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Tip of the Day
Language: VB4,VB5,VB6,VBS
Expertise: Intermediate
Jun 26, 1999

RotateLeft - Rotate a Long to the left

' Rotate a Long to the left the specified number of times
'
' NOTE: requires Power2()

Function RotateLeft(ByVal value As Long, ByVal times As Long) As Long
    Dim i As Long, signBits As Long
    
    ' no need to rotate more times than required
    times = times Mod 32
    ' return the number if it's a multiple of 32
    If times = 0 Then RotateLeft = value: Exit Function
    
    For i = 1 To times
        ' remember the 2 most significant bits
        signBits = value And &HC0000000
        ' clear those bit and shift to the left by one position
        value = (value And &H3FFFFFFF) * 2
        ' if the number was negative, then add 1
        ' if bit 30 was set, then set the sign bit
        value = value Or ((signBits < 0) And 1) Or (CBool(signBits And _
            &H40000000) And &H80000000)
    Next
    RotateLeft = value
End Function
Francesco Balena
 
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