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From "Brent Worden (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MATH-153) RandomDataImpl nextInt(int, int) nextLong(long, long)
Date Mon, 07 Aug 2006 13:21:14 GMT
    [ http://issues.apache.org/jira/browse/MATH-153?page=comments#action_12426210 ] 
            
Brent Worden commented on MATH-153:
-----------------------------------

I think we can avoid the overflow conditions simply by distributing the multiplication of
the random value.  With this, the method body would become:

double r = rand.nextDouble();
return (int)((r * upper) + ((1.0 - r) * lower) + r);


> RandomDataImpl nextInt(int, int) nextLong(long, long)
> -----------------------------------------------------
>
>                 Key: MATH-153
>                 URL: http://issues.apache.org/jira/browse/MATH-153
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: Nightly Builds, 1.1 Final
>            Reporter: Remi Arntzen
>            Priority: Critical
>             Fix For: 1.2 Final
>
>
> RandomDataImpl.nextInt(Integer.MIN_VALUE, Integer.MAX_VALUE) suffers from overflow errors.
> change
> return lower + (int) (rand.nextDouble() * (upper - lower + 1));
> to
> return (int) (lower + (long) (rand.nextDouble()*((long) upper - lower + 1)));
> additional checks must be made for the nextlong(long, long) method.
> At first I thought about using MathUtils.subAndCheck(long, long) but there is only an
int version avalible, and the problem is that subAndCheck internaly uses long values to check
for overflow just as my previous channge proposes.  The only thing I can think of is using
a BigInteger to check for the number of bits required to express the difference.

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