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From "Chris Popp (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MATH-1248) BigFraction optimizations around object creation for ZERO values and reduce()
Date Sat, 11 Jul 2015 03:08:04 GMT
Chris Popp created MATH-1248:
--------------------------------

             Summary: BigFraction optimizations around object creation for ZERO values and
reduce()
                 Key: MATH-1248
                 URL: https://issues.apache.org/jira/browse/MATH-1248
             Project: Commons Math
          Issue Type: Improvement
            Reporter: Chris Popp
            Priority: Minor


In many cases a BigFraction object may represent a fraction in its most reduced form.  Despite
this, the reduce() method doesn't bother checking whether the BigFraction needs to be reduced
before returning a new object.

This is problematic because equals() calls reduce() on both operands.  This means that doing
a simple comparison like BigFraction.ONE.equals(BigFraction.TWO) will result in two object
allocations.

Additionally, while there is a very minimal attempt at optimizing around operations that take
in a parameter of BigFraction.ZERO, it is somewhat inconsistent and incomplete.  For example,
BigFraction add(final BigFraction fraction) checks to see whether the incoming fraction is
zero and if so, returns *this*.  Why doesn't it also check whether *this* is zero and return
the incoming fraction if so, avoiding an allocation?  

This is one example, but it exists in other locations where we not only end up with allocations
but expensive arithmetic operations as well (multiplication or exponentiation).

At minimum I think the reduce() method should just return *this* if gcd <= 1.

I attached a patch with the change for reduce() and some ideas for avoiding object allocations,
attempting to follow the patterns in BigInteger.  I verified all of the tests in the commons
math pass after the changes.



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