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Re: Learning functions; roots of the quadratic; two return values

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Melzzzzz <mel@zzzzz.com> writes:
> On Wed, 07 Oct 2015 09:12:33 -0700
> Keith Thompson <kst-u@mib.org> wrote:
[...]
>> The behavior of the sqrt() function is defined by the standard.  A
>> compiler can take advantage of the fact that calling sqrt() twice with
>> the same argument will yield the same result both times, and will not
>> have side effects.
>
> Yes, I see that compiler (gcc) takes advantage of knowing contents of
> sqrt, but there is some weird constraint that make it generate calls
> for several sqrts anyway. That is it does not calls function first,
> rather it executes sqrt instruction directly, but then it checks
> result with itself (ucomisd) and if parity flag is set (unordered) it
> calls sqrt then checks result again and if parity calls sqrt again.
> This code is not present if -ffast-math or -Ofast flag is present.

I have no idea.  The standard requires a call to the standard sqrt()
function to behave in a certain way.  A compiler is free to do whatever
it likes to achieve that effect.

-- 
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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Learning functions; roots of the quadratic; two return values Alla _ <modelling.data@gmail.com> - 2015-10-03 10:43 -0700
  Re: Learning functions; roots of the quadratic; two return values Andrew Cooper <amc96@cam.ac.uk> - 2015-10-03 19:00 +0100
    Re: Learning functions; roots of the quadratic; two return values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-03 19:34 +0100
      Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-03 21:29 +0200
        Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-03 21:36 +0200
        Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-03 21:43 +0200
        Re: Learning functions; roots of the quadratic; two return values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-03 20:46 +0100
          Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-03 22:46 +0200
            Re: Learning functions; roots of the quadratic; two return values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-03 23:18 +0100
              Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-04 01:08 +0200
              Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-04 01:36 +0200
                Re: Learning functions; roots of the quadratic; two return values Ian Collins <ian-news@hotmail.com> - 2015-10-04 12:52 +1300
                Re: Learning functions; roots of the quadratic; two return values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-04 15:42 +0100
          Re: Learning functions; roots of the quadratic; two return values jacobnavia <jacob@jacob.remcomp.fr> - 2015-10-03 23:05 +0200
            Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-03 23:41 +0200
              Re: Learning functions; roots of the quadratic; two return values jacobnavia <jacob@jacob.remcomp.fr> - 2015-10-04 00:14 +0200
            Re: Learning functions; roots of the quadratic; two return values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-03 23:07 +0100
              Re: Learning functions; roots of the quadratic; two return values jacobnavia <jacob@jacob.remcomp.fr> - 2015-10-04 00:32 +0200
              Re: Learning functions; roots of the quadratic; two return values Keith Thompson <kst-u@mib.org> - 2015-10-04 12:56 -0700
                Re: Learning functions; roots of the quadratic; two return values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-04 23:41 +0100
                Re: Learning functions; roots of the quadratic; two return values Keith Thompson <kst-u@mib.org> - 2015-10-04 18:24 -0700
              Re: Learning functions; roots of the quadratic; two return values James Kuyper <jameskuyper@verizon.net> - 2015-10-04 16:36 -0400
                Re: Learning functions; roots of the quadratic; two return values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-05 00:01 +0100
                Re: Learning functions; roots of the quadratic; two return values James Kuyper <jameskuyper@verizon.net> - 2015-10-04 19:24 -0400
          Re: Learning functions; roots of the quadratic; two return values Ian Collins <ian-news@hotmail.com> - 2015-10-04 10:18 +1300
            Re: Learning functions; roots of the quadratic; two return values jacobnavia <jacob@jacob.remcomp.fr> - 2015-10-03 23:27 +0200
              Re: Learning functions; roots of the quadratic; two return values Ian Collins <ian-news@hotmail.com> - 2015-10-04 11:08 +1300
