1] = i2;
                    piTriList_out[iDstTriIndex*3+2] = i3;
                    ++iDstTriIndex; // next
                }
                else
                {
                    {
                        unsigned char * pVerts_A = pTriInfos[iDstTriIndex].vert_num;
                        pVerts_A[0]=0; pVerts_A[1]=1; pVerts_A[2]=3;
                    }
                    piTriList_out[iDstTriIndex*3+0] = i0;
                    piTriList_out[iDstTriIndex*3+1] = i1;
                    piTriList_out[iDstTriIndex*3+2] = i3;
                    ++iDstTriIndex; // next
                    {
                        unsigned char * pVerts_B = pTriInfos[iDstTriIndex].vert_num;
                        pVerts_B[0]=1; pVerts_B[1]=2; pVerts_B[2]=3;
                    }
                    piTriList_out[iDstTriIndex*3+0] = i1;
                    piTriList_out[iDstTriIndex*3+1] = i2;
                    piTriList_out[iDstTriIndex*3+2] = i3;
                    ++iDstTriIndex; // next
                }
            }
        }

        iTSpacesOffs += verts;
        assert(iDstTriIndex<=iNrTrianglesIn);
    }

    for(t=0; t<iNrTrianglesIn; t++)
        pTriInfos[t].iFlag = 0;

    // return total amount of tspaces
    return iTSpacesOffs;
}

static SVec3 GetPosition(const SMikkTSpaceContext * pContext, const int index)
{
    int iF, iI;
    SVec3 res; float pos[3];
    IndexToData(&iF, &iI, index);
    pContext->m_pInterface->m_getPosition(pContext, pos, iF, iI);
    res.x=pos[0]; res.y=pos[1]; res.z=pos[2];
    return res;
}

static SVec3 GetNormal(const SMikkTSpaceContext * pContext, const int index)
{
    int iF, iI;
    SVec3 res; float norm[3];
    IndexToData(&iF, &iI, index);
    pContext->m_pInterface->m_getNormal(pContext, norm, iF, iI);
    res.x=norm[0]; res.y=norm[1]; res.z=norm[2];
    return res;
}

static SVec3 GetTexCoord(const SMikkTSpaceContext * pContext, const int index)
{
    int iF, iI;
    SVec3 res; float texc[2];
    IndexToData(&iF, &iI, index);
    pContext->m_pInterface->m_getTexCoord(pContext, texc, iF, iI);
    res.x=texc[0]; res.y=texc[1]; res.z=1.0f;
    return res;
}


typedef union
{
    struct
    {
        int i0, i1, f;
    };
    int array[3];
} SEdge;

static void BuildNeighborsFast(STriInfo pTriInfos[], SEdge * pEdges, const int piTriListIn[], const int iNrTrianglesIn);
static void BuildNeighborsSlow(STriInfo pTriInfos[], const int piTriListIn[], const int iNrTrianglesIn);

// returns the texture area times 2
static float CalcTexArea(const SMikkTSpaceContext * pContext, const int indices[])
{
    const SVec3 t1 = GetTexCoord(pContext, indices[0]);
    const SVec3 t2 = GetTexCoord(pContext, indices[1]);
    const SVec3 t3 = GetTexCoord(pContext, indices[2]);

    const float t21x = t2.x-t1.x;
    const float t21y = t2.y-t1.y;
    const float t31x = t3.x-t1.x;
    const float t31y = t3.y-t1.y;

    const float fSignedAreaSTx2 = t21x*t31y - t21y*t31x;

    return fSignedAreaSTx2<0 ? (-fSignedAreaSTx2) : fSignedAreaSTx2;
}

static void InitTriInfo(STriInfo pTriInfos[], const int piTriListIn[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn)
{
    int f=0, i=0, t=0;
    // pTriInfos[f].iFlag is cleared in GenerateInitialVerticesIndexList() which is called before this function.

    // generate neighbor info list
    for(f=0; f<iNrTrianglesIn; f++)
        for(i=0; i<3; i++)
        {
            pTriInfos[f].FaceNeighbors[i] = -1;
            pTriInfos[f].AssignedGroup[i] = NULL;

            pTriInfos[f].vOs.x=0.0f; pTriInfos[f].vOs.y=0.0f; pTriInfos[f].vOs.z=0.0f;
            pTriInfos[f].vOt.x=0.0f; pTriInfos[f].vOt.y=0.0f; pTriInfos[f].vOt.z=0.0f;
            pTriInfos[f].fMagS = 0;
            pTriInfos[f].fMagT = 0;

            // assumed bad
            pTriInfos[f].iFlag |= GROUP_WITH_ANY;
        }

    // evaluate first order derivatives
    for(f=0; f<iNrTrianglesIn; f++)
    {
        // initial values
        const SVec3 v1 = GetPosition(pContext, piTriListIn[f*3+0]);
        const SVec3 v2 = GetPosition(pContext, piTriListIn[f*3+1]);
        const SVec3 v3 = GetPosition(pContext, piTriListIn[f*3+2]);
        const SVec3 t1 = GetTexCoord(pContext, piTriListIn[f*3+0]);
        const SVec3 t2 = GetTexCoord(pContext, piTriListIn[f*3+1]);
        const SVec3 t3 = GetTexCoord(pContext, piTriListIn[f*3+2]);

        const float t21x = t2.x-t1.x;
        const float t21y = t2.y-t1.y;
        const float t31x = t3.x-t1.x;
        const float t31y = t3.y-t1.y;
        const SVec3 d1 = vsub(v2,v1);
        const SVec3 d2 = vsub(v3,v1);

