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Re: Computer arithmetic problems worth exploring

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  Re: Computer arithmetic problems worth exploring George Neuner <gneuner2@comcast.net> - 2011-05-07 03:06 -0400
    Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-07 09:44 +0100
      Re: Computer arithmetic problems worth exploring Tom Gardner <spamjunk@blueyonder.co.uk> - 2011-05-07 11:38 +0100
        Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-07 12:21 +0100
          Re: Computer arithmetic problems worth exploring Tom Gardner <spamjunk@blueyonder.co.uk> - 2011-05-07 13:47 +0100
            Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-07 09:55 -0700
              Re: Computer arithmetic problems worth exploring Tom Gardner <spamjunk@blueyonder.co.uk> - 2011-05-07 19:27 +0100
                Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-07 13:54 -0700
                  Re: Computer arithmetic problems worth exploring George Neuner <gneuner2@comcast.net> - 2011-05-09 13:38 -0400
                    Re: Computer arithmetic problems worth exploring Robert A Duff <bobduff@shell01.TheWorld.com> - 2011-05-10 12:40 -0400
                      Re: Computer arithmetic problems worth exploring Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-05-10 20:32 +0200
              Re: Computer arithmetic problems worth exploring torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-05-09 13:42 +0200
      Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-07 04:26 -0700
        Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-07 12:13 +0100
    Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-07 14:59 -0700
      Re: Computer arithmetic problems worth exploring George Neuner <gneuner2@comcast.net> - 2011-05-09 14:14 -0400
        Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-09 20:38 +0100
        Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-09 13:55 -0700
          Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-10 09:05 +0100
            Re: Computer arithmetic problems worth exploring Jason Riedy <jason@lovesgoodfood.com> - 2011-05-10 13:24 -0400
              Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-10 18:41 +0100
              Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-11 13:56 -0700
              Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-11 14:04 -0700
              Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-11 14:06 -0700
            Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-11 13:55 -0700
              Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-11 22:15 +0100
                Re: Computer arithmetic problems worth exploring Tom Gardner <spamjunk@blueyonder.co.uk> - 2011-05-12 20:52 +0100
                  Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-12 20:20 +0100
                    Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-12 14:55 -0700
                  Re: Computer arithmetic problems worth exploring Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-05-13 12:25 +0200
                    Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-13 11:18 +0100
                      Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-14 13:19 -0700
                        Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-14 19:11 -0700
                Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-12 20:08 -0700
              Re: Computer arithmetic problems worth exploring Jason Riedy <jason@lovesgoodfood.com> - 2011-05-12 23:54 -0400
          Re: Computer arithmetic problems worth exploring George Neuner <gneuner2@comcast.net> - 2011-05-12 01:08 -0400
            Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-12 09:27 +0100
              Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-12 05:41 -0700
                Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-12 13:22 +0100
                  Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-12 07:22 -0700
                    Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-12 14:58 +0100
                      Re: Computer arithmetic problems worth exploring MitchAlsup <MitchAlsup@aol.com> - 2011-05-12 09:23 -0700
                      Non-constant initializers Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> - 2011-05-12 22:59 +0000
                        Re: Non-constant initializers Ian Collins <ian-news@hotmail.com> - 2011-05-13 11:07 +1200
                          Re: Non-constant initializers Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> - 2011-05-12 23:17 +0000
                            Re: Non-constant initializers Ian Collins <ian-news@hotmail.com> - 2011-05-13 11:20 +1200
                              Re: Non-constant initializers Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> - 2011-05-12 23:30 +0000
                                Re: Non-constant initializers Ian Collins <ian-news@hotmail.com> - 2011-05-13 11:34 +1200
                                  Re: Non-constant initializers Keith Thompson <kst-u@mib.org> - 2011-05-12 16:52 -0700
                                    Re: Non-constant initializers Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> - 2011-05-14 00:13 +0000
                                      Re: Non-constant initializers kym@kymhorsell.com - 2011-05-14 01:54 +0000
                                        Re: Non-constant initializers Columbus sailed the ocean China Blue <chine.bleu@yahoo.com> - 2011-05-14 01:07 -0700
                                          Re: Non-constant initializers kym@kymhorsell.com - 2011-05-14 09:22 +0000
                                            Re: Non-constant initializers Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> - 2011-05-14 17:14 +0000
                                  Re: Non-constant initializers Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> - 2011-05-14 00:11 +0000
                        Re: Non-constant initializers Columbus sailed the ocean China Blue <chine.bleu@yahoo.com> - 2011-05-12 16:15 -0700
                          Re: Non-constant initializers Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> - 2011-05-12 23:28 +0000
                        Re: Non-constant initializers Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-05-12 18:01 -0600
                          Re: Non-constant initializers Keith Thompson <kst-u@mib.org> - 2011-05-12 18:15 -0700
                            Re: Non-constant initializers Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-05-12 22:56 -0600
                              Re: Non-constant initializers Seebs <usenet-nospam@seebs.net> - 2011-05-13 05:18 +0000
                          Re: Non-constant initializers Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> - 2011-05-13 23:57 +0000
              Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-12 20:20 -0700
                Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-13 09:48 +0100
                  Re: Computer arithmetic problems worth exploring Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-05-13 12:55 +0200
                    Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-13 11:25 +0100
