gistfile1.go

package main

import "fmt"
import "unsafe"

func FastInvSqrt(x float32) float32 {
	xhalf := float32(0.5) * x
	i := *(*int32)(unsafe.Pointer(&x))
	i = int32(0x5f3759df) - int32(i>>1)
	x = *(*float32)(unsafe.Pointer(&i))
	x = x * (1.5 - (xhalf * x * x))
	return x
}

func main() {
	fmt.Printf("inv sqrt: %f\n", FastInvSqrt(4))
}