Microsoft KB Archive/185554

= How To General Bit Manipulation Routines =

Article ID: 185554

Article Last Modified on 11/23/2006

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APPLIES TO


 * Microsoft Visual Basic for Applications 5.0

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This article was previously published under Q185554



SUMMARY
This article outlines routines to set or reference individual bits in both a variable and an array.



MORE INFORMATION
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This article provides a set of general bit-manipulation routines for use in VBA code. NOTE: You should write a Visual C or C++ DLL to do bit manipulation if you require high performance. The routines are:    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
  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   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   Run the procedure "Main".

RESULTS: The debug window displays the following data.      80004020      FALSE 0     2000      0 

