sus , 2 months ago (edited 2 months ago)

slow inverse square root:

<span style="color:#323232;">float slowinvsqrt(float x)
</span><span style="color:#323232;">{
</span><span style="color:#323232;">    const long accuracy = 100000000;    // larger number = better accuracy
</span><span style="color:#323232;">    if (x <= 0.0f) {
</span><span style="color:#323232;">        return NAN;
</span><span style="color:#323232;">    }
</span><span style="color:#323232;">    if (x == 1.0f) {
</span><span style="color:#323232;">        return 1.0f;
</span><span style="color:#323232;">    }
</span><span style="color:#323232;">    if (x < 1.0f) {
</span><span style="color:#323232;">        return 1.0f / slowinvsqrt(1.0f/x);
</span><span style="color:#323232;">    }
</span><span style="color:#323232;">
</span><span style="color:#323232;">    int max_power = log(accuracy) / log(x);
</span><span style="color:#323232;">    long pow1 = pow(x, max_power - 1);
</span><span style="color:#323232;">    long pow2 = pow(x, max_power);
</span><span style="color:#323232;">    double current = 1.0;
</span><span style="color:#323232;">    double previous = 1.0;
</span><span style="color:#323232;">
</span><span style="color:#323232;">    for (long i = 0; i<10*accuracy; i++) {
</span><span style="color:#323232;">        current = sin(current);
</span><span style="color:#323232;">        if (i == pow1) {
</span><span style="color:#323232;">            previous = current;
</span><span style="color:#323232;">        }
</span><span style="color:#323232;">        if (i == pow2) {
</span><span style="color:#323232;">            return current / previous;
</span><span style="color:#323232;">        }
</span><span style="color:#323232;">    }
</span><span style="color:#323232;">}
</span>