Lexicographic array comparators

[Paul Sandoz]

Hi,

One common use of Unsafe is boost the performance of comparing unsigned byte[] by viewing as long[] (for example as performed by Guava or Cassandra). To reduce the dependency on Unsafe we need a public and safe equivalent that works on all platforms while meeting the performance expectations.

In the past we have discussed exposing something on ByteBuffer but i think the right thing to explore are comparators for all basic types on java.util.Arrays:

 https://bugs.openjdk.java.net/browse/JDK-8033148

This should be explored with the following issue in mind to expose an intrinsic that could be leveraged when implemented: 

 https://bugs.openjdk.java.net/browse/JDK-8044082

Some preliminary work can be found here:

  http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8033148-Arrays-lexico-compare/webrev/

The "explosion" in methods is annoying. Out of the 8 primitives 4 can be signed or unsigned. Objects can be comparable or an explicit comparator can be used. There are implicit and explicit ranges. That makes a maximum of 28 methods, but could be reduced to a minimum of 10, for all basic types.

Comparator instances, for implicit ranges, can easily be created from method refs or lambdas.

Thoughts?

Paul.