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From "Gilles (Issue Comment Edited) (JIRA)" <j...@apache.org>
Subject [jira] [Issue Comment Edited] (MATH-725) use initialized static final arrays, instead of initializing it in constructors
Date Thu, 02 Feb 2012 22:22:57 GMT

    [ https://issues.apache.org/jira/browse/MATH-725?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13199279#comment-13199279
] 

Gilles edited comment on MATH-725 at 2/2/12 10:22 PM:
------------------------------------------------------

Those arrays cannot be "static" since their size depends on a parameter ("k") passed to the
constructor.
Please clarify what you proposed (or, better: provide a patch). Thanks.

                
      was (Author: erans):
    Those arrays cannot be "static" since their size depends on a parameter ("k") passed to
the constructor.

                  
> use initialized static final arrays, instead of initializing it in constructors
> -------------------------------------------------------------------------------
>
>                 Key: MATH-725
>                 URL: https://issues.apache.org/jira/browse/MATH-725
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 2.2
>            Reporter: Eldar Agalarov
>            Priority: Minor
>             Fix For: 3.0
>
>   Original Estimate: 1h
>  Remaining Estimate: 1h
>
> The Well PRNG's implementations have arrays iRm1, iRm2, iRm3, i1, i2, i3. All these arrays
are unmodifiable, so we can replace this arrays initialization block
>         final int w = 32;
>  	final int r = (k + w - 1) / w;
>  	this.v = new int[r];
>  	this.index = 0;
>  	
>  	// precompute indirection index tables. These tables are used for optimizing access
>  	// they allow saving computations like "(j + r - 2) % r" with costly modulo operations
>  	iRm1 = new int[r];
>  	iRm2 = new int[r];
>  	i1 = new int[r];
>  	i2 = new int[r];
>  	i3 = new int[r];
>  	for (int j = 0; j < r; ++j) {
>  	iRm1[j] = (j + r - 1) % r;
>  	iRm2[j] = (j + r - 2) % r;
>  	i1[j] = (j + m1) % r;
>  	i2[j] = (j + m2) % r;
>  	i3[j] = (j + m3) % r;
>  	}
> with inline initialized static final arrays.
> This is much better and faster implementation, freed from unnecessary costly calculations
(such as %).
> Another solution: leave as is, but make all these arrays static.

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