        const float fSignedAreaSTx2 = t21x*t31y - t21y*t31x;
        //assert(fSignedAreaSTx2!=0);
        SVec3 vOs = vsub(vscale(t31y,d1), vscale(t21y,d2)); // eq 18
        SVec3 vOt = vadd(vscale(-t31x,d1), vscale(t21x,d2)); // eq 19

        pTriInfos[f].iFlag |= (fSignedAreaSTx2>0 ? ORIENT_PRESERVING : 0);

        if( NotZero(fSignedAreaSTx2) )
        {
            const float fAbsArea = fabsf(fSignedAreaSTx2);
            const float fLenOs = Length(vOs);
            const float fLenOt = Length(vOt);
            const float fS = (pTriInfos[f].iFlag&ORIENT_PRESERVING)==0 ? (-1.0f) : 1.0f;
            if( NotZero(fLenOs) ) pTriInfos[f].vOs = vscale(fS/fLenOs, vOs);
            if( NotZero(fLenOt) ) pTriInfos[f].vOt = vscale(fS/fLenOt, vOt);

            // evaluate magnitudes prior to normalization of vOs and vOt
            pTriInfos[f].fMagS = fLenOs / fAbsArea;
            pTriInfos[f].fMagT = fLenOt / fAbsArea;

            // if this is a good triangle
            if( NotZero(pTriInfos[f].fMagS) && NotZero(pTriInfos[f].fMagT))
                pTriInfos[f].iFlag &= (~GROUP_WITH_ANY);
        }
    }

    // force otherwise healthy quads to a fixed orientation
    while(t<(iNrTrianglesIn-1))
    {
        const int iFO_a = pTriInfos[t].iOrgFaceNumber;
        const int iFO_b = pTriInfos[t+1].iOrgFaceNumber;
        if(iFO_a==iFO_b)    // this is a quad
        {
            const tbool bIsDeg_a = (pTriInfos[t].iFlag&MARK_DEGENERATE)!=0 ? TTRUE : TFALSE;
            const tbool bIsDeg_b = (pTriInfos[t+1].iFlag&MARK_DEGENERATE)!=0 ? TTRUE : TFALSE;
            
            // bad triangles should already have been removed by
            // DegenPrologue(), but just in case check bIsDeg_a and bIsDeg_a are false
            if((bIsDeg_a||bIsDeg_b)==TFALSE)
            {
                const tbool bOrientA = (pTriInfos[t].iFlag&ORIENT_PRESERVING)!=0 ? TTRUE : TFALSE;
                const tbool bOrientB = (pTriInfos[t+1].iFlag&ORIENT_PRESERVING)!=0 ? TTRUE : TFALSE;
                // if this happens the quad has extremely bad mapping!!
                if(bOrientA!=bOrientB)
                {
                    //printf("found quad with bad mapping\n");
                    tbool bChooseOrientFirstTri = TFALSE;
                    if((pTriInfos[t+1].iFlag&GROUP_WITH_ANY)!=0) bChooseOrientFirstTri = TTRUE;
                    else if( CalcTexArea(pContext, &piTriListIn[t*3+0]) >= CalcTexArea(pContext, &piTriListIn[(t+1)*3+0]) )
                        bChooseOrientFirstTri = TTRUE;

                    // force match
                    {
                        const int t0 = bChooseOrientFirstTri ? t : (t+1);
                        const int t1 = bChooseOrientFirstTri ? (t+1) : t;
                        pTriInfos[t1].iFlag &= (~ORIENT_PRESERVING);    // clear first
                        pTriInfos[t1].iFlag |= (pTriInfos[t0].iFlag&ORIENT_PRESERVING); // copy bit
                    }
                }
            }
            t += 2;
        }
        else
            ++t;
    }
    
    // match up edge pairs
    {
        SEdge * pEdges = (SEdge *) malloc(sizeof(SEdge)*iNrTrianglesIn*3);
        if(pEdges==NULL)
            BuildNeighborsSlow(pTriInfos, piTriListIn, iNrTrianglesIn);
        else
        {
            BuildNeighborsFast(pTriInfos, pEdges, piTriListIn, iNrTrianglesIn);
    
            free(pEdges);
        }
    }
}


static tbool AssignRecur(const int piTriListIn[], STriInfo psTriInfos[], const int iMyTriIndex, SGroup * pGroup);
static void AddTriToGroup(SGroup * pGroup, const int iTriIndex);

static int Build4RuleGroups(STriInfo pTriInfos[], SGroup pGroups[], int piGroupTrianglesBuffer[], const int piTriListIn[], const int iNrTrianglesIn)
{
    const int iNrMaxGroups = iNrTrianglesIn*3;
    int iNrActiveGroups = 0;
    int iOffset = 0, f=0, i=0;
    for(f=0; f<iNrTrianglesIn; f++)
    {
        for(i=0; i<3; i++)
        {
            // if not assigned to a group
            if((pTriInfos[f].iFlag&GROUP_WITH_ANY)==0 && pTriInfos[f].AssignedGroup[i]==NULL)
            {
                tbool bOrPre;
                int neigh_indexL, neigh_indexR;
                const int vert_index = piTriListIn[f*3+i];
                assert(iNrActiveGroups<iNrMaxGroups);
                pTriInfos[f].AssignedGroup[i] = &pGroups[iNrActiveGroups];
                pTriInfos[f].AssignedGroup[i]->iVertexRepresentitive = vert_index;
                pTriInfos[f].AssignedGroup[i]->bOrientPreservering = (pTriInfos[f].iFlag&ORIENT_PRESERVING)!=0;
                pTriInfos[f].AssignedGroup[i]->iNrFaces = 0;
                pTriInfos[f].AssignedGroup[i]->pFaceIndices = &piGroupTrianglesBuffer[iOffset];
                ++iNrActiveGroups;

