[jira] [Created] (NUMBERS-200) Wrong output when adding two Sum instances containing special values

["Anirudh Joshi (Jira)" <ji...@apache.org>]

Anirudh Joshi created NUMBERS-200:
-------------------------------------

             Summary: Wrong output when adding two Sum instances containing special values
                 Key: NUMBERS-200
                 URL: https://issues.apache.org/jira/browse/NUMBERS-200
             Project: Commons Numbers
          Issue Type: Bug
          Components: core
            Reporter: Anirudh Joshi
             Fix For: 1.2


Here's some setup code before describing the bug :
Two sum instances are created and assigned Double.POSITIVE_INFINITY as follows:
{code:java}
Sum sum1 = Sum.create();
Sum sum2 = Sum.create();
sum1.add(Double.POSITIVE_INFINITY);
sum2.add(Double.POSITIVE_INFINITY);{code}
The `sum` and `comp` fields of both `sum` and `sum2` hold the values `Double.POSITIVE_INFINITY` and `Double.NaN` repectively. 

sum2 is added to sum1 as:
{code:java}
sum1.add(sum2);
{code}
The `Sum add(Sum other)` returns the value returned by `Sum add(double s, double c)` method.



In the Sum add(double s, double c) method, there's a bug in the return statement : 
{code:java}
return add(s).add(c); {code}
When add(c) is executed, c (i.e. sum2.c) which has a value Double.NaN, is causing the sum field of sum1 to be Double.NaN. This is due to :
{code:java}
Sum add(final double t) { // t (= c)
    final double newSum = sum + t; // Inf + Nan = NaN
    comp += ExtendedPrecision.twoSumLow(sum, t, newSum); // NaN
    sum = newSum; // NaN 
    return this;
} {code}
Hence, the chaining of add operations should be removed.


The fix would be in the `Sum add(double s, double c)` method as :
{code:java}
Sum add(double s, double c) {
    add(s);
    if (!(Double.isNan(comp) && Double.isInfinite(sum))) {
        add(c);
    }
    return this;
}{code}



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