IEEE float co-processors

[David A. Moon <Moon@SCRC-STONY-BROOK.ARPA>]

    Date: Tue, 28 Jan 86 15:12:49 est
    From: Lab Manager(Brad Miller)  <lab@rochester.arpa>

    I have not been thrilled with this ongoing meandering about floating
    point, but I'd like to take exception to your statement about leaving
    intermediate result precision unspecified. It would be nice if a
    program working on one machine also worked on another. Surely that is
    what portability is supposed to insure, not that the language is so
    general that any floating point result is OK.

Well, you see, there are two conflicting goals here.  It would be nice
for programs to be portable.  It would also be nice for the Common Lisp
community not to have to take on the job of forcing IBM and DEC to agree
on a common format and semantics for floating-point arithmetic.

What we have done is to provide some features for finding out the
characteristics of floating-point arithmetic in a particular implementation.
This may be only a half measure, but it may also be the best we can do.

Taking off my language designer hat and putting on my manufacturer hat, of
course the system my company sells conforms to the IEEE standard and otherwise
makes an effort to provide reasonable, consistent, and standardized
floating-point semantics.  Some other manufacturers do so as well.  But I
don't think we want to forbid Common Lisp to be implemented on hardware that,
for whatever reason, has different ideas about how floating-point should work.

I'm going to try not to send any more mail on this subject.