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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-1300) BitsStreamGenerator#nextBytes(byte[]) is wrong
Date Sat, 19 Dec 2015 23:30:46 GMT

    [ https://issues.apache.org/jira/browse/MATH-1300?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15065574#comment-15065574
] 

Gilles commented on MATH-1300:
------------------------------

Personally, I'm always in favour of cleaining up in the sense to make the code safer and more
understandable, before trying to grab a few milliseconds in a micro-benchmark.
If we want to focus on performance, it would be better to have a realistic use-case (e.g.
estimate how much time is spent in "nextBytes" relative to the usage of the generated numbers).

I think that we need to determine how to resolve the original issue, and perhaps open another
report for the performance improvement.


> BitsStreamGenerator#nextBytes(byte[]) is wrong
> ----------------------------------------------
>
>                 Key: MATH-1300
>                 URL: https://issues.apache.org/jira/browse/MATH-1300
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.5
>            Reporter: Rostislav Krasny
>         Attachments: MersenneTwister2.java, TestMersenneTwister.java
>
>
> Sequential calls to the BitsStreamGenerator#nextBytes(byte[]) must generate the same
sequence of bytes, no matter by chunks of which size it was divided. This is also how java.util.Random#nextBytes(byte[])
works.
> When nextBytes(byte[]) is called with a bytes array of length multiple of 4 it makes
one unneeded call to next(int) method. This is wrong and produces an inconsistent behavior
of classes like MersenneTwister.
> I made a new implementation of the BitsStreamGenerator#nextBytes(byte[]) see attached
code.



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