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From: jbs@WATSON.IBM.COM
Newsgroups: comp.arch
Subject: IEEE arithmetic
Message-ID: <9106150144.AA14442@ucbvax.Berkeley.EDU>
Date: 15 Jun 91 01:25:14 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
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           David Seal (quoting someone quoting the fortran standard):
>The missing rule is (ANSI X3.9-1978 sect 6.6):
>    "Any numeric operation whose result is not mathematically defined is
>    prohibited in the execution of an executable program. Examples are
>    dividing by zero and raising a zero-valued primary to a zero-valued or
>    negative-valued power."
>Who knows whether IEEE infinity is a "mathematically defined result"? If you
I would think it isn't: it doesn't correspond to a single mathematical real
number in the way that ordinary IEEE numbers do.

           Some comments:
     1.  The result of multiplying 2 reals is always mathematically de-
fined.  Therefore I don't see how this clause prohibits multiplies which
will overflow or underflow.
     2.  Ordinary IEEE numbers don't really correspond to single mathema-
tical real numbers, they correspond to intervals.  Inf and -inf are just
the names of the intervals on the ends.
                       James B. Shearer