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Re: Best search algorithm to find condition within a range

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Date Fri, 10 Apr 2015 02:36:36 +1000
Subject Re: Best search algorithm to find condition within a range
From Chris Angelico <rosuav@gmail.com>
Cc "python-list@python.org" <python-list@python.org>
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On Fri, Apr 10, 2015 at 2:15 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> On Fri, 10 Apr 2015 01:34 am, Chris Angelico wrote:
>
>> It's equally impossible for the addition of two positive signed
>> integers to result in a negative integer.
>
> Why oh why do C programmers tell such porkies??? *semi-wink*
>
> [steve@ando c]$ gcc add.c
> [steve@ando c]$ ./a.out
> a = 1
> b = 2147483647
> a+b = -2147483648
>
>
> Looks like a negative integer to me, but then, given that its undefined
> behaviour, perhaps the compiler flipped some pixels on the screen so it
> merely *looks* negative.

Precisely. Another compiler, or another CPU architecture, is welcome
to behave differently. *According to the C standard*, you just did
something impossible, so it's equally valid for the output to be 5, 3,
7, or 25, all of which would probably be produced by Princess Ida's
compiler. (Mind you, her compiler might do that when asked to add 2
and 2, so I'm not sure it's all that helpful a comparison. [1])

> Here's the source code:
>
> [steve@ando c]$ cat add.c
>   a = 1;
>   b = 2147483647;
>   printf("a+b = %d\n", a+b);

The first undefined part here is that this operation might not even
overflow. If the compiler uses a 64-bit int, this will simply produce
2147483648. But even assuming that it can't represent that total in a
signed int, there's nothing in the spec that says it has to become
negative.