                      Re: Computer arithmetic problems worth exploring MitchAlsup <MitchAlsup@aol.com> - 2011-05-13 08:57 -0700
                        Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-13 16:42 +0100
                          Re: Computer arithmetic problems worth exploring MitchAlsup <MitchAlsup@aol.com> - 2011-05-13 13:17 -0700
                            Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-13 21:03 +0100
                            Re: Computer arithmetic problems worth exploring Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-05-14 06:43 +0200
                              Re: Computer arithmetic problems worth exploring Tom Gardner <spamjunk@blueyonder.co.uk> - 2011-05-14 06:55 +0100
                                Re: Computer arithmetic problems worth exploring "Ken Hagan" <k.hagan@thermoteknix.com> - 2011-05-17 12:59 +0100
                                  Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-17 12:44 +0100
                                    Re: Computer arithmetic problems worth exploring Tom Gardner <spamjunk@blueyonder.co.uk> - 2011-05-17 14:07 +0100
                                      Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-17 17:20 +0100
                                    Re: Computer arithmetic problems worth exploring "Ken Hagan" <k.hagan@thermoteknix.com> - 2011-05-17 15:03 +0100
                              Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-14 08:43 +0100
                                Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-14 09:17 +0100
                            Re: Computer arithmetic problems worth exploring Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2011-05-14 09:04 -0700
                            Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-14 17:00 -0700
                        Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-14 16:58 -0700
                          Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-14 19:07 -0700
                            Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-15 09:40 +0100
                            Re: Computer arithmetic problems worth exploring Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-05-16 11:05 +0200
                              Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-16 06:44 -0700
                                Re: Computer arithmetic problems worth exploring mac <acolvin@efunct.com> - 2011-05-19 20:17 +0000
                                  Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-19 15:20 -0700
                                    Re: Computer arithmetic problems worth exploring George Neuner <gneuner2@comcast.net> - 2011-05-19 18:51 -0400
                                      Re: Computer arithmetic problems worth exploring Petter Gustad <newsmailcomp6@gustad.com> - 2011-05-20 08:01 +0200
                                        Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-20 15:09 -0700
                                      Re: Computer arithmetic problems worth exploring Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-05-20 08:54 +0200
                                        Re: Computer arithmetic problems worth exploring "Ken Hagan" <k.hagan@thermoteknix.com> - 2011-05-23 11:11 +0100
                                          Re: Computer arithmetic problems worth exploring George Neuner <gneuner2@comcast.net> - 2011-05-23 18:20 -0400
                                        Re: Computer arithmetic problems worth exploring Morten Reistad <first@last.name> - 2011-06-03 08:21 +0200
                                Re: Computer arithmetic problems worth exploring Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2011-05-19 13:31 -0700
                              Re: Computer arithmetic problems worth exploring Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2011-05-16 09:05 -0700
                                Re: Computer arithmetic problems worth exploring Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-05-16 22:37 +0200
                                  Re: Computer arithmetic problems worth exploring Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2011-05-18 23:16 -0700
                                Re: Computer arithmetic problems worth exploring ChrisQ <meru@devnull.com> - 2011-05-17 17:10 +0100
                                  Re: Computer arithmetic problems worth exploring Tom Gardner <spamjunk@blueyonder.co.uk> - 2011-05-17 17:27 +0100
                                    Re: Computer arithmetic problems worth exploring ChrisQ <meru@devnull.com> - 2011-05-17 23:08 +0100
                                    Re: Computer arithmetic problems worth exploring Tom <tggzzz@blueyonder.co.uk> - 2011-05-17 22:37 +0000
                                      Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-18 09:25 +0100
                                        Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-18 06:25 -0700
                                          Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-18 14:06 +0100
                                          Re: Computer arithmetic problems worth exploring Tom Gardner <spamjunk@blueyonder.co.uk> - 2011-05-18 19:23 +0100
                                            Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-18 13:48 -0700
                                              Re: Computer arithmetic problems worth exploring Andrew Reilly <areilly---@bigpond.net.au> - 2011-05-19 00:29 +0000
                                                Re: Computer arithmetic problems worth exploring "Ken Hagan" <k.hagan@thermoteknix.com> - 2011-05-19 13:12 +0100
                                  Re: Computer arithmetic problems worth exploring Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2011-05-18 23:27 -0700
                                    Re: Computer arithmetic problems worth exploring Quadibloc <jsavard@ecn.ab.ca> - 2011-05-19 15:19 -0700
                                      Re: Computer arithmetic problems worth exploring Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2011-05-20 07:33 -0700
                            Re: Computer arithmetic problems worth exploring Michael S <already5chosen@yahoo.com> - 2011-05-16 03:14 -0700
                              Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-16 10:43 +0100
                                Re: Computer arithmetic problems worth exploring Michael S <already5chosen@yahoo.com> - 2011-05-16 04:58 -0700
                                  Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-16 12:40 +0100
                          Re: Computer arithmetic problems worth exploring MitchAlsup <MitchAlsup@aol.com> - 2011-05-15 10:12 -0700
                  Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-14 13:22 -0700
                    Re: Computer arithmetic problems worth exploring nmm1@cam.ac.uk - 2011-05-15 09:02 +0100
                  Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-14 14:02 -0700
            Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-12 20:18 -0700
        Re: Computer arithmetic problems worth exploring Robert Myers <rbmyersusa@gmail.com> - 2011-05-09 14:32 -0700
          Re: Computer arithmetic problems worth exploring "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-09 16:08 -0700

