[jira] [Commented] (MATH-725) use initialized static final arrays, instead of initializing it in constructors

["Gilles (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MATH-725?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13189860#comment-13189860 ] 

Gilles commented on MATH-725:
-----------------------------

The problem is that arrays are _mutable_. If they are made "static", a buggy or malicious subclass of {{AbstractWell}} will be able to affect all instances.

We could do that if the arrays are never exposed, i.e. they would become "private" and their contents must be accessed through methods. Not sure whether it won't be slower in the end...


                
> 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
>   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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