static void test_mul32shift(void)
{
    int x, y;
    for(y = 0; y < height; y++)
    {
        uint32_t *data = img + y * width;

        for(x = 0; x < width ; x++)
        {
            uint32_t x = *data;
            uint8_t a, b, c, d;
            a = x >> 24;
            b = (uint8_t)(x >> 16);
            c = (uint8_t)(x >> 8);
            d = (uint8_t)x;
            a *= K;
            b *= K;
            c *= K;
            d *= K;
            *data++ = ((uint32_t)a << 24) | ((uint32_t)b << 16)
                       | ((uint16_t)c << 8) | d;
        }
    }
}

static void test_mul32tab(void)
{
    int x, y;
    for(y = 0; y < height; y++)
    {
        uint32_t *data = img + y * width;

        for(x = 0; x < width ; x++)
        {
            uint32_t x = *data;
            uint8_t t[4];
            t[0] = x >> 24;
            t[1] = (uint8_t)(x >> 16);
            t[2] = (uint8_t)(x >> 8);
            t[3] = (uint8_t)x;
            t[0] *= K;
            t[1] *= K;
            t[2] *= K;
            t[3] *= K;
            *data++ = ((uint32_t)t[0] << 24) | ((uint32_t)t[1] << 16)
                       | ((uint16_t)t[2] << 8) | t[3];
        }
    }
}