Function resize_opencv

dnn/src/fallback/resize/gi/resize_cv.cpp:1232–1400

template <typename T>
void resize_opencv(const Mat<T>& src, Mat<T>& dst, InterpolationMode ip) {
    // fake area mode missing here
    int dwidth = dst.width();
    int dheight = dst.height();
    int swidth = src.width();
    int sheight = src.height();
    int xmin = 0, xmax = dwidth, width = dwidth * dst.channels();
    double inv_scale_x = static_cast<double>(dwidth) / swidth;
    double inv_scale_y = static_cast<double>(dheight) / sheight;
    double scale_x = 1.0 / inv_scale_x;
    double scale_y = 1.0 / inv_scale_y;
    int dx, sx, dy, sy, k;
    float fx, fy;
    int cn = src.channels();
    {
        int iscale_x = saturate_cast<int>(scale_x);
        int iscale_y = saturate_cast<int>(scale_y);

        bool is_area_fast = std::abs(scale_x - iscale_x) < DBL_EPSILON &&
                            std::abs(scale_y - iscale_y) < DBL_EPSILON;
        if (ip == IMode::INTER_LINEAR && is_area_fast && iscale_x == 2 &&
            iscale_y == 2) {
            ip = IMode::INTER_AREA;
        }
        if (ip == IMode::INTER_AREA && scale_x >= 1 && scale_y >= 1) {
            if (is_area_fast) {
                int area = iscale_x * iscale_y;
                size_t srcstep = src.step();
                AlignedVector<int> _ofs(area + dwidth * cn);
                int* ofs = _ofs.data();
                int* xofs = ofs + area;
                ResizeAreaFastFunc<T> func =
                        get_resize_area_fast_func<T>();  /// need change
                for (sy = 0, k = 0; sy < iscale_y; ++sy)
                    for (sx = 0; sx < iscale_x; ++sx)
                        ofs[k++] = static_cast<int>(sy * srcstep + sx * cn);
                for (dx = 0; dx < dwidth; ++dx) {
                    int j = dx * cn;
                    sx = iscale_x * j;
                    for (k = 0; k < cn; ++k)
                        xofs[j + k] = sx + k;
                }
                func(src, dst, ofs, xofs, iscale_x, iscale_y);
                return;
            }
            ResizeAreaFunc<T> func = get_resize_area_func<T>();
            AlignedVector<DecimateAlpha> _xytab((swidth + sheight) * 2);
            DecimateAlpha *xtab = _xytab.data(), *ytab = xtab + swidth * 2;
            int xtab_size = compute_resize_area_tab(swidth, dwidth, cn, scale_x, xtab);
            int ytab_size = compute_resize_area_tab(sheight, dheight, 1, scale_y, ytab);
            AlignedVector<int> _tabofs(dheight + 1);
            int* tabofs = _tabofs.data();
            for (k = 0, dy = 0; k < ytab_size; ++k) {
                if (k == 0 || ytab[k].di != ytab[k - 1].di) {
                    megdnn_assert(ytab[k].di == dy);
                    tabofs[dy++] = k;
                }
            }