CODEWITHSUNDEEP
c#.netvb.netieeembf
BillB4
BillB4

Reputation: 29

How to convert IEEE Single to MBF Single in .NET

I need to convert an IEEE Single in .NET to the old MBF Single. There is a similar post here but it does the opposite of what I need.

Convert MBF Single and Double to IEEE

I can use either VB.NET (preferred) or C# code.

Upvotes: 0

Views: 128

Answers (1)

BillB4
BillB4

Reputation: 29

I came across an example in Borland C++ at https://community.embarcadero.com/index.php/article/technical-articles/162-programming/14799-converting-between-microsoft-binary-and-ieee-forma

I muddled through the example (I don't know C++) and came up with the following in VB.NET. It works except for the value of zero so I added a check for zero. I don't know if the C++ code also gets zero wrong or if it's my conversion. Anyway, it seems to work.

Function MTIS(value As Single) As Byte()

    Dim msbin(3) As Byte

    If value <> 0 Then ' HACK

        Dim ieee As Byte() = BitConverter.GetBytes(value)

        Dim sign As Byte
        Dim msbin_exp As Byte

        sign = ieee(3) And CByte(&H80)
        msbin_exp = msbin_exp Or ieee(3) << 1
        msbin_exp = msbin_exp Or ieee(2) >> 7

        ' An ieee exponent of 0xfe overflows in MBF
        If msbin_exp = CByte(&HFE) Then
            Throw New OverflowException("An IEEE exponent of 0xFE overflows in MBF.")
        End If

        msbin_exp += CByte(2) ' actually, -127 + 128 + 1
        msbin(3) = msbin_exp
        msbin(2) = msbin(2) Or sign
        msbin(2) = msbin(2) Or (ieee(2) And CByte(&H7F))
        msbin(1) = ieee(1)
        msbin(0) = ieee(0)

    End If

    Return msbin

End Function

Upvotes: 0

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