[9] RFR of 8023217: Additional floorDiv/floorMod/multiplyExact methods for java.lang.Math

[Brian Burkhalter]

Hi Stephen,

On Sep 29, 2015, at 3:49 AM, Stephen Colebourne <scolebourne at joda.org> wrote:

> Good to see this happen.

Glad to hear it.

> I agree a test would be good to demonstrate edge cases.

I’ll add something.

> 1)
> I think the code for floorMod(long x, int y); cannot actually
> overflow. As such, the result could just be cast without the if and
> throw.

I’ll investigate further.

> 2)
> My preferred algorithm for floorMod is:
> 
> return ((a % b) + b) % b;
> 
> as it contains no Java-side branches, although tests would be needed
> to prove performance.
> 
> This also allows an algorithm for floorDiv with no Java-side branches:
> 
> int mod = ((a % b) + b) % b;
> return (a - mod) / b;

I tested the code which was in the original issue description and found some discrepancies. I’ll need to revisit this to see what happened.

> 
> 3)
> While making changes, this code could be changed to avoid the local
> variable (just return):
> public static int floorMod(int x, int y) {
>  int r = x - floorDiv(x, y) * y;
>  return r;
> }

I agree. I saw that myself but left it as-is.

Thanks,

Brian