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From "Luc Maisonobe (JIRA)" <j...@apache.org>
Subject [jira] Resolved: (MATH-502) FastMath scalb() does not handle large magnitude exponents correctly
Date Mon, 24 Jan 2011 19:24:44 GMT

     [ https://issues.apache.org/jira/browse/MATH-502?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Luc Maisonobe resolved MATH-502.
--------------------------------

    Resolution: Fixed

fixed in subversion repository as of r1062928 for trunk and r1062929 for branch 2.X

> FastMath scalb() does not handle large magnitude exponents correctly
> --------------------------------------------------------------------
>
>                 Key: MATH-502
>                 URL: https://issues.apache.org/jira/browse/MATH-502
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 2.2, 3.0
>            Reporter: Sebb
>             Fix For: 2.2, 3.0
>
>
> scalb does not handle MAX_VALUE exponents properly:
> double scalb(-1.7976931348623157E308, 2147483647) expected -Infinity actual -8.988465674311579E307
entries [6, 5]
> double scalb(1.7976931348623157E308, 2147483647) expected Infinity actual 8.988465674311579E307
entries [7, 5]
> double scalb(-1.1102230246251565E-16, 2147483647) expected -Infinity actual -5.551115123125783E-17
entries [8, 5]
> double scalb(1.1102230246251565E-16, 2147483647) expected Infinity actual 5.551115123125783E-17
entries [9, 5]
> double scalb(-2.2250738585072014E-308, 2147483647) expected -Infinity actual -0.0 entries
[10, 5]
> double scalb(2.2250738585072014E-308, 2147483647) expected Infinity actual 0.0 entries
[11, 5]
> float scalb(3.4028235E38, 2147483647) expected Infinity actual 1.7014117E38 entries [7,
5]
> float scalb(-3.4028235E38, 2147483647) expected -Infinity actual -1.7014117E38 entries
[9, 5]
> It looks as though the problem is with the calculation of the scaledExponent - for large
values, this can wrap round, so some of the checks against its value may give misleading results.

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