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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Performance of signed vs unsigned types |
| Date | 2011-04-26 08:52 -0700 |
| Organization | None to speak of |
| Message-ID | <ln7hahypqf.fsf@nuthaus.mib.org> (permalink) |
| References | (16 earlier) <rubrum-2758E7.11484825042011@news.albasani.net> <db2h88-t8c.ln1@jones.homeip.net> <lnr58qyns1.fsf@nuthaus.mib.org> <rubrum-F140C5.20322925042011@news.albasani.net> <lnfwp5yrfp.fsf@nuthaus.mib.org> |
Keith Thompson <kst-u@mib.org> writes:
[...]
> int multiplication_would_overflow(int x, int y)
> {
> /*
> * TODO: Implement this.
> */
> return 0;
> }
[...]
I forgot to mention that, of course, it's entirely possible
to implement the multiplication_would_overflow() function in
portable C. I think I've seen versions posted here (I'm just too
lazy to track them down or recreate them). The point is that it's
very difficult to get it right (for example, INT_MIN * -1 overflows
on 2's-complement systems but not on others), and computationally
expensive, far more expensive than the multiplication itself.
On most CPUs, there's a way (which varies from one CPU to another)
to compute x * y safely and determine after the fact whether there
was an overflow, but C doesn't expose that. There typically isn't
even a non-portable way to do overflow checking in C, unless you
resort to inline assembly.
Note that I'm talking about the way C is currently defined, not
arguing that it *should* be defined that way. Personally, I'd like
to see something similar to C#'s "checked" keyword, which requires
overflow checking for an expression; the problem is that it depends
on C#'s exception mechanism, and adding exceptions to C seems to
be more than the committee is willing to do.
--
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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Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-20 14:21 +0100
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-20 09:49 -0400
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-20 15:21 +0100
Re: Performance of signed vs unsigned types Peter Nilsson <airia@acay.com.au> - 2011-04-20 15:34 -0700
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-21 17:57 +0100
Re: Performance of signed vs unsigned types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-04-21 19:26 +0100
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-20 21:45 -0700
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-21 06:20 -0400
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-21 13:54 -0700
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-21 18:50 -0400
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-21 16:16 -0700
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-21 19:27 -0400
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-21 17:24 -0700
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-21 21:00 -0400
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-21 21:33 -0700
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-22 08:22 +0100
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-22 14:25 -0700
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-22 09:21 -0400
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-22 14:22 -0700
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-22 17:58 -0400
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-22 17:33 -0700
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-23 09:01 -0400
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-23 14:07 -0700
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-23 18:14 -0400
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-25 11:42 -0700
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-25 22:34 -0400
Re: Performance of signed vs unsigned types gordonb.nw63u@burditt.org (Gordon Burditt) - 2011-04-26 10:59 -0500
Re: Performance of signed vs unsigned types "madamemandm@yahoo.com" <madamemandm@yahoo.com> - 2011-04-22 07:55 -0700
Re: Performance of signed vs unsigned types Noob <root@127.0.0.1> - 2011-04-22 17:03 +0200
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-22 08:42 -0700
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-22 14:15 -0700
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-22 15:23 -0700
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-22 17:37 -0700
Re: Performance of signed vs unsigned types Seebs <usenet-nospam@seebs.net> - 2011-04-23 02:46 +0000
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-23 14:04 -0700
Re: Performance of signed vs unsigned types Barry Schwarz <schwarzb@dqel.com> - 2011-04-23 14:28 -0700
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-25 11:43 -0700
Re: Performance of signed vs unsigned types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-04-23 23:38 +0100
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-25 11:46 -0700
Re: Performance of signed vs unsigned types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-04-25 22:43 +0100