                AddTriToGroup(pTriInfos[f].AssignedGroup[i], f);
                bOrPre = (pTriInfos[f].iFlag&ORIENT_PRESERVING)!=0 ? TTRUE : TFALSE;
                neigh_indexL = pTriInfos[f].FaceNeighbors[i];
                neigh_indexR = pTriInfos[f].FaceNeighbors[i>0?(i-1):2];
                if(neigh_indexL>=0) // neighbor
                {
                    const tbool bAnswer =
                        AssignRecur(piTriListIn, pTriInfos, neigh_indexL,
                                    pTriInfos[f].AssignedGroup[i] );
                    
                    const tbool bOrPre2 = (pTriInfos[neigh_indexL].iFlag&ORIENT_PRESERVING)!=0 ? TTRUE : TFALSE;
                    const tbool bDiff = bOrPre!=bOrPre2 ? TTRUE : TFALSE;
                    assert(bAnswer || bDiff);
                }
                if(neigh_indexR>=0) // neighbor
                {
                    const tbool bAnswer =
                        AssignRecur(piTriListIn, pTriInfos, neigh_indexR,
                                    pTriInfos[f].AssignedGroup[i] );

                    const tbool bOrPre2 = (pTriInfos[neigh_indexR].iFlag&ORIENT_PRESERVING)!=0 ? TTRUE : TFALSE;
                    const tbool bDiff = bOrPre!=bOrPre2 ? TTRUE : TFALSE;
                    assert(bAnswer || bDiff);
                }

                // update offset
                iOffset += pTriInfos[f].AssignedGroup[i]->iNrFaces;
                // since the groups are disjoint a triangle can never
                // belong to more than 3 groups. Subsequently something
                // is completely screwed if this assertion ever hits.
                assert(iOffset <= iNrMaxGroups);
            }
        }
    }

    return iNrActiveGroups;
}

static void AddTriToGroup(SGroup * pGroup, const int iTriIndex)
{
    pGroup->pFaceIndices[pGroup->iNrFaces] = iTriIndex;
    ++pGroup->iNrFaces;
}

static tbool AssignRecur(const int piTriListIn[], STriInfo psTriInfos[],
                 const int iMyTriIndex, SGroup * pGroup)
{
    STriInfo * pMyTriInfo = &psTriInfos[iMyTriIndex];

    // track down vertex
    const int iVertRep = pGroup->iVertexRepresentitive;
    const int * pVerts = &piTriListIn[3*iMyTriIndex+0];
    int i=-1;
    if(pVerts[0]==iVertRep) i=0;
    else if(pVerts[1]==iVertRep) i=1;
    else if(pVerts[2]==iVertRep) i=2;
    assert(i>=0 && i<3);

    // early out
    if(pMyTriInfo->AssignedGroup[i] == pGroup) return TTRUE;
    else if(pMyTriInfo->AssignedGroup[i]!=NULL) return TFALSE;
    if((pMyTriInfo->iFlag&GROUP_WITH_ANY)!=0)
    {
        // first to group with a group-with-anything triangle
        // determines it's orientation.
        // This is the only existing order dependency in the code!!
        if( pMyTriInfo->AssignedGroup[0] == NULL &&
            pMyTriInfo->AssignedGroup[1] == NULL &&
            pMyTriInfo->AssignedGroup[2] == NULL )
        {
            pMyTriInfo->iFlag &= (~ORIENT_PRESERVING);
            pMyTriInfo->iFlag |= (pGroup->bOrientPreservering ? ORIENT_PRESERVING : 0);
        }
    }
    {
        const tbool bOrient = (pMyTriInfo->iFlag&ORIENT_PRESERVING)!=0 ? TTRUE : TFALSE;
        if(bOrient != pGroup->bOrientPreservering) return TFALSE;
    }

    AddTriToGroup(pGroup, iMyTriIndex);
    pMyTriInfo->AssignedGroup[i] = pGroup;

    {
        const int neigh_indexL = pMyTriInfo->FaceNeighbors[i];
        const int neigh_indexR = pMyTriInfo->FaceNeighbors[i>0?(i-1):2];
        if(neigh_indexL>=0)
            AssignRecur(piTriListIn, psTriInfos, neigh_indexL, pGroup);
        if(neigh_indexR>=0)
            AssignRecur(piTriListIn, psTriInfos, neigh_indexR, pGroup);
    }



    return TTRUE;
}


static tbool CompareSubGroups(const SSubGroup * pg1, const SSubGroup * pg2);
static void QuickSort(int* pSortBuffer, int iLeft, int iRight, unsigned int uSeed);
static STSpace EvalTspace(int face_indices[], const int iFaces, const int piTriListIn[], const STriInfo pTriInfos[], const SMikkTSpaceContext * pContext, const int iVertexRepresentitive);

static tbool GenerateTSpaces(STSpace psTspace[], const STriInfo pTriInfos[], const SGroup pGroups[],
                             const int iNrActiveGroups, const int piTriListIn[], const float fThresCos,
                             const SMikkTSpaceContext * pContext)
{
    STSpace * pSubGroupTspace = NULL;
    SSubGroup * pUniSubGroups = NULL;
    int * pTmpMembers = NULL;
    int iMaxNrFaces=0, iUniqueTspaces=0, g=0, i=0;
    for(g=0; g<iNrActiveGroups; g++)
        if(iMaxNrFaces < pGroups[g].iNrFaces)
            iMaxNrFaces = pGroups[g].iNrFaces;

    if(iMaxNrFaces == 0) return TTRUE;

