RFR: 8271602: Add Math.ceilDiv() family parallel to Math.floorDiv() family

[Brian Burkhalter]

On Tue, 31 Aug 2021 07:22:17 GMT, Raffaello Giulietti <github.com+70726043+rgiulietti at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/Math.java line 1501:
>> 
>>> 1499:         // if the signs are the same and modulo not zero, round up
>>> 1500:         if ((x ^ y) >= 0 && (q * y != x)) {
>>> 1501:             return q + 1;
>> 
>> In `floorDiv()` this line is `r--` and there is only one return statement in the method. I think the accepted convention is to return as soon as possible like is done here, so perhaps it would be good to change `floorDiv()` to match? In any cases the two should be consistent.
>
> Yes, I tend to return as soon as possible (btw, it's a q (for quotient) rather than a r (for remainder).
> I can of course modify the floorDiv() family to match this convention but I would like not to open an issue just for that. What is best?

I think it's fine to make small changes like this without opening another issue.

>> src/java.base/share/classes/java/lang/Math.java line 1591:
>> 
>>> 1589:      *       is zero exactly when {@code x % y} is zero as well.</li>
>>> 1590:      *   <li>If neither of {@code ceilMod}(x, y) or {@code x % y} is zero,
>>> 1591:      *       their results differ exactly when the signs of the arguments are the same.<br>
>> 
>> I would say "If neither `ceilMod(x, y)`nor `x % y` is zero".  Also same question as above: by "exactly when" do you intend "if any only if"?
>
> OK, but for consistency then even floorMod() should be changed. Would this require another JBS issue (or CSR)?

If the specifications of the new methods are consistent with their respective `floorX()` analogs then they are fine as-is and no need to change the analogs to match.

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PR: https://git.openjdk.java.net/jdk/pull/5285