[
http://issues.apache.org/jira/browse/MATH-153?page=comments#action_12424472 ]
Remi Arntzen commented on MATH-153:
-----------------------------------
once Math-154 (MathUtils addAndCheck and subAndCheck for long values)
is commited nextLong(long, long) could become
public long nextLong(long lower, long upper) {
if (lower >= upper) {
throw new IllegalArgumentException(
"upper bound must be > lower bound");
}
RandomGenerator rand = getRan();
boolean overFlow = false;
try {
MathUtils.subAndCheck(upper, lower);
} catch (ArithmeticException thrown) {
overFlow = true;
}
long returnValue;
if (upper - lower == Long.MAX_VALUE) {
//upper - lower + 1 = Long.MAX_VALUE + 1 = *overflow error*;
overFlow = true;
}
if (!overFlow) {
returnValue = lower + (long) (rand.nextDouble() * (upper -
lower + 1)
);
} else {
returnValue = rand.nextLong();
while (returnValue > upper || returnValue < lower) {
returnValue = rand.nextLong();
}
}
return returnValue;
}
> 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
>
> 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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