Fraction

[Dmitry Nadezhin]

Hello Joe,

Thank you for the clarification.

What do you think about using BigBinary to solve the problem of a
calculation class with higher precision.
BigBinary implements arbitrary precision binary floating-point numbers
and arithmetic operations on them.
Although it rounds, the precision and rounding direction are controlled.
It seems to me that binary floating-point numbers are more natural
than decimal for scientific applications.
Should such a class be in the JDK or outside?

If you don't think that BigBinary is appropriate, then let me ask some
other questions.
IEEE 754-2008 defines three basic binary formats: Binary32, Binary64,
Binary128 .
Binary32 and Binary64 are already known in JDK as Float and Double
(with rounding to nearest even).
Should there be a software emulation of Binary128 in JDK (as a class
with two private long fields)?
Should the JDK have a class with static methods that implement
arithmetic operations on floats and doubles with directed rounding like
http://java.net/projects/projectfortress/sources/sources/content/ProjectFortress/src/com/sun/fortress/numerics/DirectedRounding.java
?
Is there a chance that Binary128 or DirectedRounding methods would be
internalized in hotspot?

These questions are important to me because I am working on an
interval arithmetic library
http://kenai.com/projects/jinterval/ and could use these new classes.

I understand that the addition of numerical features to the JDK is closed.
However, if there is a chance to add any new classes, I'd be glad to
contibute to their development.

Cheers,

   -Dima


On Fri, Jan 6, 2012 at 2:46 AM, Joe Darcy <joe.darcy at oracle.com> wrote:
> Hello,
>
>
> On 1/1/2012 8:54 AM, Tom Eugelink wrote:
>>
>>
>> Hello guys,
>>
>> I was wondering if it was of any interest to OpenJFX to have a calculation
>> class that does not round. I've got "Fraction" laying around, which does
>> math using two BigIntegers, so it never even rounds. The API is roughly
>> equivalent to BigDecimal, so you have methods like add, divide, etc.
>>
>> Any interest in adding such a class to Java?
>>
>
> The BigDecimal class can already preform exact computations.  To get exact
> behavior, use the version of add, subtract, etc. that takes a single
> BigDecimal argument or the version that takes a BigDecimal argument and a
> MathContext argument and pass a MathContext object with a precision of 0.
>  Of the four basic arithmetic operations, the most interesting operation is
> divide since it can result in infinite inputs (fractions that are
> non-terminating in decimal) from finite inputs while the other operations
> cannot.
>
> In terms of its representation, BigDecimal class uses a floating-point style
> scaled representation so that very large or very small numbers that are
> low-precision don't use a lot of storage.
>
> When doing general computations, there is a need to round result
> periodically to avoid unbounded growth in the sizes of the numbers being
> operated on.  BigDecimal supports various rounding operations, including
> rounding to a given number of places after the decimal point and rounding to
> a given number of total digits.  These styles of rounding are relatively
> easy to understand, but still quite vexing for numerical analysis.
>
> The rounding options I'm familiar with for rational packages are fixed slash
> vs floating-slash, that is, given constraints on the sizes of the numerator
> and denominator, return the nearest fraction to the exact result.  AFAIK,
> such system are less studied if not more difficult to work with than
> traditional rounding.
>
> In short, while there would be some use cases, without additional
> justification I don't see the need to add a rational number package to the
> JDK.
>
> Cheers,
>
> -Joe
>