RandomDataImpl.nextInt does not distribute uniformly for negative lower bound
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Key: MATH-724
URL: https://issues.apache.org/jira/browse/MATH-724
Project: Commons Math
Issue Type: Bug
Affects Versions: Nightly Builds
Reporter: Dennis Hendriks
When using the RandomDataImpl.nextInt function to get a uniform sample in a [lower, upper]
interval, when the lower value is less than zero, the output is not uniformly distributed,
as the lowest value is practically never returned.
See the attached NextIntUniformTest.java file. It uses a [-3, 5] interval. For several values
between 0 and 1, testNextIntUniform1 prints the return value of RandomDataImpl.nextInt (as
double and as int). We see that -2 through 5 are returned several times. The -3 value however,
is only returned for 0.0, and is thus under-respresented in the integer samples. The output
of test method testNextIntUniform2 also clearly shows that value -3 is never sampled.
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