RFR: 8186958: Need method to create pre-sized HashMap

[XenoAmess]

On Wed, 23 Mar 2022 18:41:59 GMT, XenoAmess <duke at openjdk.java.net> wrote:

> 8186958: Need method to create pre-sized HashMap

@stuart-marks 

I think making these functions at Collections is slightly better than place them to their own classes.

The first step is to make such functions.

The second step is to change some usage to these functions.

I ran the jmh locally, and find it far better performance to use int calculations, than double.

Benchmark                                                       Mode  Cnt           Score          Error  Units
CalculateHashMapCapacityTestJMH.testCalculateHashMapCapacity1  thrpt   50           0.429 ��        0.006  ops/s
CalculateHashMapCapacityTestJMH.testCalculateHashMapCapacity2  thrpt   50  4703157194.777 �� 25674718.597  ops/s
CalculateHashMapCapacityTestJMH.testCalculateHashMapCapacity3  thrpt   50  4729596276.529 �� 16516214.791  ops/s

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PR: https://git.openjdk.java.net/jdk/pull/7928