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https://issues.apache.org/jira/browse/NUMBERS-204?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alex Herbert resolved NUMBERS-204.
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Fix Version/s: 1.2
Resolution: Fixed
Added in commit:
c8457580f049c7e8ad7507651ccd9bf8ff05aca5
> Sum class may incorrectly sum products if their round-off is sub-normal
> -----------------------------------------------------------------------
>
> Key: NUMBERS-204
> URL: https://issues.apache.org/jira/browse/NUMBERS-204
> Project: Commons Numbers
> Issue Type: Bug
> Components: core
> Affects Versions: 1.1
> Reporter: Alex Herbert
> Assignee: Alex Herbert
> Priority: Trivial
> Fix For: 1.2
>
>
> The Sum class can be used to compute a sum of products with extended
> precision by computing the round-off component of each product and using that
> in the sum.
> When the round-off is sub-normal this computation may be incorrect as
> intermediate sub-normal numbers may lose significant bits.
> This test currently fails due to a 1 ULP rounding error in computing the
> round-off. This is combined with the exact product to create an incorrect sum.
> {code:java}
> @ParameterizedTest
> @CsvSource({
> // Round-off == 0.0
> "-2.73551683292218E-154, -1.0861547555023299E-154",
> // Round-off = 4.9E-324
> "1.4134286753429383E-154, -4.1395762189346144E-154",
> })
> void testSumOfProduct_tiny(double x, double y) {
> final Sum s = Sum.create();
> s.addProduct(x, y);
> Assertions.assertEquals(x * y, s.getAsDouble());
> }
> {code}
> The productLow method currently uses downscaling if the arguments are too
> large for the computation. Applying upscaling to the arguments so the product
> and its round-off are both normal numbers corrects this rounding error.
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