RFR: JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort) [v10]

[Laurent Bourgès]

> * improved  mixed insertion sort (makes whole sorting faster)
> * introduced Radix which sort shows several times boost of performance and has linear complexity instead of n*ln(n)
> * improved merging sort for almost sorted data
> * optimized parallel sorting
> * improved step for pivot candidates and pivot partitioning
> * extended existing tests
> * added benchmarking JMH tests
> * suggested better buffer allocation: if no memory, it is switched to in-place sorting with no OutOfMemoryError, threshold is 1/16th heap
> 
> I am going on previous PR by Vladimir Yaroslavskyi: https://github.com/openjdk/jdk/pull/3938

Laurent Bourgès has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains one commit:

  JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort)
  * Optimized mixed insertion sort
  * Optimized insertion sort
  * Optimized Radix sort
  * Updated microbenchmark

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Changes: https://git.openjdk.org/jdk/pull/13568/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13568&range=09
  Stats: 4477 lines in 4 files changed: 1713 ins; 1404 del; 1360 mod
  Patch: https://git.openjdk.org/jdk/pull/13568.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13568/head:pull/13568

PR: https://git.openjdk.org/jdk/pull/13568