[jira] [Resolved] (MATH-904) FastMath.pow deviates from Math.pow for negative, finite base values with an exponent 2^52 < y < 2^53

["Gilles (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MATH-904?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Gilles resolved MATH-904.
-------------------------

    Resolution: Fixed

Fixed in revision 1413916.
                
> FastMath.pow deviates from Math.pow for negative, finite base values with an exponent 2^52 < y < 2^53 
> ------------------------------------------------------------------------------------------------------
>
>                 Key: MATH-904
>                 URL: https://issues.apache.org/jira/browse/MATH-904
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.0
>            Reporter: Thomas Neidhart
>             Fix For: 3.1
>
>
> As reported by Jeff Hain:
> pow(double,double):
> Math.pow(-1.0,5.000000000000001E15) = -1.0
> FastMath.pow(-1.0,5.000000000000001E15) = 1.0
> ===> This is due to considering that power is an even
> integer if it is >= 2^52, while you need to test
> that it is >= 2^53 for it.
> ===> replace
> "if (y >= TWO_POWER_52 || y <= -TWO_POWER_52)"
> with
> "if (y >= 2*TWO_POWER_52 || y <= -2*TWO_POWER_52)"
> and that solves it.

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