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Hi Ned,
> As I understand you propose the following.
In item 3 case is about string not about implementations.
So I would say:
-----
3. If a string matches the syntax, we have two cases.
a) A string doesn't contain rational number literal or both decimal and hexadecimal number literals.
Then 1788.1 constructor behaves as in 1788.
b) An string contains rational number literal or both decimal and hexadecimal number literals.
If s is a string with level 1 value x, then 1788.1 level 2 constructor
may return *any* interval containing x.
If s = [l,u] is not an interval literal because l > u, then level 1
constructor has no value. 1788.1 level 2 constructor may return
either Empty/NaI or *any* interval which contains [u,l].
-------
> So, if we have an input containing [hex,dec], presently an
> implementation of IEEE P1788.1 and an implementation of IEEE P1788 can
> produce different results. This can happen with your suggestion as
> well.
The last paragraph of section 9.8 of 1788 says
"An implementation may relax at Level 2 the accuracy mode of some input strings (too long strings or strings
with a rational number literal). Nevertheless, the constructor shall either return a Level 2 result containing
the Level 1 value, or signal an exception, see 7.5.3."
So implementation of 1788 may have behavior (3b). It is relaxation of accuracy mode.
However, accuracy can't be worse than "valid" (see 7.5.4).
If 1788 constructor would return Empty on string "[ 0x0p0 , 1]",
then it is not relaxation of accuracy mode. It is containment violation.
Best Regards,
Dima
----- Original Message -----
From: nedialk@xxxxxxxxxxx
To: dmitry.nadezhin@xxxxxxxxxx
Cc: stds-1788@xxxxxxxxxxxxxxxxx
Sent: Saturday, August 13, 2016 2:50:25 PM GMT +03:00 Iraq
Subject: Re: Motion P1788.1/M005 to avoid non-conforming interval standards
> b) if string s = [l,u] is not an interval literal because l > u.Hi Dmitry,
Thank your for your suggestions. As I understand you propose the
following. (Please correct me if I misunderstood something).
1. The text for interval literals in 1788.1 should be the same as in
1788; that is, we have the same syntax.
2. If a string (input to 1788.1 implementation) does not match the
syntax, a constructor in 1788.1 behaves in the same way as in 1788.
3. If a string matches the syntax, we have two cases.
a) An implementation of a 1788.1 constructor is not relaxed. Then
it behaves as in 1788.
b) An implementation of a 1788.1 constructor is relaxed (not
supporting rational and hex numbers).
If s is a string s with level 1 value x, then level 2 constructor
may return *any* interval containing x.
If s = [l,u] is not an interval literal because l > u, then level 1
constructor has no value. 1788.1 level 2 constructor may return
either Empty/NaI or *any* interval which contains [u,l].
====
My preference would be to keep the simpler text for the literals syntax
in 1788.1 and the rest as they are. However, I can see an issue with
respect to
"A program built on top of an implementation of IEEE P1788.1 should
compile and run, and give identical output within roundoff, using an
implementation of IEEE Std 1788TM-2015, or any superset of the former."
So, if we have an input containing [hex,dec], presently an
implementation of IEEE P1788.1 and an implementation of IEEE P1788 can
produce different results. This can happen with your suggestion as
well.
It seems that if the input to a 1788.1 program is valid, then "it should
compile and run, and give identical output within roundoff, using an
implementation of IEEE Std 1788TM-2015, or any superset of the
former."
Perhaps a simple solution is to introduce "valid input" in the above
quoted text.
What do we do from this point? Perhaps the Chair can give directions
based on procedural rules?
Best regards,
Ned
> On Aug 8, 2016, at 02:45, Dmitry Nadezhin <dmitry.nadezhin@xxxxxxxxxx> wrote:
>
> I would like to suggest a solution for 1788.1 which is compatible
> with sections 9.8 "Constructors" and 7.5.3 "Level 2 operations"
> of the "General Requirements" part of the standard 1788.
>
> 1788 defines syntax of interval literal by grammar 9.7.6 .
> Each interval literal matches the syntax.
> However, there may be a string which matches the syntax but which is not an interval literal.
> These are strings [l,u] where l and u are number literals but l > u.
>
> The syntax for Interval literals in 1788.1 would be the same as in 1788.
> However 1788.1 has a relaxed support for those strings which
> contain rational literals or which are mixed-radix [l,u] strings
> where one of l or u is a decimal literal and another is a hexadecimal literal.
>
> If string s doesn't match the syntax of 1788 interval literals
> level 1 constructor is undefined
> 1788.1 level 2 constructor must return Empty bare interval or NaI decorated interval.
>
> If string s matches the syntax of 1788 interval literal and its support by 1788.1 is not relaxed
> then 1788.1 must determine
> either string s is an interval literal
> or it is not an interval literal (when s=[l,u] and l>u).
> If it is an interval literal and its level 1 value is x
> then 1788.1 level 2 constructor must return hull(x).
> If it is not an interval literal then 1788.1 level 2 constructor must return Empty or NaI.
>
> If string s matches the syntax of 1788 interval literal and its support by 1788.1 is relaxed,
> then:
> a) if string s is an interval literal with level 1 value x.
> 1788.1 level 2 constructor may return any interval which contains x.
> Level 1 constructor has not value.
> 1788.1 level 2 constructor may return
> either Empty/NaI
> or any interval which contains [u,l] .
> Notice that the easiest behavior of 1788.1 level 2 constructor is to return Entire
> when support of input string s is relaxed in 1788.1.
>
> -Dima