Power of two

This code has been declared by its author to be Public Domain code.

Power of two by Rottbott (Posted 22 years ago)
Updated for a 2x speed increase! (Shl instead of ^.)
; Returns the next power of two down from a positive integer Function PowerOfTwo(N) ; Optimise for smaller numbers If (N And $FFFF0000) <> 0 Start = 31 Else Start = 15 EndIf ; Find power For i = Start To 0 Step -1 Number = 1 Shl i If (N And Number) = Number Then Return Number Next ; N is 0 or less Return 0 End Function

Power of two by Rottbott

(Posted 22 years ago)

Updated for a 2x speed increase! (Shl instead of ^.)

; Returns the next power of two down from a positive integer
Function PowerOfTwo(N)

	; Optimise for smaller numbers
	If (N And $FFFF0000) <> 0
		Start = 31
	Else
		Start = 15
	EndIf

	; Find power
	For i = Start To 0 Step -1
		Number = 1 Shl i
		If (N And Number) = Number Then Return Number
	Next

	; N is 0 or less
	Return 0

End Function

Comments

Koriolis

(Posted 22 years ago)

Try that

Const CONST_PowerOfTwo_LOG2# = 0.69314718055994530941723212145818
Function PowerOfTwo(N)
;	Return 1 Shl Int(Floor(Log(N)/Log(2)))
	Return 1 Shl Int(Floor(Log(N)/CONST_PowerOfTwo_LOG2))
End Function

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