Re: the language

From	raltbos@xs4all.nl (Richard Bos)
Newsgroups	comp.lang.c
Subject	Re: the language
Date	2014-12-18 14:30 +0000
Organization	Go wash your mouth.
Message-ID	<5492e381.575484@news.xs4all.nl> (permalink)
References	(11 earlier) <m6sc87$hmj$1@speranza.aioe.org> <ek259a5e27tr5bel88c6o07qah84o349v1@4ax.com> <5492c298.300765@news.xs4all.nl> <LjAkw.152595$Sn4.106292@fx10.iad> <2ea98619-63fc-4ab6-b7cc-40e0d292726f@googlegroups.com>

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Malcolm McLean <malcolm.mclean5@btinternet.com> wrote:

> On Thursday, December 18, 2014 1:07:00 PM UTC, Richard Damon wrote:
> > 
> > It isn't that far of a reach to say that if a compiler claims that it 
> > generates code for processor X, that this means that if the manufacturer 
> > of that processor defines the behavior of a certain operation that C 
> > leaves as undefined, then that definition would apply to the C program 
> > apparently doing that operation.
> > 
> Let's say a chip designer, reasonably, provides an assembly instruction
> 
> shift accumulator right by value in register x.
> 
> let's say he also, reasonably, defines, if x = 32, the accumulator shall
> be cleared to 0 (its a 32 bit system).
> 
> Someone writes in C
> 
> /* x = 32; */ 
> a <<= x;

That's left, not right, but let's assume a >>= x; .

> a could be cleared. Or the compiler writer could, quite reasonably, say
> "undefined behaviour, best catch it by terminating the program with
> an error message".

He could indeed, from a C POV, quite reasonably do both. And in fact I
would expect a debugging compiler (or GCC invoked in a special debugging
mode for that chip) to take the latter tack; while still expecting an
optimising compiler, or GCC invoked with -O3, to take the first
approach.
The horror, for some people, of undefined behaviour is that both of
those are allowed and you don't know which you're going to get if you
write hacky code and someone else compiles it[42]. The beauty of
undefined behaviour, for others is that both of those are allowed, and
you can get the one which is optimal for your circumstances depending on
how you choose to compile your code - and you can still avoid it by not
writing hacky code!

Richard

[42] So we say, like the doctor whose patient told him that it hurt when
he pinched the bit between his fingers: "Don't Do That, Then."

Thread

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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