Re: the language (and the role of Undefined Behavior therein)

From	glen herrmannsfeldt <gah@ugcs.caltech.edu>
Newsgroups	comp.lang.c
Subject	Re: the language (and the role of Undefined Behavior therein)
Date	2015-08-24 03:45 +0000
Organization	Aioe.org NNTP Server
Message-ID	<mre404$ccu$1@speranza.aioe.org> (permalink)
References	(6 earlier) <1f86d431-4ab2-447e-830b-5878781225fc@googlegroups.com> <lnsi7d1n7c.fsf@kst-u.example.com> <044f1f29-894c-46c1-9ff2-61ba5191c3f5@googlegroups.com> <lnbne014z3.fsf@kst-u.example.com> <026de000-b3bd-44b7-914e-0274671a3687@googlegroups.com>

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David Kleinecke <dkleinecke@gmail.com> wrote:

(snip)

> It is true that every computer I know about executes a multiplication
> into a "register" twice as long as the multipliers. But C simply 
> truncates that back modula INT_MAX+1 (actually it's bit more
> complicated. Even though C provides no way getting the higher half
> of a multiplication I enevr heard a complaint. Odd.   

I have complained, though not recently. In TeX, Knuth suggests that
one routine be rewritten in assembler if possible. That routine
does a multiply generating a double length product, and then uses
that as a dividend in a divide operation.

The processors (most) that generate a double length product also
usually accept a double length dividend. 

Though many processors generate the double length product,
they don't all do it the same way. Specifically, the way the
high bit of the low half is defined might be different.
That is especially true on sign magnitude and ones complement,
but I have seen it on twos complement, too.

-- glen

Thread

Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-18 16:19 -0700
  Re: the language (and the role of Undefined Behavior therein) Richard Damon <Richard@Damon-Family.org> - 2015-08-18 21:15 -0400
    Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-19 10:11 -0700
      Re: the language (and the role of Undefined Behavior therein) Ike Naar <ike@iceland.freeshell.org> - 2015-08-19 19:58 +0000
        Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-19 14:09 -0700
      Re: the language (and the role of Undefined Behavior therein) James Kuyper <jameskuyper@verizon.net> - 2015-08-19 16:10 -0400
        Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-19 16:01 -0700
          Re: the language (and the role of Undefined Behavior therein) James Kuyper <jameskuyper@verizon.net> - 2015-08-19 20:23 -0400
            Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-20 10:35 -0700
              Re: the language (and the role of Undefined Behavior therein) Keith Thompson <kst-u@mib.org> - 2015-08-20 12:32 -0700
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-20 13:31 -0700
                Re: the language (and the role of Undefined Behavior therein) donalhambra@gmail.com - 2015-08-20 14:23 -0700
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-20 16:13 -0700
                Re: the language (and the role of Undefined Behavior therein) Keith Thompson <kst-u@mib.org> - 2015-08-20 17:48 -0700
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-21 01:32 -0700
                Re: the language (and the role of Undefined Behavior therein) Keith Thompson <kst-u@mib.org> - 2015-08-21 18:34 -0700
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-21 22:11 -0700
                Re: the language (and the role of Undefined Behavior therein) Richard Damon <Richard@Damon-Family.org> - 2015-08-22 09:41 -0400
                Re: the language (and the role of Undefined Behavior therein) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-22 16:59 +0000
                Re: the language (and the role of Undefined Behavior therein) James Kuyper <jameskuyper@verizon.net> - 2015-08-22 23:30 -0400
                Re: the language (and the role of Undefined Behavior therein) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-24 03:36 +0000
                Re: the language (and the role of Undefined Behavior therein) James Kuyper <jameskuyper@verizon.net> - 2015-08-24 00:25 -0400
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-23 22:57 -0700
                Re: the language (and the role of Undefined Behavior therein) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-24 19:49 +0000
                Re: the language (and the role of Undefined Behavior therein) Tim Rentsch <txr@alumni.caltech.edu> - 2015-09-06 14:43 -0700
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-23 16:27 -0700
                Re: the language (and the role of Undefined Behavior therein) Richard Damon <Richard@Damon-Family.org> - 2015-08-23 21:15 -0400
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-23 20:18 -0700
                Re: the language (and the role of Undefined Behavior therein) raltbos@xs4all.nl (Richard Bos) - 2015-08-22 14:37 +0000
                Re: the language (and the role of Undefined Behavior therein) David Kleinecke <dkleinecke@gmail.com> - 2015-08-22 19:12 -0700
                Re: the language (and the role of Undefined Behavior therein) James Kuyper <jameskuyper@verizon.net> - 2015-08-22 23:38 -0400
                Re: the language (and the role of Undefined Behavior therein) David Kleinecke <dkleinecke@gmail.com> - 2015-08-23 20:01 -0700
                Re: the language (and the role of Undefined Behavior therein) Keith Thompson <kst-u@mib.org> - 2015-08-23 21:56 -0700
                Re: the language (and the role of Undefined Behavior therein) David Kleinecke <dkleinecke@gmail.com> - 2015-08-24 17:25 -0700
                Re: the language (and the role of Undefined Behavior therein) Keith Thompson <kst-u@mib.org> - 2015-08-24 18:21 -0700
                Re: the language (and the role of Undefined Behavior therein) James Kuyper <jameskuyper@verizon.net> - 2015-08-24 22:22 -0400
                Re: the language (and the role of Undefined Behavior therein) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-25 14:31 +0000
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-25 09:22 -0700
                Re: the language (and the role of Undefined Behavior therein) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-25 18:55 +0000
                Re: the language (and the role of Undefined Behavior therein) Keith Thompson <kst-u@mib.org> - 2015-08-25 12:33 -0700
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-25 16:23 -0700
                Re: the language (and the role of Undefined Behavior therein) James Kuyper <jameskuyper@verizon.net> - 2015-08-24 00:31 -0400
                Re: the language (and the role of Undefined Behavior therein) Keith Thompson <kst-u@mib.org> - 2015-08-24 10:32 -0700
                Re: the language (and the role of Undefined Behavior therein) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-08-22 23:54 -0700
                Re: the language (and the role of Undefined Behavior therein) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-24 03:45 +0000
                Re: the language (and the role of Undefined Behavior therein) Tim Rentsch <txr@alumni.caltech.edu> - 2015-09-07 08:11 -0700
      Re: the language (and the role of Undefined Behavior therein) Richard Damon <Richard@Damon-Family.org> - 2015-08-23 18:46 -0400
        Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-23 19:04 -0700
          Re: the language (and the role of Undefined Behavior therein) Richard Damon <Richard@Damon-Family.org> - 2015-08-23 23:40 -0400
            Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-23 22:48 -0700
              Re: the language (and the role of Undefined Behavior therein) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-08-24 00:38 -0700
  Re: the language (and the role of Undefined Behavior therein) James Kuyper <jameskuyper@verizon.net> - 2015-08-18 21:22 -0400
  Re: the language (and the role of Undefined Behavior therein) Ike Naar <ike@iceland.freeshell.org> - 2015-08-20 21:44 +0000
    Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-08-20 16:48 -0700
    Re: the language (and the role of Undefined Behavior therein) Philip Lantz <prl@canterey.us> - 2015-08-20 23:41 -0700

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