ChrisA

[1] http://diamond.boisestate.edu/gas/princess_ida/webop/pi_10d.html

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Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 02:44 -0700
  Re: Best search algorithm to find condition within a range Dave Angel <davea@davea.name> - 2015-04-07 09:29 -0400
    Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 07:10 -0700
      Re: Best search algorithm to find condition within a range Dave Angel <davea@davea.name> - 2015-04-07 10:26 -0400
      Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-08 00:34 +1000
    Re: Best search algorithm to find condition within a range Denis McMahon <denismfmcmahon@gmail.com> - 2015-04-07 14:29 +0000
      Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 07:36 -0700
        Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-08 00:49 +1000
          Re: Best search algorithm to find condition within a range Grant Edwards <invalid@invalid.invalid> - 2015-04-07 15:05 +0000
            Re: Best search algorithm to find condition within a range Dave Angel <davea@davea.name> - 2015-04-07 11:23 -0400
            Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-08 01:37 +1000
            Re: Best search algorithm to find condition within a range MRAB <python@mrabarnett.plus.com> - 2015-04-07 17:02 +0100
        Re: Best search algorithm to find condition within a range MRAB <python@mrabarnett.plus.com> - 2015-04-07 16:00 +0100
          Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 08:43 -0700
            Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-08 08:51 +1000
              Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-08 11:46 +1000
        Re: Best search algorithm to find condition within a range Dave Angel <davea@davea.name> - 2015-04-07 11:04 -0400
        Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-07 09:06 -0600
          Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 08:47 -0700
            Re: Best search algorithm to find condition within a range Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-04-07 20:06 -0400
            Re: Best search algorithm to find condition within a range Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-04-08 12:49 +1200
        Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-08 08:36 +1000
          Re: Best search algorithm to find condition within a range Cameron Simpson <cs@zip.com.au> - 2015-04-08 08:51 +1000
        Re: Best search algorithm to find condition within a range Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-04-07 20:01 -0400
        Re: Best search algorithm to find condition within a range albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-18 18:08 +0000
          Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-19 23:02 +1000
            Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-19 17:56 +0300
              Re: Best search algorithm to find condition within a range Gene Heskett <gheskett@wdtv.com> - 2015-04-19 11:17 -0400
              Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-20 12:53 +1000
            Re: Best search algorithm to find condition within a range Dave Angel <davea@davea.name> - 2015-04-19 14:52 -0400
            Re: Best search algorithm to find condition within a range Paul Rubin <no.email@nospam.invalid> - 2015-04-19 13:44 -0700
            Re: Best search algorithm to find condition within a range albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-25 14:49 +0000
      Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 09:18 -0700
  Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-07 08:32 -0600
    Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 08:40 -0700
      Re: Best search algorithm to find condition within a range Dave Angel <davea@davea.name> - 2015-04-07 12:33 -0400
        Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 10:07 -0700
          Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-07 11:44 -0600
            Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-08 10:38 +1000
              Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-08 11:18 +1000
                Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-08 08:37 -0600
              Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 23:19 -0700
                Re: Best search algorithm to find condition within a range Mel Wilson <mwilson@the-wire.com> - 2015-04-08 13:39 +0000
                Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-08 07:56 -0700
                Re: Best search algorithm to find condition within a range Mel Wilson <mwilson@the-wire.com> - 2015-04-08 17:33 +0000
                Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-08 12:28 -0700
                Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-08 12:36 -0700
                Re: Best search algorithm to find condition within a range Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-04-08 21:28 +0100
                Re: Best search algorithm to find condition within a range Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-04-08 21:29 +0100
          Re: Best search algorithm to find condition within a range Terry Reedy <tjreedy@udel.edu> - 2015-04-07 14:55 -0400
          Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-07 13:19 -0600
            Re: Best search algorithm to find condition within a range Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-07 20:27 +0100
              Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 15:35 -0700
                Re: Best search algorithm to find condition within a range Dave Angel <davea@davea.name> - 2015-04-07 20:38 -0400
                Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-07 17:35 -0600
                Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-08 00:28 -0700
                Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-08 08:35 -0600
                Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-08 00:35 -0700
          Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-08 05:25 +1000
          Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-07 13:28 -0600
          Re: Best search algorithm to find condition within a range Serhiy Storchaka <storchaka@gmail.com> - 2015-04-07 23:57 +0300
          Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-08 10:18 +1000
            Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-08 07:31 +0300
      Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-07 14:15 -0600
      Re: Best search algorithm to find condition within a range Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-04-07 21:42 +0100
    Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-08 08:55 +1000
      Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-07 17:30 -0600
  Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-08 08:57 +1000
    Re: Best search algorithm to find condition within a range Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-04-08 12:59 +1200
      Re: Best search algorithm to find condition within a range Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-04-08 02:39 +0100
      Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 23:12 -0700
    Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-08 11:49 +1000
      Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-09 12:32 +1000
        Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-09 12:39 +1000
          Re: Best search algorithm to find condition within a range wxjmfauth@gmail.com - 2015-04-08 23:14 -0700
    Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-07 22:50 -0700
    Re: Best search algorithm to find condition within a range wxjmfauth@gmail.com - 2015-04-07 23:07 -0700
      Re: Best search algorithm to find condition within a range wxjmfauth@gmail.com - 2015-04-07 23:18 -0700
        Re: Best search algorithm to find condition within a range Denis McMahon <denismfmcmahon@gmail.com> - 2015-04-08 17:27 +0000
          Re: Best search algorithm to find condition within a range wxjmfauth@gmail.com - 2015-04-08 10:50 -0700
    Re: Best search algorithm to find condition within a range BartC <bc@freeuk.com> - 2015-04-08 22:22 +0100
      Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 01:06 +0300
        Re: Best search algorithm to find condition within a range Chris Kaynor <ckaynor@zindagigames.com> - 2015-04-08 17:01 -0700
        Re: Best search algorithm to find condition within a range BartC <bc@freeuk.com> - 2015-04-09 10:19 +0100
          Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 13:00 +0300
            Re: Best search algorithm to find condition within a range Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2015-04-09 13:57 +0200
              Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 15:45 +0300
                Re: Best search algorithm to find condition within a range Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2015-04-09 14:56 +0200
                Re: Best search algorithm to find condition within a range Dave Angel <davea@davea.name> - 2015-04-09 09:19 -0400
                Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 16:33 +0300
                Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 16:49 +0300
                Re: Best search algorithm to find condition within a range Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2015-04-09 15:57 +0200
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 00:08 +1000
                Re: Best search algorithm to find condition within a range Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2015-04-09 16:53 +0200
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 01:02 +1000
                Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-09 08:12 -0700
                Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-10 01:21 +1000
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 01:36 +1000
                Re: Best search algorithm to find condition within a range MRAB <python@mrabarnett.plus.com> - 2015-04-09 17:40 +0100
                Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-09 07:54 -0700
                Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-09 09:03 -0600
                Re: Best search algorithm to find condition within a range jonas.thornvall@gmail.com - 2015-04-09 08:21 -0700
                Re: Best search algorithm to find condition within a range Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-09 10:23 -0600
                Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-10 01:11 +1000
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 01:34 +1000
                Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-10 02:15 +1000
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 02:36 +1000
                Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-10 03:49 +1000
                Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 19:25 +0300
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 02:43 +1000
                Re: Best search algorithm to find condition within a range Grant Edwards <invalid@invalid.invalid> - 2015-04-09 16:53 +0000
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 03:00 +1000
                Re: Best search algorithm to find condition within a range Grant Edwards <invalid@invalid.invalid> - 2015-04-09 17:44 +0000
                Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-10 03:41 +1000
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 04:07 +1000
                Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 21:14 +0300
                Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 21:11 +0300
                Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 20:43 +0300
                Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-10 03:35 +1000
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 03:56 +1000
                Re: Best search algorithm to find condition within a range Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-10 23:18 +1000
                Re: Best search algorithm to find condition within a range Chris Angelico <rosuav@gmail.com> - 2015-04-10 23:41 +1000
                Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 21:15 +0300
                Re: Best search algorithm to find condition within a range Rustom Mody <rustompmody@gmail.com> - 2015-04-10 09:39 -0700
                Re: Best search algorithm to find condition within a range Marko Rauhamaa <marko@pacujo.net> - 2015-04-09 16:28 +0300

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