Re: CHAR_BIT is not eight

From	Mr Flibble <flibble@reddwarf.jmc.corp>
Newsgroups	comp.lang.c++
Subject	Re: CHAR_BIT is not eight
Message-ID	<20221015124549.000031e1@reddwarf.jmc.corp> (permalink)
References	(7 earlier) <tibo3h$24fcq$1@dont-email.me> <20221014144746.00000b28@reddwarf.jmc.corp> <tibtfd$1sps$1@gioia.aioe.org> <20221014210120.00005b43@reddwarf.jmc.corp> <tie65c$2n1ei$1@dont-email.me>
Organization	Jupiter Mining Corporation
Date	2022-10-15 12:45 +0100

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On Sat, 15 Oct 2022 13:39:24 +0200
David Brown <david.brown@hesbynett.no> wrote:

> On 14/10/2022 22:01, Mr Flibble wrote:
> > On Fri, 14 Oct 2022 14:58:54 -0000 (UTC)
> > Muttley@dastardlyhq.com wrote:
> >   
> >> On Fri, 14 Oct 2022 14:47:46 +0100
> >> Mr Flibble <flibble@reddwarf.jmc.corp> wrote:  
> >>> On Fri, 14 Oct 2022 15:27:13 +0200
> >>> David Brown <david.brown@hesbynett.no> wrote:  
> >>>> Yes, it is always /possible/.  But the complications and effort
> >>>> involved is unlikely to be worth the effort, and you'd still end
> >>>> up with something taking a massive amount of code space.  (With
> >>>> "massive" being relative to the small code memories of such
> >>>> systems.)
> >>>>
> >>>> It's not uncommon in my coding to build up a few lists at the
> >>>> startup of the system - lists of "run" functions or software
> >>>> timers, etc. Modules might register such callbacks or functions
> >>>> when initialised. In "big system" C++, you might just use a
> >>>> vector for that - adding your timer objects to your vector as
> >>>> needed. It's simple and easy in the code.
> >>>>
> >>>> But in a resource-constraint embedded system, where efficiency of
> >>>> code space, ram space and run-time is important (though run-time
> >>>> efficiency is usually less important for startup code), that's
> >>>> not what you would do.  You make your timer class have the
> >>>> required list link pointers in the class, have each registering
> >>>> function declare their timer object with static lifetime, and
> >>>> your registration function links them together.
> >>>>
> >>>> There's no doubt that this takes a bit more effort to write than
> >>>> an off-the-shelf std::vector.  But it is vastly simpler than
> >>>> faffing around making your own allocator, avoids the use of any
> >>>> kind of dynamic memory (using neither the standard heap nor a
> >>>> home-made allocation system), and pulls in a tiny fraction of the
> >>>> amount of library code.
> >>>>
> >>>> std::array<> is free - it's just a nice wrapper around a plain
> >>>> C-style array.  
> >>>
> >>> List link pointers? Again there is no reason to not use std::list
> >>> with a suitable allocator even on such resource constrained
> >>> hardware and I disagree that the resultant text size and ram
> >>> usage would be any worse than anything you could come up with by
> >>> hand.  
> >>
> >> If the memory layout is hard coded at boot time why even bother
> >> pulling in std::list or any kind of container as you don't need
> >> their generic functionality which will almost certainly waste
> >> EEPROM space. With embedded development you often literally have
> >> to worry about every byte you use both in ROM and RAM and whether
> >> the mainloop is going to be fast enough to do its job.  
> > 
> > In C++ you don't pay for what you don't use: in the case of a C++
> > class template only the member functions instantiated will exist in
> > the text segment.
> >   
> 
> There are always /lots/ of other functions that get pulled in from 
> libraries.  Remember, for small embedded systems the libraries are
> not shared dynamic libraries that you don't see.
> 
> Just for a quick test, I made a minimal C++ main() function and
> compiled for a modern microcontroller.  With an empty main(), it was
> about 8400 bytes code of common library code.  Adding a
> "std::list<int>" object and using a couple of pops and pushes adds
> about 7 KB code to the program.
> 
> If you are making a lot of use of the standard containers, that's
> fine - and there's a lot of overlap and sharing in this extra code.
> But in small systems, this kind of stuff can get significant -
> microcontrollers with 32 KB flash are common, and it's nice to be
> able to program them in C++.  In the C++ /language/, you pay very
> little (not quite nothing) for features that you don't use, but that
> does not apply equally to the more advanced standard library classes.
> 
> It's the same in C, of course - call just one little time conversion 
> function and you can find half your flash is used for locale handling 
> and time zones.
> 
> The needs of embedded systems vary enormously - for many, the cost in 
> code space or run-time efficiency for using a std::list or
> std::vector is negligible.  But for others, it is very far from
> negligible.
> 
> (It is relatively rare that you have to worry about /every/ byte of
> code or data space, however - though it does happen.)

