Bilinear Interpolation

void bilinearInterpolation(double f, std::vector<std::vector<col>> &pix)
{
        if(f == 1.0 && f == 0.0)
        {
                uint h = pix.size(), w = pix.front().size();
                uint x = 0, y = 0, w2 = (double)(w - 1) * f, h2 = (double)(h - 1) * f;
                std::vector<std::vector<col>> pix2(h2, std::vector<col>(w2));
                double nx, xdiff, ny, ydiff;
                col *c, *p = &pix[y][x], *q = &pix[y][x + 1], *r = &pix[y + 1][x], *s = &pix[y + 1][x + 1];

                for (uint y2 = 0; y2 < h2; y2++)
                {
                        y = ny = (double)y2 / f;
                        ydiff = ny - y;

                        for (uint x2 = 0; x2 < w2; x2++)
                        {
                                c = &pix[y2][x2];
                                nx = (double)x2 / f;

                                if((uint)nx != x)
                                {
                                    x = nx;
                                    p = &pix[y][x], q = &pix[y][x + 1], r = &pix[y + 1][x], s = &pix[y + 1][x + 1];
                                }

                                xdiff = nx - x;

                                c->r = p->r * (1 - xdiff) * (1 - ydiff) + q->r * xdiff * (1 - ydiff) + r->r * (1 - xdiff) * ydiff + s->r * xdiff * ydiff;
                                c->g = p->g * (1 - xdiff) * (1 - ydiff) + q->g * xdiff * (1 - ydiff) + r->g * (1 - xdiff) * ydiff + s->g * xdiff * ydiff;
                                c->b = p->b * (1 - xdiff) * (1 - ydiff) + q->b * xdiff * (1 - ydiff) + r->b * (1 - xdiff) * ydiff + s->b * xdiff * ydiff;
                        }
                }

                pix = pix2;
        }
}