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From "Alex D Herbert (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (RNG-87) MultiplyWithCarry256
Date Fri, 29 Mar 2019 22:51:00 GMT

    [ https://issues.apache.org/jira/browse/RNG-87?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16805528#comment-16805528
] 

Alex D Herbert commented on RNG-87:
-----------------------------------

{quote}I agree, but wonder why JMH doesn't take its baseline into account (in "warmup"?)
{quote}
I think the attitude of JMH is that they present the raw data and it is up to you to interpret
it correctly. Basically they report the timings as is and expect you to know it is there.

In most cases this overhead will be a lesser fraction of the total time for processing the
actual work payload of interest. However in our case the RNG is so fast that the payload gets
lost in the overhead.

If all you wish to do is get the time for a few methods and pick the fastest then the overhead
(being constant) does not matter. It only matters when you would like to report the relative
time between methods accurately. In this case the larger the overhead as a fraction of total
runtime the less accurate the relative time, unless you correctly subtract the overhead.
{quote}Use cases...
{quote}
I will have a think. However it may be a mute point. Analysis will likely show that those
generators that are fastest when nothing is using the output will still be the fastest when
the output is put to some task.

 

> MultiplyWithCarry256
> --------------------
>
>                 Key: RNG-87
>                 URL: https://issues.apache.org/jira/browse/RNG-87
>             Project: Commons RNG
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.3
>            Reporter: Alex D Herbert
>            Assignee: Alex D Herbert
>            Priority: Minor
>              Labels: performance
>         Attachments: MWC_256.jpg, MWC_256_2.jpg, MWC_256_3.jpg, MWC_256_3.png, Shuffle.jpg,
big.jpg, small.jpg
>
>          Time Spent: 40m
>  Remaining Estimate: 0h
>
> The {{MultiplyWithCarry256}} currently uses a length 256 array for internal state. This
is cycled through continuously. The current implementation refills the state every 256 calls
to next:
> {code:java}
> public int next() {
>     if (index == Q_SIZE) { // Whole state used up.
>         // Refill.
>         for (int i = 0; i < Q_SIZE; i++) {
>             final long t = A * (state[i] & 0xffffffffL) + carry;
>             carry = (int) (t >> 32);
>             state[i] = (int) t;
>         }
>         // Reset current index.
>         index = 0;
>     }
>     return state[index++];
> }
> {code}
> This can be changed to continuously update the state for only a single index on each
call to next:
> {code:java}
> public int next() {
>     // Produce an index in the range 0-255
>     final int i = index++ & 0xFF;
>     final long t = A * (state[i] & 0xffffffffL) + carry;
>     carry = (int) (t >> 32);
>     return state[i] = (int) t;
> }
> {code}
> This avoids an {{if}} statement check and *marginally* improves performance. It has the
advantage of not advancing the state further ahead than necessary.
> MWC_256B is the new version. JMH results from the GenerationPerformance benchmark.
> {noformat}
> openjdk version "1.8.0_191"
> OpenJDK Runtime Environment (build 1.8.0_191-8u191-b12-2ubuntu0.16.04.1-b12)
> OpenJDK 64-Bit Server VM (build 25.191-b12, mixed mode)
> {noformat}
> ||numValues||randomSourceName||Method||Score||Error||Median||
> |1|SPLIT_MIX_64|nextInt|0.00478|4.45e-05|0.00477|
> |1|MWC_256|nextInt|0.00521|1.69e-05|0.00521|
> |1|MWC_256B|nextInt|0.00519|0.000321|0.00512|
> |100|SPLIT_MIX_64|nextInt|0.421|0.0131|0.418|
> |100|MWC_256|nextInt|0.452|0.000968|0.452|
> |100|MWC_256B|nextInt|0.443|0.00183|0.442|
> |10000|SPLIT_MIX_64|nextInt|41.7|0.0725|41.7|
> |10000|MWC_256|nextInt|44.5|2.25|43.9|
> |10000|MWC_256B|nextInt|42.6|0.037|42.6|
> |1000000|SPLIT_MIX_64|nextInt|3.77e+03|21.2|3.77e+03|
> |1000000|MWC_256|nextInt|4.16e+03|12.8|4.16e+03|
> |1000000|MWC_256B|nextInt|3.98e+03|120|3.96e+03|
> {noformat}
> java version "11.0.2" 2019-01-15 LTS
> Java(TM) SE Runtime Environment 18.9 (build 11.0.2+9-LTS)
> Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.2+9-LTS, mixed mode)
> {noformat}
> ||numValues||randomSourceName||Method||Score||Error||Median||
> |1|SPLIT_MIX_64|nextInt|0.00469|4.98e-06|0.00469|
> |1|MWC_256|nextInt|0.00553|2.09e-05|0.00553|
> |1|MWC_256B|nextInt|0.00493|4.32e-05|0.00492|
> |100|SPLIT_MIX_64|nextInt|0.435|0.000624|0.435|
> |100|MWC_256|nextInt|0.467|0.00284|0.466|
> |100|MWC_256B|nextInt|0.455|0.00105|0.455|
> |10000|SPLIT_MIX_64|nextInt|43|4.94|41.9|
> |10000|MWC_256|nextInt|45.8|0.132|45.8|
> |10000|MWC_256B|nextInt|43|0.033|43|
> |1000000|SPLIT_MIX_64|nextInt|3.7e+03|7.88|3.7e+03|
> |1000000|MWC_256|nextInt|4.17e+03|45.3|4.15e+03|
> |1000000|MWC_256B|nextInt|4.12e+03|4.76|4.12e+03|



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