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