Fast InvSqrt in Max

The InvSqr numbers look good but the SQR numbers are quite a bit off (the results of the functions)

EDIT: this is the same as Knotz's first post but also shows a result for comparison of accuracy.

Function InvSqrtKnotz:Float(x:Float)

	Local xhalf:Float = 0.5*x
	Local i:Int = (Int Ptr(Varptr(x)))[0]
	i = $5f3759df - (i Shr 1)
	x = (Float Ptr(Varptr(i)))[0]
	x = x*(1.5 - xhalf*x*x)
	Return x

End Function

Function InvSqrtAntMan:Float(x:Float)

	Local i = $5f3759df - (Int Ptr(Varptr(x))[0] Shr 1)
	Local ox:Float = (Float Ptr(Varptr(i))[0])
	Return  ox *(1.5 - ((0.5*x)*ox*ox))
	
End Function

Function InvSqrtFredborg:Float(x:Float)

	Local i:Int = $5f3759df - (Int Ptr(Varptr(x))[0] Shr 1)
	Return  (Float Ptr(Varptr(i))[0]) *(1.5 - ((0.5*x)*(Float Ptr(Varptr(i))[0])*(Float Ptr(Varptr(i))[0])))
	
End Function

Function InvSqrtSOS:Float(x:Float)

    Local xhalf:Float = 0.5*x
	Local i:Int = $5f3759df - (Int Ptr(Varptr(x))[0] Shr 1)
	Local ox:Float = (Float Ptr(Varptr(i))[0])
	Return ox *(1.5 - (xhalf*ox*ox))
	
End Function

Function InvSqrtAza:Float(x:Float)

	Local xhalf:Float = 0.5*x
	Local ip:Int Ptr=Int Ptr(Varptr(x))
	ip[0]=$5f3759df-(ip[0] Shr 1)
	Return x *(1.5 - (xhalf*x*x))

End Function

Function InvSqrtPlain:Float(x:Float)

	Return 1.0/Sqr(x)
	
End Function

Function SqrtKnotz:Float(x:Float)

	Local xhalf:Float = 0.5*x
	Local i:Int = (Int Ptr(Varptr(x)))[0]
	i = ($be6f0000 - i) Shr 1
	x = (Float Ptr(Varptr(i)))[0]
	x = x*(1.5 - xhalf*x*x)
	Return x

End Function

Function SqrtAntMan:Float(x:Float)

	Local i = ($be6f0000 - (Int Ptr(Varptr(x))[0])) Shr 1
	Local ox:Float = (Float Ptr(Varptr(i))[0])
	Return  ox *(1.5 - ((0.5*x)*ox*ox))
	
End Function

Function SqrtFredborg:Float(x:Float)

	Local i:Int = ($be6f0000 - (Int Ptr(Varptr(x))[0])) Shr 1
	Return  (Float Ptr(Varptr(i))[0]) *(1.5 - ((0.5*x)*(Float Ptr(Varptr(i))[0])*(Float Ptr(Varptr(i))[0])))
	
End Function


Function SqrtSOS:Float(x:Float)

    Local xhalf:Float = 0.5*x
	Local i:Int = ($be6f0000 - (Int Ptr(Varptr(x))[0])) Shr 1
	Local ox:Float = (Float Ptr(Varptr(i))[0])
	Return ox *(1.5 - (xhalf*ox*ox))
	
End Function

Function SqrtAza:Float(x:Float)

	Local xhalf:Float = 0.5*x
	Local ip:Int Ptr=Int Ptr(Varptr(x))
	ip[0]=($be6f0000 - ip[0]) Shr 1
	Return x *(1.5 - (xhalf*x*x))

End Function

Function SqrtPlain:Float(x:Float)

	Return Sqr(x)
	
End Function

Function Benchmark(label:String, func:Float(x:Float))

	Local startTime:Long = MilliSecs()
	For Local ii:Int=1 To 10000000
		func(Float(ii))
	Next
	Local endTime:Long = MilliSecs() - startTime
	Local result:Float = func(5.0)
	Print label + ":~t~t" + endTime + "ms" + "~t~tfunc(5.0):"+result


End Function

Print "~nInvSqrt:"
'Benchmark("Raw C",InvSqrt)
Benchmark("Knotz   ",InvSqrtKnotz)
Benchmark("Artman  ",InvSqrtAntman)
Benchmark("Fredborg",InvSqrtFredborg)
Benchmark("SOS     ",InvSqrtSOS)
Benchmark("Azathoth",InvSqrtAza)
Benchmark("1/Sqr() ",InvSqrtPlain)


Print "~nSqrt:"
'Benchmark("Raw C",Sqrt)
Benchmark("Knotz   ",SqrtKnotz)
Benchmark("Artman  ",SqrtAntman)
Benchmark("Fredborg",SqrtFredborg)
Benchmark("SOS     ",SqrtSOS)
Benchmark("Azathoth",SqrtAza)
Benchmark("Sqr()   ",SqrtPlain)