    // make initial allocations
    pSubGroupTspace = (STSpace *) malloc(sizeof(STSpace)*iMaxNrFaces);
    pUniSubGroups = (SSubGroup *) malloc(sizeof(SSubGroup)*iMaxNrFaces);
    pTmpMembers = (int *) malloc(sizeof(int)*iMaxNrFaces);
    if(pSubGroupTspace==NULL || pUniSubGroups==NULL || pTmpMembers==NULL)
    {
        if(pSubGroupTspace!=NULL) free(pSubGroupTspace);    
        if(pUniSubGroups!=NULL) free(pUniSubGroups);    
        if(pTmpMembers!=NULL) free(pTmpMembers);    
        return TFALSE;
    }


    iUniqueTspaces = 0;
    for(g=0; g<iNrActiveGroups; g++)
    {
        const SGroup * pGroup = &pGroups[g];
        int iUniqueSubGroups = 0, s=0;

        for(i=0; i<pGroup->iNrFaces; i++)   // triangles
        {
            const int f = pGroup->pFaceIndices[i];  // triangle number
            int index=-1, iVertIndex=-1, iOF_1=-1, iMembers=0, j=0, l=0;
            SSubGroup tmp_group;
            tbool bFound;
            SVec3 n, vOs, vOt;
            if(pTriInfos[f].AssignedGroup[0]==pGroup) index=0;
            else if(pTriInfos[f].AssignedGroup[1]==pGroup) index=1;
            else if(pTriInfos[f].AssignedGroup[2]==pGroup) index=2;
            assert(index>=0 && index<3);

            iVertIndex = piTriListIn[f*3+index];
            assert(iVertIndex==pGroup->iVertexRepresentitive);

            // is normalized already
            n = GetNormal(pContext, iVertIndex);
            
            // project
            vOs = vsub(pTriInfos[f].vOs, vscale(vdot(n,pTriInfos[f].vOs), n));
            vOt = vsub(pTriInfos[f].vOt, vscale(vdot(n,pTriInfos[f].vOt), n));
            if( VNotZero(vOs) ) vOs = Normalize(vOs);
            if( VNotZero(vOt) ) vOt = Normalize(vOt);

            // original face number
            iOF_1 = pTriInfos[f].iOrgFaceNumber;
            
            iMembers = 0;
            for(j=0; j<pGroup->iNrFaces; j++)
            {
                const int t = pGroup->pFaceIndices[j];  // triangle number
                const int iOF_2 = pTriInfos[t].iOrgFaceNumber;

                // project
                SVec3 vOs2 = vsub(pTriInfos[t].vOs, vscale(vdot(n,pTriInfos[t].vOs), n));
                SVec3 vOt2 = vsub(pTriInfos[t].vOt, vscale(vdot(n,pTriInfos[t].vOt), n));
                if( VNotZero(vOs2) ) vOs2 = Normalize(vOs2);
                if( VNotZero(vOt2) ) vOt2 = Normalize(vOt2);

                {
                    const tbool bAny = ( (pTriInfos[f].iFlag | pTriInfos[t].iFlag) & GROUP_WITH_ANY )!=0 ? TTRUE : TFALSE;
                    // make sure triangles which belong to the same quad are joined.
                    const tbool bSameOrgFace = iOF_1==iOF_2 ? TTRUE : TFALSE;

                    const float fCosS = vdot(vOs,vOs2);
                    const float fCosT = vdot(vOt,vOt2);

                    assert(f!=t || bSameOrgFace);   // sanity check
                    if(bAny || bSameOrgFace || (fCosS>fThresCos && fCosT>fThresCos))
                        pTmpMembers[iMembers++] = t;
                }
            }

            // sort pTmpMembers
            tmp_group.iNrFaces = iMembers;
            tmp_group.pTriMembers = pTmpMembers;
            if(iMembers>1)
            {
                unsigned int uSeed = INTERNAL_RND_SORT_SEED;    // could replace with a random seed?
                QuickSort(pTmpMembers, 0, iMembers-1, uSeed);
            }

            // look for an existing match
            bFound = TFALSE;
            l=0;
            while(l<iUniqueSubGroups && !bFound)
            {
                bFound = CompareSubGroups(&tmp_group, &pUniSubGroups[l]);
                if(!bFound) ++l;
            }
            
            // assign tangent space index
            assert(bFound || l==iUniqueSubGroups);
            //piTempTangIndices[f*3+index] = iUniqueTspaces+l;

            // if no match was found we allocate a new subgroup
            if(!bFound)
            {
                // insert new subgroup
                int * pIndices = (int *) malloc(sizeof(int)*iMembers);
                if(pIndices==NULL)
                {
                    // clean up and return false
                    int s=0;
                    for(s=0; s<iUniqueSubGroups; s++)
                        free(pUniSubGroups[s].pTriMembers);
                    free(pUniSubGroups);
                    free(pTmpMembers);
                    free(pSubGroupTspace);
                    return TFALSE;
                }
                pUniSubGroups[iUniqueSubGroups].iNrFaces = iMembers;
                pUniSubGroups[iUniqueSubGroups].pTriMembers = pIndices;
                memcpy(pIndices, tmp_group.pTriMembers, iMembers*sizeof(int));
                pSubGroupTspace[iUniqueSubGroups] =
                    EvalTspace(tmp_group.pTriMembers, iMembers, piTriListIn, pTriInfos, pContext, pGroup->iVertexRepresentitive);
                ++iUniqueSubGroups;
            }

