masking and shifting in VB

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  14 years ago

  by harish139

  a

  , Grenada

  Joined 14 years ago

  i want to know about bit masking and shifting operations in VB
  i know it in C but how to do the foleeing c operation in VB
  

  i want to extract 90 
  a=  (&H90820002 & &HFF0000) >> 24
  

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  14 years ago

  by sync_or_swim

  Rob Bickel

  S. Wales, United Kingdom

  Joined 15 years ago
  Harish,
  
  You will have to give a better description of what you are trying to do!!!  Just saying "I want to extract 90" doesn't tell us much.  Do you want to extract characters in a certain position?  In this case, the characters at positions 7 and 8? or do you want to extract the two characters after the characters a= (&H?
  
  This example will demonstrate how to use InStr, Mid and Left to extract the two characters after the first &H in the given string:
  Private Sub Command1_Click()
  Dim strInput As String
  Dim strOutput As String
  strInput = "a=  (&H90820002 & &HFF0000) >> 24"
  If InStr(1, strInput, "&H") Then
      strOutput = Mid(strInput, InStr(1, strInput, "&H") + 2)
      strOutput = Left(strOutput, 2)
  End If
  Label1.Caption = strOutput
  End Sub
  
  This works by first using the "InStr" function (which searches a string for another string and returns the position at which that string starts) to return the start of the string "&H".  It then chops off everything before this string and the string itself using the "Mid"  function(which returns everything to the right of a given point - in this case the start position of the string &H + 2 chars for the &H itself).  So the line:
  strOutput = Mid(strInput, InStr(1, strInput, "&H") + 2)
  Will start with the string:
  a=  (&H90820002 & &HFF0000) >> 24
  and chop off the beginning to give:
  90820002 & &HFF0000) >> 24
  It then uses the "Left" function which works like the Mid function but will return everything to the left of a given point.  In this case:
  strOutput = Left(strOutput, 2)
  will return the first two characters of our string:
  90
  
  I apologise if this is not what you require but you will never get the desired reply if you post obscure questions!!  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  14 years ago

  by Zorro_ot

  Oliver Tell

  Hamburg, Germany

  Joined 15 years ago

  harish139 wrote:

  i want to know about bit masking and shifting operations in VB
  i know it in C but how to do the foleeing c operation in VB
  

  i want to extract 90 
  a=  (&H90820002 & &HFF0000) >> 24
  

  
  Usually there is no need for high level computer languages to support operations like bit masking or shifting of bit masks. These operations are low level operations and when a computer language has a set of commands of them, they usually are compiled 1:1 into assembler code.
  High level computer languages deliver a set of constants that represents the results of bit masks. Just have a look at the MouseMove event, especially on 'button' and 'shift'.
  If you still need bit masking and shifting (e.g. some graphical tasks), you can use the basic logic operations: AND, OR, XOR.
  
  
  

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  14 years ago

  by sallu_shan

  Arsalan Tamiz

  Karachi, Pakistan

  Joined 15 years ago

  You can use mathmaticaly formula for shifting (since vb does not support any bit shifting operator)

  First we should understand how shifting works

  Right Shifting will always decrease number while Left Shifting will always increase number

  E.g.

  1001 >> 1  = 100               (1 bit removed from right)

  1001 << 1 = 10010            (1 bit added at right)

  Therefore:

  RightShift = number / 2 ^ bits      (number >> bits)

  LeftShift = number * 2 ^ bits       (number << bits)

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