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#1494

In article <0ca8ca5b-e73e-418a-935f-0fcc17fdf404@q14g2000prh.googlegroups.com>,
Quadibloc  <jsavard@ecn.ab.ca> wrote:
>
>> There were a lot of examples in the 1970s of how a hexadecimal
>> base could cause an error build up of that magnitude per step,
>> but almost all were bogus as they took truncation as a basic
>> assumption!
>
>Of course, IBM System/360 floating-point *did* truncate instead of
>round. That simplified implementation of the low-end machines by
>increasing the commonalities between fixed-point arithmetic and
>floating-point arithmetic.

Quite.  And its justified reputation for poor accuracy was due to
that, almost entirely.

>I do agree with you, though, that superfluous precision, except for
>wasting storage space and computation time, is not intrinsically
>harmful, even if that precision is present or absent in a capricious
>manner - when the rounding, and the variation in precision are both
>unbiased.

Even the latter is fairly minor.  I have used twos' complement,
rounded to nearest, floating-point, and that was fine.


Regards,
Nick Maclaren.

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#1498

On May 12, 8:58 am, n...@cam.ac.uk wrote:
> In article <0ca8ca5b-e73e-418a-935f-0fcc17fdf...@q14g2000prh.googlegroups.com>,
>
> Quadibloc  <jsav...@ecn.ab.ca> wrote:
>
> >> There were a lot of examples in the 1970s of how a hexadecimal
> >> base could cause an error build up of that magnitude per step,
> >> but almost all were bogus as they took truncation as a basic
> >> assumption!
>
> >Of course, IBM System/360 floating-point *did* truncate instead of
> >round. That simplified implementation of the low-end machines by
> >increasing the commonalities between fixed-point arithmetic and
> >floating-point arithmetic.
>
> Quite.  And its justified reputation for poor accuracy was due to
> that, almost entirely.

That, and the fact that the first System/360 implementations did not
compute with a guard digit prior to truncation (which was quickly and
quietly fixed.)

Mitch

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#1502 — Non-constant initializers

Hey guys,

I've been writing some code that I would prefer to be maximally
portable.  As I have mostly used Linux, gcc is pretty much the only C
compiler I've ever used under UN*X.  I'd like to use non-constant
initializers for some global variables.  I'm pretty sure I can get it
to work the way I want under gcc, but what of other compilers?  The
gcc documentation in info format says that ISO C99 allows this, and so
I expect some compilers built in the 90's will support the feature,
but to what extent is this true?

What I mean to learn is the general prevalence of this C feature.  If
there's no support for certain well-known platforms (maybe SunOS or
OSF/1, whatever) I may consider a different solution to the original
problem, but I'd like to know what I'm getting in to before I start
trying to read the docs for every bloody C compiler that ever hit the
'net in the last twenty years.

Thanks if you can shed any light on this subject.



Fred the Freshwater Catfish

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#1503 — Re: Non-constant initializers

On 05/13/11 10:59 AM, Fred the Freshwater Catfish wrote:
> Hey guys,
>
> I've been writing some code that I would prefer to be maximally
> portable.  As I have mostly used Linux, gcc is pretty much the only C
> compiler I've ever used under UN*X.  I'd like to use non-constant
> initializers for some global variables.  I'm pretty sure I can get it
> to work the way I want under gcc, but what of other compilers?  The
> gcc documentation in info format says that ISO C99 allows this, and so
> I expect some compilers built in the 90's will support the feature,
> but to what extent is this true?