            // output tspace
            {
                const int iOffs = pTriInfos[f].iTSpacesOffs;
                const int iVert = pTriInfos[f].vert_num[index];
                STSpace * pTS_out = &psTspace[iOffs+iVert];
                assert(pTS_out->iCounter<2);
                assert(((pTriInfos[f].iFlag&ORIENT_PRESERVING)!=0) == pGroup->bOrientPreservering);
                if(pTS_out->iCounter==1)
                {
                    *pTS_out = AvgTSpace(pTS_out, &pSubGroupTspace[l]);
                    pTS_out->iCounter = 2;  // update counter
                    pTS_out->bOrient = pGroup->bOrientPreservering;
                }
                else
                {
                    assert(pTS_out->iCounter==0);
                    *pTS_out = pSubGroupTspace[l];
                    pTS_out->iCounter = 1;  // update counter
                    pTS_out->bOrient = pGroup->bOrientPreservering;
                }
            }
        }

        // clean up and offset iUniqueTspaces
        for(s=0; s<iUniqueSubGroups; s++)
            free(pUniSubGroups[s].pTriMembers);
        iUniqueTspaces += iUniqueSubGroups;
    }

    // clean up
    free(pUniSubGroups);
    free(pTmpMembers);
    free(pSubGroupTspace);

    return TTRUE;
}

static STSpace EvalTspace(int face_indices[], const int iFaces, const int piTriListIn[], const STriInfo pTriInfos[],
                          const SMikkTSpaceContext * pContext, const int iVertexRepresentitive)
{
    STSpace res;
    float fAngleSum = 0;
    int face=0;
    res.vOs.x=0.0f; res.vOs.y=0.0f; res.vOs.z=0.0f;
    res.vOt.x=0.0f; res.vOt.y=0.0f; res.vOt.z=0.0f;
    res.fMagS = 0; res.fMagT = 0;

    for(face=0; face<iFaces; face++)
    {
        const int f = face_indices[face];

        // only valid triangles get to add their contribution
        if( (pTriInfos[f].iFlag&GROUP_WITH_ANY)==0 )
        {
            SVec3 n, vOs, vOt, p0, p1, p2, v1, v2;
            float fCos, fAngle, fMagS, fMagT;
            int i=-1, index=-1, i0=-1, i1=-1, i2=-1;
            if(piTriListIn[3*f+0]==iVertexRepresentitive) i=0;
            else if(piTriListIn[3*f+1]==iVertexRepresentitive) i=1;
            else if(piTriListIn[3*f+2]==iVertexRepresentitive) i=2;
            assert(i>=0 && i<3);

            // project
            index = piTriListIn[3*f+i];
            n = GetNormal(pContext, index);
            vOs = vsub(pTriInfos[f].vOs, vscale(vdot(n,pTriInfos[f].vOs), n));
            vOt = vsub(pTriInfos[f].vOt, vscale(vdot(n,pTriInfos[f].vOt), n));
            if( VNotZero(vOs) ) vOs = Normalize(vOs);
            if( VNotZero(vOt) ) vOt = Normalize(vOt);

            i2 = piTriListIn[3*f + (i<2?(i+1):0)];
            i1 = piTriListIn[3*f + i];
            i0 = piTriListIn[3*f + (i>0?(i-1):2)];

            p0 = GetPosition(pContext, i0);
            p1 = GetPosition(pContext, i1);
            p2 = GetPosition(pContext, i2);
            v1 = vsub(p0,p1);
            v2 = vsub(p2,p1);

            // project
            v1 = vsub(v1, vscale(vdot(n,v1),n)); if( VNotZero(v1) ) v1 = Normalize(v1);
            v2 = vsub(v2, vscale(vdot(n,v2),n)); if( VNotZero(v2) ) v2 = Normalize(v2);

            // weight contribution by the angle
            // between the two edge vectors
            fCos = vdot(v1,v2); fCos=fCos>1?1:(fCos<(-1) ? (-1) : fCos);
            fAngle = (float) acos(fCos);
            fMagS = pTriInfos[f].fMagS;
            fMagT = pTriInfos[f].fMagT;

            res.vOs=vadd(res.vOs, vscale(fAngle,vOs));
            res.vOt=vadd(res.vOt,vscale(fAngle,vOt));
            res.fMagS+=(fAngle*fMagS);
            res.fMagT+=(fAngle*fMagT);
            fAngleSum += fAngle;
        }
    }

    // normalize
    if( VNotZero(res.vOs) ) res.vOs = Normalize(res.vOs);
    if( VNotZero(res.vOt) ) res.vOt = Normalize(res.vOt);
    if(fAngleSum>0)
    {
        res.fMagS /= fAngleSum;
        res.fMagT /= fAngleSum;
    }

    return res;
}

static tbool CompareSubGroups(const SSubGroup * pg1, const SSubGroup * pg2)
{
    tbool bStillSame=TTRUE;
    int i=0;
    if(pg1->iNrFaces!=pg2->iNrFaces) return TFALSE;
    while(i<pg1->iNrFaces && bStillSame)
    {
        bStillSame = pg1->pTriMembers[i]==pg2->pTriMembers[i] ? TTRUE : TFALSE;
        if(bStillSame) ++i;
    }
    return bStillSame;
}

static void QuickSort(int* pSortBuffer, int iLeft, int iRight, unsigned int uSeed)
{
    int iL, iR, n, index, iMid, iTmp;

