/. repost

[mtbg]

float InvSqrt (float x) {
float xhalf = 0.5f*x;
int i = *(int*)&x;
i = 0x5f3759df - (i>>1);
x = *(float*)&i;
x = x*(1.5f - xhalf*x*x);
return x;
}This function appears in the Quake 3 source. It's reportedly about four times faster than 1.0/sqrt(x). There's a paper on how it works, and whence the magic number. Wow. (Link

Comments

[benfrantzdale]

That is totally awesome.

[mtbg]

I figured you'd appreciate it :D

[macdaddyfrosh]

I liked the interview with the guy who wrote a special-purpose sqrt just for a fluid dynamics app...people really do this for a living?