Re: More physical source files

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: More physical source files
Date	2015-07-04 15:42 -0700
Organization	None to speak of
Message-ID	<lnlhevwnna.fsf@kst-u.example.com> (permalink)
References	(10 earlier) <39cf9193-5d10-4db9-b766-9452d7c1b0bf@googlegroups.com> <ln4mll18ak.fsf@kst-u.example.com> <71c62ee8-0007-446b-9004-c6def341205a@googlegroups.com> <lnpp47ww8j.fsf@kst-u.example.com> <d5e66ec9-845a-4dd4-8df0-ad913b4d2adb@googlegroups.com>

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Malcolm McLean <malcolm.mclean5@btinternet.com> writes:
> On Saturday, July 4, 2015 at 8:36:53 PM UTC+1, Keith Thompson wrote:
>> You can write a program that uses floating-point whose output *doesn't*
>> depend on unspecified, undefined, or implementation-defined behavior.
>> Such a program may be strictly confoming.
>>
> A C program can't output reals. It can only output bits, which are
> often interpreted as integers or rationals for the user.

Arguable, but I didn't say anything about outputting reals, or even
floating-point values.

>                                                          If you
> insist that no integer shall be off by even one place, and you are
> face with a perverse implementation designed to break your program,
> it becomes difficult to use floating point. Relax the requirements
> a bit, and it becomes quite easy.

Using floating-point in a strictly conforming program is difficult,
given C's lax requirements for floating-point precision.  (On the
other hand, strict conformance is not usually a requirement;
reasonable portability is almost always good enough.)

For example, I believe this program:

    #include <stdio.h>
    int main(void) {
        if (0.0 < 1.0) puts("ok");
        else           puts("OOPS");
    }

is strictly conforming (ignoring the possibility of errors on the puts()
call).  This program:

    #include <stdio.h>
    int main(void) {
        if (1.0 + 1.0 > 1.0) puts("ok");
        else                 puts("OOPS");
    }

is probably not strictly conforming, given that the accuracy of
floating-point "+" is implementation-defined (N1570 5.2.4.2.2p6).
On the other hand, I would argue that if the program prints "OOPS",
then the implementation violates N1570 6.5.6p5:

    The result of the binary + operator is the sum of the operands.

But there's no good way to define how much of an error would render
an implementation non-conforming.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-06-27 11:19 -0700
  Re: More physical source files Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-06-27 11:54 -0700
    Re: More physical source files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-27 21:20 +0100
  Re: More physical source files Bartc <bc@freeuk.com> - 2015-06-27 20:24 +0100
    Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-06-29 07:14 -0700
      Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-06-29 08:16 -0700
        Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-06-30 08:24 -0700
          Re: More physical source files Robert Wessel <robertwessel2@yahoo.com> - 2015-06-30 12:15 -0500
          Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-06-30 15:14 -0700
            Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-01 08:38 -0700
              Re: More physical source files glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-01 16:43 +0000
                Re: More physical source files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-01 18:52 +0100
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-01 11:21 -0700
                Re: More physical source files glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-01 18:36 +0000
                Re: More physical source files Richard Damon <Richard@Damon-Family.org> - 2015-07-01 22:33 -0400
                Re: More physical source files glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-02 19:11 +0000
              Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-01 11:08 -0700
                Re: More physical source files Richard Damon <Richard@Damon-Family.org> - 2015-07-01 22:30 -0400
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-02 08:29 -0700
                Re: More physical source files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-02 17:56 +0100
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-02 13:21 -0400
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-03 08:54 -0700
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-04 12:23 -0400
                Re: More physical source files Martin Shobe <martin.shobe@yahoo.com> - 2015-07-04 11:36 -0500
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-02 16:42 -0700
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-03 08:54 -0700
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-03 10:05 -0700
                Re: More physical source files glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-03 21:57 +0000
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-04 00:30 -0400
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-04 08:08 -0700
                Re: More physical source files Richard Damon <Richard@Damon-Family.org> - 2015-07-04 12:21 -0400
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-05 09:22 -0700
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-05 09:49 -0700
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-05 18:16 -0700
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-06 08:37 -0700
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-06 12:56 -0400
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-06 11:59 -0700
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-06 15:45 -0400
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-06 13:14 -0700
                Re: More physical source files Philip Lantz <prl@canterey.us> - 2015-07-07 01:10 -0700
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-07 08:00 -0700
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-07 07:55 -0700
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-07 13:13 -0400
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-08 08:35 -0700
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-08 12:31 -0400
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-09 08:50 -0700
                Re: More physical source files Richard Heathfield <rjh@cpax.org.uk> - 2015-07-09 16:56 +0100
                Re: More physical source files Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-09 13:31 -0700
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-09 15:03 -0700
                Re: More physical source files Ian Collins <ian-news@hotmail.com> - 2015-07-10 10:54 +1200
                Re: More physical source files David Kleinecke <dkleinecke@gmail.com> - 2015-07-10 09:52 -0700
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-09 14:32 -0400
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-05 13:41 -0400
                Re: More physical source files Richard Damon <Richard@Damon-Family.org> - 2015-07-05 14:17 -0400
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-04 12:36 -0700
                Re: More physical source files Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-04 15:19 -0700
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-04 15:42 -0700
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-04 19:04 -0400
                Re: More physical source files Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-05 03:25 -0700
                Re: More physical source files Keith Thompson <kst-u@mib.org> - 2015-07-05 09:18 -0700
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-05 14:11 -0400
                Re: More physical source files Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-05 13:41 -0700
                Re: More physical source files James Kuyper <jameskuyper@verizon.net> - 2015-07-04 12:50 -0400
      Re: More physical source files Bartc <bc@freeuk.com> - 2015-06-29 17:20 +0100
  Re: More physical source files Rosario19 <Ros@invalid.invalid> - 2015-06-28 11:57 +0200

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