[2008] Code is redundant.

[Troy Lundin]

I have not posted here nor have I worked with this code for a while.

I have a function that can read a value from a byte buffer in bits. I choose bits so that nybbles may be read. I have another function that determines if a certain bit is set or not. I use the two functions to read the value from the buffer. Here are the functions:

Public Shared Function Unsigned(ByVal Index As Integer, ByVal Length As Integer) As Long

            ' Check if the buffer is empty
            If Buffer.Length <= 0 Then
                Throw New InvalidOperationException("The buffer is empty. Load a file into it using OpenFile.")
                Exit Function
            End If

            ' Check the length to read to make sure it is valid
            If Length > 64 OrElse Length < 1 Then
                Throw New ArgumentException("Length cannot be greater than 64 or less than 1.")
                Exit Function
            End If

            ' Check if reading will extend past the end of the buffer
            If Index + (Length * 8) > Buffer.Length Then
                Throw New ArgumentException("End of buffer reached.")
                Exit Function
            End If

            ' The bit currently being checked
            Dim Bit As Integer = 0
            Dim Total As Long = 0

            Do
                ' Check each bit to see if it is set
                If BitflagState(Index, Length, Bit) Then
                    Total = Total Or (1 << Bit)
                End If
                Bit += 1
            Loop Until Bit = Length

            Return Total
        End Function

Public Shared Function BitflagState(ByVal Index As Int32, ByVal Length As Int32, ByVal Bit As Integer) As Boolean
            Try
                Return CBool(Unsigned(Index, Length) And (1 << Bit))
            Catch ex As Exception
                ShowErrorDialog(ex.StackTrace, ex.Message)
            End Try
        End Function

Now, the code just loops continuously until I get a stack overflow exception. The obvious reason is that the functions are not compatible. I was wondering how I could accomplish this. I want to be able to read values from a byte buffer but also read them bit by bit. Any ideas?

[dbasnett]

where is it looping continuously? have you walked it through the debugger?

[Troy Lundin]

I apologize for that. When the debugger hits this line:

Return CBool(Unsigned(Index, Length) And (1 << Bit))

It jumps back to the start of the Unsigned function and loops from there.

[dbasnett]

so put a break on that line and single step the debugger from there. is everything what you expect?

[Troy Lundin]

I confused you.

I start with the function Unsigned. It reads all the way to "If BitflagState(Index, Length, Bit) Then" and it jumps to the function BitflagState. When it reaches the line "Return CBool(Unsigned(Index, Length) And (1 << Bit))" in function BitflagState, it jumps back to the function Unsigned.

This is the way it was written but not the way I expected it to work. Weird, eh? The loop continues until the error occurs.

What I was looking for was a way to make the function Unsigned work correctly. I want it to read from a byte array one bit at a time.

So, if I set the Length property to 8 then it will read 8 bits from the array. I could have sworn this worked last time I used it but it doesn't now.

Any ideas on how I could fix this?

[techgnome]

It's not that they aren't compatible.... you've got a circular reference... Unsigned calls BitState, which calls Unsigned, which calls bitState, which calls.... you see where this is going? It's a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box inside a box BOOOM!

-tg

[Troy Lundin]

@techgnome: I understand that. I just do not understand how to get it to work right. Or rather, how to fix it.

[dbasnett]

seperate the do function and call it after the cbool(unsigned...

[Troy Lundin]

Ok. I figured out a solution. I changed the Do...Loop to a For...Next like so:

For Bit As Integer = 0 To Length - 1
    ' Check each bit to see if it is set
    If CBool(Buffer(Index) And (1 << Bit)) Then
        Total = Total Or (1 << Bit)
    End If
    If Bit Mod 8 = 0 AndAlso bit > 0 Then
        Index = Index + 1
    End If
Next Bit

The second part of that code allows me to read the next byte if the Length property allows it. Please let me know if there is a simpler way of doing this. Thanks.