RFR 8200696 : Optimal initial capacity of java.lang.Class.enumConstantDirectory

[David Holmes]

Hi Ivan,

On 4/04/2018 9:22 AM, Ivan Gerasimov wrote:
> Hello!
> 
> Yet another occurrence of not-optimally pre-sized HashMap.
> 
> When java.lang.Class.enumConstantDirectory is created, the initial 
> capacity is set to be (2 * universe.length), which is more than 
> necessary in some cases.
> 
> Choosing the capacity optimally will allow us to save a few bytes with 
> some enum classes.

How are you defining optimal? The bug report only gives one example 
where the current calculation produces a too large value. If the HashMap 
itself rounds up the initial capacity to a power of 2, how much extra 
space do we need compared to universe.length? Do we just need to pass 
(universe.length+1) to get the smallest power of 2 greater than 
universe.length?

Thanks,
David

> Would you please help review this trivial fix?
> 
> BUGURL: https://bugs.openjdk.java.net/browse/JDK-8200696
> WEBREV: http://cr.openjdk.java.net/~igerasim/8200696/00/webrev/
>