    // Random
    unsigned int t=uSeed&31;
    t=(uSeed<<t)|(uSeed>>(32-t));
    uSeed=uSeed+t+3;
    // Random end

    iL=iLeft; iR=iRight;
    n = (iR-iL)+1;
    assert(n>=0);
    index = (int) (uSeed%n);

    iMid=pSortBuffer[index + iL];


    do
    {
        while(pSortBuffer[iL] < iMid)
            ++iL;
        while(pSortBuffer[iR] > iMid)
            --iR;

        if(iL <= iR)
        {
            iTmp = pSortBuffer[iL];
            pSortBuffer[iL] = pSortBuffer[iR];
            pSortBuffer[iR] = iTmp;
            ++iL; --iR;
        }
    }
    while(iL <= iR);

    if(iLeft < iR)
        QuickSort(pSortBuffer, iLeft, iR, uSeed);
    if(iL < iRight)
        QuickSort(pSortBuffer, iL, iRight, uSeed);
}


static void QuickSortEdges(SEdge * pSortBuffer, int iLeft, int iRight, const int channel, unsigned int uSeed);
static void GetEdge(int * i0_out, int * i1_out, int * edgenum_out, const int indices[], const int i0_in, const int i1_in);

static void BuildNeighborsFast(STriInfo pTriInfos[], SEdge * pEdges, const int piTriListIn[], const int iNrTrianglesIn)
{
    // build array of edges
    unsigned int uSeed = INTERNAL_RND_SORT_SEED;                // could replace with a random seed?
    int iEntries=0, iCurStartIndex=-1, f=0, i=0;
    for(f=0; f<iNrTrianglesIn; f++)
        for(i=0; i<3; i++)
        {
            const int i0 = piTriListIn[f*3+i];
            const int i1 = piTriListIn[f*3+(i<2?(i+1):0)];
            pEdges[f*3+i].i0 = i0 < i1 ? i0 : i1;           // put minimum index in i0
            pEdges[f*3+i].i1 = !(i0 < i1) ? i0 : i1;        // put maximum index in i1
            pEdges[f*3+i].f = f;                            // record face number
        }

    // sort over all edges by i0, this is the pricy one.
    QuickSortEdges(pEdges, 0, iNrTrianglesIn*3-1, 0, uSeed);    // sort channel 0 which is i0

    // sub sort over i1, should be fast.
    // could replace this with a 64 bit int sort over (i0,i1)
    // with i0 as msb in the quicksort call above.
    iEntries = iNrTrianglesIn*3;
    iCurStartIndex = 0;
    for(i=1; i<iEntries; i++)
    {
        if(pEdges[iCurStartIndex].i0 != pEdges[i].i0)
        {
            const int iL = iCurStartIndex;
            const int iR = i-1;
            //const int iElems = i-iL;
            iCurStartIndex = i;
            QuickSortEdges(pEdges, iL, iR, 1, uSeed);   // sort channel 1 which is i1
        }
    }

    // sub sort over f, which should be fast.
    // this step is to remain compliant with BuildNeighborsSlow() when
    // more than 2 triangles use the same edge (such as a butterfly topology).
    iCurStartIndex = 0;
    for(i=1; i<iEntries; i++)
    {
        if(pEdges[iCurStartIndex].i0 != pEdges[i].i0 || pEdges[iCurStartIndex].i1 != pEdges[i].i1)
        {
            const int iL = iCurStartIndex;
            const int iR = i-1;
            //const int iElems = i-iL;
            iCurStartIndex = i;
            QuickSortEdges(pEdges, iL, iR, 2, uSeed);   // sort channel 2 which is f
        }
    }

    // pair up, adjacent triangles
    for(i=0; i<iEntries; i++)
    {
        const int i0=pEdges[i].i0;
        const int i1=pEdges[i].i1;
        const int f = pEdges[i].f;
        tbool bUnassigned_A;

        int i0_A, i1_A;
        int edgenum_A, edgenum_B=0; // 0,1 or 2
        GetEdge(&i0_A, &i1_A, &edgenum_A, &piTriListIn[f*3], i0, i1);   // resolve index ordering and edge_num
        bUnassigned_A = pTriInfos[f].FaceNeighbors[edgenum_A] == -1 ? TTRUE : TFALSE;

        if(bUnassigned_A)
        {
            // get true index ordering
            int j=i+1, t;
            tbool bNotFound = TTRUE;
            while(j<iEntries && i0==pEdges[j].i0 && i1==pEdges[j].i1 && bNotFound)
            {
                tbool bUnassigned_B;
                int i0_B, i1_B;
                t = pEdges[j].f;
                // flip i0_B and i1_B
                GetEdge(&i1_B, &i0_B, &edgenum_B, &piTriListIn[t*3], pEdges[j].i0, pEdges[j].i1);   // resolve index ordering and edge_num
                //assert(!(i0_A==i1_B && i1_A==i0_B));
                bUnassigned_B =  pTriInfos[t].FaceNeighbors[edgenum_B]==-1 ? TTRUE : TFALSE;
                if(i0_A==i0_B && i1_A==i1_B && bUnassigned_B)
                    bNotFound = TFALSE;
                else
                    ++j;
            }