How do you derive the initialiser values?

-- 
Ian Collins

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#1505 — Re: Non-constant initializers

On Fri, May 13, 2011 at 11:07:09AM +1200, Ian Collins wrote:
> On 05/13/11 10:59 AM, Fred the Freshwater Catfish wrote:
> >Hey guys,
> >
> >I've been writing some code that I would prefer to be maximally
> >portable.  As I have mostly used Linux, gcc is pretty much the only C
> >compiler I've ever used under UN*X.  I'd like to use non-constant
> >initializers for some global variables.  I'm pretty sure I can get it
> >to work the way I want under gcc, but what of other compilers?  The
> >gcc documentation in info format says that ISO C99 allows this, and so
> >I expect some compilers built in the 90's will support the feature,
> >but to what extent is this true?
> 
> How do you derive the initialiser values?

It should end up being a function call most of the time.



Fred the Freshwater Catfish

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#1506 — Re: Non-constant initializers

On 05/13/11 11:17 AM, Fred the Freshwater Catfish wrote:
> On Fri, May 13, 2011 at 11:07:09AM +1200, Ian Collins wrote:
>> On 05/13/11 10:59 AM, Fred the Freshwater Catfish wrote:
>>> Hey guys,
>>>
>>> I've been writing some code that I would prefer to be maximally
>>> portable.  As I have mostly used Linux, gcc is pretty much the only C
>>> compiler I've ever used under UN*X.  I'd like to use non-constant
>>> initializers for some global variables.  I'm pretty sure I can get it
>>> to work the way I want under gcc, but what of other compilers?  The
>>> gcc documentation in info format says that ISO C99 allows this, and so
>>> I expect some compilers built in the 90's will support the feature,
>>> but to what extent is this true?
>>
>> How do you derive the initialiser values?
>
> It should end up being a function call most of the time.

Then you either want C++, or a singleton fiddle as posted else-thread.

-- 
Ian Collins

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#1508 — Re: Non-constant initializers

On Fri, May 13, 2011 at 11:20:30AM +1200, Ian Collins wrote:
> On 05/13/11 11:17 AM, Fred the Freshwater Catfish wrote:
> >On Fri, May 13, 2011 at 11:07:09AM +1200, Ian Collins wrote:
> >>On 05/13/11 10:59 AM, Fred the Freshwater Catfish wrote:
> >>>Hey guys,
> >>>
> >>>I've been writing some code that I would prefer to be maximally
> >>>portable.  As I have mostly used Linux, gcc is pretty much the only C
> >>>compiler I've ever used under UN*X.  I'd like to use non-constant
> >>>initializers for some global variables.  I'm pretty sure I can get it
> >>>to work the way I want under gcc, but what of other compilers?  The
> >>>gcc documentation in info format says that ISO C99 allows this, and so
> >>>I expect some compilers built in the 90's will support the feature,
> >>>but to what extent is this true?
> >>
> >>How do you derive the initialiser values?
> >
> >It should end up being a function call most of the time.
> 
> Then you either want C++, or a singleton fiddle as posted else-thread.

Sorry, I'm not using C++.



Fred the Freshwater Catfish

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#1509 — Re: Non-constant initializers

On 05/13/11 11:30 AM, Fred the Freshwater Catfish wrote:
> On Fri, May 13, 2011 at 11:20:30AM +1200, Ian Collins wrote:
>> On 05/13/11 11:17 AM, Fred the Freshwater Catfish wrote:
>>> On Fri, May 13, 2011 at 11:07:09AM +1200, Ian Collins wrote:
>>>> On 05/13/11 10:59 AM, Fred the Freshwater Catfish wrote:
>>>>> Hey guys,
>>>>>
>>>>> I've been writing some code that I would prefer to be maximally
>>>>> portable.  As I have mostly used Linux, gcc is pretty much the only C
>>>>> compiler I've ever used under UN*X.  I'd like to use non-constant
>>>>> initializers for some global variables.  I'm pretty sure I can get it
>>>>> to work the way I want under gcc, but what of other compilers?  The
>>>>> gcc documentation in info format says that ISO C99 allows this, and so
>>>>> I expect some compilers built in the 90's will support the feature,
>>>>> but to what extent is this true?
>>>>
>>>> How do you derive the initialiser values?
>>>
>>> It should end up being a function call most of the time.
>>
>> Then you either want C++, or a singleton fiddle as posted else-thread.
>
> Sorry, I'm not using C++.

But you require a C++ feature...

You could compile all but main() as C and compile the source file 
containing main() and your initialisers as C++.

