From owner-freebsd-hackers  Mon Nov  6 08:37:12 1995
Return-Path: owner-hackers
Received: (from root@localhost)
          by freefall.freebsd.org (8.6.12/8.6.6) id IAA01136
          for hackers-outgoing; Mon, 6 Nov 1995 08:37:12 -0800
Received: from gandalf.me.ksu.edu (root@gandalf.me.ksu.edu [129.130.41.86])
          by freefall.freebsd.org (8.6.12/8.6.6) with ESMTP id IAA01129
          for <hackers@freebsd.org>; Mon, 6 Nov 1995 08:37:05 -0800
Received: from bilbo.me.ksu.edu (joed@bilbo.me.ksu.edu [129.130.41.87]) by gandalf.me.ksu.edu (8.6.10/8.6.9) with ESMTP id KAA05694; Mon, 6 Nov 1995 10:36:50 -0600
Received: (from joed@localhost) by bilbo.me.ksu.edu (8.6.9/8.6.9) id KAA23017; Mon, 6 Nov 1995 10:34:37 -0600
From: Joe Diehl <joed@engg.ksu.edu>
Message-Id: <199511061634.KAA23017@bilbo.me.ksu.edu>
Subject: Re: Pentium BUG
To: Jerry.Kendall@vmicls.com, hackers@freebsd.org
Date: Mon, 6 Nov 1995 10:34:37 -0600 (CST)
In-Reply-To: <9511061410.AA16785.gonzo@vmicls.com> from "Jerry Kendall" at Nov 6, 95 09:10:22 am
X-Mailer: ELM [version 2.4 PL24]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Content-Length: 1144      
Sender: owner-hackers@freebsd.org
Precedence: bulk

As Jerry Kendall wrote:
> 
> A while ago, I read somewhere, a little test procedure that I could do
> to test and see if my Pentium had this 'well-known' bug.
> 
> Does anyone know what this procedure is ???
> 
> Jerry
> 

Here's a small little program to test for the bug:

    #include <stdio.h>

    int main()
    {
        double x,y,z;

        x = 4195835.0;
        y = 3145727.0;
        z = x - (x / y) * y;
        printf("%f\n",z);
        return 0;
    }                   

As you can see, by simply algebra, z should always == 0; however, on
a Pentium with the FDIV bug, you can get odd answers with certain 
numbers.  In this case, the answer will be 256 if you have the bug,
and 0 if you don't...

Here is the sig of the guy who either wrote the code or posted the code
without any credit given to the author...
          ___
         |0 0| Thanks,
         | ^ | Duck
         (\_/) Wm. David "Duck" McDonald, Anderson SC USA
   ,______| |  and.factm.tr@ocf.compuserve.com
    \______/   TOP-DUCK@genie.geis.com      
   

Enjoy... :-) 
 
---
Joe Diehl <joed@engg.ksu.edu>
Engineering Computing Center
Kansas State University