                Re: Learning functions; roots of the quadratic; two return values Richard Damon <Richard@Damon-Family.org> - 2015-10-03 18:38 -0400
                Re: Learning functions; roots of the quadratic; two return values Ian Collins <ian-news@hotmail.com> - 2015-10-04 11:47 +1300
          Re: Learning functions; roots of the quadratic; two return values raltbos@xs4all.nl (Richard Bos) - 2015-10-04 14:07 +0000
            Re: Learning functions; roots of the quadratic; two return values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-04 15:48 +0100
              Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-04 18:59 +0200
                Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-04 20:06 +0200
              Re: Learning functions; roots of the quadratic; two return values Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-04 15:21 -0700
                Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-05 05:25 +0000
        Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-03 21:48 +0200
          Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-04 00:31 +0200
    Re: Learning functions; roots of the quadratic; two return values alla.rashitova@gmail.com - 2015-10-05 08:40 -0700
      Re: Learning functions; roots of the quadratic; two return values Richard Heathfield <rjh@cpax.org.uk> - 2015-10-05 17:10 +0100
      Re: Learning functions; roots of the quadratic; two return values Barry Schwarz <schwarzb@dqel.com> - 2015-10-05 10:41 -0700
  Re: Learning functions; roots of the quadratic; two return values "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-10-03 12:04 -0700
    Re: Learning functions; roots of the quadratic; two return values Philip Lantz <prl@canterey.us> - 2015-10-03 12:48 -0700
    Re: Learning functions; roots of the quadratic; two return values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-03 20:55 +0100
      Re: Learning functions; roots of the quadratic; two return values "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-10-03 13:27 -0700
      Re: Learning functions; roots of the quadratic; two return values jacobnavia <jacob@jacob.remcomp.fr> - 2015-10-03 23:08 +0200
        Re: Learning functions; roots of the quadratic; two return values Richard Heathfield <rjh@cpax.org.uk> - 2015-10-03 22:52 +0100
    Re: Learning functions; roots of the quadratic; two return values Rosario19 <Ros@invalid.invalid> - 2015-10-04 20:46 +0200
      Re: Learning functions; roots of the quadratic; two return values Keith Thompson <kst-u@mib.org> - 2015-10-04 15:47 -0700
      Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-05 03:06 +0200
        Re: Learning functions; roots of the quadratic; two return values Rosario19 <Ros@invalid.invalid> - 2015-10-05 05:31 +0200
          Re: Learning functions; roots of the quadratic; two return values Rosario19 <Ros@invalid.invalid> - 2015-10-05 11:58 +0200
            Re: Learning functions; roots of the quadratic; two return values Rosario19 <Ros@invalid.invalid> - 2015-10-05 12:00 +0200
              Re: Learning functions; roots of the quadratic; two return values Rosario19 <Ros@invalid.invalid> - 2015-10-05 12:06 +0200
          Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-05 12:39 +0200
            Re: Learning functions; roots of the quadratic; two return values Bartc <bc@freeuk.com> - 2015-10-05 12:20 +0100
              Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-05 13:50 +0200
              Re: Learning functions; roots of the quadratic; two return values Richard Heathfield <rjh@cpax.org.uk> - 2015-10-05 12:57 +0100
        Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-05 05:40 +0000
          Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-05 08:30 +0200
          Re: Learning functions; roots of the quadratic; two return values Philip Lantz <prl@canterey.us> - 2015-10-05 10:03 -0700
            Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-05 22:25 +0000
              Re: Learning functions; roots of the quadratic; two return values James Kuyper <jameskuyper@verizon.net> - 2015-10-05 19:26 -0400
                Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-06 03:44 +0000
                Re: Learning functions; roots of the quadratic; two return values James Kuyper <jameskuyper@verizon.net> - 2015-10-06 10:55 -0400
                Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-06 23:07 +0200
                Re: Learning functions; roots of the quadratic; two return values James Kuyper <jameskuyper@verizon.net> - 2015-10-06 18:35 -0400