-- 
Ian Collins

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#1510 — Re: Non-constant initializers

Ian Collins <ian-news@hotmail.com> writes:
> On 05/13/11 11:30 AM, Fred the Freshwater Catfish wrote:
>> On Fri, May 13, 2011 at 11:20:30AM +1200, Ian Collins wrote:
>>> On 05/13/11 11:17 AM, Fred the Freshwater Catfish wrote:
>>>> On Fri, May 13, 2011 at 11:07:09AM +1200, Ian Collins wrote:
>>>>> On 05/13/11 10:59 AM, Fred the Freshwater Catfish wrote:
>>>>>> Hey guys,
>>>>>>
>>>>>> I've been writing some code that I would prefer to be maximally
>>>>>> portable.  As I have mostly used Linux, gcc is pretty much the only C
>>>>>> compiler I've ever used under UN*X.  I'd like to use non-constant
>>>>>> initializers for some global variables.  I'm pretty sure I can get it
>>>>>> to work the way I want under gcc, but what of other compilers?  The
>>>>>> gcc documentation in info format says that ISO C99 allows this, and so
>>>>>> I expect some compilers built in the 90's will support the feature,
>>>>>> but to what extent is this true?
>>>>>
>>>>> How do you derive the initialiser values?
>>>>
>>>> It should end up being a function call most of the time.
>>>
>>> Then you either want C++, or a singleton fiddle as posted else-thread.
>>
>> Sorry, I'm not using C++.
>
> But you require a C++ feature...
>
> You could compile all but main() as C and compile the source file 
> containing main() and your initialisers as C++.

Or, rather than using a non-constant initializer, you can call a routine
from main() that initialize the objects.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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#1556 — Re: Non-constant initializers

On Thu, May 12, 2011 at 04:52:43PM -0700, Keith Thompson wrote:
> Ian Collins <ian-news@hotmail.com> writes:
> > On 05/13/11 11:30 AM, Fred the Freshwater Catfish wrote:
> >> On Fri, May 13, 2011 at 11:20:30AM +1200, Ian Collins wrote:
> >>> On 05/13/11 11:17 AM, Fred the Freshwater Catfish wrote:
> >>>> On Fri, May 13, 2011 at 11:07:09AM +1200, Ian Collins wrote:
> >>>>> On 05/13/11 10:59 AM, Fred the Freshwater Catfish wrote:
> >>>>>> Hey guys,
> >>>>>>
> >>>>>> I've been writing some code that I would prefer to be maximally
> >>>>>> portable.  As I have mostly used Linux, gcc is pretty much the only C
> >>>>>> compiler I've ever used under UN*X.  I'd like to use non-constant
> >>>>>> initializers for some global variables.  I'm pretty sure I can get it
> >>>>>> to work the way I want under gcc, but what of other compilers?  The
> >>>>>> gcc documentation in info format says that ISO C99 allows this, and so
> >>>>>> I expect some compilers built in the 90's will support the feature,
> >>>>>> but to what extent is this true?
> >>>>>
> >>>>> How do you derive the initialiser values?
> >>>>
> >>>> It should end up being a function call most of the time.
> >>>
> >>> Then you either want C++, or a singleton fiddle as posted else-thread.
> >>
> >> Sorry, I'm not using C++.
> >
> > But you require a C++ feature...
> >
> > You could compile all but main() as C and compile the source file 
> > containing main() and your initialisers as C++.
> 
> Or, rather than using a non-constant initializer, you can call a routine
> from main() that initialize the objects.

That's a pretty good idea, but I was looking for something convenient
to set-up global-scope variables in a library.  No big deal, but I
thought I could be clever about it.



Fred the Freshwater Catfish

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#1558 — Re: Non-constant initializers

In comp.arch Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> wrote:
...
> That's a pretty good idea, but I was looking for something convenient
> to set-up global-scope variables in a library.  No big deal, but I
> thought I could be clever about it.

On some platforms its the linker that's responsible for once-only
runtime initialisations. If you name a routine in a special way,
or make sure it's in a code segment with a special name, the linker
sets up code to ensure the code gets called before main(). No need
for static "has it been done yet" variables or explicit calls.

This is how gnu C++ compilers typically arrange for global initialisations.

Unlike the idea of calling C++ from C (which usually won't work), just
hanging off this hook generally does work -- if you can find the documentation.

