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Re: contradiction about the INFINITY macro

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From Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups comp.std.c
Subject Re: contradiction about the INFINITY macro
Date Mon, 11 Oct 2021 12:39:50 -0700
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James Kuyper <jameskuyper@alumni.caltech.edu> writes:
> On 10/9/21 4:17 PM, Vincent Lefevre wrote:
>> In article <86wnmoov7c.fsf@linuxsc.com>,
>>   Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>>> What occurs is defined behavior and (for implementations that do
>>> not have the needed value for infinity) violates a constraint.
>>> A diagnostic must be produced.
>> 
>> If this is defined behavior, where is the result of an overflow
>> defined by the standard? (I can see only 7.12.1p5, but this is
>> for math functions; here, this is a constant that overflows.)
>
> "For decimal floating constants, and also for hexadecimal floating
> constants when FLT_RADIX is not a power of 2, the result is either
> the nearest representable value, or the larger or smaller representable
> value immediately adjacent to the nearest representable value, chosen in
> an implementation-defined manner.
> For hexadecimal floating constants when FLT_RADIX is a power of 2, the
> result is correctly rounded." (6.4.4.2p3)
>
> In the case of overflow, for a type that cannot represent infinity,
> there is only one "nearest representable value", which is DBL_MAX.

But does that apply when a constraint is violated?

6.4.4p2, a constraint, says:

    Each constant shall have a type and the value of a constant shall be
    in the range of representable values for its type.

A "constraint", aside from triggering a required diagnostic, is a
"restriction, either syntactic or semantic, by which the exposition of
language elements is to be interpreted", which is IMHO a bit vague.

My mental model is that if a program violates a constraint and the
implementation still accepts it (i.e., the required diagnostic is a
non-fatal warning) the program's behavior is undefined -- but the
standard doesn't say that.  Of course if the implementation rejects the
program, it has no behavior.

For what it's worth, given this:

    double too_big = 1e1000;

gcc, clang, and tcc all print a warning and set too_big to infinity.
That's obviously valid if the behavior is undefined.  I think it's also
valid if the behavior is defined; the nearest representable value is
DBL_MAX, and the larger representable value immediately adjacent to
DBL_MAX is infinity.

It doesn't seem to me to be particularly useful to say that a program
can be rejected, but its behavior is defined if the implementation
chooses not to reject it.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */

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Thread

contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-09-30 01:47 +0000
  Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-29 19:05 -0700
    Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-09-30 11:24 +0000
      Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-30 08:38 -0700
        Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-10-01 09:05 +0000
          Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-01 12:20 -0700
            Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-10-04 09:26 +0000
              Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-04 10:34 -0700
                Re: contradiction about the INFINITY macro Geoff Clare <geoff@clare.See-My-Signature.invalid> - 2021-10-05 13:53 +0100
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-10-06 00:12 +0000
                Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-07 07:05 -0700
                Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-07 07:51 -0700
                Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-08 11:41 -0700
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-10-09 19:49 +0000
                Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-09 14:28 -0700
          Re: contradiction about the INFINITY macro Jakob Bohm <jb-usenet@wisemo.com.invalid> - 2021-10-01 22:55 +0200
            Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-01 14:26 -0700
          Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-08 08:30 -0700
            Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-08 11:40 -0700
              Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-17 21:00 -0800
            Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-10-09 20:05 +0000
              Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-11 12:40 -0400
              Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-17 21:02 -0800
      Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-08 00:02 -0700
        Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-10-09 20:17 +0000
          Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-11 12:40 -0400
            Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-11 12:39 -0700
              Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-11 21:04 -0400
                Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-11 18:33 -0700
                Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-03 12:03 -0800
                Re: contradiction about the INFINITY macro Richard Damon <Richard@Damon-Family.org> - 2022-01-03 16:45 -0500
                Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-03 14:36 -0800
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-04 02:10 -0500
                Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-17 10:09 -0800
              Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-03 11:55 -0800
            Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-10-26 10:01 +0000
              Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-26 12:53 -0400
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-10-28 09:38 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-28 11:23 -0400
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-10-29 12:12 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-30 02:08 -0400
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-08 02:44 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-08 01:46 -0500
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-08 10:56 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-08 13:50 -0500
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-09 02:48 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-09 00:50 -0500
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-09 10:12 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-09 12:51 -0500
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-10 12:48 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-10 12:03 -0500
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-12 23:17 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-12 21:03 -0500
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-15 09:18 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-15 14:25 -0500
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-16 01:17 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-16 10:29 -0500
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-12-08 10:09 +0000
                Re: contradiction about the INFINITY macro Derek Jones <derek@NOSPAM-knosof.co.uk> - 2021-11-16 11:32 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-16 10:35 -0500
          Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-11-09 07:13 -0800
            Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-10 13:16 +0000
              Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-11-10 08:02 -0800
                Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-10 15:01 -0800
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-13 00:30 +0000
                Re: contradiction about the INFINITY macro Thomas Koenig <tkoenig@netcologne.de> - 2021-12-02 22:14 +0000
                Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-03 12:48 -0800
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-12 23:55 +0000
                Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-11-15 07:59 -0800
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-15 23:39 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-15 20:00 -0500
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-16 01:28 +0000
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-11-16 01:57 +0000
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-11-16 09:52 -0500
                Re: contradiction about the INFINITY macro Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-16 19:00 -0800
                Re: contradiction about the INFINITY macro Vincent Lefevre <vincent-news@vinc17.net> - 2021-12-08 10:56 +0000
                Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-03 12:56 -0800
                Re: contradiction about the INFINITY macro James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-03 22:45 -0800
                Re: contradiction about the INFINITY macro Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-17 05:35 -0800
  Re: contradiction about the INFINITY macro Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-09-30 03:20 +0100

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