            if(!bNotFound)
            {
                int t = pEdges[j].f;
                pTriInfos[f].FaceNeighbors[edgenum_A] = t;
                //assert(pTriInfos[t].FaceNeighbors[edgenum_B]==-1);
                pTriInfos[t].FaceNeighbors[edgenum_B] = f;
            }
        }
    }
}

static void BuildNeighborsSlow(STriInfo pTriInfos[], const int piTriListIn[], const int iNrTrianglesIn)
{
    int f=0, i=0;
    for(f=0; f<iNrTrianglesIn; f++)
    {
        for(i=0; i<3; i++)
        {
            // if unassigned
            if(pTriInfos[f].FaceNeighbors[i] == -1)
            {
                const int i0_A = piTriListIn[f*3+i];
                const int i1_A = piTriListIn[f*3+(i<2?(i+1):0)];

                // search for a neighbor
                tbool bFound = TFALSE;
                int t=0, j=0;
                while(!bFound && t<iNrTrianglesIn)
                {
                    if(t!=f)
                    {
                        j=0;
                        while(!bFound && j<3)
                        {
                            // in rev order
                            const int i1_B = piTriListIn[t*3+j];
                            const int i0_B = piTriListIn[t*3+(j<2?(j+1):0)];
                            //assert(!(i0_A==i1_B && i1_A==i0_B));
                            if(i0_A==i0_B && i1_A==i1_B)
                                bFound = TTRUE;
                            else
                                ++j;
                        }
                    }
                    
                    if(!bFound) ++t;
                }

                // assign neighbors
                if(bFound)
                {
                    pTriInfos[f].FaceNeighbors[i] = t;
                    //assert(pTriInfos[t].FaceNeighbors[j]==-1);
                    pTriInfos[t].FaceNeighbors[j] = f;
                }
            }
        }
    }
}

static void QuickSortEdges(SEdge * pSortBuffer, int iLeft, int iRight, const int channel, unsigned int uSeed)
{
    unsigned int t;
    int iL, iR, n, index, iMid;

    // early out
    SEdge sTmp;
    const int iElems = iRight-iLeft+1;
    if(iElems<2) return;
    else if(iElems==2)
    {
        if(pSortBuffer[iLeft].array[channel] > pSortBuffer[iRight].array[channel])
        {
            sTmp = pSortBuffer[iLeft];
            pSortBuffer[iLeft] = pSortBuffer[iRight];
            pSortBuffer[iRight] = sTmp;
        }
        return;
    }

    // Random
    t=uSeed&31;
    t=(uSeed<<t)|(uSeed>>(32-t));
    uSeed=uSeed+t+3;
    // Random end

    iL=iLeft, iR=iRight;
    n = (iR-iL)+1;
    assert(n>=0);
    index = (int) (uSeed%n);

    iMid=pSortBuffer[index + iL].array[channel];

    do
    {
        while(pSortBuffer[iL].array[channel] < iMid)
            ++iL;
        while(pSortBuffer[iR].array[channel] > iMid)
            --iR;

        if(iL <= iR)
        {
            sTmp = pSortBuffer[iL];
            pSortBuffer[iL] = pSortBuffer[iR];
            pSortBuffer[iR] = sTmp;
            ++iL; --iR;
        }
    }
    while(iL <= iR);

    if(iLeft < iR)
        QuickSortEdges(pSortBuffer, iLeft, iR, channel, uSeed);
    if(iL < iRight)
        QuickSortEdges(pSortBuffer, iL, iRight, channel, uSeed);
}

// resolve ordering and edge number
static void GetEdge(int * i0_out, int * i1_out, int * edgenum_out, const int indices[], const int i0_in, const int i1_in)
{
    *edgenum_out = -1;
    
    // test if first index is on the edge
    if(indices[0]==i0_in || indices[0]==i1_in)
    {
        // test if second index is on the edge
        if(indices[1]==i0_in || indices[1]==i1_in)
        {
            edgenum_out[0]=0;   // first edge
            i0_out[0]=indices[0];
            i1_out[0]=indices[1];
        }
        else
        {
            edgenum_out[0]=2;   // third edge
            i0_out[0]=indices[2];
            i1_out[0]=indices[0];
        }
    }
    else
    {
        // only second and third index is on the edge
        edgenum_out[0]=1;   // second edge
        i0_out[0]=indices[1];
        i1_out[0]=indices[2];
    }
}



static void DegenPrologue(STriInfo pTriInfos[], int piTriList_out[], const int iNrTrianglesIn, const int iTotTris)
{
    int iNextGoodTriangleSearchIndex=-1;
    tbool bStillFindingGoodOnes;

    // locate quads with only one good triangle
    int t=0;
    while(t<(iTotTris-1))
    {
        const int iFO_a = pTriInfos[t].iOrgFaceNumber;
        const int iFO_b = pTriInfos[t+1].iOrgFaceNumber;
        if(iFO_a==iFO_b)    // this is a quad
        {
            const tbool bIsDeg_a = (pTriInfos[t].iFlag&MARK_DEGENERATE)!=0 ? TTRUE : TFALSE;
            const tbool bIsDeg_b = (pTriInfos[t+1].iFlag&MARK_DEGENERATE)!=0 ? TTRUE : TFALSE;
            if((bIsDeg_a^bIsDeg_b)!=0)
            {
                pTriInfos[t].iFlag |= QUAD_ONE_DEGEN_TRI;
                pTriInfos[t+1].iFlag |= QUAD_ONE_DEGEN_TRI;
            }
            t += 2;
        }
        else
            ++t;
    }

