Go port of Quake III Fast Approx Inverse Square Root algorithm

qrsqrt.go

// This is the Quake III Q_rsqrt Fast Approx Inverse Square Root algorithm

package main

import (
	"fmt"
	"math"
)

const threehalfs float32 = 1.5

func qrsqrt(number float32) float32 {
	i := math.Float32bits(number)
	i = 0x5f3759df - (i >> 1)
	y := math.Float32frombits(i)

	x2 := number * 0.5
	return y * (threehalfs - (x2 * y * y))
}

func main() {
	fmt.Println(qrsqrt(27)) // prints 0.19215362 for 0.154% error
}