Date: Mon, 24 May 1999 16:56:42 -0500
From: Eric Rudd <rudd AT cyberoptics DOT com>
Subject: Re: More x87 weirdness
To: djgpp-workers AT delorie DOT com
Message-id: <3749CB1A.9A12D076@cyberoptics.com>
Organization: CyberOptics
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Reply-To: djgpp-workers AT delorie DOT com

Eli Zaretskii wrote:

> On Wed, 19 May 1999, Eric Rudd wrote:
>
> > Eli Zaretskii wrote:
> >
> > > While testing stability of multiple exceptions fired at high rates, I've
> > > bumped into a strange phenomenon.  Perhaps somebody could help me
> > > understand what goes on and maybe correct a bug.
> > >
> > > Here's the test program.  Note that if you want to build it with stock
> > > v2.02, you need a patched itimer.c.

I don't know what's causing this strange behavior either, but I have a few data
points:

1. While shelled out to DOS from Win95 v950B on a 266-MHz P II, I found that the
SIGFPE messages generally stopped within 400 ticks or so, frequently within 100
ticks.  With Windows not running, it was more like a couple of thousand ticks,
though there was great variability.

2. On my home computer, which is a completely Windows-free 200-MHz Pentium MMX,
typically the program would run for a couple of thousand ticks before the SIGFPE
messages would stop.

Since there is a much greater interrupt latency under Windows, perhaps something
funny is happening when a tick occurs during an interrupt, and there is some
pending floating-point exception.

-Eric Rudd
rudd AT cyberoptics DOT com