Try using std::list with a custom allocator as I originally suggested;
also your quote of 7KB sounds highly dubious and anecdotal.

/Flibble

Thread

CHAR_BIT is not eight Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-10-12 15:57 -0700
  Re: CHAR_BIT is not eight "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-12 16:01 -0700
  Re: CHAR_BIT is not eight Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-10-12 17:16 -0700
    Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-13 11:38 +0200
    Re: CHAR_BIT is not eight Michael S <already5chosen@yahoo.com> - 2022-11-16 06:24 -0800
      Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-11-17 11:04 +0100
        Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-11-17 16:40 +0000
          Re: CHAR_BIT is not eight Richard Damon <Richard@Damon-Family.org> - 2022-11-17 23:23 -0500
            Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-11-18 08:16 +0100
              Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-11-18 16:33 +0000
                Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-11-18 18:54 +0100
            Re: CHAR_BIT is not eight Michael S <already5chosen@yahoo.com> - 2022-11-18 03:47 -0800
              Re: CHAR_BIT is not eight scott@slp53.sl.home (Scott Lurndal) - 2022-11-18 14:52 +0000
            Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-11-18 16:32 +0000
              Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-11-18 19:05 +0100
                Re: CHAR_BIT is not eight scott@slp53.sl.home (Scott Lurndal) - 2022-11-18 18:16 +0000
  Re: CHAR_BIT is not eight Juha Nieminen <nospam@thanks.invalid> - 2022-10-13 08:02 +0000
    Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-13 08:08 +0000
      Re: CHAR_BIT is not eight Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-15 11:35 +0200
        Re: CHAR_BIT is not eight Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-10-15 02:53 -0700
          Re: CHAR_BIT is not eight Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-15 11:57 +0200
            Re: CHAR_BIT is not eight Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-10-15 03:05 -0700
            Re: CHAR_BIT is not eight Juha Nieminen <nospam@thanks.invalid> - 2022-10-17 06:18 +0000
            Re: CHAR_BIT is not eight Lynn McGuire <lynnmcguire5@gmail.com> - 2022-10-17 15:29 -0500
    Re: CHAR_BIT is not eight Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-10-13 02:06 -0700
      Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-13 11:42 +0200
        Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-13 15:36 +0000
          Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-13 23:06 +0200
            Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-13 22:30 +0100
              Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-14 15:27 +0200
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-14 14:47 +0100
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-14 14:58 +0000
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-14 21:01 +0100
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-15 10:28 +0000
                Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-15 13:39 +0200
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-15 12:45 +0100
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-15 15:18 +0000
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-15 16:24 +0100
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-15 15:34 +0000
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-15 16:39 +0100
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-15 15:53 +0000
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-15 16:55 +0100
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-15 15:57 +0000
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-15 16:59 +0100
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-17 15:27 +0000
                Re: CHAR_BIT is not eight "daniel...@gmail.com" <danielaparker@gmail.com> - 2022-10-17 09:04 -0700
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-17 16:13 +0000
                Re: CHAR_BIT is not eight red floyd <no.spam.here@its.invalid> - 2022-10-17 09:44 -0700
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-17 17:47 +0100
                Re: CHAR_BIT is not eight Manfred <noname@add.invalid> - 2022-10-18 01:10 +0200
                Re: CHAR_BIT is not eight "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-17 16:22 -0700
                Re: CHAR_BIT is not eight Paul N <gw7rib@aol.com> - 2022-10-18 05:13 -0700
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-18 15:04 +0000
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-18 17:40 +0100
                Re: CHAR_BIT is not eight "daniel...@gmail.com" <danielaparker@gmail.com> - 2022-10-18 12:14 -0700
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-19 15:12 +0000
