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Q102692: FIX: FP Emulator Converts REAL to INTEGER Incorrectly

Article: Q102692
Product(s): Microsoft Fortran Compiler
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 02-NOV-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft FORTRAN PowerStation for MS-DOS 
-------------------------------------------------------------------------------

SYMPTOMS
========

When an application developed in Microsoft FORTRAN PowerStation runs on a
computer that does not have a math coprocessor installed, the code may convert a
REAL variable or expression to an INTEGER variable incorrectly, resulting in
incorrect results.

CAUSE
=====

When an application immediately converts the results of a REAL calculation to an
INTEGER value, the code does not remove the results from the coprocessor
emulator stack. The numeric conversion routine __ftol (float to long) uses this
extended coprocessor-stack-based value instead of the truncated contents stored
in the variable. The __ftol function incorrectly rounds down the
extended-precision result.

RESOLUTION
==========

To work around this problem, use the NINT (round to nearest integer) intrinsic
function to explicitly convert the expression or variable to an INTEGER.

The /Ox optimization compiler option switch may resolve this error. Among other
optimizations, the /Ox switch calculates constant expressions at compile time.
These calculations may correctly convert the REAL number to an INTEGER while the
run-time calculation produces the incorrectly rounded result.

STATUS
======

Microsoft has confirmed this to be a problem in PowerStation versions 1.0 and
1.0a for MS-DOS. This problem has been resolved with FORTRAN PowerStation
maintenance release version 1.0a for MS-DOS.

FORTRAN Powerstation version 1.0 can be differentiated from the maintenance
release version 1.0a by invoking the linker. Typing "link32 | more" from the
\f32\BIN directory will show version 2.8 for FORTRAN Powerstation version 1.0,
and it will show 1.0f for the maintenance release version 1.0a.

MORE INFORMATION
================

The FORTRAN PowerStation floating-point emulator is a virtual dynamic- link
library (DLL) in the Phar Lap MS-DOS extender. To duplicate this problem on a
computer with a math coprocessor installed, type the following at the MS-DOS
command prompt:

  SET TNT=-FPEM

This statement causes the MS-DOS extender to ignore the math coprocessor and use
the emulator code for all math operations.

The following code example prints the word "Failed" when it runs with the
floating-point emulator:

Sample Code 1
-------------

C Compiler options needed: none

     x =  3.0
     z = -3. ** x
     i =  z
     if (i .ne. -27) then
       print *, 'Failed'
     else
       print *, 'OK'
     end if
     end

The following code example demonstrates using the NINT intrinsic function to
avoid this error. This code prints the word "OK" even when a math coprocessor is
not available.

Sample Code 2
-------------

C Compiler options needed: none

        x =  3.0
        z = -3. ** x
        i =  nint(z)
        if (i .ne. -27) then
          print *, 'Failed'
        else
          print *, 'OK'
        end if
        end

Additional query words: 1.00 Phar Lap DOSXMSF.EXE

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbFortranSearch kbZNotKeyword3
Version           : :
Issue type        : kbbug
Solution Type     : kbfix

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