Re: Performance of signed vs unsigned types Seebs <usenet-nospam@seebs.net> - 2011-04-24 11:34 +0000
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-25 11:47 -0700
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-25 12:32 -0700
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-25 20:25 -0700
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-26 07:45 -0700
Re: Performance of signed vs unsigned types lawrence.jones@siemens.com - 2011-04-24 23:50 -0400
Re: Performance of signed vs unsigned types Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-04-25 02:13 -0700
Re: Performance of signed vs unsigned types Ian Collins <ian-news@hotmail.com> - 2011-04-25 21:36 +1200
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-25 11:48 -0700
Re: Performance of signed vs unsigned types lawrence.jones@siemens.com - 2011-04-25 16:32 -0400
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-25 15:22 -0700
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-25 20:32 -0700
Re: Performance of signed vs unsigned types "io_x" <a@b.c.invalid> - 2011-04-26 09:42 +0200
Re: Performance of signed vs unsigned types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-04-26 12:04 +0100
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-26 08:15 -0700
Re: Performance of signed vs unsigned types Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-04-26 08:35 -0700
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-26 08:52 -0700
Re: Performance of signed vs unsigned types Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-04-26 09:15 -0700
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-26 10:22 -0700
Re: Performance of signed vs unsigned types gordonb.s68qo@burditt.org (Gordon Burditt) - 2011-04-26 19:59 -0500
Re: Performance of signed vs unsigned types "madamemandm@yahoo.com" <madamemandm@yahoo.com> - 2011-04-27 14:15 -0700
Re: Performance of signed vs unsigned types "io_x" <a@b.c.invalid> - 2011-04-28 12:15 +0200
Re: Performance of signed vs unsigned types Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-04-28 03:26 -0700
Re: Performance of signed vs unsigned types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-04-28 12:09 +0100
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-28 08:03 -0400
Re: Performance of signed vs unsigned types Seebs <usenet-nospam@seebs.net> - 2011-04-28 16:44 +0000
Re: Performance of signed vs unsigned types Gordon Burditt <gordon@hammy.burditt.org> - 2011-04-29 05:42 -0500
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-25 20:27 -0700
Re: Performance of signed vs unsigned types Ian Collins <ian-news@hotmail.com> - 2011-04-26 15:30 +1200
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-26 00:14 -0700
Re: Performance of signed vs unsigned types Ian Collins <ian-news@hotmail.com> - 2011-04-26 20:23 +1200
Re: Performance of signed vs unsigned types Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-04-26 04:17 -0700
Re: Performance of signed vs unsigned types Ike Naar <ike@sverige.freeshell.org> - 2011-04-22 06:46 +0000
Re: Performance of signed vs unsigned types James Kuyper <jameskuyper@verizon.net> - 2011-04-22 09:37 -0400
Re: Performance of signed vs unsigned types Michael Press <rubrum@pacbell.net> - 2011-04-25 11:49 -0700
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-22 09:09 -0700
Re: Performance of signed vs unsigned types "madamemandm@yahoo.com" <madamemandm@yahoo.com> - 2011-04-22 09:46 -0700
Re: Performance of signed vs unsigned types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-04-22 20:21 +0100
Re: Performance of signed vs unsigned types "Scott Fluhrer" <sfluhrer@ix.netcom.com> - 2011-04-20 10:06 -0400
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-20 15:28 +0100
Re: Performance of signed vs unsigned types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-04-20 16:11 +0100
Re: Performance of signed vs unsigned types Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-04-20 08:14 -0700
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-20 16:24 +0100
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-20 17:09 +0100
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-20 17:19 +0100
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-20 12:09 -0700
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-20 21:39 +0100
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-20 15:01 -0700
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-21 11:16 +0100
Re: Performance of signed vs unsigned types "Scott Fluhrer" <sfluhrer@ix.netcom.com> - 2011-04-20 13:06 -0400
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-20 18:16 +0100
Re: Performance of signed vs unsigned types gordonb.bfd7y@burditt.org (Gordon Burditt) - 2011-04-21 11:22 -0500
Re: Performance of signed vs unsigned types Thomas Scrace <tom@scrace.org> - 2011-04-21 19:27 +0100
Re: Performance of signed vs unsigned types Keith Thompson <kst-u@mib.org> - 2011-04-21 12:09 -0700
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