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

Stephen Colebourne scolebourne at joda.org
Wed Feb 22 14:37:42 UTC 2012

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/viewbug.do?bugid=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

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