    // reorder list so all degen triangles are moved to the back
    // without reordering the good triangles
    iNextGoodTriangleSearchIndex = 1;
    t=0;
    bStillFindingGoodOnes = TTRUE;
    while(t<iNrTrianglesIn && bStillFindingGoodOnes)
    {
        const tbool bIsGood = (pTriInfos[t].iFlag&MARK_DEGENERATE)==0 ? TTRUE : TFALSE;
        if(bIsGood)
        {
            if(iNextGoodTriangleSearchIndex < (t+2))
                iNextGoodTriangleSearchIndex = t+2;
        }
        else
        {
            int t0, t1;
            // search for the first good triangle.
            tbool bJustADegenerate = TTRUE;
            while(bJustADegenerate && iNextGoodTriangleSearchIndex<iTotTris)
            {
                const tbool bIsGood = (pTriInfos[iNextGoodTriangleSearchIndex].iFlag&MARK_DEGENERATE)==0 ? TTRUE : TFALSE;
                if(bIsGood) bJustADegenerate=TFALSE;
                else ++iNextGoodTriangleSearchIndex;
            }

            t0 = t;
            t1 = iNextGoodTriangleSearchIndex;
            ++iNextGoodTriangleSearchIndex;
            assert(iNextGoodTriangleSearchIndex > (t+1));

            // swap triangle t0 and t1
            if(!bJustADegenerate)
            {
                int i=0;
                for(i=0; i<3; i++)
                {
                    const int index = piTriList_out[t0*3+i];
                    piTriList_out[t0*3+i] = piTriList_out[t1*3+i];
                    piTriList_out[t1*3+i] = index;
                }
                {
                    const STriInfo tri_info = pTriInfos[t0];
                    pTriInfos[t0] = pTriInfos[t1];
                    pTriInfos[t1] = tri_info;
                }
            }
            else
                bStillFindingGoodOnes = TFALSE; // this is not supposed to happen
        }

        if(bStillFindingGoodOnes) ++t;
    }

    assert(bStillFindingGoodOnes);  // code will still work.
    assert(iNrTrianglesIn == t);
}

static void DegenEpilogue(STSpace psTspace[], STriInfo pTriInfos[], int piTriListIn[], const SMikkTSpaceContext * pContext, const int iNrTrianglesIn, const int iTotTris)
{
    int t=0, i=0;
    // deal with degenerate triangles
    // punishment for degenerate triangles is O(N^2)
    for(t=iNrTrianglesIn; t<iTotTris; t++)
    {
        // degenerate triangles on a quad with one good triangle are skipped
        // here but processed in the next loop
        const tbool bSkip = (pTriInfos[t].iFlag&QUAD_ONE_DEGEN_TRI)!=0 ? TTRUE : TFALSE;

        if(!bSkip)
        {
            for(i=0; i<3; i++)
            {
                const int index1 = piTriListIn[t*3+i];
                // search through the good triangles
                tbool bNotFound = TTRUE;
                int j=0;
                while(bNotFound && j<(3*iNrTrianglesIn))
                {
                    const int index2 = piTriListIn[j];
                    if(index1==index2) bNotFound=TFALSE;
                    else ++j;
                }

                if(!bNotFound)
                {
                    const int iTri = j/3;
                    const int iVert = j%3;
                    const int iSrcVert=pTriInfos[iTri].vert_num[iVert];
                    const int iSrcOffs=pTriInfos[iTri].iTSpacesOffs;
                    const int iDstVert=pTriInfos[t].vert_num[i];
                    const int iDstOffs=pTriInfos[t].iTSpacesOffs;
                    
                    // copy tspace
                    psTspace[iDstOffs+iDstVert] = psTspace[iSrcOffs+iSrcVert];
                }
            }
        }
    }

    // deal with degenerate quads with one good triangle
    for(t=0; t<iNrTrianglesIn; t++)
    {
        // this triangle belongs to a quad where the
        // other triangle is degenerate
        if( (pTriInfos[t].iFlag&QUAD_ONE_DEGEN_TRI)!=0 )
        {
            SVec3 vDstP;
            int iOrgF=-1, i=0;
            tbool bNotFound;
            unsigned char * pV = pTriInfos[t].vert_num;
            int iFlag = (1<<pV[0]) | (1<<pV[1]) | (1<<pV[2]);
            int iMissingIndex = 0;
            if((iFlag&2)==0) iMissingIndex=1;
            else if((iFlag&4)==0) iMissingIndex=2;
            else if((iFlag&8)==0) iMissingIndex=3;

            iOrgF = pTriInfos[t].iOrgFaceNumber;
            vDstP = GetPosition(pContext, MakeIndex(iOrgF, iMissingIndex));
            bNotFound = TTRUE;
            i=0;
            while(bNotFound && i<3)
            {
                const int iVert = pV[i];
                const SVec3 vSrcP = GetPosition(pContext, MakeIndex(iOrgF, iVert));
                if(veq(vSrcP, vDstP)==TTRUE)
                {
                    const int iOffs = pTriInfos[t].iTSpacesOffs;
                    psTspace[iOffs+iMissingIndex] = psTspace[iOffs+iVert];
                    bNotFound=TFALSE;
                }
                else
                    ++i;
            }
            assert(!bNotFound);
        }
    }
}