Re: Getting started with AVR and C

From	James Kuyper <jameskuyper@verizon.net>
Newsgroups	comp.arch.embedded, comp.lang.c
Subject	Re: Getting started with AVR and C
Date	2012-11-28 19:02 -0500
Organization	A noiseless patient Spider
Message-ID	<50B6A618.5000708@verizon.net> (permalink)
References	(4 earlier) <k95j21$otc$1@dont-email.me> <k95joi$qcq$1@reader1.panix.com> <JaGdnWuCkdH4wyvNnZ2dnUVZ_oOdnZ2d@web-ster.com> <k9632c$9h4$1@reader1.panix.com> <JaGdnWGCkdFvAyvNnZ2dnUVZ_oOdnZ2d@web-ster.com>

Cross-posted to 2 groups.

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On 11/28/2012 06:32 PM, Tim Wescott wrote:
> On Wed, 28 Nov 2012 22:26:20 +0000, Grant Edwards wrote:
> 
>> On 2012-11-28, Tim Wescott <tim@seemywebsite.com> wrote:
...
>>> I would expect that gcc would be ANSI compliant, and would therefore
>>> promote both 16-bit integers to 32-bit before doing the multiply.
>>
>> Nope.  On the target in question (AVR), an "int" is 16 bits (at least by
>> default).  Same for msp430 (and maybe for some of the H8 targets). I
>> think there is a command-line option for some 16-bit targets to tell gcc
>> to use 32-bit representations for "int" instead of the defautl 16 bits.
> 
> You mean "Absolutely", not "Nope".  At least you do if you're referring 
> to a 16-bit int as being conformant to ANSI C.
> 
> Per ANSI C99 (http://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf), 
> page 34, the minimum allowable value of INT_MAX is 32767.  That fits 
> nicely inside a 16-bit signed number.

I'm not sure the point you're making here. The type resulting from
integer promotions is always either an 'int' or an 'unsigned int', and
they occur only for values of other integer types whose entire range can
be represented in the promoted type. Therefore, if int is 16 bits,
int16_t operands will not be promoted at all, much less promoted to a
32-bit int, in conflict with what you said you expected of an ANSI
compliant compiler. That's what his "Nope" was referring to.

On such a platform, the usual arithmetic conversions will cause one of
the operands to be converted implicitly to a 32-bit int if the other one
is explicitly converted to a 32-bit int.  However, section 6.3.1.1p2
defines what an "integer promotion" is, and that definition doesn't
include those conversions.

Thread

Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-25 04:18 +0700
  Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-11-24 17:09 -0500
  Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-24 22:12 +0000
    statement / expression contexts in C Ivan Shmakov <oneingray@gmail.com> - 2012-11-28 12:54 +0700
    Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-28 13:37 +0700
      Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-28 14:49 +0000
      Re: Getting started with AVR and C Frank Miles <fpm@u.washington.edu> - 2012-11-28 17:53 +0000
        Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-28 18:05 +0000
          Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 12:56 -0600
            Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-28 21:45 +0000
              Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 15:55 -0600
              Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-29 01:35 +0100
                Re: Getting started with AVR and C Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-11-29 01:47 +0100
                Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 09:24 +0100
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 01:18 +0000
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 20:07 -0600
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:23 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 11:01 -0500
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 19:19 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 14:32 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 11:44 -0800
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 21:23 +0000
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 18:15 -0800
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-11-29 22:17 +0200
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 12:36 -0800
                Re: Getting started with AVR and C Stephen Sprunk <stephen@sprunk.org> - 2012-11-29 16:22 -0600
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 18:36 -0800
                Re: Getting started with AVR and C "Boudewijn Dijkstra" <sp4mtr4p.boudewijn@indes.com> - 2012-12-11 10:53 +0100
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-12-11 14:53 +0000
                Unicode Ivan Shmakov <oneingray@gmail.com> - 2012-12-14 23:25 +0700
                Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-15 14:30 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-15 12:24 -0800
                Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-15 18:02 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-15 15:45 -0800
                Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-16 22:55 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-16 23:20 -0800
                Re: Getting started with AVR and C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:27 +0200
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-12-17 11:17 +0000
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-17 14:07 +0000
                Re: Getting started with AVR and C Nobody <nobody@nowhere.com> - 2012-12-16 03:28 +0000
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-16 10:40 +0200
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 02:31 +0000
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 03:36 +0000
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 03:55 +0000
                Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 09:37 +0100
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 11:31 +0000
                Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 13:44 +0100
                Re: Getting started with AVR and C Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-11-29 13:22 +0100
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 13:32 +0000
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 11:28 -0800
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 13:20 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 09:07 -0500
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 09:17 -0500
                Re: Getting started with AVR and C pete <pfiland@mindspring.com> - 2012-11-29 18:25 -0500
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 22:46 -0500
                Re: Getting started with AVR and C lawrence.jones@siemens.com - 2012-11-30 11:47 -0500
                Re: Getting started with AVR and C Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-17 03:53 -0800
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 11:38 -0800
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 15:21 -0500
            Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-28 22:26 +0000
              Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 17:32 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 19:02 -0500
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 18:29 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 23:39 -0500
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.please> - 2012-11-29 00:59 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 07:57 -0500
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-29 13:02 -0600
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:19 +0000
                Re: Getting started with AVR and C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-11-29 12:03 +0200
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 11:39 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 08:04 -0500
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:17 +0000
            Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 19:19 -0600
              Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 23:44 -0500
        Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 13:15 -0500
          Re: Getting started with AVR and C Arlet Ottens <usenet+5@c-scape.nl> - 2012-11-28 19:17 +0100
            Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 19:30 -0600
              Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:29 +0000
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-11-29 16:36 +0000
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-11-29 22:40 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 13:55 -0800
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 22:06 +0000
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 14:22 -0800
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 21:59 +0000
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-11-30 08:29 +0000
  Re: Getting started with AVR and C Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-11-25 05:41 -0800
  Re: Getting started with AVR and C Rosario1903 <Rosario@invalid.invalid> - 2012-11-27 10:21 +0100

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