Q108409: BUG: Access Violation/Hang on Divide by Zero with Intrinsic

Article: Q108409
Product(s): Microsoft Fortran Compiler
Version(s): 1.0
Operating System(s): 
Keyword(s): kberrmsg kbLangFortran
Last Modified: 02-NOV-1999

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The information in this article applies to:

- Microsoft Fortran Powerstation 32 for Windows NT, version 1.0 
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SYMPTOMS
========

The following error may not be produced when a divide by zero exception
involving an intrinsic function occurs at run time:

  run-time error M6103: MATH
  floating-point error: divide by 0

If such a program is compiled with the -Ox option, a Dr. Watson "Application
Error" message box specifying "Exception: access violation" may be generated.
Otherwise, the application may hang.

The following occurs using Fortran PowerStation 32, version 4.0:

1. Using the -Ox compile option causes an Application Error at run-time.

2. Using no compile options, the following appropriate run-time error is
  generated:

  run-time error M6103: MATH
  - floating-point error: divide by zero

CAUSE
=====

This unexpected behavior occurs when the divide by zero exception occurs in the
argument list of the SIN, COS, or SQRT intrinsic functions. ABS, EXP, and TAN
also produce incorrect behavior that is slightly different from the behavior
mentioned above.

RESOLUTION
==========

Explicitly check denominators in arguments to the SIN, COS, TAN, ABS, EXP, or
SQRT intrinsic function for zero values before performing a divide operation.

STATUS
======

Microsoft has confirmed this to be a problem in the products listed at the
beginning of this article. We are researching this problem and will post new
information here in the Microsoft Knowledge Base as it becomes available.

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

The intrinsic function ABS generates the appropriate run-time error regardless
of optimization.

The intrinsic function EXP generates the appropriate run-time error with -Ox, and
hangs otherwise.

The intrinsic function TAN returns 0 (zero) with -Ox, and hangs otherwise. For
this particular function, the compiler may generate the following warning when
compiling with /Ox:

  warning F4723: potential divide by 0

The following sample code illustrates the symptoms described above:

Sample Code
-----------

  C Compile options needed: -Ox causes an Application Error to occur
  C Compile options needed: none causes the application to hang

        a = 0.
        b = 1.
        write (*,*) a,b !no effect when commented out
        c= SQRT(b/a) !GPF here
        write (*,*) a,b,c  !no effect when commented out
        end

Additional query words: 1.00 4.00 lock halt gp-fault

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Keywords          : kberrmsg kbLangFortran 
Technology        : kbAudDeveloper kbFortranSearch kbZNotKeyword2 kbFORTRANPower32100NT
Version           : :1.0

=============================================================================

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