Re: Should -fcross-jumping be part of -O1?

[Robert Dewar <dewar at gnat dot com>]

Ian Lance Taylor wrote:

> Granted.  I was thinking of the ability to prove algorithm
> characteristics based on the IEEE spec, which is something I've done
> in the past.  To me that is accurate floating point.  But I can see
> that others may think that accurate floating point means something
> else.

You don't really mean what you are saying here. The IEEE spec is a 
hardware/software spec about the behavior of certain floating-point 
operations. It has hardly anything to say about the relationship between 
these operations and semantics of high level languages.

So what you were really doing, assuming you were not working in machine 
language :-) was to prove some properties under some set of assumptions 
about mapping of language operations to IEEE operations. Yes, I know 
that the latest C standard does have something to say about that, so you 
could also be referring to that standard, but you can't just say you are 
referring to the IEEE standard and let it go at that.

So you can't just say "accurate floating-point means IEEE". That's not
good enough, you have to further specify what you expect in terms of the
semantics of the language you are using.

For a rather complete discussion of these issues see Sam Figueroa's 
thesis: http://www.cs.nyu.edu/csweb/Research/Theses/figueroa_sam.pdf
("A Rigorous Framework for Fully Supporting the IEEE Standard for 
Floating-Point Arithmetic in High-Level Programming Languages").