/* explain https://www.youtube.com/watch?v=p8u_k2LIZyo */

#include <stdio.h>

float Q_rsqrt(float number)
{
    long i;
    float x2, y;
    const float threehalfs = 1.5F;

    x2 = number*0.5F;
    y = number;
    i = *(long *) &y;
    i = 0x5f3759df - (i >> 1);
    printf("i = %lu\n", i);
    y = *( float *) &i;
    printf("y = %f\n", y);
    y = y * (threehalfs - (x2*y*y));

    return y;
}

int main()
{
    float n = 5.0;
    float f = Q_rsqrt(n);
    printf("1/sqrt(%f) = %f", n, f);
    return 0;
}