Handle overflow in probability computation
diff --git a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/PascalDistribution.java b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/PascalDistribution.java
index 94d385b..55b27ab 100644
--- a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/PascalDistribution.java
+++ b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/PascalDistribution.java
@@ -112,10 +112,16 @@
// Special case exploiting cancellation.
ret = Math.pow(probabilityOfSuccess, numberOfSuccesses);
} else {
- ret = BinomialCoefficientDouble.value(x +
- numberOfSuccesses - 1, numberOfSuccesses - 1) *
- Math.pow(probabilityOfSuccess, numberOfSuccesses) *
- Math.pow(1.0 - probabilityOfSuccess, x);
+ final int n = x + numberOfSuccesses - 1;
+ if (n < 0) {
+ // overflow
+ // The binomial coefficient -> inf when n -> inf
+ ret = 0.0;
+ } else {
+ ret = BinomialCoefficientDouble.value(n, numberOfSuccesses - 1) *
+ Math.pow(probabilityOfSuccess, numberOfSuccesses) *
+ Math.pow(1.0 - probabilityOfSuccess, x);
+ }
}
return ret;
}
@@ -130,10 +136,17 @@
// Special case exploiting cancellation.
ret = logProbabilityOfSuccess * numberOfSuccesses;
} else {
- ret = LogBinomialCoefficient.value(x +
- numberOfSuccesses - 1, numberOfSuccesses - 1) +
- logProbabilityOfSuccess * numberOfSuccesses +
- log1mProbabilityOfSuccess * x;
+ final int n = x + numberOfSuccesses - 1;
+ if (n < 0) {
+ // overflow
+ // The binomial coefficient -> inf when n -> inf
+ ret = Double.NEGATIVE_INFINITY;
+ } else {
+ ret = LogBinomialCoefficient.value(x +
+ numberOfSuccesses - 1, numberOfSuccesses - 1) +
+ logProbabilityOfSuccess * numberOfSuccesses +
+ log1mProbabilityOfSuccess * x;
+ }
}
return ret;
}
