Re: Adding thousands separators

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: Adding thousands separators
Date	2012-02-26 13:40 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2012Feb26.144051@mips.complang.tuwien.ac.at> (permalink)
References	(4 earlier) <e0aafffd-115b-46e1-9d24-b1a799fd2286@1g2000yqv.googlegroups.com> <2012Feb23.175123@mips.complang.tuwien.ac.at> <urWdnWjhQ_uO4dvSnZ2dnUVZ_sadnZ2d@supernews.com> <jic1lr$bvv$1@online.de> <mumdncAYfoTXZ9TSnZ2dnUVZ_oudnZ2d@supernews.com>

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Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>Bernd Paysan <bernd.paysan@gmx.de> wrote:
>> What I remember is that GCC once failed to compile
>> 
>> (u1 + u2) < u1
>> 
>> correctly (which is just a check for carry when adding u1 + u2), because 
>> u1 + u2 will only be < u1 if there is an overflow, and overflow results 
>> are undefined, so it could as well assume that this condition is false 
>> all the time.
>
>I'm pretty sure that this wasn't true, and if it did happen it was a
>bug that got fixed.  Unsigned arithmetic is always well-defined, and
>overflows are computed modulo the word size.  Only signed overflow is
>undefined, and the simple rule is to use unsigned arithmetic if you
>think you might overflow.

I don't remember the idiom above ever failing, and I think I would
have noticed, because this idiom is used in the implementation of D+
on systems with downgraded long longs, and I don't remember such a
bug.

However, I tried to test for MININT efficiently with n-1>n, and gcc
miscompiled this test into false.  One might think that one can work
around this misfeature of gcc by forcing an unsigned - and signed >
through casts, but this does not work at least in gcc-2.95 (and maybe
other versions).  It does not help that this bug has been fixed in
later versions, because we don't want to restrict ourself to just the
latest version of gcc, especially because later versions tend to
produce much slower code (we try to work around that, but it's hard to
keep up).

>As opposed to a portable assembler, I take it.  This really was the
>decision of the technical committee that produced C90 rather than any
>compiler writer

AFAIK the ANSI C TC did not standardize many things because the
implementations varied (no common practice), or because they wanted to
support implementations on a wide range of hardware.

For example, they explicitly wrote that they support 2s-complement,
1's-complement, and sign-magnitude hardware; with that in mind, one
may be able to define common properties of signed integer overflow on
any of these arithmetics, but it's probably too complicated and not
worth the effort, so they didn't.  OTOH, for unsigned arithmetic there
is only one representation, and all hardware overflows the same way,
so they standardized that.

Of course, if you have a statement by the C90 committee from the time
that states that they did not standardize these things so that
compilers could "optimize" code, I would be interested in a reference.
However, if that was their intention, I wonder why they standardized,
e.g., unsigned overflow behaviour; after all, not standardizing it
would allow even more "optimizations".

>and AFAIK all industrial-strength compilers follow
>the specification and optimize on that basis, not on the basis of some
>ill-defined notion of what a portable assembly language might be.
>This is nothing to do with GCC per se,

I talked to a guy from Sun's compiler group and he said that their
compiler does not break code like gcc does.  I have not verified this
claim, though.

Concerning the claim that the proper behaviour of a C compiler is
ill-defined, it's not: earlier versions of gcc (up to about 2.95, with
a few exceptions like the one above) behaved properly even with -O,
and even recent versions behave mostly properly if you turn of
"optimization".  So it's not as if the gcc people don't know how to
compile the code properly, they just prefer to miscompile it (I guess
it gives slightly better results on the SPEC benchmarks).

>Indeed, but C is not one of those either: it's somewhere in between,
>which perhaps explains its success!

It was successful before gcc started miscompiling; it's still
successful, but has lost quite a bit of popularity since then.

A part of why it is still somewhat successful is that those of us who
need a portable assembler have no alternative yet; we work around the
miscompilations that gcc produces, but once we get an alternative, we
will switch.  Then the C part of gcc will only be used for legacy
code.  Or do you think that there are projects who are looking for a
language that combines the disadvantages of Java with the
disadvantages of a portable assembler without offering the benefits of
either?

