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https://issues.apache.org/jira/browse/RNG-79?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16784305#comment-16784305
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Alex D Herbert commented on RNG-79:
-----------------------------------
Just checked a different machine with JDK 8 and 11.
Still virtually identical (although the more complete method using multiply
with the most bits just edges ahead):
||Method||Score||Error||Median||
|nextDoubleBaseline|404.73|0.90|404.70|
|nextDoubleUsingBitsToDouble|327.09|5.04|327.54|
|nextDoubleUsingMultiply52bits|327.89|5.85|328.41|
|nextDoubleUsingMultiply53bits|329.47|2.98|329.64|
|nextFloatBaseline|407.04|3.03|407.40|
|nextFloatUsingBitsToFloat|321.18|13.81|320.95|
|nextFloatUsingMultiply23bits|332.84|0.89|332.86|
|nextFloatUsingMultiply24bits|326.90|13.32|327.88|
If you are OK with this then I'll commit the benchmark to master and open a
ticket to update the {{NumberFactory.}}
> Benchmark methods for producing nextDouble
> ------------------------------------------
>
> Key: RNG-79
> URL: https://issues.apache.org/jira/browse/RNG-79
> Project: Commons RNG
> Issue Type: New Feature
> Components: core
> Affects Versions: 1.3
> Reporter: Alex D Herbert
> Assignee: Alex D Herbert
> Priority: Minor
> Time Spent: 40m
> Remaining Estimate: 0h
>
> Benchmark the speed of methods for producing a {{double}} from a {{long}}:
> {code:java}
> long v;
> double d1 = Double.longBitsToDouble(0x3FFL << 52 | v >>> 12) - 1.0;
> double d2 = (v >>> 12) * 0x1.0p-52d; // 1.0 / (1L << 52);
> double d3 = (v >>> 11) * 0x1.0p-53d; // 1.0 / (1L << 53);
> {code}
> Method d1 and d2 are both currently employed in the {{NumberFactory}}
> (makeDouble(int,int) and makeDouble(long)). However they suffer from
> producing a double whose least significant bit is always 0, i.e. they produce
> half of all possible double values from 0-1. This is discussed in the
> reference for the [XorShiRo generators|http://xoshiro.di.unimi.it/].
> This task will benchmark the methods using JMH. A switch to method d3 may be
> appropriate as it generates more values. This is the method employed in JDK
> 1.7 ThreadLocalRandom.
> A similar analysis can be made for producing a float:
> {code:java}
> int v;
> double f1 = Float.intBitsToFloat(0x7f << 23 | v >>> 9) - 1.0f;
> double f2 = (v >>> 9) * 0x1.0p-23f; // 1.0f / (1 << 23);
> double f3 = (v >>> 8) * 0x1.0p-24f; // 1.0f / (1 << 24)
> {code}
> Method f2 is currently used in the {{NumberFactory}}.
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