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https://issues.apache.org/jira/browse/MATH-471?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12981216#action_12981216
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Gilles commented on MATH-471:
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{quote}
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.
{quote}
This is not a bug, but expected behaviour. But I certainly agree that it does
not hurt to mention the conversion issue for the unwary.
However, shouldn't there be emphasis, in the user guide, that CM is a "double"
precision library? A quick poll of the code gives the following numbers:
Occurrences of the string "float ": *41* (roughly half of which were introduced
with this patch)
Occurrences of the string "double ": *4061*
Also, I'm curious as to what use case you were having that requires comparing
{{float}} numbers.
Finally if we want to help users avoid such pitfalls, I think that we should
consider refactoring {{MathUtils}} so that similar methods that should behave
differently for different types are in _different_ classes (exactly as with
classes {{Float}} and {{Double}}). Thus, we should create {{MathUtilsDouble}}
(or assume that the current {{MathUtils}} is for {{double}} utilities) and
{{MathUtilsFloat}}.
> 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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