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Re: Understanding C89/C99 aliasing

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From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: Understanding C89/C99 aliasing
Date Tue, 08 Dec 2015 19:15:52 -0800
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glen herrmannsfeldt <gah@ugcs.caltech.edu> writes:
> Keith Thompson <kst-u@mib.org> wrote:
[...]
>> The purpose of a C compiler is to generate an executable program that
>> behaves as the source program specifies.  Generating CPU instructions is
>> how it achieves that purpose.
>
> OK, but consider the restriction on shift values, that they be 
> non-negative and less than the bit width of the value being shifted.
>
> In the case of an abstract machine, why not an abstract machine
> that can do negative or large shifts? But the people who build real
> machines often don't allow for that.

Of course the characteristics of the C abstract machine are influenced
by real machines.

[...]

> In general, C is much easier to learn for people who have previously
> done assembly programming. They are used to thinking about addresses
> and what happens at an addresed locatation. Also, as above, the 
> properties of instructions like shift.
>
> The allowable operations in C tend to be close to those of actual
> machines, unlike some other languages that I don't need to mention.
>
> Most C statements generate code approximately proportional to the
> size of the C statements. Again, unlike many other languages.

That's usually true, but I still find it easier to think about C
programs in terms of their behavior rather than the code the compiler
happens to generate for them.  (I don't always even know or care what
target CPU I'm generating code for.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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Thread

Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-18 11:25 -0800
  Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 01:39 +0000
    Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-18 19:55 -0800
      Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 14:37 +0000
        Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-19 07:07 -0800
          Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 22:58 +0000
    Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-18 20:00 -0800
  Re: Understanding C89/C99 aliasing Nick Bowler <nbowler@draconx.ca> - 2015-11-19 15:44 +0000
    Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-19 09:46 -0800
      Re: Understanding C89/C99 aliasing Martin Shobe <martin.shobe@yahoo.com> - 2015-11-19 13:28 -0600
        Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-19 11:54 -0800
          Re: Understanding C89/C99 aliasing Martin Shobe <martin.shobe@yahoo.com> - 2015-11-19 14:41 -0600
            Re: Understanding C89/C99 aliasing Martin Shobe <martin.shobe@yahoo.com> - 2015-11-19 14:46 -0600
              Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-19 13:16 -0800
          Re: Understanding C89/C99 aliasing Nick Bowler <nbowler@draconx.ca> - 2015-11-19 21:11 +0000
            Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-19 13:34 -0800
              Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 23:12 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-19 15:18 -0800
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-20 02:21 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-19 18:40 -0800
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-21 00:32 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-20 16:47 -0800
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-21 01:14 +0000
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-20 20:25 -0600
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-21 10:17 +0000
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-21 18:11 -0600
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-22 00:58 +0000
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 14:41 -0600
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-23 00:58 +0000
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 19:33 -0600
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-26 01:16 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-25 21:57 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-26 18:01 -0600
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-27 10:17 -0800
                Re: Understanding C89/C99 aliasing Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 23:38 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-28 07:22 -0800
                Re: Understanding C89/C99 aliasing Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-08 08:51 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-22 18:34 -0800
                Re: Understanding C89/C99 aliasing James Kuyper <jameskuyper@verizon.net> - 2015-11-23 06:48 -0500
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-11-23 08:28 -0800
                Re: Understanding C89/C99 aliasing Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 09:21 -0800
                Re: Understanding C89/C99 aliasing raltbos@xs4all.nl (Richard Bos) - 2015-11-27 17:45 +0000
                Re: Understanding C89/C99 aliasing Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 10:13 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-27 10:50 -0800
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-11-27 13:46 -0800
                Re: Understanding C89/C99 aliasing Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-28 08:57 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-28 11:00 -0800
                Re: Understanding C89/C99 aliasing Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-08 09:04 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-08 10:42 -0800
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-12-08 10:54 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-08 11:44 -0800
                Re: Understanding C89/C99 aliasing glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-12-09 00:11 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-08 16:39 -0800
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-12-08 19:15 -0800
                Re: Understanding C89/C99 aliasing glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-12-09 04:21 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-09 09:04 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-08 22:15 -0600
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-09 07:04 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-09 14:29 -0600
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-12-09 13:06 -0800
                Re: Understanding C89/C99 aliasing glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-12-09 22:58 +0000
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-10 11:35 -0600
                Re: Understanding C89/C99 aliasing James Kuyper <jameskuyper@verizon.net> - 2015-12-10 12:58 -0500
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-10 10:12 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-10 13:39 -0600
                Re: Understanding C89/C99 aliasing raltbos@xs4all.nl (Richard Bos) - 2015-12-10 22:45 +0000
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-11 12:27 -0600
                Re: Understanding C89/C99 aliasing James Kuyper <jameskuyper@verizon.net> - 2015-12-10 20:30 -0500
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-10 13:54 -0600
                Re: Understanding C89/C99 aliasing James Kuyper <jameskuyper@verizon.net> - 2015-12-10 20:57 -0500
                Re: Understanding C89/C99 aliasing glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-12-11 03:44 +0000
                Re: Understanding C89/C99 aliasing James Kuyper <jameskuyper@verizon.net> - 2015-12-11 07:26 -0500
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-11 11:58 -0600
                Re: Understanding C89/C99 aliasing Richard Damon <Richard@Damon-Family.org> - 2015-12-11 23:17 -0500
                Re: Understanding C89/C99 aliasing James Kuyper <jameskuyper@verizon.net> - 2015-12-11 14:00 -0500
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-09 13:17 -0800
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-12-09 14:22 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-09 15:06 -0800
                Re: Understanding C89/C99 aliasing glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-12-09 23:18 +0000
                Re: Understanding C89/C99 aliasing James Kuyper <jameskuyper@verizon.net> - 2015-12-09 18:48 -0500
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-09 15:49 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-10 12:44 -0600
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-10 11:12 -0800
                Re: Understanding C89/C99 aliasing raltbos@xs4all.nl (Richard Bos) - 2015-12-10 20:18 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-10 12:29 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-10 16:19 -0600
                Re: Understanding C89/C99 aliasing raltbos@xs4all.nl (Richard Bos) - 2015-12-10 22:49 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-10 14:58 -0800
                Re: Understanding C89/C99 aliasing raltbos@xs4all.nl (Richard Bos) - 2015-12-15 18:25 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-15 10:50 -0800
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-12-15 11:32 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-15 12:20 -0800
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-12-15 13:08 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-15 13:24 -0800
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-12-15 14:35 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-15 15:34 -0800
                Re: Understanding C89/C99 aliasing David Brown <david.brown@hesbynett.no> - 2015-12-16 00:00 +0100
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-15 15:47 -0800
                Re: Understanding C89/C99 aliasing David Brown <david.brown@hesbynett.no> - 2015-12-16 11:08 +0100
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-16 09:45 -0800
                Re: Understanding C89/C99 aliasing David Brown <david.brown@hesbynett.no> - 2015-12-17 13:51 +0100
                Re: Understanding C89/C99 aliasing Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-12-17 05:10 -0800
                Re: Understanding C89/C99 aliasing Richard Heathfield <rjh@cpax.org.uk> - 2015-12-17 13:46 +0000
                Re: Understanding C89/C99 aliasing David Brown <david.brown@hesbynett.no> - 2015-12-17 15:24 +0100
                Re: Understanding C89/C99 aliasing Jerry Stuckle <jstucklex@attglobal.net> - 2015-12-17 09:57 -0500
                Re: Understanding C89/C99 aliasing Les Cargill <lcargill99@comcast.com> - 2015-12-17 09:39 -0600
                Re: Understanding C89/C99 aliasing Jerry Stuckle <jstucklex@attglobal.net> - 2015-12-17 12:12 -0500
                Re: Understanding C89/C99 aliasing Les Cargill <lcargill99@comcast.com> - 2015-12-17 12:27 -0600
                Re: Understanding C89/C99 aliasing Jerry Stuckle <jstucklex@attglobal.net> - 2015-12-17 14:22 -0500
                Re: Understanding C89/C99 aliasing Les Cargill <lcargill99@comcast.com> - 2015-12-17 17:58 -0600
                Re: Understanding C89/C99 aliasing Jerry Stuckle <jstucklex@attglobal.net> - 2015-12-17 20:26 -0500
                Re: Understanding C89/C99 aliasing Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-12-17 20:35 -0500
                Re: Understanding C89/C99 aliasing Jerry Stuckle <jstucklex@attglobal.net> - 2015-12-17 21:49 -0500
                Re: Understanding C89/C99 aliasing Les Cargill <lcargill99@comcast.com> - 2015-12-17 20:52 -0600
                Re: Understanding C89/C99 aliasing Jerry Stuckle <jstucklex@attglobal.net> - 2015-12-17 22:01 -0500
                Re: Understanding C89/C99 aliasing Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-12-17 20:55 -0800
                Re: Understanding C89/C99 aliasing Jerry Stuckle <jstucklex@attglobal.net> - 2015-12-18 08:40 -0500
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-17 09:10 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-15 14:27 -0800
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-12-15 16:30 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-16 12:47 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-15 14:32 -0800
                Re: Understanding C89/C99 aliasing Öö Tiib <ootiib@hot.ee> - 2015-12-09 08:09 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-09 09:10 -0800
                Re: Understanding C89/C99 aliasing Öö Tiib <ootiib@hot.ee> - 2015-12-09 10:38 -0800
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-09 11:18 -0800
                Re: Understanding C89/C99 aliasing glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-12-09 19:14 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-09 11:27 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-12-09 15:03 -0600
                Re: Understanding C89/C99 aliasing Öö Tiib <ootiib@hot.ee> - 2015-12-10 01:23 -0800
                Re: Understanding C89/C99 aliasing raltbos@xs4all.nl (Richard Bos) - 2015-12-10 20:21 +0000
                Re: Understanding C89/C99 aliasing Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-09 13:06 -0800
                Re: Understanding C89/C99 aliasing glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-12-09 00:00 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-12-08 16:27 -0800
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-12-09 01:18 +0000
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-12-08 19:13 -0800
                Re: Understanding C89/C99 aliasing Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-09 13:04 -0800
                Re: Understanding C89/C99 aliasing raltbos@xs4all.nl (Richard Bos) - 2015-12-10 20:07 +0000
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-23 17:03 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-23 15:39 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-23 18:11 -0600
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-24 01:13 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-24 09:29 -0800
              Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-20 09:10 -0600
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-20 10:08 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-21 19:02 -0600
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-21 18:17 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-21 20:52 -0600
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-21 19:28 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 20:00 -0600
                Re: Understanding C89/C99 aliasing Keith Thompson <kst-u@mib.org> - 2015-11-20 19:12 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-20 23:10 -0600
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-20 23:07 -0800
                Re: Understanding C89/C99 aliasing Stephen Sprunk <stephen@sprunk.org> - 2015-11-21 18:37 -0600
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-21 10:29 +0000
                Re: Understanding C89/C99 aliasing supercat@casperkitty.com - 2015-11-21 10:04 -0800
                Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-21 19:35 +0000
          Re: Understanding C89/C99 aliasing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 23:07 +0000

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