Public Comment Number PC-UK0135

ISO/IEC CD 9899 (SC22N2620) Public Comment

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

Date: 1998-02-25
Author: N.M Maclaren
Author Affiliation: Self
Postal Address:
    University of Cambridge,
    Computer Laboratory,
    New Museums Site,
    Pembroke Street,
    Cambridge CB3 3QG,
    United Kingdom
E-mail Address: <nmm1@cam.ac.uk>
Telephone Number: +44 1223 334761
Fax Number:       +44 1223 334679
Number of individual comments: 1


Comment 1. 

Category: Normative change to existing feature retaining the original intent

Committee Draft subsection: 7.6.4.2

Title: feholdexcept is sometimes unimplementable


Detailed description:

This is unimplementable on some hardware.  For example, it requires the
continuation after the invalid exception, when continuing after underflow
is wanted, even on systems that distinguish the various levels of
exception.  And, yes, there are systems where continuing after underflow is
possible but not after invalid - I manage one!

From both the software engineering and implementability point of view,
this needs an extra argument specifying the minimum set of exceptions to
mask.  I suggest making the changes:

    #include <fenv.h>
    int feholdexcept(fenv_p *envp, int excepts);

    ..., and installs a non-stop (continue on exceptions) mode, if
    available, for an implementation-defined set of exceptions that
    includes all those specified in the parameter excepts.