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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: floating point comparison
Date: 1997/08/06
Message-ID: <dewar.870870402@merv>#1/1
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Organization: New York University
Newsgroups: 
 comp.lang.ada,sci.math.num-analysis,comp.software-eng,comp.theory,sci.math
Date: 1997-08-06T00:00:00+00:00
List-Id: <comp.lang.ada>


<<The hairiest part about relying on the IEEE standard is that there are
no well-defined methods for mapping from the source language to the
machine level.  For example, can an implementer use an extra-long
80-bit representation instead of a 64-bit representation to implement
double precision floating point?  If you expect your answers to agree
to the bit level, the answer is NO; but if you expect your code to run
fast on the x86 architecture, you'd better relax your requirements and
allow a bit of fuzz in your implementation.
>>

That is a fair comment (in fact I have a PhD student, Sam Figueroa,
whose thesis precisely addresses the issue of how IEEE 754/854 should
be mapped into high level languages). Note also that this is the issue
that LCAS, recently approved despite the US negative vote, addresses
(or is it LIAS these days -- Language Independent Arithmetic Standard)

But things are not as bad as you suggest in practice, and in particular
your comment on efficiency on the x86 is technically wrong. You can place
the x86 floating-point into 64 bit mode, so that there is no efficiency
penalty, and indeed at least some C compilers on the x86 do this.