Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!mit-amt!peter
From: peter@mit-amt.MEDIA.MIT.EDU (Peter Schroeder)
Newsgroups: comp.sys.hp
Subject: Re: extreme performance degradation in c compiler on HP9000/835
Message-ID: <751@mit-amt.MEDIA.MIT.EDU>
Date: 25 Sep 89 16:01:00 GMT
References: <721@mit-amt.MEDIA.MIT.EDU> <3770023@hpcllz2.HP.COM>
Reply-To: peter@media-lab.media.mit.edu (Peter Schroeder)
Organization: MIT Media Lab, Cambridge MA
Lines: 26

In article <3770023@hpcllz2.HP.COM> dhandly@hpcllz2.HP.COM (Dennis Handly)

>relaxation techniques.  The user took some of the SIN and COS function calls
>out of the look to see if it went faster?  The end result was that with
>less function calls, it took longer.  When I ran the same program on MPE XL,
>series 900, it aborted with an overflow.  Using the +T option on HP-UX
>also caused the overflow.  
>
>It turned out that the SIN and COS caused the result to be -1..+1

As many readers of this group have discovered the problem was indeed an
overflow and subsequent dispatch of exception handling to software.

I did that loop for timing purposes on some c++ programs that I had written
and never bothered to look at the actual result.

Now, the interesting point is that with the new ANSI/IEEE floating point
stuff bad floating point operations don't cause core dumps anymore. It is
indeed possible to enable this property once again with a little assembly
program that Daryl (daryl@hpcllla.hp.com) sent to me [Daryl: can we post
this here, so everybody can take advantage of this fix?].

Thanks everyone for your help!

Peter
peter@media-lab.media.mit.edu