RFR: 8332826: Make hashCode methods in ArraysSupport friendlier [v2]

[Pavel Rappo]

On Tue, 28 May 2024 19:13:50 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> Pavel Rappo has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix incorrect utf16 hashCode adaptation
>
> src/java.base/share/classes/jdk/internal/util/ArraysSupport.java line 252:
> 
>> 250:         return switch (length) {
>> 251:             case 0 -> initialValue;
>> 252:             case 1 -> 31 * initialValue + (int) a[fromIndex];
> 
> Suggestion:
> 
>             case 1 -> 31 * initialValue + (int) a[fromIndex]; // sign extension

To be honest, I don't think that this cast is needed. A better solution than to add a comment would be to delete all `(int)` casts from new `hashCode*` methods of `ArraysSupport`.

Those `(int)` casts migrated from `hashCode` methods of `Arrays` where there were used if neither of two `+` operands were of type `int`. But in `ArraysSupport` it's no longer the case: `31 * initialValue` is always `int` because `initialValue` is. So, `a[fromIndex]` is promoted to `int` by the virtue of https://docs.oracle.com/javase/specs/jls/se22/html/jls-5.html#jls-5.6.

For more confidence, consider that the `private static int hashCode` methods (implementation) of `ArraysSupport` do not have those casts.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19414#discussion_r1618835934