H3Index _faceIjkToH3()

in src/h3lib/lib/h3Index.c [641:725]
54 lines of code
15 McCabe index (conditional complexity)

H3Index _faceIjkToH3(const FaceIJK* fijk, int res) {
    // initialize the index
    H3Index h = H3_INIT;
    H3_SET_MODE(h, H3_HEXAGON_MODE);
    H3_SET_RESOLUTION(h, res);

    // check for res 0/base cell
    if (res == 0) {
        if (fijk->coord.i > MAX_FACE_COORD || fijk->coord.j > MAX_FACE_COORD ||
            fijk->coord.k > MAX_FACE_COORD) {
            // out of range input
            return H3_NULL;
        }

        H3_SET_BASE_CELL(h, _faceIjkToBaseCell(fijk));
        return h;
    }

    // we need to find the correct base cell FaceIJK for this H3 index;
    // start with the passed in face and resolution res ijk coordinates
    // in that face's coordinate system
    FaceIJK fijkBC = *fijk;

    // build the H3Index from finest res up
    // adjust r for the fact that the res 0 base cell offsets the indexing
    // digits
    CoordIJK* ijk = &fijkBC.coord;
    for (int r = res - 1; r >= 0; r--) {
        CoordIJK lastIJK = *ijk;
        CoordIJK lastCenter;
        if (isResClassIII(r + 1)) {
            // rotate ccw
            _upAp7(ijk);
            lastCenter = *ijk;
            _downAp7(&lastCenter);
        } else {
            // rotate cw
            _upAp7r(ijk);
            lastCenter = *ijk;
            _downAp7r(&lastCenter);
        }

        CoordIJK diff;
        _ijkSub(&lastIJK, &lastCenter, &diff);
        _ijkNormalize(&diff);

        H3_SET_INDEX_DIGIT(h, r + 1, _unitIjkToDigit(&diff));
    }

    // fijkBC should now hold the IJK of the base cell in the
    // coordinate system of the current face

    if (fijkBC.coord.i > MAX_FACE_COORD || fijkBC.coord.j > MAX_FACE_COORD ||
        fijkBC.coord.k > MAX_FACE_COORD) {
        // out of range input
        return H3_NULL;
    }

    // lookup the correct base cell
    int baseCell = _faceIjkToBaseCell(&fijkBC);
    H3_SET_BASE_CELL(h, baseCell);

    // rotate if necessary to get canonical base cell orientation
    // for this base cell
    int numRots = _faceIjkToBaseCellCCWrot60(&fijkBC);
    if (_isBaseCellPentagon(baseCell)) {
        // force rotation out of missing k-axes sub-sequence
        if (_h3LeadingNonZeroDigit(h) == K_AXES_DIGIT) {
            // check for a cw/ccw offset face; default is ccw
            if (_baseCellIsCwOffset(baseCell, fijkBC.face)) {
                h = _h3Rotate60cw(h);
            } else {
                h = _h3Rotate60ccw(h);
            }
        }

        for (int i = 0; i < numRots; i++) h = _h3RotatePent60ccw(h);
    } else {
        for (int i = 0; i < numRots; i++) {
            h = _h3Rotate60ccw(h);
        }
    }

    return h;
}