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Re: PATCH: HUGE_VAL should be Infinity


On Thu, Nov 30, 2000 at 01:22:46PM -0500, John David Anglin wrote:
> My currently suggested fix for the hugeval and mzero tests is to make
> them expected fails.  The patch is here
> <http://gcc.gnu.org/ml/gcc-patches/2000-10/msg00615.html>.
> 
> >   In message <200010180419.AAA21005@hiauly1.hia.nrc.ca>you write:
> ...
> >   > I spent time on it because hppa hardware
> >   > nominally has an ieee compatible floating unit.
> > Correct, except as you note, the lack of an fneg instruction on PA1.0 and
> > PA1.1 chips makes it impossible to perform an efficient negation operation.
> 
> According to my tests, at least some PA1.1 chips have the fneg instruction.
> I ran tests with it on the 735 that I have.  However, probably some PA1.1
> chips don't have it or the HP hardware engineers forgot to tell the software
> folks about it (or maybe they noticed bugs in the implementation).  Anyway,
> the fneg on the 735 behaves the same as subtracting from 0.  Thus, there
> is no advantage in using it.

Or possibly HP/UX catches the unimplemented instruction trap and simulates the
unimplemented instruction, and then restarts the program.  Obviously if that is
the case, you don't want the compiler doing this for performance intensive
code.  I remember UNIX V6 doing this on a PDP-11/40 to emulate the 11/45
floating point, and being able to tell from the front console's blinking lights
when somebody was doing a stat package.

-- 
Michael Meissner, Red Hat, Inc.
PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886, USA
Work:	  meissner@redhat.com		phone: +1 978-486-9304
Non-work: meissner@spectacle-pond.org	fax:   +1 978-692-4482

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