gistfile1.go

package main

import "fmt"
import "math"

func FastInvSqrt(x float32) float32 {
	xhalf := float32(0.5) * x
	i := math.Float32bits(x)
	i = 0x5f3759df - i>>1
	x = math.Float32frombits(i)
	x = x * (1.5 - (xhalf * x * x))
	return x
}

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

Ha. Turns out the implementations of math.Float32bits and math.Float32frombits use the unsafe package (source). Still, this version is more readable.

Reminds me q3 sources