-- 
If there was no warming or cooling trend, then the chance of 2007
being tied with 1998 [130 year record!] would be quite high.
  -- No Pressure <no.pressure.at.all@gmail.com>, 11 Dec 2010 05:20:39 -0800

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#1561 — Re: Non-constant initializers

In article <4dcde0cd$0$24911$afc38c87@news.optusnet.com.au>, kym@kymhorsell.com 
wrote:

> In comp.arch Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> wrote:
> ...
> > That's a pretty good idea, but I was looking for something convenient
> > to set-up global-scope variables in a library.  No big deal, but I
> > thought I could be clever about it.
> 
> On some platforms its the linker that's responsible for once-only
> runtime initialisations. If you name a routine in a special way,
> or make sure it's in a code segment with a special name, the linker
> sets up code to ensure the code gets called before main(). No need
> for static "has it been done yet" variables or explicit calls.
> 
> This is how gnu C++ compilers typically arrange for global initialisations.
> 
> Unlike the idea of calling C++ from C (which usually won't work), just
> hanging off this hook generally does work -- if you can find the 
> documentation.

Unfortunately this solution is not guarenteed to be available on all platforms.

-- 
Damn the living - It's a lovely life.           I'm whoever you want me to be.
Silver silverware - Where is the love?       At least I can stay in character.
Oval swimming pool - Where is the love?    Annoying Usenet one post at a time.
Damn the living - It's a lovely life.                              In 1492....

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#1565 — Re: Non-constant initializers

In comp.arch Columbus sailed the ocean China Blue <chine.bleu@yahoo.com> wrote:
> In article <4dcde0cd$0$24911$afc38c87@news.optusnet.com.au>, kym@kymhorsell.com 
> wrote:
>> In comp.arch Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> wrote:
>> ...
>> > That's a pretty good idea, but I was looking for something convenient
>> > to set-up global-scope variables in a library.  No big deal, but I
>> > thought I could be clever about it.
>> On some platforms its the linker that's responsible for once-only
>> runtime initialisations. If you name a routine in a special way,
>> or make sure it's in a code segment with a special name, the linker
>> sets up code to ensure the code gets called before main(). No need
>> for static "has it been done yet" variables or explicit calls.
>> This is how gnu C++ compilers typically arrange for global initialisations.
>> Unlike the idea of calling C++ from C (which usually won't work), just
>> hanging off this hook generally does work -- if you can find the 
>> documentation.
> Unfortunately this solution is not guarenteed to be available on all platforms.

That's the agreed meaning of "on some platforms", yes.

---
Scientists are always changing their story and as a Conservative, I
have no tolerance for ambiguity.  It proves that all science is lies 
and the only thing we can trust is right wing rhetoric.
  -- BONZO@27-32-240-172 [86 nyms and counting], 14 Jan 2011 14:46 +1100

CORRECTION: True science, (remember that?) can be trusted, but this "science" 
is ALL LIES!
  -- BONZO@27-32-240-172 [86 nyms and counting], 19 Feb 2011 14:46 +1100

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#1569 — Re: Non-constant initializers

On Sat, May 14, 2011 at 09:22:27AM +0000, kym@kymhorsell.com wrote:
> In comp.arch Columbus sailed the ocean China Blue <chine.bleu@yahoo.com> wrote:
> > In article <4dcde0cd$0$24911$afc38c87@news.optusnet.com.au>, kym@kymhorsell.com 
> > wrote:
> >> In comp.arch Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> wrote:
> >> ...
> >> > That's a pretty good idea, but I was looking for something convenient
> >> > to set-up global-scope variables in a library.  No big deal, but I
> >> > thought I could be clever about it.
> >> On some platforms its the linker that's responsible for once-only
> >> runtime initialisations. If you name a routine in a special way,
> >> or make sure it's in a code segment with a special name, the linker
> >> sets up code to ensure the code gets called before main(). No need
> >> for static "has it been done yet" variables or explicit calls.
> >> This is how gnu C++ compilers typically arrange for global initialisations.
> >> Unlike the idea of calling C++ from C (which usually won't work), just
> >> hanging off this hook generally does work -- if you can find the 
> >> documentation.
> > Unfortunately this solution is not guaranteed to be available on all platforms.
> 
> That's the agreed meaning of "on some platforms", yes.


Yeah.  I know gcc supports constructor and destructor function
attributes, with some sort of "priority" ranking, but I haven't fooled
with it enough to make it work.  I don't know how other compilers fare
in this respect, but it seems like the kind feature that gets
implemented differently by each compiler.  I might end up using
zero-length arrays in structure definitions if I find it's popular
enough, but I'm really trying not to make my application require weird
stuff just to compile, or in fact to tie my application to gcc.



