Slow smooth blink an LED

gistfile1.txt

    { // do this every 1ms or two
        static int16_t x;
        static int16_t a;
        int16_t y = 0x4000 - (((int32_t)x * x) >> 16);
        a = (a & 0x0fff) + (((int32_t)y * y) >> 16);
        LED_io_pin = a >> 12;
        x += 35; // slow blink speed
    }