                Re: Learning functions; roots of the quadratic; two return values raltbos@xs4all.nl (Richard Bos) - 2015-10-14 11:08 +0000
                Re: Learning functions; roots of the quadratic; two return values James Kuyper <jameskuyper@verizon.net> - 2015-10-14 11:11 -0400
                Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-14 22:22 +0200
                Re: Learning functions; roots of the quadratic; two return values James Kuyper <jameskuyper@verizon.net> - 2015-10-14 17:17 -0400
                Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-14 23:45 +0200
                Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-15 00:11 +0000
                Re: Learning functions; roots of the quadratic; two return values Bartc <bc@freeuk.com> - 2015-10-15 01:37 +0100
                Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-15 05:52 +0000
                Re: Learning functions; roots of the quadratic; two return values James Kuyper <jameskuyper@verizon.net> - 2015-10-14 21:54 -0400
                Re: Learning functions; roots of the quadratic; two return values asetofsymbols@gmail.com - 2015-10-14 22:40 -0700
                Re: Learning functions; roots of the quadratic; two return values asetofsymbols@gmail.com - 2015-10-15 05:00 -0700
                Re: Learning functions; roots of the quadratic; two return values supercat@casperkitty.com - 2015-10-15 11:58 -0700
                Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-15 06:04 +0000
                Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-06 23:18 +0000
                Re: Learning functions; roots of the quadratic; two return values supercat@casperkitty.com - 2015-10-06 16:31 -0700
                Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-07 00:38 +0000
                Re: Learning functions; roots of the quadratic; two return values supercat@casperkitty.com - 2015-10-06 21:19 -0700
                Re: Learning functions; roots of the quadratic; two return values James Kuyper <jameskuyper@verizon.net> - 2015-10-06 22:15 -0400
                Re: Learning functions; roots of the quadratic; two return values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-07 08:45 +0000
                Re: Learning functions; roots of the quadratic; two return values Melzzzzz <mel@zzzzz.com> - 2015-10-07 05:19 +0200
                Re: Learning functions; roots of the quadratic; two return values Keith Thompson <kst-u@mib.org> - 2015-10-07 09:12 -0700
                Re: Learning functions; roots of the quadratic; two return values Melzzzzz <mel@zzzzz.com> - 2015-10-08 00:53 +0200
                Re: Learning functions; roots of the quadratic; two return values Keith Thompson <kst-u@mib.org> - 2015-10-07 16:23 -0700
              Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-06 02:16 +0200
                Re: Learning functions; roots of the quadratic; two return values supercat@casperkitty.com - 2015-10-06 15:43 -0700
                Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-07 02:48 +0200
                Re: Learning functions; roots of the quadratic; two return values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-14 14:00 -0700
                Re: Learning functions; roots of the quadratic; two return values regis <regis.barbanchon@free.fr> - 2015-10-14 23:23 +0200
  Re: Learning functions; roots of the quadratic; two return values Geoff <geoff@invalid.invalid> - 2015-10-03 12:50 -0700
  Re: Learning functions; roots of the quadratic; two return values Bartc <bc@freeuk.com> - 2015-10-03 21:16 +0100
    Re: Learning functions; roots of the quadratic; two return values alla.rashitova@gmail.com - 2015-10-05 09:02 -0700
      Re: Learning functions; roots of the quadratic; two return values Richard Heathfield <rjh@cpax.org.uk> - 2015-10-05 17:13 +0100
  Re: Learning functions; roots of the quadratic; two return values Barry Schwarz <schwarzb@dqel.com> - 2015-10-03 15:37 -0700
  Re: Learning functions; roots of the quadratic; two return values Rosario19 <Ros@invalid.invalid> - 2015-10-05 23:44 +0200
    Re: Learning functions; roots of the quadratic; two return values Geoff <geoff@invalid.invalid> - 2015-10-05 18:37 -0700
    Re: Learning functions; roots of the quadratic; two return values Barry Schwarz <schwarzb@dqel.com> - 2015-10-05 19:24 -0700
      Re: Learning functions; roots of the quadratic; two return values Rosario19 <Ros@invalid.invalid> - 2015-10-06 07:36 +0200
    Re: Learning functions; roots of the quadratic; two return values Rosario19 <Ros@invalid.invalid> - 2015-10-06 07:34 +0200

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