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Re: Writing efficient normal distribution function (for learning purposes).

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Juha Nieminen <nospam@thanks.invalid> writes:
>> And
>> possibly -ffast-math if the OP is happy with imprecise (aka wrong)
>> results.
>
>   How are the results imprecise/wrong when using -ffast-math?
>
>   Granted, I don't know every single detail, but I have the impression
> that what it does is that it skips some of the most pedantic rules of
> IEEE floating point math in favor of faster code. These minute pedantic
> rules do not affect the accuracy of the end result in any significant
> way (more than what can be expected from floating point values anyways).

It's not that -ffast-math is bad or anything (I use it happily
myself), but if precise results are important it's a good idea to
check what it does in detail, and make sure things are OK.  One can
always, of course, use -ffast-math, and then _disable_ some of the
finer-grained options it enabled.

For instance: -ffast-math enables -funsafe-math-optimizations, which
enables -freciprocal-math, which: "Allows the reciprocal of a value to
be used instead of dividing by the value if this enables optimizations
... Note that this loses precision and increases the number of flops
operating on the value."

-funsafe-math-optimizations also enables fassociative-math, and
changing the order of operations can affect the precision of the
result in a way that the programmer didn't expect.

-ffast-math also enables -ffinite-math-only, which of course will
cause infinities etc to not be handled as expected.

etc.

-miles

-- 
`There are more things in heaven and earth, Horatio,
 Than are dreamt of in your philosophy.'

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Writing efficient normal distribution function (for learning purposes). Luca Cerone <luca.cerone@gmail.com> - 2012-02-17 07:41 -0800
  Re: Writing efficient normal distribution function (for learning purposes). "Asger Joergensen" <Junk@Asger-P.dk> - 2012-02-17 16:45 +0000
    Re: Writing efficient normal distribution function (for learning purposes). lucacerone <luca.cerone@gmail.com> - 2012-02-17 09:36 -0800
      Re: Writing efficient normal distribution function (for learning purposes). "Asger Joergensen" <Junk@Asger-P.dk> - 2012-02-17 17:50 +0000
        Re: Writing efficient normal distribution function (for learning purposes). lucacerone <luca.cerone@gmail.com> - 2012-02-19 01:59 -0800
          Re: Writing efficient normal distribution function (for learning purposes). lucacerone <luca.cerone@gmail.com> - 2012-02-19 02:49 -0800
            Re: Writing efficient normal distribution function (for learning purposes). "Asger Joergensen" <Junk@Asger-P.dk> - 2012-02-19 11:53 +0000
            Re: Writing efficient normal distribution function (for learning purposes). Miles Bader <miles@gnu.org> - 2012-02-19 23:09 +0900
              Re: Writing efficient normal distribution function (for learning purposes). Joshua Maurice <joshuamaurice@gmail.com> - 2012-02-19 13:34 -0800
                Re: Writing efficient normal distribution function (for learning purposes). Marc <marc.glisse@gmail.com> - 2012-02-19 22:10 +0000
                Re: Writing efficient normal distribution function (for learning purposes). Miles Bader <miles@gnu.org> - 2012-02-20 09:14 +0900
                Re: Writing efficient normal distribution function (for learning purposes). Juha Nieminen <nospam@thanks.invalid> - 2012-02-20 10:24 +0000
                Re: Writing efficient normal distribution function (for learning purposes). Miles Bader <miles@gnu.org> - 2012-02-20 19:57 +0900
                Re: Writing efficient normal distribution function (for learning purposes). Dombo <dombo@disposable.invalid> - 2012-02-20 21:07 +0100
                Re: Writing efficient normal distribution function (for learning purposes). Juha Nieminen <nospam@thanks.invalid> - 2012-02-21 08:41 +0000
                Re: Writing efficient normal distribution function (for learning purposes). 88888 Dihedral <dihedral88888@googlemail.com> - 2012-02-21 01:10 -0800
                Re: Writing efficient normal distribution function (for learning purposes). Miles Bader <miles@gnu.org> - 2012-02-20 09:04 +0900
              Re: Writing efficient normal distribution function (for learning purposes). lucacerone <luca.cerone@gmail.com> - 2012-02-20 02:26 -0800
    Re: Writing efficient normal distribution function (for learning purposes). Juha Nieminen <nospam@thanks.invalid> - 2012-02-17 20:42 +0000
      Re: Writing efficient normal distribution function (for learning purposes). "Asger Joergensen" <Junk@Asger-P.dk> - 2012-02-17 22:20 +0000
  Re: Writing efficient normal distribution function (for learning purposes). Juha Nieminen <nospam@thanks.invalid> - 2012-02-17 20:52 +0000
  Re: Writing efficient normal distribution function (for learning purposes). Victor Bazarov <v.bazarov@comcast.invalid> - 2012-02-17 15:57 -0500
  Re: Writing efficient normal distribution function (for learning purposes). Joshua Maurice <joshuamaurice@gmail.com> - 2012-02-17 15:01 -0800
    Re: Writing efficient normal distribution function (for learning purposes). Victor Bazarov <v.bazarov@comcast.invalid> - 2012-02-18 08:44 -0500
      Re: Writing efficient normal distribution function (for learning purposes). Paavo Helde <myfirstname@osa.pri.ee> - 2012-02-18 09:20 -0600
  Re: Writing efficient normal distribution function (for learning purposes). Paavo Helde <myfirstname@osa.pri.ee> - 2012-02-18 09:36 -0600
    Re: Writing efficient normal distribution function (for learning purposes). glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-18 20:19 +0000
      Re: Writing efficient normal distribution function (for learning purposes). Miles Bader <miles@gnu.org> - 2012-02-19 10:32 +0900
  Re: Writing efficient normal distribution function (for learning purposes). lucacerone <luca.cerone@gmail.com> - 2012-02-20 02:36 -0800
  Re: Writing efficient normal distribution function (for learning purposes). gwowen <gwowen@gmail.com> - 2012-02-20 06:48 -0800
    Re: Writing efficient normal distribution function (for learning purposes). lucacerone <luca.cerone@gmail.com> - 2012-02-21 04:32 -0800

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