Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!dptg!ulysses!andante!alice!ark
From: ark@alice.UUCP (Andrew Koenig)
Newsgroups: comp.lang.c
Subject: Re: IEEE floating point format
Message-ID: <9740@alice.UUCP>
Date: 4 Aug 89 17:31:57 GMT
References: <2170002@hpldsla.HP.COM> <9697@alice.UUCP> <3554@buengc.BU.EDU> <3591@buengc.BU.EDU>
Organization: AT&T Bell Laboratories, Liberty Corner NJ
Lines: 24

In article <3591@buengc.BU.EDU>, bph@buengc.BU.EDU (Blair P. Houghton) writes:

> Next question:  do C compilers (math libraries, I expect I should mean)
> on IEEE-FP-implementing machines generally limit doubles to normalized
> numbers, or do they blithely allow precision to waft away in the name
> of a slight increase in the number-range?

> I expect the answer is "the compiler has nothing to do with it", so the
> next question would be, are there machines that don't permit the loss
> of precision without specific orders to do so?

If you implement IEEE floating point, you must implement denormalized
numbers -- they're part of the spec.

I don't see, though, why you describe denormalized numbers as `the
loss of precision'.  Compared with the alternative, it's a gain in
precision.  After all, the only other thing you could do would be
to underflow to 0, which would lose all precision.

I don't remember whether IEEE requires you to be able to generate
a trap as a side effect of an operation whose result is denormalized.
-- 
				--Andrew Koenig
				  ark@europa.att.com