Fred the Freshwater Catfish

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#1555 — Re: Non-constant initializers

On Fri, May 13, 2011 at 11:34:23AM +1200, Ian Collins wrote:
> On 05/13/11 11:30 AM, Fred the Freshwater Catfish wrote:
> >On Fri, May 13, 2011 at 11:20:30AM +1200, Ian Collins wrote:
> >>On 05/13/11 11:17 AM, Fred the Freshwater Catfish wrote:
> >>>On Fri, May 13, 2011 at 11:07:09AM +1200, Ian Collins wrote:
> >>>>On 05/13/11 10:59 AM, Fred the Freshwater Catfish wrote:
> >>>>>Hey guys,
> >>>>>
> >>>>>I've been writing some code that I would prefer to be maximally
> >>>>>portable.  As I have mostly used Linux, gcc is pretty much the only C
> >>>>>compiler I've ever used under UN*X.  I'd like to use non-constant
> >>>>>initializers for some global variables.  I'm pretty sure I can get it
> >>>>>to work the way I want under gcc, but what of other compilers?  The
> >>>>>gcc documentation in info format says that ISO C99 allows this, and so
> >>>>>I expect some compilers built in the 90's will support the feature,
> >>>>>but to what extent is this true?
> >>>>
> >>>>How do you derive the initialiser values?
> >>>
> >>>It should end up being a function call most of the time.
> >>
> >>Then you either want C++, or a singleton fiddle as posted else-thread.
> >
> >Sorry, I'm not using C++.
> 
> But you require a C++ feature...
> 
> You could compile all but main() as C and compile the source file 
> containing main() and your initialisers as C++.

I guess, but then my code would be tainted by C++.  I'd rather avoid
requiring C++ in the build toolchain to compile the software.


Fred the Freshwater Catfish

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#1504 — Re: Non-constant initializers

In article <OgcdY5.Lcq.Cst0A@btdt.invalid>,
 Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> wrote:

> Hey guys,
> 
> I've been writing some code that I would prefer to be maximally
> portable.  As I have mostly used Linux, gcc is pretty much the only C
> compiler I've ever used under UN*X.  I'd like to use non-constant
> initializers for some global variables.  I'm pretty sure I can get it
> to work the way I want under gcc, but what of other compilers?  The
> gcc documentation in info format says that ISO C99 allows this, and so
> I expect some compilers built in the 90's will support the feature,
> but to what extent is this true?
> 
> What I mean to learn is the general prevalence of this C feature.  If
> there's no support for certain well-known platforms (maybe SunOS or
> OSF/1, whatever) I may consider a different solution to the original
> problem, but I'd like to know what I'm getting in to before I start
> trying to read the docs for every bloody C compiler that ever hit the
> 'net in the last twenty years.

I use an alternative strategy: if I want to implement
        static double XYZ = nonconstant-expression;

I instead do
        #define XYZ (*XYZ_())
        static double *XYZ_(void) {
            static double xyz;
            static bool initialised = false;
            LOCK
                if (!initialised) {
                    xyz = nonconstant-expression;
                    initialised = true;
                }
            UNLOCK
            return &xyz;
        }

XYZ will be an lvalue just like any other variable; it gets initialised on the 
first use; the initialisation can be any complicated as desired, using any 
dependencies desired, without depending on the compiler and loader to sneak in 
the initialisation code in the right order.

-- 
Damn the living - It's a lovely life.           I'm whoever you want me to be.
Silver silverware - Where is the love?       At least I can stay in character.
Oval swimming pool - Where is the love?    Annoying Usenet one post at a time.
Damn the living - It's a lovely life.                              In 1492....

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#1507 — Re: Non-constant initializers

On Thu, May 12, 2011 at 04:15:36PM -0700, Columbus sailed the ocean China Blue wrote:
> In article <OgcdY5.Lcq.Cst0A@btdt.invalid>,
>  Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> wrote:
> 
> > Hey guys,
> > 
> > I've been writing some code that I would prefer to be maximally
> > portable.  As I have mostly used Linux, gcc is pretty much the only C
> > compiler I've ever used under UN*X.  I'd like to use non-constant
> > initializers for some global variables.  I'm pretty sure I can get it
> > to work the way I want under gcc, but what of other compilers?  The
> > gcc documentation in info format says that ISO C99 allows this, and so
> > I expect some compilers built in the 90's will support the feature,
> > but to what extent is this true?
> > 
> > What I mean to learn is the general prevalence of this C feature.  If
> > there's no support for certain well-known platforms (maybe SunOS or
> > OSF/1, whatever) I may consider a different solution to the original
> > problem, but I'd like to know what I'm getting in to before I start
> > trying to read the docs for every bloody C compiler that ever hit the
> > 'net in the last twenty years.
> 
> I use an alternative strategy: if I want to implement
>         static double XYZ = nonconstant-expression;
> 
> I instead do
>         #define XYZ (*XYZ_())
>         static double *XYZ_(void) {
>             static double xyz;
>             static bool initialised = false;
>             LOCK
>                 if (!initialised) {
>                     xyz = nonconstant-expression;
>                     initialised = true;
>                 }
>             UNLOCK
>             return &xyz;
>         }
> 
> XYZ will be an lvalue just like any other variable; it gets initialised on the 
> first use; the initialisation can be any complicated as desired, using any 
> dependencies desired, without depending on the compiler and loader to sneak in 
> the initialisation code in the right order.