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2011: http://www.euroforth.org/ef11/

Thread

Adding thousands separators "Ed" <nospam@invalid.com> - 2012-02-13 21:24 +1100
  Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-02-13 13:05 -0800
    Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-02-16 10:19 +1100
  Re: Adding thousands separators Hans Bezemer <the.beez.speaks@gmail.com> - 2012-02-15 08:48 +0100
    Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-02-23 22:46 -0800
      Re: Adding thousands separators "A. K." <akk@nospam.org> - 2012-02-24 08:07 +0100
      Re: Adding thousands separators Hans Bezemer <the.beez.speaks@gmail.com> - 2012-02-24 15:00 +0100
        Re: Adding thousands separators "Elizabeth D. Rather" <erather@forth.com> - 2012-02-24 08:29 -1000
          Re: Adding thousands separators Hans Bezemer <the.beez.speaks@gmail.com> - 2012-02-25 00:11 +0100
        Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-02-27 23:28 -0800
          Re: Adding thousands separators Alex McDonald <blog@rivadpm.com> - 2012-02-28 01:37 -0800
            Re: Adding thousands separators Ron Aaron <rambamist@gmail.com> - 2012-02-28 15:06 +0200
          Re: Adding thousands separators Hans Bezemer <the.beez.speaks@gmail.com> - 2012-02-29 09:29 +0100
            Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-02-29 03:00 -0600
              Re: Adding thousands separators The Beez <the.beez.speaks@gmail.com> - 2012-02-29 03:44 -0800
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-02-29 11:19 -0600
            Re: Adding thousands separators hughaguilar96@yahoo.com - 2012-02-29 22:48 -0800
              Re: Adding thousands separators Hans Bezemer <the.beez.speaks@gmail.com> - 2012-03-01 08:38 +0100
                Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-03-01 00:57 -0800
                Re: Adding thousands separators Hans Bezemer <the.beez.speaks@gmail.com> - 2012-03-01 18:23 +0100
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-01 17:22 -0800
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-03-01 18:00 -0800
                Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-03-01 22:14 -0800
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-02 06:58 -0800
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-03-02 11:07 -0800
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-03-02 13:13 -0600
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-02 11:25 -0800
                Re: Adding thousands separators Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-03-03 11:00 +0000
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-03-03 03:17 -0800
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-03-03 12:30 +0000
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-03 11:39 -0800
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-03-06 16:31 -0800
                Re: Adding thousands separators mhx@iae.nl (Marcel Hendrix) - 2012-03-03 15:52 +0200
                Re: Adding thousands separators Coos Haak <chforth@hccnet.nl> - 2012-03-03 16:23 +0100
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-03-03 10:19 -0800
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-03 12:35 -0800
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-03-03 11:02 -0600
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-03-03 17:25 +0000
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-03-03 10:14 -0800
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-03-03 14:14 -0600
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-03-03 14:52 -0800
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-03-04 03:39 -0600
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-03-04 15:02 +0000
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-03-03 14:11 -0600
                Re: Adding thousands separators Bernd Paysan <bernd.paysan@gmx.de> - 2012-03-03 23:49 +0100
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-03-03 15:50 -0800
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-03-04 15:38 +0000
                Re: Adding thousands separators Bernd Paysan <bernd.paysan@gmx.de> - 2012-03-04 18:08 +0100
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-03-04 11:20 -0600
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-03-04 17:45 +0000
                Re: Adding thousands separators Bernd Paysan <bernd.paysan@gmx.de> - 2012-03-04 23:50 +0100
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-03-05 14:39 +0000
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-03-06 13:01 -0800
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-03-12 16:05 +0000
                Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-03-03 15:45 -0800
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-03 17:56 -0800
                Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-03-05 15:41 -0800
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-06 11:27 -0800
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-03 11:01 -0800
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-02 05:53 -0800
                Re: Adding thousands separators Bernd Paysan <bernd.paysan@gmx.de> - 2012-03-03 01:49 +0100
      Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-02-29 17:20 +1100
        Re: Adding thousands separators "A. K." <akk@nospam.org> - 2012-02-29 07:51 +0100
        Re: Adding thousands separators hughaguilar96@yahoo.com - 2012-02-29 21:26 -0800
          Re: Adding thousands separators "WJ" <w_a_x_man@yahoo.com> - 2012-03-03 03:45 +0000
          Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-03-04 20:49 +1100
            Re: Adding thousands separators Hans Bezemer <the.beez.speaks@gmail.com> - 2012-03-04 15:16 +0100
              Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-03-06 15:06 +1100
                Re: Adding thousands separators Hans Bezemer <the.beez.speaks@gmail.com> - 2012-03-06 08:32 +0100
            Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-03-05 15:06 -0800
              Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-03-06 15:03 +1100
              Re: Adding thousands separators hwfwguy@gmail.com - 2012-03-06 20:29 -0800
                Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-03-06 23:18 -0800
                Re: Adding thousands separators John Passaniti <john.passaniti@gmail.com> - 2012-03-07 06:07 -0800
                Re: Adding thousands separators hwfwguy@gmail.com - 2012-03-07 06:36 -0800
                Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-03-07 16:19 -0800
                Re: Adding thousands separators Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-03-08 10:51 +0000
  Re: Adding thousands separators Doug Hoffman <glidedog@gmail.com> - 2012-02-15 20:18 -0500
    Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-02-17 12:29 +1100
      Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-17 09:42 -0800
        Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-02-20 15:24 +0000
          Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-20 20:41 -0800
            Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-02-21 16:46 +0000
              Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-02-21 12:23 -0600
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-21 11:32 -0800
                Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-02-22 12:46 +1100
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-02-22 10:08 +0000
                Re: Adding thousands separators "Elizabeth D. Rather" <erather@forth.com> - 2012-02-22 08:51 -1000
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-22 14:28 -0800
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-02-23 13:13 +0000
                Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-02-24 14:32 +1100
                Re: Adding thousands separators "Elizabeth D. Rather" <erather@forth.com> - 2012-02-23 19:53 -1000
                Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-03-03 12:47 +1100
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-03-02 22:26 -0800
                Re: Adding thousands separators Jan Coombs <jan_2011-02@murray-microft.co.uk> - 2012-03-03 14:32 +0000
                Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-03-04 21:31 +1100
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-03-04 10:07 -0800
                Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-03-06 15:31 +1100
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-03-05 22:26 -0800
                Re: Adding thousands separators Josh Grams <josh@qualdan.com> - 2012-03-06 12:32 +0000
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-24 05:04 -0800
                Re: Adding thousands separators "Elizabeth D. Rather" <erather@forth.com> - 2012-02-24 08:30 -1000
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-02-22 04:28 -0600
                Re: Adding thousands separators stephenXXX@mpeforth.com (Stephen Pelc) - 2012-02-22 14:59 +0000
                Re: Adding thousands separators stephenXXX@mpeforth.com (Stephen Pelc) - 2012-02-22 18:05 +0000
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-22 07:49 -0800
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-02-22 12:46 -0800
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-22 18:24 -0800
                Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-02-24 13:23 +1100
              Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-21 11:29 -0800
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-02-22 09:56 +0000
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-22 07:37 -0800
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-02-22 10:30 -0600
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-02-22 16:24 +0000
                Re: Adding thousands separators Brad <hwfwguy@gmail.com> - 2012-02-23 07:44 -0800
                Re: Adding thousands separators Bernd Paysan <bernd.paysan@gmx.de> - 2012-02-23 17:54 +0100
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-02-23 16:51 +0000
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-02-23 11:49 -0600
                Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-02-23 13:26 -0800
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-02-23 15:58 -0600
                Re: Adding thousands separators Bernd Paysan <bernd.paysan@gmx.de> - 2012-02-26 02:25 +0100
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-02-26 03:24 -0600
                Re: Adding thousands separators anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-02-26 13:40 +0000
                Re: Adding thousands separators Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-02-26 11:06 -0600
                Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-23 15:02 -0800
  Re: Adding thousands separators Doug Hoffman <glidedog@gmail.com> - 2012-02-16 13:21 -0500
  Re: Adding thousands separators Paul Rubin <no.email@nospam.invalid> - 2012-02-16 20:44 -0800
    Re: Adding thousands separators Coos Haak <chforth@hccnet.nl> - 2012-02-17 21:32 +0100
  Re: Adding thousands separators "A. K." <akk@nospam.org> - 2012-02-17 22:41 +0100
    Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-17 18:52 -0800
      Re: Adding thousands separators "A. K." <akk@nospam.org> - 2012-02-18 10:39 +0100
        Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-02-18 21:22 +1100
          Re: Adding thousands separators "A. K." <akk@nospam.org> - 2012-02-18 13:12 +0100
            Re: Adding thousands separators "Peter Knaggs" <pjk@bcs.org.uk> - 2012-02-18 16:30 +0000
              Re: Adding thousands separators Jan Coombs <jan_2011-02@murray-microft.co.uk> - 2012-02-18 17:08 +0000
              Re: Adding thousands separators BruceMcF <agila61@netscape.net> - 2012-02-18 14:46 -0800
            Re: Adding thousands separators "Ed" <nospam@invalid.com> - 2012-03-04 20:47 +1100
  Re: Adding thousands separators Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-02-28 17:03 -0800
  Re: Adding thousands separators "WJ" <w_a_x_man@yahoo.com> - 2012-03-01 18:13 +0000
    Re: Adding thousands separators Alex McDonald <blog@rivadpm.com> - 2012-03-01 12:46 -0800
  Re: Adding thousands separators "WJ" <w_a_x_man@yahoo.com> - 2012-03-01 18:52 +0000

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