How To General Bit Manipulation Routines (185554)

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    Name           Description
   -----------------------------------------------------------------------

   BitMask        Returns a mask used by the other routines to set or test
                  the value of a bit in a variable.

   BitSet         Turns a bit "on" or "off".

   BitFlip        Changes the state of a bit.

   BitTest        Returns the state of a bit.

   ArrayBitSet    Turns a bit "on" or "off".

   ArrayBitFlip   Changes the state of a bit.

   ArrayBitTest   Returns the state of a bit.
				

The Array routines assume 32 bits per element, starting with bits 0..31 in the lowest element, bits 32..63 in the second element, and so forth. The array does not have to be 0-based. If you specify a bit number that falls outside the bounds of the array, the operation leaves the data unchanged.

The routines have one or more of the following parameters:

     X        A Long value containing 32 bits to be manipulated.

   A()      An array containing bits to be manipulated.

   Value    TRUE to set a bit, FALSE to reset a bit.

   N        A number indicating the bit to manipulate. In the case of a
            single Long variable, valid ranges are 0..31. In the case of an
            array, valid values are 0..(number of elements * 32) - 1. Any
            value of N outside this range is ignored. In the case of a
            function, a FALSE is returned.

The BitTest and ArrayBitTest functions return TRUE (-1) if the bit is 1 and FALSE (0) if the bit is 0 (zero).

Sample Code

1. Create a new project and add the following code to a module:

         Function BitMask(ByVal N As Long) As Long
         Dim I As Long, Mask As Long
           If N < 0 Or N > 31 Then
             BitMask = 0
           ElseIf N = 31 Then
             BitMask = &H80000000
           Else
             Mask = 1
             For I = 1 To N
               Mask = Mask + Mask
             Next I
             BitMask = Mask
           End If
         End Function
   
         Sub BitSet(X As Long, ByVal N As Long, ByVal Value As Boolean)
           If Value Then
             X = X Or BitMask(N)
           Else
             X = X And Not BitMask(N)
           End If
         End Sub
   
         Sub BitFlip(X As Long, ByVal N As Long)
           X = X Xor BitMask(N)
         End Sub
   
         Function BitTest(X As Long, ByVal N As Long) As Boolean
         ' Return False if invalid N
           BitTest = (X And BitMask(N)) <> 0
         End Function
   
         Sub ArrayBitSet(A() As Long, ByVal N As Long, _
                         ByVal Value As Boolean)
         Dim Element As Integer
           Element = N \ 32 + LBound(A)
           If Element <= UBound(A) And N >= 0 Then
             BitSet A(Element), N Mod 32, Value
           End If
         End Sub
   
         Sub ArrayBitFlip(A() As Long, ByVal N As Long)
         Dim Element As Integer
           Element = N \ 32 + LBound(A)
           If Element <= UBound(A) And N >= 0 Then
             BitFlip A(Element), N Mod 32
           End If
         End Sub
   
         Function ArrayBitTest(A() As Long, ByVal N As Long) As Boolean
         ' Returns False if invalid N.
         Dim Element As Integer
           Element = N \ 32 + LBound(A)
           If Element <= UBound(A) And N >= 0 Then
             ArrayBitTest = BitTest(A(Element), N Mod 32)
           Else
             ArrayBitTest = False
           End If
         End Function
   						

2. You can the use the functions in code as follows. Add the following code to the module:

         Sub Main()
            Dim Bits As Long, aBits(0 To 2) As Long
            Bits = &H8000C000&
            BitSet Bits, 5, True
            BitSet Bits, 15, False
            ArrayBitSet aBits(), 45, True
            Debug.Print Hex$(Bits), BitTest(Bits, 4)
            Debug.Print Hex$(aBits(0)), Hex$(aBits(1)), Hex$(aBits(2))
         End Sub
   						

3. Run the procedure "Main".
   
   RESULTS: The debug window displays the following data.

         80004020      FALSE
         0      2000      0