PRB: Converting MBF to IEEE in Visual Basic for Windows

The information in this article applies to:

• Professional and Enterprise Editions of Microsoft Visual Basic, 16-bit only, for Windows, version 4.0

SYMPTOMS

Data files created with older Microsoft Basic products (Quick Basic, GW-Basic, and Basica (IBM and Compaq licensed Basic)) may not be readable by Visual Basic for Windows.

CAUSE

Prior to the IEEE floating point standard being widely accepted, Microsoft used an internal floating point format known as Microsoft Binary Format (MBF). The IEEE standard was introduced later and became the industry standard.

Early versions of Microsoft QuickBASIC and GW-Basic supported only MBF format. In Microsoft Basic Professional Development System (PDS) and Visual Basic for MS-DOS, functions are available to convert between MBF and IEEE formats. As Microsoft moved toward complete acceptance of the IEEE standard, however, support for the MBF format was removed.

Visual Basic for Windows uses the IEEE standard. The MBF format, however, is incompatible with the IEEE standard and data saved in this manner will not be readable.

WORKAROUND

The PDS and Visual Basic for MS-DOS products contained functions that convert between MBF format and IEEE format. These functions are not available in Visual Basic for Windows. Here are two possible solutions to this dilemma:

1. A program can be written in PDS or Visual Basic for MS-DOS that re-creates the file containing the MBF data. After reading the file information into PDS or Visual Basic for MS-DOS, you can use the MKxMBF$ functions (see the manuals for PDS or Visual Basic for MS-DOS or their Help menus) to convert the data to IEEE format. This method is preferred for two reasons:

       - It converts your data to IEEE so that other programs can access
         your files.
   

       - If you use method 2, your program will need an extra DLL that
         you must distribute with your application.
   

2. Previously, there was no way to convert the data from Visual Basic for Windows. But now there is a DLL available to do this. This DLL (MBF2IEEE.DLL) contains functions that simulate the MKS, MKD, CVS, and CVD functions that were present in some of the MS-DOS-based Basic products. These functions (MKS, MKD, CVS, and CVD) do not exist in Visual Basic for Windows, thus the need for this DLL. The MORE INFORMATION section below gives details about the DLL and explains how to download it from the Microsoft Software Library.

STATUS

This behavior is by design.

MORE INFORMATION

Details About Method Two: Using Mbf2ieee.dll

NOTE: These functions all do conversions between Microsoft Binary Format (MBF) and IEEE floating point values. Some of the newer MS-DOS-based Basic products had versions of these functions that worked differently. For example, they let you look at an IEEE number as a string without converting it to MBF. The routines described here are only provided as a way of retrieving old MBF data.

These functions provide conversions between IEEE floating point values and Microsoft Binary Format (MBF) floating point values. Below is a set of declare statements which must be included in a Visual Basic program which calls these functions:

   Public Declare Function Cvs Lib "MBF2IEEE.DLL" (X As String) As Single
   Public Declare Function Cvd Lib "MBF2IEEE.DLL" (X As String) As Double
   Public Declare Function Mks Lib "MBF2IEEE.DLL" (X As Single) As String
   Public Declare Function Mkd Lib "MBF2IEEE.DLL" (X As Double) As String

CVS and CVD Functions

These functions accept a 4-byte (CVS) or 8-byte (CVD) string as an argument. They expect the bit pattern of this string to represent a single or double precision MBF value, respectively. The function returns an IEEE result.

   Dim MBF As String, IEEE As Single
   ' load the string from a file, etc.
   IEEE = CVS(MBF)

MKS and MKD Functions

These functions accept an IEEE single (MKS), or double (MKD) precision value as an argument. It then converts this value into a 4-byte or 8-byte MBF value and returns it in a string.

   Dim MBF AS String, IEEE As Single
   MBF = MKS(IEEE)
   ' Now write the MBF value out to disk

Potential Problems

There are differences between the IEEE format and MBF. For this reason precision may be lost during the translations. It is also possible that a number cannot be converted between the two formats. If this is the case, a Visual Basic Overflow (Error #6) is generated. This is a trappable error, so handle the error accordingly.

How to Get Mbf2ieee.dll

The following file is available for download from the Microsoft Software Library:

 ~ mbf2ieee.exe (size: 25002 bytes) 

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Source Code Included in Mbf2ieee.exe

In addition to the .dll itself, the source code is also provided, so you can make modifications and recompile if you have Microsoft C. To recompile and build a new .DLL file, you must use Microsoft C because the routines are specific to Microsoft C and rely on the way Microsoft C returns floating point Values. This source code does not compile with Borland C.

To recompile with Microsoft C, use the following command line statements to build the DLL:

    cl -ALw -Ow -W2 -Zp -Tp mbf2ieee.c
    link /nod c:\vb\cdk\vbapi.lib mbf2ieee, mbf2ieee.dll, NUL, sdllcew
       oldnames libw, mbf2ieee
    rc -t mbf2ieee.dll
    implib mbf2ieee.lib mbf2ieee.def