numerical results differ after irrelevant code change

[Michael D. Berger]

> -----Original Message-----
> From: Robert Dewar [mailto:dewar@adacore.com] 
> Sent: Sunday, May 08, 2011 11:13
> To: Michael D. Berger
> Cc: gcc@gcc.gnu.org
> Subject: Re: numerical results differ after irrelevant code change
> 
[...]
> 
> This kind of result is quite expected on an x86 using the old 
> style (default) floating-point (becauae of extra precision in 
> intermediate results).
> 

How does the extra precision lead to the variable result?
Also, is there a way to prevent it?  It is a pain in regression testing.

Thanks,
Mike.

--
Michael D. Berger
m.d.berger@ieee.org