[Mono-list] More .NET and mono floating point inconsistencies

Rodrigo Kumpera kumpera at gmail.com
Fri Feb 20 14:59:29 EST 2009


I have commited the fixed from Kornél for all bugs that have tests.

On Fri, Feb 20, 2009 at 12:14 AM, ddambro <ddambro at gmail.com> wrote:

>
> Hi,
>
> Thanks for looking into my issues.  I hope my post didn't come across as
> rude or anything, I was really just looking to ask if it was better to post
> issues here or directly to Bugzilla.  I'm sure there are far more important
> issues than my weird floating point inconsistencies.
>
> For the curious, I am an AI researcher working on Evolutionary Computation.
> I tend to use Windows and .NET to run my code, but my research group has
> several large computing clusters that could massively speed up my
> experiments, but they only run Linux. Also academia tends to shy away from
> "Windows Only" software, so if I can say "Runs in Linux" when I release my
> code to the public, it's a pretty big boon for me as well as the people who
> want to run it.  However, because of the floating point issues described,
> experiments run on mono are not compatible with experiments run on .NET, as
> over the course of a simulation, the small errors propagate over thousands
> of time steps into large differences in the final AI behavior.  Thus, if I
> used both mono and .NET, not only would I have to be mindful of which
> experiment was run on which platform when I do analysis and demonstrations,
> but when I release my results to the public I would also have to mark
> arbitrary sets of experiments as "mono only" or ".NET only."
>
>
> Kornél Pál wrote:
> >
> > Hi,
> >
> > Thanks for the test cases, I'll invetigate these as well and try to fix
> > them.
> >
> > The best way to get bugs fixed is to produce test cases and report them
> > in buzilla.
> >
> > You can help more if you are able to provide a patch to fix the bugs.
> >
> > Note that for some reasons Novell guys seem to ignore this bug mostly
> > because they have other things to do and their approval is required for
> > these changes.
> >
> > Could you please describe your scenario (application name, purpose, etc.
> > if they are public) where you need these floating point roundings and
> > describe why these bugs are critical for you.
> >
> > Providing some description may raise component owners' attention.
> >
> > Kornél
> >
> > ddambro wrote:
> >> I previously posted about some differences I noticed between the
> floating
> >> point math in .NET and mono
> >>
> http://www.nabble.com/Mono-and-.Net-Floating-Point-Inconsistencies-to21428695ef1367.html
> >> here .  The bug report can be found
> >> https://bugzilla.novell.com/show_bug.cgi?id=467201 here .  The patch
> >> provided (Thank you!) fixes several issues I was encountering, but
> >> unfortunately it led me to discover a couple more.  The following two
> >> code
> >> samples were tested x86 machines using Linux mono 2.2 with the patch
> >> found
> >> in the bug report, a clean Windows mono 2.0.1, and the latest version of
> >> .NET targeting 3.0 framework and x86.
> >>
> >> ---
> >> 1.
> >>
> >> using System;
> >> using System.Runtime.CompilerServices;
> >>
> >> class Testing
> >> {
> >>     [MethodImpl(MethodImplOptions.NoInlining)]
> >>     public static void Main()
> >>     {
> >>         float f1=200;
> >>
> >>         float distance=Distance(300, 500, 387.5f, 362.5f);
> >>
> >>         float dist = 1 - (distance / f1);
> >>
> >>         float distSqud = dist * dist;
> >>
> >>         Console.WriteLine(distSqud.ToString("R"));
> >>
> >>         foreach (byte b in BitConverter.GetBytes(distSqud))
> >>             Console.WriteLine(b);
> >>
> >>     }
> >>
> >>     public static float Distance(float x1, float y1, float x2, float y2)
> >>     {
> >>         float xDist = x1 - x2;
> >>         float yDist = y1 - y2;
> >>         float dist = (float)Math.Sqrt(xDist * xDist + yDist * yDist);
> >>         return dist;
> >>     }
> >>
> >> On .NET this code produces:
> >> 0.0342619047
> >> 54
> >> 86
> >> 12
> >> 61
> >>
> >> and on mono it produces:
> >> 0.03426191
> >> 55
> >> 86
> >> 12
> >> 61
> >>
> >> ---
> >> 2.
> >>
> >> using System;
> >> using System.Runtime.CompilerServices;
> >>
> >> class Testing
> >> {
> >>     [MethodImpl(MethodImplOptions.NoInlining)]
> >>     public static void Main()
> >>     {
> >>         float distance = Distance(616.161255f, 391.2928f, 550.8382f,
> >> 131.006973f);
> >>         Console.WriteLine(distance.ToString("R"));
> >>
> >>         foreach (byte b in BitConverter.GetBytes(distance))
> >>             Console.WriteLine(b);
> >>     }
> >>
> >>     public static float Distance(float x1, float y1, float x2, float y2)
> >>     {
> >>         float xDist = x1 - x2;
> >>         float yDist = y1 - y2;
> >>         float dist = (float)Math.Sqrt(xDist * xDist + yDist * yDist);
> >>
> >>         Console.WriteLine(dist.ToString("R"));
> >>
> >>         foreach (byte b in BitConverter.GetBytes(dist))
> >>             Console.WriteLine(b);
> >>
> >>         return dist;
> >>     }
> >> }
> >>
> >> On .NET this code produces:
> >> 268.3576
> >> 198
> >> 45
> >> 134
> >> 67
> >> 268.3576
> >> 198
> >> 45
> >> 134
> >> 67
> >>
> >> and on mono it produces:
> >> 268.357635
> >> 199
> >> 45
> >> 134
> >> 67
> >> 268.357635
> >> 199
> >> 45
> >> 134
> >> 67
> >>
> >> ---
> >> These seem to be very similar to the issues I was encountering before,
> >> but
> >> they are not fixed by the patch.  What is the best way to resolve these
> >> inconsistencies?
> >>
> >> Thanks,
> >> David
> > _______________________________________________
> > Mono-list maillist  -  Mono-list at lists.ximian.com
> > http://lists.ximian.com/mailman/listinfo/mono-list
> >
> >
>
> --
> View this message in context:
> http://www.nabble.com/More-.NET-and-mono-floating-point-inconsistencies-tp22018718p22114104.html
> Sent from the Mono - General mailing list archive at Nabble.com.
>
> _______________________________________________
> Mono-list maillist  -  Mono-list at lists.ximian.com
> http://lists.ximian.com/mailman/listinfo/mono-list
>
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