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Groups > comp.lang.c > #53801

Re: the language

From Nobody <nobody@nowhere.invalid>
Newsgroups comp.lang.c
Subject Re: the language
Date 2014-12-03 15:42 +0000
Organization A noiseless patient Spider
Message-ID <pan.2014.12.03.15.42.24.662000@nowhere.invalid> (permalink)
References <bgfc7at635gna5mll0ifmnlp6iq86prijn@4ax.com> <m5ldok$sai$1@news.mixmin.net> <fbd0ee6f-e0ed-4bd5-9390-1cbf44de7e1f@googlegroups.com>

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On Wed, 03 Dec 2014 02:23:14 -0800, Malcolm McLean wrote:

>> undefined behaviour which has defined behaviour on machine a programmer
>> uses, is defined behaviour if has also definied basis of the behaviour.
>>
> Undefined behaviour means "undefined by by the C standard", not "existing
> in some abstract quantum state of undefinability". On most real hardware,
> the results of UB can easily be determined by someone with a bit of
> knowledge about the processor's instruction set and how the compiler is
> likely to treat the code.

Knowledge about the hardware is less relevant than knowledge of the
compiler's internals. And unlike the former, the latter changes with each
new version of the compiler.

When optimisation is enabled, modern compilers are sufficiently complex
that anyone who thinks that they understand how the compiler is likely to
treat the code is almost certainly wrong. Even the people who wrote the
compiler probably can't reliably predict how it will actually compile
anything beyond the most trivial expression.

UB is no longer about simply getting the implementation-specific behaviour
of whatever instructions arise from a mechanical translation of C
expressions to assembler.

Modern compilers will specifically identify the bounds of defined
behaviour and use those in optimising the code. Signed arithmetic will be
assumed not to overflow. Any expression used as the second operand to / or
% will be assumed to be non-zero (and not just within the / or % operation
itself).

