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From: jbs@WATSON.IBM.COM
Newsgroups: comp.arch
Subject: IEEE arithmetic
Message-ID: <9106040049.AA21430@ucbvax.Berkeley.EDU>
Date: 4 Jun 91 00:53:08 GMT
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          Jerry Callen says:
This may be obvious, but let's not confuse "compiler and runtime system
behavior" with "floating point hardware behavior." Yes, Fortran on 360/370
systems behaves as you describe. In PL/1 it is possible to completely ignore
exponent overflow if you wish and get meaningless results.
Similarly, IEEE overflow behavior is under programmer control. If you WANT to
ignore overflow and then just check to see if some error occurred at the
end of the calculation you may do so; if you want to know immediately, you can
do that, too.

          I believe most users will find it difficult to do these things.
I, for example, do not know how do this in fortran on the IBM Risc System
6000.  This is a problem for other users on other machines as the "How to
detect NaN's" thread in comp.lang.fortran shows.
          Also it is desirable that any method for doing this should be
portable across IEEE systems (since IEEE is supposed to promote portabil-
ity) and have no significant performance impact when exceptions do not
occur (since otherwise users are encouraged to run in an unsafe way and
IEEE is supposed to promote safety).
                          James B. Shearer