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From "Sebb (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MATH-471) MathUtils.equals(double, double) does not work properly for floats
Date Wed, 12 Jan 2011 23:55:47 GMT

    [ https://issues.apache.org/jira/browse/MATH-471?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12981020#action_12981020
] 

Sebb commented on MATH-471:
---------------------------

I now realise that the 3rd example above may not be easy - or even possible - to fix, but
it does offer a good example of the difficulties of comparing floating point numbers!

> MathUtils.equals(double, double) does not work properly for floats
> ------------------------------------------------------------------
>
>                 Key: MATH-471
>                 URL: https://issues.apache.org/jira/browse/MATH-471
>             Project: Commons Math
>          Issue Type: Bug
>            Reporter: Sebb
>         Attachments: Math471.patch
>
>
> MathUtils.equals(double, double) does not work properly for floats.
> There is no equals(float,float) so float parameters are automatically promoted to double.
However, that is not necessarily appropriate, given that the ULP for a double is much smaller
than the ULP for a float.
> So for example:
> {code}
> double oneDouble = 1.0d;
> assertTrue(MathUtils.equals(oneDouble, Double.longBitsToDouble(1 + Double.doubleToLongBits(oneDouble))));
// OK
> float oneFloat = 1.0f;
> assertTrue(MathUtils.equals(oneFloat, Float.intBitsToFloat(1 + Float.floatToIntBits(oneFloat))));
// FAILS
> float  f1 = 333.33334f;
> double d1 = 333.33334d;
> assertTrue(MathUtils.equals(d1, f1)); // FAILS
> {code}
> I think the equals() methods need to be duplicated with the appropriate changes for floats
to avoid any problems with the promotion of floats.

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