Groups > comp.os.linux.development.apps > #449

Re: cast double to short problem

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From	Grant Edwards <invalid@invalid.invalid>
Newsgroups	comp.os.linux.development.apps
Subject	Re: cast double to short problem
Date	Wed, 7 Mar 2012 15:23:39 +0000 (UTC)
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On 2012-03-07, Noob <root@127.0.0.1> wrote:
> Grant Edwards wrote:
>
>> $ man round
>> #include <math.h>
>> i = (short) round(MyDoubleValue * 100.0);
>
> Depending on so-called rounding modes, some CPUs do not round as
> mathematicians expect.

IMO, depending on 1.5 or 2.5 being rounded one way or the other is a
bug, but I realize that in some statistical applications it matters.

However, the CPU type should have nothing to do with it -- the
behavior of the libm round() function is well defined to "round
halfway cases away from zero".  If you want half-way values to round
to nearest even then the round() man page says that you should call
rint().

> See, for example, the "nearest even" mode where both 1.5 and 2.5
> (which can be represented exactly in binary FP) are rounded to 2.
>
> http://www.ocf.berkeley.edu/~horie/rounding.html

-- 
Grant Edwards               grant.b.edwards        Yow! PARDON me, am I
                                  at               speaking ENGLISH?
                              gmail.com

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Thread

cast double to short problem Bill M <wpmccormick@just_about_everywhere.com> - 2012-03-06 16:52 -0600
  Re: cast double to short problem Grant Edwards <invalid@invalid.invalid> - 2012-03-06 23:21 +0000
    Re: cast double to short problem Bill M <wpmccormick@just_about_everywhere.com> - 2012-03-06 17:36 -0600
      Re: cast double to short problem Grant Edwards <invalid@invalid.invalid> - 2012-03-07 00:30 +0000
        Re: cast double to short problem Noob <root@127.0.0.1> - 2012-03-07 11:17 +0100
          Re: cast double to short problem Grant Edwards <invalid@invalid.invalid> - 2012-03-07 15:23 +0000
    Re: cast double to short problem "Ersek, Laszlo" <lacos@caesar.elte.hu> - 2012-03-07 19:33 +0100
      Re: cast double to short problem Grant Edwards <invalid@invalid.invalid> - 2012-03-07 20:13 +0000
        Re: cast double to short problem Bill M <wpmccormick@just_about_everywhere.com> - 2012-03-08 11:45 -0600

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