Requesting approval of some changes
P1788
Discussions, mainly among the editors (Keil, Melquiond, Nazhedin, Nedialkov, Pryce, W.v.Gudenberg) together with Michel Hack and Vincent Lefevre, have raised some changes we think desirable or essential:
1. (Essential) Taking the intervalPart of NaI shall signal an exception,
to be called IntvlPartOfNaI.
Rationale: This is a dangerous operation as it creates a valid bare interval
(Empty) from an invalid interval.
2. (Essential) Various changes to the start of Clause 7 "Flavors".
Rationale: Christian saw that currently, trying to describe conformance for
both "included" and "non-included" flavors leads to contradictions.
Indeed §7 never actually defines what a flavor *is*!
We shall define a flavor to be an interval arithmetic that has certain core
behavior (as currently set out in §7.1 but tightened up).
Then we define the notions of a flavor being (a) "provided" and (b) "included",
which are independent of each other.
This is similar to the tightening of the spec of number formats that we did
recently, distinguishing "format", "provided format" and "supported format".
These changes also were to let one specify conformance precisely.
Text will be circulated shortly.
3. (Desirable) Several people like the idea that an implementation shall have a
user-selectable mode of operation where as soon as one goes outside "common
evaluations" an exception is signaled (possibly terminating execution but
that is beyond the remit of the standard).
E.g. [1,2]/[0,1] would cause this, as would sqrt([-1,1]).
Overflow would also cause it, e.g. [0,realmax]+[0,realmax].
This makes 1788 behave like "classical" Moore interval arithmetic.
I suggest the exception be called "NonClassicalOperation".
Comments:
- I suggest only require it for decorated intervals.
- But maybe also for compressed intervals if provided? More generally, if the
decoration drops below the threshold t, whether t is com or some other
value, terminate execution?
- In effect this implements the "classical flavor", but doesn't need to be
called a separate flavor.
If no one speaks against these changes, I shall ask the Chair that they be treated as a "consensus motion" and approved without a vote.
Regards
John Pryce