On 08.07.2014 4:44, Martin Buchholz wrote:
On Mon, Jul 7, 2014 at 9:41 AM, Martin Buchholz <[email protected]
<mailto:[email protected]>> wrote:
I'd like to offer an alternative version of this change. webrev
coming soon.
Here's the promised webrev.
http://cr.openjdk.java.net/~martin/webrevs/openjdk9/IdentityHashMap-capacity/
<http://cr.openjdk.java.net/%7Emartin/webrevs/openjdk9/IdentityHashMap-capacity/>
- Fixes a typo in the javadoc.
- removes the "threshold" field (WAT, a cache to avoid multiplying by 3?)
- optimizes 3*x into x + x << 1
My personal preference would be x + x + x, but I thought JIT can do this
kind of optimizations itself.
Out of curiosity I've created a microbenchmark:
Benchmark Mode Samples Score Score
error Units
o.s.MyBenchmark.testMethod_01_X3 avgt 200 5.900
0.041 ns/op
o.s.MyBenchmark.testMethod_02_PPP avgt 200 6.029
0.035 ns/op
o.s.MyBenchmark.testMethod_03_PSH avgt 200 5.907
0.071 ns/op
On my machine 3*x and x + (x<<1) appear to be of the same speed (#1 and
#3 above).
x + x + x (case #2) happens to be ~2% slower.
Given the optimization doesn't introduce any speedup, wouldn't it be
better to use 3*x for its clarity?
Sincerely yours,
Ivan
- adds more test assertions
- removes the unusual 4/3 slack space for expansion on deserialization.
TODO: the test should be testng-ified, I think.
