Re: Fwd: IEEE-SA Daily email notification - You have 1 new notice(s).
On Tue, 01 Aug 2017 13:09:26 +0200, Oliver Heimlich wrote:
> Neither IEEE 1788 nor IEEE 754 consider infinities as numbers.
Actually they do (see entry for "number" in the glossary), but that's
not the point. They still distinguish between finite and infinite
numbers, and only finite numbers can be members of an interval when
the interval is viewed as a set.
> In IEEE 754 the values inf and -inf denote the result of an overflow.
In 754 they *also* denote exact results of operations involving zero or
infinity. The flags can be used to tell the difference. It is in 1788
that they only denote overflow or unboundedness.
> In IEEE 1788 these special values are used to denote boundaries of an
> unbound interval -- not numbers.
Correction: not members.
They are used as numbers when reporting the width of an unbounded interval.
In that case they don't necessarily denote overflow, as the interval may
have originally been given as unbounded, as opposed to being the result
of a bounded operation but with unrepresentable bounds, i.e. oveflow.
In that case the distinction can be made in the decoration -- but only by
observing a change from COM to DAC.
(I wonder if we missed something here, in the 1788 decoration system:
distinguishing unboundedness due to propagation from that due to overflow.)
> So, I don't understand what you disagree with.
Now, that is a valid point, made *repeatedly* in this forum, and in 1788.
Besides, 1788.1 is NOT the place for trying to re-introduce the EDP, as
1788.1 is intended to be a *subset* of 1788. Unfortunately the EDP battle
was lost in P1788, a few years ago, when its scope was reduced from an
early "reliable computing" to just one technique for achieving that, namely
Interval Arithmetic.
The proper place for proposing standardized "Complete Arithmetic", of
which the EDP is but one component, is really 754-2028, as the current
revision (754-2018, in progress) deliberately restricted itself to
corrections and clarifications, and not new requirements. There *is*
actually a partially-open door, as 754-2018 is considering adding new
*recommended* operations such as two-sum, to lay the foundation for a
possible new requirement in 2028. Unfortunately Complete Arithmetic
is a rather big undertaking to specify completely (pun intended), and
the 754-2018 WG is nearing the end of its term... It was this lack
of completeness that (in my opinion at least) derailed the attempt to
include EDP as a requirement in 1788. (It *is* a recommendation there.)
Michel.
---Sent: 2017-08-01 12:39:16 UTC