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Groups > comp.arch.embedded > #10614
| From | Tim Wescott <tim@seemywebsite.com> |
|---|---|
| Subject | Re: Getting started with AVR and C |
| Newsgroups | comp.arch.embedded, comp.lang.c |
| 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> |
| Message-ID | <JaGdnWOCkdGuJSvNnZ2dnUVZ_oOdnZ2d@web-ster.com> (permalink) |
| Date | 2012-11-28 19:19 -0600 |
Cross-posted to 2 groups.
On Wed, 28 Nov 2012 12:56:37 -0600, Tim Wescott wrote: > On Wed, 28 Nov 2012 18:05:06 +0000, Grant Edwards wrote: > >> On 2012-11-28, Frank Miles <fpm@u.washington.edu> wrote: >>> >>>> Generally, the result is as wide as the widest of the operands, >>>> or "int", if no operand is wider than "int". The result then may >>>> be truncated on function application or assignment. (For >>>> instance, i += j is 0 if i is 1, j is 255, and both are declared >>>> to be of the 8-bit unsigned integer uint8_t type.) >>>> >>>> >>> 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. 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. Just for clarification, since what I said above seems to be easy to misread unless you pay close attention to context: take "promote both 16- bit integers to 32-bit" and add in the context (about casting one or more of the 16 bit values); the result reads "promote both 16-bit integers to 32-bit _if you cast just one 16-bit integer to 32 bit_". The primary intent of my comment above was to point out that while an ANSI C compliant compiler will convert both operands to and the result to 32-bits if you cast just one operand to 32 bits, there are compilers out there that won't. I did not mean to say -- and indeed it is not the case -- that a compiler with 16-bit integers will automatically promote them to 32 bits just because you want them to, or even just because the result is getting stuck into a 32-bit number. For a nice ANSI-C compliant compiler you only have to tell it once (by casting one of the operands). For at least one compiler that I have used in the past, you had to tell it so over and over again (by casting everything to 32 bits, oh joy). -- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
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Getting started with AVR and C Robert Roland <fake@ddress.no> - 2012-11-24 17:41 +0100
Re: Getting started with AVR and C hamilton <hamilton@nothere.com> - 2012-11-24 09:55 -0700
Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-25 10:39 +0100
Re: Getting started with AVR and C Rene <a@b.c> - 2012-11-24 18:03 +0100
Re: Getting started with AVR and C Rene <a@b.c> - 2012-12-10 13:21 +0100
Re: Getting started with AVR and C Christopher Head <chead@is.invalid> - 2012-12-10 18:33 -0800
Re: Getting started with AVR and C Rene <a@b.c> - 2012-12-11 12:34 +0100
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.please> - 2012-11-24 12:44 -0600
Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-24 11:12 -0800
Re: Getting started with AVR and C mike <ham789@netzero.net> - 2012-11-24 11:28 -0800
Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-24 11:42 -0800
Re: Getting started with AVR and C mike <ham789@netzero.net> - 2012-11-25 07:01 -0800
Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-25 20:14 +0100
Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-25 03:18 +0700
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
Re: Getting started with AVR and C Dave Nadler <drn@nadler.com> - 2012-11-24 21:01 -0800
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 me@linnix.info-for.us - 2012-11-30 09:26 -0800
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-30 13:22 -0800
Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-30 14:10 -0800
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-30 15:16 -0800
Re: Getting started with AVR and C Mel Wilson <mwilson@the-wire.com> - 2012-11-30 17:36 -0500
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-30 15:18 -0800
Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-01 10:08 +0200
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-01 00:45 -0800
Re: Getting started with AVR and C Ed Beroset <beroset@mindspring.com> - 2012-12-01 08:00 -0500
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-01 13:22 -0800
Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-01 17:33 -0800
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-01 17:43 -0800
Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-02 14:13 -0800
Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-04 20:34 -0500
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-04 18:25 -0800
Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-05 07:55 -0500
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 12:11 -0800
Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-05 07:52 -0800
Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-05 11:02 -0500
Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-05 21:28 +0200
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 12:21 -0800
Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-05 23:05 +0200
Re: Getting started with AVR and C Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2012-12-05 23:22 +0200
Re: Getting started with AVR and C Niklas Holsti <niklas.holsti@tidorum.invalid> - 2012-12-06 00:00 +0200
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 12:17 -0800
Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-05 23:10 +0200
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 15:25 -0800
Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-06 07:15 +0200
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 21:52 -0800
Re: Getting started with AVR and C Lanarcam <lanarcam1@yahoo.fr> - 2012-12-06 20:59 +0100
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-06 12:38 -0800
Re: Getting started with AVR and C George Neuner <gneuner2@comcast.net> - 2012-12-06 20:39 -0500
Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-06 22:31 -0500
Re: Getting started with AVR and C Mel Wilson <mwilson@the-wire.com> - 2012-12-05 16:32 -0500
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 15:25 -0800
Re: Getting started with AVR and C dp <dp@tgi-sci.com> - 2012-12-05 17:04 -0800
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 22:01 -0800
Re: Getting started with AVR and C Ian Malcolm <See.My.Sig.for.email@totally.invalid> - 2012-12-06 14:05 +0000
Re: Getting started with AVR and C dp <dp@tgi-sci.com> - 2012-12-06 10:28 -0800
Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-06 16:58 -0800
Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-06 07:34 -0800
Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-06 10:55 -0500
Re: Getting started with AVR and C Rich Webb <bbew.ar@mapson.nozirev.ten> - 2012-12-06 11:11 -0500
Re: Getting started with AVR and C Rocky <RobertGush@gmail.com> - 2012-12-06 21:38 -0800
Re: Getting started with AVR and C dp <dp@tgi-sci.com> - 2012-12-07 03:49 -0800
Re: Getting started with AVR and C Robert Wessel <robertwessel2@yahoo.com> - 2012-12-01 02:58 -0600
Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-01 17:28 +0200
Re: Getting started with AVR and C Robert Wessel <robertwessel2@yahoo.com> - 2012-12-01 11:55 -0600
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 Christopher Head <chead@is.invalid> - 2012-11-28 23:24 -0800
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 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
Re: Getting started with AVR and C dbr@kbrx.com - 2012-11-24 21:49 +0000
Re: Getting started with AVR and C MK <mk@nospam.co.uk> - 2012-11-25 12:24 +0000
Re: Getting started with AVR and C Ian Malcolm <See.My.Sig.for.email@totally.invalid> - 2012-11-26 00:08 +0000
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