package fastsqrt

import "math"

const magic32 = 0x5F375A86

func FastInvSqrt32(n float32) float32 {
	// If n is negative return NaN
	if n < 0 {
		return float32(math.NaN())
	} // n2 and th are for one iteration of Newton's method later
	n2, th := n*0.5, float32(1.5) // Use math.Float32bits to represent the float32, n, as
	// an uint32 without modification.
	b := math.Float32bits(n) // Use the new uint32 view of the float32 to shift the bits
	// of the float32 1 to the right, chopping off 1 bit from
	// the fraction part of the float32.
	b = magic32 - (b >> 1) // Use math.Float32frombits to convert the uint32 bits back
	// into their float32 representation, again no actual change
	// in the bits, just a change in how we treat them in memory.
	// f is now our answer of 1 / sqrt(n)
	f := math.Float32frombits(b) // Perform one iteration of Newton's method on f to improve
	// accuracy
	f *= th - (n2 * f * f)

	// And return our fast inverse square root result
	return f
}