Bit Flags

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

Bit Flags by rdodson41

2005

Bit flags are can be used to set parameters for a function. The value that is inputed as a parameter when calling the function is an integer, which is the sum of all the bits of parameters you want. For example:

In the B+ function create window, there are many different style flags you can have. You pick which styles you want, and add up there bit values. This is the integer that is used as the flag. The default is 15, which would mean the window has a title bar, is resizable, has a menu, and has a status bar.

This is useful for many things, so have fun with it!

Repeat
	Print
	flag=Int(Input$("Flag:>"))
	bit=Int(Input$("Bit:>"))
	Select bitflag(flag,bit)
		Case 0
			Print "Bit "+bit+" has not been found in flag "+flag+"."
		Case 1
			Print "Bit "+bit+" has been found in flag "+flag+"."
	End Select
Forever



Function bitflag(flag,bit)
	p=0
	Repeat
		If 2^p>11 Then Exit
		p:+1
	Forever	
	p:-1	
	For i=p To 0 Step -1
		If flag-(2^i)>=0 Then
			flag:-(2^i)
			If 2^i=bit Then Return 1
		End If
	Next
	Return 0
End Function

Comments

Koriolis

2005

There is far more simple:

Function bitflag(flag,bit)
	Return (flag Shr bit) And 1
End Function

Note: in this version 'bit' starts at 0, not 1 (if you want it 1 base just do "Return (flag Shr (bit-1)) And 1")

rdodson41

2005

Oh, huh... and i spent and hour trying to figure this one out...

rdodson41

2005

It would be this:

Function BitFlag(flag,bit)
	Return (flag & bit)=bit
End Function

Unfortunatly 'And' is only a logical opperater, not a bitwise opperator. So you have to use the & symbol.

Techlord

2005

A working Example.

;flags (multiple of 2)
fullbright=1 
vertexcolors=2 
flatshaded=4 
disablefog=8
disablebackfaceculling=16 
forcealphablending=32

;assignment
fx=fullbright+vertexcolors+disablefog

Print("fx="+fx+":")

;evaluate; use '/' and If's only.
If fx/fullbright And 1 Print("fullbright") ;do stuff
If fx/vertexcolors And 1  Print("vertexcolors")
If fx/flatshaded And 1 Print("flatshaded")
If fx/disablefog And 1 Print("disablefog")
If fx/disablebackfaceculling And 1 Print("disablebackfaceculling")
If fx/forcealphablending And 1 Print("forcealphablending")

Code Archives Forum