RFR: 8281631: HashMap.putAll can cause redundant space waste [v3]

[Andrew Haley]

On Fri, 11 Feb 2022 18:13:36 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> @RogerRiggs 
>> so you recommend `(int) Math.min(((m.size() * 4L + 2L) / 3L), Integer.MAX_VALUE)`? OK then, changed it.
>> please review again, thanks!
>
> Works for me.  Thanks

Just multiply by 0.75.

On a modern design, floating-point multiply is 4 clocks latency, 4 ops/clock throughput. FP max is 2 clocks latency, conversions int-float and vice versa 3 clocks latency, 4 ops/clock throughput.
Long division is 7-9 clocks, 2ops/clock throughput. Shift and add 2 clocks, 2/3 ops/clock througput. Compare is 1 clock, 3 ops/clock throughput, conditional move is 1 clock, 3 ops/clock throughput.

Seems like it's a wash.

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PR: https://git.openjdk.java.net/jdk/pull/7431