Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
| From | Grant Edwards <invalid@invalid.invalid> |
|---|---|
| Newsgroups | comp.arch.embedded, comp.lang.c |
| Subject | Re: Getting started with AVR and C |
| Date | 2012-11-28 22:26 +0000 |
| Organization | PANIX Public Access Internet and UNIX, NYC |
| Message-ID | <k9632c$9h4$1@reader1.panix.com> (permalink) |
| References | (2 earlier) <0.4196fd606ae8a0c4ce3e.20121124221204GMT.87zk26y7kb.fsf@bsb.me.uk> <86pq2y1bcy.fsf@gray.siamics.net> <k95j21$otc$1@dont-email.me> <k95joi$qcq$1@reader1.panix.com> <JaGdnWuCkdH4wyvNnZ2dnUVZ_oOdnZ2d@web-ster.com> |
Cross-posted to 2 groups.
On 2012-11-28, Tim Wescott <tim@seemywebsite.com> wrote:
> On Wed, 28 Nov 2012 18:05:06 +0000, Grant Edwards wrote:
>>> And you have to be careful about how/when any expansions occur. For
>>> example with gcc-avr, if you want
>>>
>>> int32_t = int16_t * int16_t
>>>
>>> (the full 32 bit result of a 16x16 bit multiply), you have to cast each
>>> of the 16-bit operands to 32bits.
>>
>> Shouldn't casting just one of the 16 bit values work the same as casting
>> both of them?
>
> Yes. But that's if you take "should" as indicating a moral direction,
> rather than as an indication of what you can reasonably expect from every
> tool chain.
>
> 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.
> But I've worked with compilers in the past that didn't do this, so
> when writing code that may be used in multiple places, I up-cast the
> same way one votes in Chicago: early and often.
If, like AVR and msp430, an "int" is 16 bits, then you must cast at
least one of the two operands to a 32 bit integer type if you want a
16x16=>32 multiply.
--
Grant Edwards grant.b.edwards Yow! Mr and Mrs PED, can I
at borrow 26.7% of the RAYON
gmail.com TEXTILE production of the
INDONESIAN archipelago?
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll 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
csiph-web