Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!ucsd!swrinde!elroy.jpl.nasa.gov!freedom!xanth!mcdowell
From: mcdowell@xanth.msfc.nasa.gov (Jonathan McDowell)
Newsgroups: comp.lang.fortran
Subject: Re: IEEE exceptions
Message-ID: <mcdowell.667579808@xanth>
Date: 26 Feb 91 14:50:08 GMT
References: <91963@lll-winken.LLNL.GOV>
Sender: root@freedom.msfc.nasa.gov (Super-User)
Distribution: usa
Organization: NASA/MSFC
Lines: 68

macq@miguel.llnl.gov (Don MacQueen) writes:
[ Gets an error message due to IEEE exceptions in Sun fortran, integrating
a normal distribution].

Sun fortran lets you divide by zero and other fun things during your program
and only lets you know at the end. I actually find this quite useful as I use
the NaN (Not a Number) value (obtained by y=0./0.) as a null value for missing
data, to avoid the nastiness of using -999.9 etc. But not letting you know until

the end of the program is silly.

 I generated Don's error with the following simple program:

xanth{mcdowell}[59]t% cat test.f
        y=exp(-400.0)
        write (*,*) y
        end             
xanth{mcdowell}[60]t% a.out
  0.
 Warning: the following IEEE floating-point arithmetic exceptions 
 occurred in this program and were never cleared: 
 Inexact;  Underflow; 

>Can I assume that 'Inexact' is occurring for the same reason that underflow is 
occurring?  
>What exactly (or inexactly?) does inexact mean? 
 It would appear so; I guess that inexact means 'some exception that loses preci
sion' 
(as opposed to 'Invalid Operand' which you get when you replace the exp above wi
th a
sqrt) and is followed by the name of the specific exception that has occurred. 

>What does it mean to 'clear an exception?'

 I remove the annoying error message from the above program with
xanth{mcdowell}[66]t% cat test.f
        y=exp(-400.0)
        write (*,*) y
        call sys_exit
        END
c-------------------------------------------
       subroutine sys_exit
c Avoid nasty error message on exit
       integer ierr,ieee_flags
       character out*16
       ierr=ieee_flags ('clear','exception','all',out)
       end
                        
xanth{mcdowell}[67]t% a.out
 0.
                                                                          
Of course, this also stops any 'Invalid Operand' warnings that
you may incur.


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 |  Jonathan McDowell                 |  phone : (205)544-????                 |

 |  Space Science Lab ES65            | uucp:                                  |

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