                Re: CHAR_BIT is not eight scott@slp53.sl.home (Scott Lurndal) - 2022-10-19 15:35 +0000
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-20 16:16 +0000
                Re: CHAR_BIT is not eight Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-15 20:13 +0200
                Re: CHAR_BIT is not eight Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-15 20:11 +0200
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-15 20:03 +0100
                Re: CHAR_BIT is not eight Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-16 07:51 +0200
                Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-16 17:03 +0200
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-16 16:34 +0100
                Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-16 18:51 +0200
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-16 18:11 +0100
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-16 19:18 +0100
                Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-16 22:02 +0200
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-16 21:19 +0100
                Re: CHAR_BIT is not eight scott@slp53.sl.home (Scott Lurndal) - 2022-10-16 21:24 +0000
                Re: CHAR_BIT is not eight "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-16 14:38 -0700
                Re: CHAR_BIT is not eight "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-16 14:48 -0700
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-16 22:39 +0100
                Re: CHAR_BIT is not eight scott@slp53.sl.home (Scott Lurndal) - 2022-10-16 23:49 +0000
                Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-17 09:54 +0200
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-17 17:31 +0100
                Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-17 19:56 +0200
                Re: CHAR_BIT is not eight Muttley@dastardlyhq.com - 2022-10-17 15:29 +0000
                Re: CHAR_BIT is not eight Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-10-17 17:33 +0100
                Re: CHAR_BIT is not eight Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-10-15 11:55 -0700
                Re: CHAR_BIT is not eight "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-15 13:06 -0700
                Re: CHAR_BIT is not eight Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-10-15 15:42 -0700
                Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-16 19:10 +0200
                Re: CHAR_BIT is not eight Vir Campestris <vir.campestris@invalid.invalid> - 2022-10-16 21:28 +0100
                Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-17 10:09 +0200
                Re: CHAR_BIT is not eight "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-16 13:35 -0700
                Re: CHAR_BIT is not eight "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-16 13:36 -0700
      Re: CHAR_BIT is not eight Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-11-02 17:46 -0700
    Re: CHAR_BIT is not eight Bo Persson <bo@bo-persson.se> - 2022-10-13 11:10 +0200
      Re: CHAR_BIT is not eight Juha Nieminen <nospam@thanks.invalid> - 2022-10-13 10:49 +0000
        Re: CHAR_BIT is not eight Juha Nieminen <nospam@thanks.invalid> - 2022-10-13 12:05 +0000
          Re: CHAR_BIT is not eight Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-10-13 06:34 -0700
          Re: CHAR_BIT is not eight Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-10-13 15:24 +0100
        Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-13 15:59 +0200
          Re: CHAR_BIT is not eight Juha Nieminen <nospam@thanks.invalid> - 2022-10-14 05:54 +0000
            Re: CHAR_BIT is not eight Paavo Helde <eesnimi@osa.pri.ee> - 2022-10-14 09:16 +0300
              Re: CHAR_BIT is not eight Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-11-16 05:41 -0800
                Re: CHAR_BIT is not eight Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-11-16 10:38 -0800
                Re: CHAR_BIT is not eight Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-12-05 11:42 -0800
                Re: CHAR_BIT is not eight Öö Tiib <ootiib@hot.ee> - 2022-12-06 01:03 -0800
                Re: CHAR_BIT is not eight Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-12-28 20:49 -0800
            Re: CHAR_BIT is not eight Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-10-14 00:17 -0700
              Re: CHAR_BIT is not eight David Brown <david.brown@hesbynett.no> - 2022-10-14 15:33 +0200
              Re: CHAR_BIT is not eight Vir Campestris <vir.campestris@invalid.invalid> - 2022-10-16 21:37 +0100
                Re: CHAR_BIT is not eight Lynn McGuire <lynnmcguire5@gmail.com> - 2022-10-17 15:24 -0500
  Re: CHAR_BIT is not eight Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-15 11:34 +0200

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