static void find_best_method(BlurMethod *blur, double r2)
{
    static const int index[][4] = {
        { 1, 2, 3, 4 },
        { 1, 2, 3, 5 },
        { 1, 2, 4, 6 },
    };

    double mu[5];
    if (r2 < 1.9) {
        blur->level = blur->prefilter = blur->filter = 0;

        if (r2 < 0.5) {
            mu[2] = 0.085 * r2 * r2 * r2;
            mu[1] = 0.5 * r2 - 4 * mu[2];
            mu[3] = mu[4] = 0;
        } else {
            calc_gauss(mu, 4, r2);
        }
    } else {
        double mul = 1;
        if (r2 < 6.693) {
            blur->level = 0;

            if (r2 < 2.8)
                blur->prefilter = 1;
            else if (r2 < 4.4)
                blur->prefilter = 2;
            else
                blur->prefilter = 3;

            blur->filter = blur->prefilter - 1;
        } else {
            frexp((r2 + 0.7) / 26.5, &blur->level);
            blur->level = (blur->level + 3) >> 1;
            mul = pow(0.25, blur->level);
            r2 *= mul;

            if (r2 < 3.15 - 1.5 * mul)
                blur->prefilter = 0;
            else if (r2 < 5.3 - 5.2 * mul)
                blur->prefilter = 1;
            else
                blur->prefilter = 2;

            blur->filter = blur->prefilter;
        }
        calc_coeff(mu + 1, index[blur->filter], blur->prefilter, r2, mul);
    }

    for (int i = 1; i <= 4; ++i)
        blur->coeff[i - 1] = (int)(0x10000 * mu[i] + 0.5);
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.