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Re: C arithmetic question.

From James Kuyper <jameskuyper@verizon.net>
Newsgroups comp.lang.c
Subject Re: C arithmetic question.
Date 2012-01-20 17:32 -0500
Organization A noiseless patient Spider
Message-ID <jfcq1p$sjd$1@dont-email.me> (permalink)
References (1 earlier) <0eb6c644-ac1e-4de6-8d8a-c1978a8ce255@b10g2000pbd.googlegroups.com> <rubrum-05D6FB.15510218012012@news.albasani.net> <jf7st7$i9u$1@dont-email.me> <rubrum-579D41.12414020012012@news.albasani.net> <jfcp91$n7r$1@dont-email.me>

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On 01/20/2012 05:19 PM, James Kuyper wrote:
> On 01/20/2012 03:41 PM, Michael Press wrote:
>> In article <jf7st7$i9u$1@dont-email.me>,
>>  James Kuyper <jameskuyper@verizon.net> wrote:
>>
>>> On 01/18/2012 06:51 PM, Michael Press wrote:
>>>> In article 
>>>> <0eb6c644-ac1e-4de6-8d8a-c1978a8ce255@b10g2000pbd.googlegroups.com>,
>>>>  Peter Nilsson <airia@acay.com.au> wrote:
>>>>
>>>>> Michael Press <rub...@pacbell.net> wrote:
>>>>>> [-58ul % 37 == 23]
>>>>>> ...
>>>>>> 23 cannot be the right answer because
>>>>>> 37 does not divide -58 - 23 = -81.
>>>>>
>>>>> You have the explanation in the other posts.
>>> ...
>>>> The lesson is to use a library designed to
>>>> do arithmetic rather than expecting it from C.
>>>
>>> Do you really believe that a%(long)b is so much more complicated than
>>> a%b that a special library is called for?
>>>
>>> I would guess that you are probably thinking of this as just one issue
>>> among many, the totality of which justifies use of a special library -
>>> so what are those other issues? How would the behavior of that library
>>> differ from that of ordinary C arithmetic?
>>
>> I already said what I expect from the % operation.
> 
> So, your unmet expectations for the % operation are the totality of your
> objections to C arithmetic? It seems overkill to condemn all of C
> arithmetic on the basis of one operator; or, for that matter, to favor
> using an entire library of functions as a work-around for such a
> problem. Using the new Generic feature, you could create a single
> type-generic function to replace that operator.

Let me expand upon that comment. The key reason for your unmet
expectations in this case was the "usual arithmetic conversions"
(6.1.3.8). Those same conversions apply to many other arithmetic
operators: *, /, +, -, <, <=, >, >=, ==, !=, bitwise &, ^, bitwise |,
?:. The corresponding compound assignment operators, and the ++ and --
operators all have their behavior defined in terms of those operator, so
they perform the usual arithmetic conversions, too. Is the % operator
really the only one where the usual arithmetic conversions cause a
result that doesn't meet your expectations? That seems quite implausible
to me.
-- 
James Kuyper

