double rounding in x86

[Tom Lynch]

> prattacs.Stanford.EDU
> This sort of compiler nondeterminism is very nasty quite apart from
> questions of IEEE compliance.  Debugging under these conditions makes
> one realize how dependent debugging is on the usual programmer's
> understanding of the laws of causality in a program---one tears one's
> hair out trying to figure out what is going on.

Indeed, that is what this question is about.  Perhaps x86 should
have a mode where the exponents a limited to match the significand
precision.  Addition of such a mode would require agreement
among people doing the math on these part around the industry.

-tom