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From "Heinrich Bohne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (NUMBERS-119) BigFraction(double) constructor does not treat subnormal numbers correctly
Date Tue, 25 Jun 2019 09:08:00 GMT

    [ https://issues.apache.org/jira/browse/NUMBERS-119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16872173#comment-16872173
] 

Heinrich Bohne commented on NUMBERS-119:
----------------------------------------

About the code coverage decrease in the method {{reduce()}} caused by PR #56 (the coverage
decrease in {{ArithmeticUtils}} is a myth invented by Coveralls, my IDE even shows that the
condition in line 112 is always false):

Since the local variable {{k}} had to be set inside the conditional tree that depends on the
value of the exponent rather than outside it as was previously the case, I thought I would
also make a special case for zero, because it doesn't make sense for the denominator of a
zero-fraction to be 2^1074^. It didn't occur to me that this would have an effect on the
code coverage.

However, with this change, the uncovered line in the method {{reduce()}} becomes unreachable,
because the zero fraction created from this double constructor was the only case where the
fraction was not already reduced to lowest terms. This renders the {{reduce()}} method obsolete
anyway, which could be the target of a new JIRA ticket.

> BigFraction(double) constructor does not treat subnormal numbers correctly
> --------------------------------------------------------------------------
>
>                 Key: NUMBERS-119
>                 URL: https://issues.apache.org/jira/browse/NUMBERS-119
>             Project: Commons Numbers
>          Issue Type: Bug
>          Components: fraction
>    Affects Versions: 1.0
>            Reporter: Heinrich Bohne
>            Priority: Minor
>          Time Spent: 1h
>  Remaining Estimate: 0h
>
> The constructor {{BigFraction(double)}} does not take into account the fact that, when
the biased exponent of a {{double}} value is {{0}} and the mantissa is not {{0}} (i.e. when
the value represents a subnormal number), the actual exponent in effect is not {{-1023}} but
{{-1022}} (or, in other words, the effective exponent bias is not {{1023}} but {{1022}}).
> The value of the created {{BigFraction}} is therefore not equal to the value of the passed
{{double}} argument.



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