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https://issues.apache.org/jira/browse/RNG-191?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18062479#comment-18062479
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Alex Herbert commented on RNG-191:
----------------------------------
I have prepared a modification of the code to use the Math multiply methods for
the PHILOX_4X64 generator only.
JMH results on a Mac M2 Max in ns/operation:
| |nextLong| | |nextLongN| | |
|JDK|Original|UM|Relative|Original|UM|Relative|
|1.8.0_473|15.709|15.569|0.991|16.503|16.669|1.010|
|11.0.29|9.754|5.390|0.553|11.014|5.604|0.509|
|17.0.17|9.087|3.621|0.398|10.240|4.420|0.432|
|21.0.9|9.053|2.172|0.240|10.170|2.797|0.275|
|25.0.2|9.104|2.164|0.238|10.207|2.792|0.274|
Performance agrees with previous results from the testing benchmarks. On JDK 11
performance doubles and increases even more on higher JDKs.
PR is here: [PR 192|https://github.com/apache/commons-rng/pull/192]
> Use java.lang.invoke to dynamically call Math multiply high methods
> -------------------------------------------------------------------
>
> Key: RNG-191
> URL: https://issues.apache.org/jira/browse/RNG-191
> Project: Commons RNG
> Issue Type: Improvement
> Components: core
> Reporter: Alex Herbert
> Priority: Minor
>
> The following generators rely on a 128-bit multiplication result from two
> 64-bit longs:
> * L128_X128_MIX
> * L128_X256_MIX
> * L128_X1024_MIX
> * PHILOX_4X64
> Java added support to java.lang.Math to compute the upper 64-bit result with
> potential intrinsic calls to native functions:
> ||Method||JDK||Notes||
> |[multiplyHigh (Javadoc JDK
> 21)|https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/Math.html#multiplyHigh(long,long)]|9|Convert
> to unsigned using:
> Math.multiplyHigh(a, b) + ((a >> 63) & b) + ((b >> 63) & a)|
> |[unsignedMultiplyHigh (Javadoc JDK
> 21)|https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/Math.html#unsignedMultiplyHigh(long,long)]|18|
> |
> Since Commons RNG targets Java 8 these methods cannot be used. The current
> RNGs use a software implementation to compose the upper bits of the 128-bit
> result. However the methods can be used with a
> [MethodHandle|https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/invoke/MethodHandle.html]
> introduced in Java 7:
> {code:java}
> // find the method
> MethodHandle h = MethodHandles.publicLookup()
> .findStatic(Math.class,
> "unsignedMultiplyHigh",
> MethodType.methodType(long.class, long.class, long.class));
> // invoke (snippet)
> long a, b;
> try {
> long r = (long) h2.invokeExact(a, b);
> } catch (Throwable e) {
> throw new RuntimeException(e);
> }
> {code}
> Investigate the use of MethodHandle within the named RNGs.
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