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HiWords and LoWords from Long Values

Author:

Steve McMahon(steve@vbaccelerator.com)

Keywords:

Bit Manipulation

Updated:

21/02/99

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When translating C code to VB, you quite often come across the HiWord and LoWord operators, used to pack two integers into a long value. A simple translation of HiWord code will run into difficulties when unsigned integer arithmetic is being used in the C code and the highest bit of the long value can be set. Since VB doesn't support unsigned arithmetic we have to strip out the high bit and add it back again later to avoid overflows and misleading results.

Start a new project then add a module. Add the following code to the module:

Public Property Get LoWord(ByRef lThis As Long) As Long
   LoWord = (lThis And &HFFFF&)
End Property

Public Property Let LoWord(ByRef lThis As Long, ByVal lLoWord As Long)
   lThis = lThis And Not &HFFFF& Or lLoWord
End Property

Public Property Get HiWord(ByRef lThis As Long) As Long
   If (lThis And &H80000000) = &H80000000 Then
      HiWord = ((lThis And &H7FFF0000) \ &H10000) Or &H8000&
   Else
      HiWord = (lThis And &HFFFF0000) \ &H10000
   End If
End Property

Public Property Let HiWord(ByRef lThis As Long, ByVal lHiWord As Long)
   If (lHiWord And &H8000&) = &H8000& Then
      lThis = lThis And Not &HFFFF0000 Or ((lHiWord And &H7FFF&) * &H10000) Or &H80000000
   Else
      lThis = lThis And Not &HFFFF0000 Or (lHiWord * &H10000)
   End If
End Property




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Copyright © 1998-1999, Steve McMahon ( steve@vbaccelerator.com). All Rights Reserved.
Last updated: 21/02/99