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C arithmetic question. Michael Press <rubrum@pacbell.net> - 2012-01-18 10:32 -0800
  Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-18 14:03 -0500
    Re: C arithmetic question. TheGunslinger <mikiesrunsbaal.sec@sbcglobal.net> - 2012-01-18 19:30 -0800
      Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-19 08:10 -0500
  Re: C arithmetic question. Markus Wichmann <nullplan@gmx.net> - 2012-01-18 21:14 +0100
    Re: C arithmetic question. "BartC" <bc@freeuk.com> - 2012-01-19 10:44 +0000
      Re: C arithmetic question. Seebs <usenet-nospam@seebs.net> - 2012-01-21 21:32 +0000
  Re: C arithmetic question. Peter Nilsson <airia@acay.com.au> - 2012-01-18 13:51 -0800
    Re: C arithmetic question. Michael Press <rubrum@pacbell.net> - 2012-01-18 15:51 -0800
      Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-18 20:50 -0500
        Re: C arithmetic question. Michael Press <rubrum@pacbell.net> - 2012-01-20 12:41 -0800
          Re: C arithmetic question. Keith Thompson <kst-u@mib.org> - 2012-01-20 14:11 -0800
            Re: C arithmetic question. gazelle@shell.xmission.com (Kenny McCormack) - 2012-01-20 22:43 +0000
          Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-20 17:19 -0500
            Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-20 17:32 -0500
              And jacob navia <jacob@spamsink.net> - 2012-01-20 23:52 +0100
                Re: And Markus Wichmann <nullplan@gmx.net> - 2012-01-21 19:23 +0100
                Re: And Keith Thompson <kst-u@mib.org> - 2012-01-21 13:20 -0800
                Re: And jacob navia <jacob@spamsink.net> - 2012-01-21 23:02 +0100
                Re: And Markus Wichmann <nullplan@gmx.net> - 2012-01-22 15:24 +0100
                Re: And Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-22 15:40 +0000
                Re: And blp@cs.stanford.edu (Ben Pfaff) - 2012-01-21 11:02 -0800
          Re: C arithmetic question. Rui Maciel <rui.maciel@gmail.com> - 2012-01-24 18:53 +0000
      Re: C arithmetic question. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-19 02:09 +0000
      Re: C arithmetic question. Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-01-18 23:00 -0700
        Re: C arithmetic question. Michael Press <rubrum@pacbell.net> - 2012-01-18 23:14 -0800
          Re: C arithmetic question. Ike Naar <ike@sverige.freeshell.org> - 2012-01-19 08:41 +0000
            Re: C arithmetic question. Michael Press <rubrum@pacbell.net> - 2012-01-20 12:43 -0800
              Re: C arithmetic question. Kaz Kylheku <kaz@kylheku.com> - 2012-01-20 22:17 +0000
                Re: C arithmetic question. Michael Press <rubrum@pacbell.net> - 2012-01-21 00:12 -0800
              Re: C arithmetic question. Seebs <usenet-nospam@seebs.net> - 2012-01-21 21:32 +0000
                Re: C arithmetic question. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-21 23:21 +0000
                Re: C arithmetic question. Robert Wessel <robertwessel2@yahoo.com> - 2012-01-22 00:48 -0600
                Re: C arithmetic question. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-22 11:45 +0000
                Re: C arithmetic question. Robert Wessel <robertwessel2@yahoo.com> - 2012-01-22 21:46 -0600
                Re: C arithmetic question. Kaz Kylheku <kaz@kylheku.com> - 2012-01-23 04:17 +0000
                Re: C arithmetic question. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-23 11:19 +0000
                Re: C arithmetic question. Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-26 10:41 -0800
                Re: C arithmetic question. Seebs <usenet-nospam@seebs.net> - 2012-01-23 07:58 +0000
                Re: C arithmetic question. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-23 11:06 +0000
                Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-23 07:03 -0500
                Re: C arithmetic question. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-23 17:27 +0000
          Re: C arithmetic question. Keith Thompson <kst-u@mib.org> - 2012-01-19 02:38 -0800
            Re: C arithmetic question. Dr Nick <3-nospam@temporary-address.org.uk> - 2012-01-20 07:30 +0000
          Re: C arithmetic question. Nomen Nescio <nobody@dizum.com> - 2012-01-19 12:28 +0100
            Re: C arithmetic question. Michael Press <rubrum@pacbell.net> - 2012-01-20 12:44 -0800
              Re: C arithmetic question. 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-20 13:14 -0800
          Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-19 08:45 -0500
          Re: C arithmetic question. Chad <cdalten@gmail.com> - 2012-01-24 08:14 -0800
            Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-24 12:15 -0500
              Re: C arithmetic question. Chad <cdalten@gmail.com> - 2012-01-24 09:26 -0800
                Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-24 12:39 -0500
                Re: C arithmetic question. Chad <cdalten@gmail.com> - 2012-01-24 10:03 -0800
                Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-24 13:23 -0500
                Re: C arithmetic question. Chad <cdalten@gmail.com> - 2012-01-24 10:40 -0800
                Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-24 14:35 -0500
                Re: C arithmetic question. Chad <cdalten@gmail.com> - 2012-01-24 12:04 -0800
                Re: C arithmetic question. Chad <cdalten@gmail.com> - 2012-01-24 12:02 -0800
                Re: C arithmetic question. Kleuske <kleuske@nowhere.net> - 2012-01-24 20:26 +0000
                Re: C arithmetic question. Chad <cdalten@gmail.com> - 2012-01-24 13:45 -0800
                Re: C arithmetic question. James Kuyper <jameskuyper@verizon.net> - 2012-01-24 15:40 -0500
                Re: C arithmetic question. Chad <cdalten@gmail.com> - 2012-01-24 12:09 -0800
      Re: C arithmetic question. Rui Maciel <rui.maciel@gmail.com> - 2012-01-24 18:48 +0000
    Re: C arithmetic question. "osmium" <r124c4u102@comcast.net> - 2012-01-19 08:12 -0600
  Re: C arithmetic question. Geoff <geoff@invalid.invalid> - 2012-01-20 15:33 -0800
    Re: C arithmetic question. Kleuske <kleuske@nowhere.net> - 2012-01-27 08:17 +0000
      Re: C arithmetic question. Geoff <geoff@invalid.invalid> - 2012-01-27 13:37 -0800

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