Code review request: 6282196 There should be Math.mod(number, modulo) methods

[Stephen Colebourne]

Can you explain why the mod implementation differs from that in JSR-310?
https://github.com/ThreeTen/threeten/blob/master/src/main/java/javax/time/MathUtils.java#L401

The code ((a % b) + b) % b;  is short and involves no branches, which
should aid performance and inlining. Is this to do with accepting a
negative second argument? Perofmance testing?

I'd like to see performance numbers comparing the two approaches, as
JSR-310 might need to continue using the double % version if it is
faster.

Similarly, the proposed floorDiv requires evaluation of the complex if
statement every time, whereas the JSR-310 one only requires an if
check against zero. Whats the rationale for the difference, which is
intuitively (non-proven) slower.

thanks
Stephen


On 22 February 2012 14:24, Roger Riggs <Roger.Riggs at oracle.com> wrote:
> Hi,
>
> 6282196 There should be Math.mod(number, modulo) methods
> <http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6282196>
>
> Requests that floor and modulus methods be provided for primitive types.
> Floor division is pretty straight-forward, rounding toward minus infinity.
> For modulus of int and long, the sign and range follow  the exiting floor
> method
> in java.util.Math and satisfy the relation that mod(x, y) = (x - floorDiv(x,
> y) * y).
>
> Please review and comment,
>    http://cr.openjdk.java.net/~rriggs/6282196.1/
>
> Thanks, Roger
>
>