RFR: 8275821: Optimize random number generators developed in JDK-8248862 using Math.unsignedMultiplyHigh()

[Vamsi Parasa]

This change optimizes random number generators using Math.unsignedMultiplyHigh()

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Commit messages:
 - Update Math.java
 - 8275821: Optimize random number generators developed in JDK-8248862 using Math.unsignedMultiplyHigh()

Changes: https://git.openjdk.java.net/jdk/pull/6206/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6206&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275821
  Stats: 31 lines in 3 files changed: 0 ins; 28 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6206.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6206/head:pull/6206

PR: https://git.openjdk.java.net/jdk/pull/6206