Fast Inverse Square Root

fast_invsqrt.cpp

// from https://pizer.wordpress.com/2008/10/12/fast-inverse-square-root/
float InvSqrt(float x){
   uint32_t i = 0x5F1F1412 - (*(uint32_t*)&x >> 1);
   float tmp = *(float*)&i;
   return tmp * (1.69000231f - 0.714158168f * x * tmp * tmp);
}

// from http://rrrola.wz.cz/inv_sqrt.html
float inv_sqrt(float x)
{ union { float f; uint32 u; } y = {x};
y.u = 0x5F1FFF77ul – (y.u >> 1);
return 0.703974056f * y.f * (2.38919526f – x * y.f * y.f);
}