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the language Rosario193 <Rosario@invalid.invalid> - 2014-11-26 21:54 +0100
  Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-26 21:56 +0100
    Re: the language John Bode <jfbode1029@gmail.com> - 2014-11-26 13:45 -0800
      Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 11:52 +0100
      Re: the language "Bill Cunningham" <nospam@nspam.invalid> - 2014-12-01 23:25 -0500
      Re: the language "Bill Cunningham" <nospam@nspam.invalid> - 2014-12-02 00:56 -0500
        Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-04 14:52 +0100
          Re: the language "Osmium" <r124c4u102@comcast.net> - 2014-12-04 08:07 -0600
            Re: the language Geoff <geoff@invalid.invalid> - 2014-12-04 10:20 -0800
  Re: the language Mark Storkamp <mstorkamp@yahoo.com> - 2014-11-26 15:11 -0600
    Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 12:16 +0100
      Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 12:18 +0100
  Re: the language John Bode <jfbode1029@gmail.com> - 2014-11-26 13:12 -0800
    Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-11-27 00:37 +0000
    Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-27 01:13 +0000
  Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-11-26 22:45 +0000
    Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-27 07:41 +0100
  Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-27 08:12 +0100
    Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-11-27 01:43 -0600
      Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 11:56 +0100
        Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-11-28 09:08 -0600
          Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 20:58 +0100
            Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-11-28 19:22 -0600
              Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-02 02:59 +0100
                Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-12-02 02:53 +0000
                Re: the language Les Cargill <lcargill99@comcast.com> - 2014-12-01 21:25 -0600
                Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-12-02 06:22 +0000
  Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-11-27 08:37 +0000
    Re: the language Reinhardt Behm <rbehm@hushmail.com> - 2014-11-27 16:44 +0800
      Re: the language gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-27 15:35 +0000
        Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-11-27 11:58 -0500
          Re: the language jt@toerring.de (Jens Thoms Toerring) - 2014-11-27 22:44 +0000
            Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 09:52 +0100
            Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-11-28 12:53 -0800
          Re: the language Thomas Jahns <jahns@idontlikespam.dkrz.de> - 2014-11-28 10:07 +0100
            Re: the language Thomas Jahns <jahns@idontlikespam.dkrz.de> - 2014-11-28 14:57 +0100
            Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-11-28 13:09 -0800
    Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 12:01 +0100
      Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-11-28 14:46 +0000
    Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-11-28 13:16 -0800
      Re: the language gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-28 22:09 +0000
        Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-01 03:40 -0800
      Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 14:42 -0800
        Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-01 03:22 -0800
      Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-11-28 23:09 +0000
        Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 16:14 -0800
          Re: the language BartC <bc@freeuk.com> - 2014-11-29 01:42 +0000
          Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-11-29 01:42 +0000
            Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-29 04:03 -0800
          Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-01 00:55 -0800
            Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-02 05:42 +0000
        Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-11-28 19:25 -0500
        Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-01 03:21 -0800
          Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-01 14:02 +0000
            Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-05 10:18 -0800
              Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-07 08:25 +0000
                Re: the language Öö Tiib <ootiib@hot.ee> - 2014-12-07 10:44 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-07 19:17 +0000
                Re: the language Öö Tiib <ootiib@hot.ee> - 2014-12-07 15:48 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-08 05:45 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-08 03:27 -0800
                Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-12-08 06:00 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-08 06:17 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-08 03:37 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-08 12:53 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-16 04:21 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-16 12:43 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-16 14:46 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-17 00:23 +0000
                Re: the language JohnF <john@please.see.sig.for.email.com> - 2014-12-17 07:01 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-17 07:22 +0000
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-17 11:56 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-17 05:43 -0800
                Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 18:30 +0100
                Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 18:41 +0100
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-17 14:34 +0000
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-18 02:15 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-17 22:31 -0500
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-18 17:19 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-18 07:52 +0000
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-18 17:21 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-18 18:15 +0000
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-19 01:20 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 07:48 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 07:40 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 12:54 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 09:54 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 15:19 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 11:00 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 16:13 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 11:27 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 16:45 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 13:48 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 19:10 +0000
                Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-12-19 21:17 -0600
                Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-12-19 21:32 -0600
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-19 16:49 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 17:00 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 13:57 -0500
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-19 14:31 -0800
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-19 20:29 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 20:36 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-17 07:18 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-17 15:45 +0000
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-17 16:50 +0000
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-17 17:24 +0000
                Re: the language Robert Wessel <robertwessel2@yahoo.com> - 2014-12-18 02:07 -0600
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-18 12:04 +0000
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-12-18 08:06 -0500
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-18 08:30 -0500
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-12-19 00:11 -0500
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-19 07:00 +0000
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-19 08:43 -0800
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-12-19 23:29 -0500
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-20 00:37 -0800
                Re: the language gazelle@shell.xmission.com (Kenny McCormack) - 2014-12-20 08:45 +0000
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-20 09:45 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-20 03:17 -0800
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-18 06:09 -0800
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-18 14:30 +0000
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-18 14:23 +0000
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-18 08:18 -0800
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-12-20 12:22 -0500
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-20 13:36 -0500
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-20 11:43 -0800
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-20 11:37 -0800
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-20 20:10 +0000
                Re: the language Robert Wessel <robertwessel2@yahoo.com> - 2014-12-21 15:02 -0600
                Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-12-21 22:02 +0000
                Re: the language Stephen Sprunk <stephen@sprunk.org> - 2014-12-21 23:49 -0600
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-21 17:45 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-18 10:29 -0800
                Re: the language Robert Wessel <robertwessel2@yahoo.com> - 2014-12-20 05:29 -0600
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-20 11:32 -0800
                Re: the language Robert Wessel <robertwessel2@yahoo.com> - 2014-12-21 15:23 -0600
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-22 23:39 -0800
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-20 20:22 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-18 10:24 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-18 18:36 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-19 09:24 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 17:53 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-20 11:48 -0800
                Re: the language JohnF <john@please.see.sig.for.email.com> - 2014-12-19 02:20 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 08:31 +0000
                Re: the language JohnF <john@please.see.sig.for.email.com> - 2014-12-19 09:31 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 10:10 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-19 07:08 -0800
                Re: the language JohnF <john@please.see.sig.for.email.com> - 2014-12-20 06:39 +0000
                Re: the language John Forkosh <forkosh@panix.com> - 2014-12-20 07:32 +0000
                Re: the language Greg Martin <greg.at.softsprocket@dot.com> - 2015-01-04 17:02 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2015-01-04 12:40 -0500
                Re: the language Greg Martin <greg.at.softsprocket@dot.com> - 2015-01-04 18:02 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2015-01-05 09:47 -0500
                Re: the language Greg Martin <greg.at.softsprocket@dot.com> - 2015-01-05 15:14 +0000
                Re: the language Keith Thompson <kst-u@mib.org> - 2015-01-05 08:42 -0800
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-01-06 00:14 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2015-01-05 13:19 -0500
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2015-01-04 15:59 -0500
                Re: the language Keith Thompson <kst-u@mib.org> - 2015-01-04 14:30 -0800
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-01-04 15:44 -0800
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2015-01-05 13:36 -0500
  Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 12:07 +0100
  Re: the language "ocq (an evil corporate man)" <ocq@maili.ng> - 2014-12-02 23:16 +0100
    Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-03 02:23 -0800
      Re: the language "ocq (an evil corporate man)" <ocq@maili.ng> - 2014-12-03 15:55 +0100
      Re: the language Nobody <nobody@nowhere.invalid> - 2014-12-03 15:42 +0000
        Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-04 04:49 -0800
          Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-04 09:07 -0800
            Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-04 10:08 -0800
              Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-04 11:49 -0800
                Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-05 12:32 +0100
          Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-04 22:17 +0000
  Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 18:17 +0100
    Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-18 18:12 +0000
      Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 23:15 +0100
        Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 23:50 +0100
    Re: the language "ocq (an evil corporate man)" <ocq@maili.ng> - 2014-12-19 02:34 +0100

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