(j3.2006) Fw: a question on MERGE and expression evaluation

[Jim Xia]

----- Forwarded by Jim Xia/Toronto/IBM on 11/18/2010 03:08 PM -----

From:
Jim Xia/Toronto/IBM
To:
j3-bounces at j3-fortran.org
Date:
11/18/2010 02:46 PM
Subject:
a question on MERGE and expression evaluation


Hi

We have a piece of code that a user claims should result in a 
divide-by-zero exception.

       real a(10), y(10)
       a = 0.0
       y = merge(1.0/a, 0.0, a>0.0)
       print *, y
                   end

None of the compilers I have tried (XLF, NAG and ifort) result in 
exception.  The standard is also conflicting in saying whether or not 
1.0/a should be evaluated at the function invocation time.

Here are some quoted text from F08



12.5.3  seems to say 1.0/a should be evaluated at the function call.




13.2.3 seems to suggest 1.0/a need not to be evaluated since evaluation 
with undefined value can result in side-effects.

Although I'm taking the 13.2.3 as a strong argument, F03 indeed spells out 
the intention of omitting evaluation of actual argument in Annex C (C 9.5)



However, that section is deleted in F08.

So the question is: should 1.0/a be evaluated upon the function call to 
MERGE()?


Cheers,



Jim Xia

XL Fortran Compiler Test
IBM Toronto Lab at 8200 Warden Ave, Markham, On, L6G 1C7
Phone (905) 413-3444  Tie-line 313-3444
email: jimxia at ca.ibm.com
D2/YF7/8200 /MKM

http://www.ibm.com/software/awdtools/fortran/xlfortran
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