dispatch_once calls on every load from it
Performance improvements, as reported by the perf testing buildbot:
Histogram -18.81%
TwoSum -17.42%
RGBHistogram -9.65%
Regressions:
InsertionSort 5.59%
ArrayOfRef 3.99%
SwiftStructuresInsertionSort 5.29%
PrimeNum 6.09%
These regressions are bogus. The tests that "regressed" don't do any
hashing at all.
Swift SVN r23995
And make sure that all those public identifiers are preceeded with underscores.
I marked these public-modifiers with "// @testable" to document why they are public.
If some day we have a @testable attribute it should be used instead of those public-modifiers.
Again, this is needed for enabling dead internal function elimination in the stdlib.
Swift SVN r22657
This function mixes the bits in the hash value, which improves Dictionary
performance for keys with bad hashes.
PrecommitBenchmark changes with greater than 7% difference:
``````````Dictionary2`,```1456.00`,```1508.00`,```1502.00`,````624.00`,````607.00`,````592.00`,`864.00`,``145.9%
``````````Dictionary3`,```1379.00`,```1439.00`,```1408.00`,````585.00`,````567.00`,````552.00`,`827.00`,``149.8%
````````````Histogram`,````850.00`,````849.00`,````851.00`,```1053.00`,```1049.00`,```1048.00`,`199.00`,``-19.0%
````````````````Prims`,```1999.00`,```2005.00`,```2018.00`,```1734.00`,```1689.00`,```1701.00`,`310.00`,```18.4%
``````````StrSplitter`,```2365.00`,```2334.00`,```2316.00`,```1979.00`,```1997.00`,```2000.00`,`337.00`,```17.0%
```````````````TwoSum`,```1551.00`,```1568.00`,```1556.00`,```1771.00`,```1741.00`,```1716.00`,`165.00`,```-9.6%
Regressions are in benchmarks that use `Int` as dictionary key: we are just
doing more work than previously (hashing an `Int` was an identity function).
rdar://17962402
Swift SVN r21142
