From: Konrad Meyer <konrad@...>
Date: 2007-10-14T17:02:12+09:00
Subject: Re: Bug: Numeric#divmod calculates wrongly

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Quoth Dirk Traulsen:
> Am 8 Oct 2007 um 19:49 hat Dirk Traulsen geschrieben:
>=20
> > Output:
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D
> > ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-mswin32]=20
> ..=20
> > x.divmod(y)
> > -----------
> > [6, 0.08]
> > [6, 0.00666666666666667]
> > [6, 0.0466666666666667]
> > [6, 0.0766666666666667]
> > [8, 0.00333333333333341]
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D
> >=20
> > As you can see the divisor 7 is wrongly displayed as 6, while the=20
> > modulos are correct.
> >=20
>=20
> I tested Numeric#divmod on two more systems: SUSE 10.1 and Kubuntu=20
> 6.10.
> They both run Ruby 1.8.4 and under both systems Numeric#divmod works=20
> correctly!
> So this bug was either introduced between Ruby 1.8.4 and 1.8.6 or it is=20
> a problem depending on the OS.
>=20
> Could somebody please confirm these findings? Especially with other=20
> System and Ruby version combinations this would be really helpful to=20
> nail down this massive bug. A computer should really calculate=20
> correctly...
>=20
> Dirk Traulsen
>=20
>=20
> The testcode:
>=20
> x=3D[0.58, 0.59, 0.63, 0.66, 0.67]
> y=3D1/12.0
>=20
> z1=3Dx.map {|a| a/y}
> z2=3Dx.map {|a| a.divmod(y).inspect}
>=20
> a=3D[RUBY_VERSION, RUBY_RELEASE_DATE, RUBY_PLATFORM]
> puts "ruby #{a[0]} (#{a[1]}) [#{a[2]}]"
> puts
> print 'x=3D'
> p x
> puts 'y=3D1/12.0'
> puts
> puts "x/y\n---"
> puts z1
> puts
> puts "x.divmod(y)\n-----------"
> puts z2
>=20
>=20
> gives under
> SUSE 10.1:
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D
> ruby 1.8.4 (2005-12-24) [i586-linux]
>=20
> x=3D[0.58, 0.59, 0.63, 0.66, 0.67]
> y=3D1/12.0
>=20
> x/y
> ---
> 6.96
> 7.08
> 7.56
> 7.92
> 8.04
>=20
> x.divmod(y)
> -----------
> [6.0, 0.08]
> [7.0, 0.00666666666666667]
> [7.0, 0.0466666666666667]
> [7.0, 0.0766666666666667]
> [8.0, 0.00333333333333341]
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D
>=20
>=20
> and Kubuntu 6.10:
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D
> ruby 1.8.4 (2005-12-24) [i586-linux]
>=20
> x=3D[0.58, 0.59, 0.63, 0.66, 0.67]
> y=3D1/12.0
>=20
> x/y
> ---
> 6.96
> 7.08
> 7.56
> 7.92
> 8.04
>=20
> x.divmod(y)
> -----------
> [6.0, 0.08]
> [7.0, 0.00666666666666667]
> [7.0, 0.0466666666666667]
> [7.0, 0.0766666666666667]
> [8.0, 0.00333333333333341]
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D

I can't confirm this (incorrect) behaviour.

0.58.divmod(1/12.0) # =3D> [6.0, 0.08]
0.59.divmod(1/12.0) # =3D> [7.0, 0.00666666666666667]

Ruby 1.8.6, Fedora 7.

Regards,
=2D-=20
Konrad Meyer <konrad@tylerc.org> http://konrad.sobertillnoon.com/

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