Hey, is that how you ancients did things in the 80's era?  I hope
there's a better way.



Fred the Freshwater Catfish

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#1511 — Re: Non-constant initializers

Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> writes:
>
> I've been writing some code that I would prefer to be maximally
> portable.  As I have mostly used Linux, gcc is pretty much the only C
> compiler I've ever used under UN*X.  I'd like to use non-constant
> initializers for some global variables.  I'm pretty sure I can get it
> to work the way I want under gcc, but what of other compilers?  The
> gcc documentation in info format says that ISO C99 allows this, and so
> I expect some compilers built in the 90's will support the feature,
> but to what extent is this true?

Where does the documentation say this is allowed by C99?  The C99
standard says

  All the expressions in an initializer for an object that has static
  storage duration shall be constant expressions or string literals.

(Section 6.7.8 paragraph 4)
-- 
"It used to be that the USA was pretty good at producing stuff teenaged 
boys could lose a finger or two playing with."	-- James Nicoll

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#1513 — Re: Non-constant initializers

Joe Pfeiffer <pfeiffer@cs.nmsu.edu> writes:
> Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> writes:
>> I've been writing some code that I would prefer to be maximally
>> portable.  As I have mostly used Linux, gcc is pretty much the only C
>> compiler I've ever used under UN*X.  I'd like to use non-constant
>> initializers for some global variables.  I'm pretty sure I can get it
>> to work the way I want under gcc, but what of other compilers?  The
>> gcc documentation in info format says that ISO C99 allows this, and so
>> I expect some compilers built in the 90's will support the feature,
>> but to what extent is this true?
>
> Where does the documentation say this is allowed by C99?  The C99
> standard says
>
>   All the expressions in an initializer for an object that has static
>   storage duration shall be constant expressions or string literals.
>
> (Section 6.7.8 paragraph 4)

I think this is the relevant section of the gcc document:

    6.23 Non-Constant Initializers
    ==============================
    
    As in standard C++ and ISO C99, the elements of an aggregate
    initializer for an automatic variable are not required to
    be constant expressions in GNU C.  Here is an example of an
    initializer with run-time varying elements:
    
         foo (float f, float g)
         { 
           float beat_freqs[2] = { f-g, f+g };
           /* ... */
         }
    
C90 requires constant expression for all initializers.  C99 permits
non-constant expressions, but only for automatic variables.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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#1527 — Re: Non-constant initializers

Keith Thompson <kst-u@mib.org> writes:

> Joe Pfeiffer <pfeiffer@cs.nmsu.edu> writes:
>> Fred the Freshwater Catfish <usenet.fred@bdtd.invalid> writes:
>>> I've been writing some code that I would prefer to be maximally
>>> portable.  As I have mostly used Linux, gcc is pretty much the only C
>>> compiler I've ever used under UN*X.  I'd like to use non-constant
>>> initializers for some global variables.  I'm pretty sure I can get it
>>> to work the way I want under gcc, but what of other compilers?  The
>>> gcc documentation in info format says that ISO C99 allows this, and so
>>> I expect some compilers built in the 90's will support the feature,
>>> but to what extent is this true?
>>
>> Where does the documentation say this is allowed by C99?  The C99
>> standard says
>>
>>   All the expressions in an initializer for an object that has static
>>   storage duration shall be constant expressions or string literals.
>>
>> (Section 6.7.8 paragraph 4)
>
> I think this is the relevant section of the gcc document:
>
>     6.23 Non-Constant Initializers
>     ==============================
>     
>     As in standard C++ and ISO C99, the elements of an aggregate
>     initializer for an automatic variable are not required to
>     be constant expressions in GNU C.  Here is an example of an
>     initializer with run-time varying elements:
>     
>          foo (float f, float g)
>          { 
>            float beat_freqs[2] = { f-g, f+g };
>            /* ... */
>          }
>     
> C90 requires constant expression for all initializers.  C99 permits
> non-constant expressions, but only for automatic variables.

The OP said he wanted non-constant initializers for global variables,
not for automatic variables.
-- 
"It used to be that the USA was pretty good at producing stuff teenaged 
boys could lose a finger or two playing with."	-- James Nicoll

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