RFR: 8283892: Compress and expand bits [v4]

[Paul Sandoz]

> Add support to compress bits and expand bits of `int` and `long` values, see Hacker's Delight (2nd edition), section 7.4.
> 
> Compressing or expanding bits of an `int` or `long` value can be composed to enable general permutations, and the "sheep and goats" operation (SAG) see Hacker's Delight (2nd edition), section 7.7. SAG can be used to perform a stable binary radix sort.
> 
> The compress and expand functionality maps efficiently to hardware instructions, such as `PEXT` and `PDEP` on x86 hardware. Thus the implementations can be very efficient on supporting hardware. Intrinsification will occur in a separate PR.
> 
> This [paper](https://arxiv.org/pdf/1706.00990.pdf) investigates the beneficial performance impact of the `PDEP` instruction, and by extension the `expand` method, when applied to the implementation of a bit-vector select operation in succinct data structures (for example `select(r)` returns the position of the `r`th 1).
> 
> Testing-wise the approach take is three fold:
> 1. Tests compared against simple implementations that are easy to read and verify against the JDK implementations (which later will also be made intrinsic). To compensate all tests are also run flipping the test methods and the methods under test.
> 2. Tests composed of compress and expand and vice versa.
> 3. Tests with known mask patterns, whose expected values are easily derived from the inputs.

Paul Sandoz has updated the pull request incrementally with two additional commits since the last revision:

 - Fix typo.
 - Provide examples.

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8115/files
  - new: https://git.openjdk.java.net/jdk/pull/8115/files/da49874b..96d90e1a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8115&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8115&range=02-03

  Stats: 186 lines in 2 files changed: 186 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8115.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8115/head:pull/8115

PR: https://git.openjdk.java.net/jdk/pull/8115