[2005] Reading Bits in a Byte Array

[Daystar]

Okay here is the problem, I want to read a Base64 Encoded Message. Which can be converted back to a Byte Array. But I need to read the bits in specific positions to retrieve the information. In VB.Net is this possible or does the program need to be written in C# or C++?

I am using the following count to return the bit value

  Public Function GetBits(byVal [Byte] as Byte, OffSet as Integer, Count as Integer) As Integer
   Return ([Byte] >> Offset) + ((1 << Count) - 1)
 End Function

The following should return the bit count that needs to be read for the total bits used to encode the profession in the string.

  bits_per_profession = code * 2 + 4

Since they say it should be stored in the second byte since the first 8 bits are set aside for version information I am doing the following.

  dim cBits as Integer = GetBits([ByteArray](2), 0, 2)

It just seems that doesn't return anything useful.

[jmcilhinney]

To read a single bit you you can perform a logical AND operation:

Public Function GetBit(ByVal data As Byte, ByVal position As Integer) As Boolean
    If position < 0 OrElse position > 7 Then
        Throw New ArgumentException("Value must be within the range 0 to 7 inclusive.", "position")
    End If
 
    Dim mask As Byte = CByte(2 ^ position)
 
    Return (data And mask) = mask
End Function

[Shaggy Hiker]

Bits_per_proffession = code >>1 +4

You say that the byte you need is byte 2, but then you look at ByteArray(2). Since .NET is 0 based, that is the third byte in the array.

[Daystar]

Bits_per_proffession = code >>1 +4

You say that the byte you need is byte 2, but then you look at ByteArray(2). Since .NET is 0 based, that is the third byte in the array.

I explained it wrong.

Example of the data string

OwUUEOX9W4O1j7aExDKCs4yDACA

Example from the older strings

A0MAxm24oCbD/h3Qmol0JEAA

I am assuming it is Base64 Encoded Stream

 Private mArr() as Byte
 Public Sub GetBytes(byVal [String] as String)
    mArr() = Convert.FromBase64String([String])
 End Sub

 Public Function DispVal(byVal [Byte] as Byte) as Integer
    Return GetBits([Byte], 2, 6)
 End Sub

For some reason that always returns really funny numbers. Also the correct code was

  bits_per_profession = code * 2 + 4

The unknown is the code

If I reversed that when reading those bits would it return the right value?