ACC2000: How to Convert Unsigned Integers to Long Integers

'*************************************************************
'Declarations section of the module.
'*************************************************************

Option Explicit

'=============================================================
' Arithmetic Method:
' ------------------
' Create the following ar_ConvertFromUnsignedInteger& (Uint%)
'    and ar_ConvertToUnsignedInteger% (Bytes&) function in the
'    Module. This first function reads in an unsigned integer
'    and returns the converted value as a long. The second
'    function reads in a long and returns an unsigned integer.
'=============================================================

Function ar_ConvertFromUnsignedInteger& (Uint%)
   If Uint% < 0 Then
      ar_ConvertFromUnsignedInteger& = Uint% + 65536
   Else
      ar_ConvertFromUnsignedInteger% = Uint%
   End If
End Function

Function ar_ConvertToUnsignedInteger% (Bytes&)
   If Bytes& > 32767 Then
      ar_ConvertToUnsignedInteger% = Bytes& - 65536
   Else
      ar_ConvertToUnsignedInteger% = Bytes&
   End If
End Function

'=============================================================
' Bitwise Method:
' ---------------
' Create the following bw_ConvertFromUnsignedInteger& (Uint%)
'    and bw_ConvertToUnsignedInteger% (Bytes&) function in the
'    Module. This first function reads in an unsigned integer
'    and returns the converted value as a long. The second
'    function reads in a long and returns an unsigned integer.
'    The message box statement in the second function is used
'    to prevent an overflow message when the value passed to
'    the function is greater than 64 kilobytes.
' To illustrate what is taking place in the first bitwise function:
'    Uint% equals -23584, a value returned from an external dynamic
'    link library that is an unsigned integer and must be
'    converted to an long:
'        1010001111100000 (-23584)
'    AND   11111111111111 (7FFF)
'        ----------------
'          10001111100000 (41952)
'=============================================================

Function bw_ConvertToUnsignedInteger% (Bytes&)
   Dim x%
   If Bytes& > 65535 Then
      MsgBox "You passed a value larger than 65535"
      Exit Function
   End If

   x% = Bytes& And &H7FFF
   bw_ConvertToUnsignedInteger% = x% Or -(Bytes& And &H8000)
End Function

Function bw_ConvertFromUnsignedInteger& (Uint%)
   bw_ConvertFromUnsignedInteger& = Uint% And &HFFFF&

'-------------------------------------------------------------
' The &HFFFF& requires the & at the end of the hex number. This
'    qualifies the hex number as 32-bit versus 16-bit.
'-------------------------------------------------------------

End Function

Declare Function External_Call% Lib "your.dll" (ByVal ValueToPass%) 

x% = External_Call(bw_ConvertToUnsignedInteger%(41952))
y& = bw_ConvertFromUnsignedInteger&(x%)