private static double binomialCCdf()

in commons-numbers-gamma/src/main/java/org/apache/commons/numbers/gamma/BoostBeta.java [956:997]

• 34 lines of code
• 8 McCabe index (conditional complexity)

    private static double binomialCCdf(int n, int k, double x, double y) {
        double result = Math.pow(x, n);

        if (result > Double.MIN_NORMAL) {
            double term = result;
            for (int i = n - 1; i > k; --i) {
                term *= ((i + 1) * y) / ((n - i) * x);
                result += term;
            }
        } else {
            // First term underflows so we need to start at the mode of the
            // distribution and work outwards:
            int start = (int) (n * x);
            if (start <= k + 1) {
                start = k + 2;
            }
            // Update:
            // Carefully compute this term to guard against extreme parameterisation
            result = binomialTerm(n, start, x, y);
            if (result == 0) {
                // OK, starting slightly above the mode didn't work,
                // we'll have to sum the terms the old fashioned way:
                for (int i = start - 1; i > k; --i) {
                    result += binomialTerm(n, i, x, y);
                }
            } else {
                double term = result;
                final double startTerm = result;
                for (int i = start - 1; i > k; --i) {
                    term *= ((i + 1) * y) / ((n - i) * x);
                    result += term;
                }
                term = startTerm;
                for (int i = start + 1; i <= n; ++i) {
                    term *= (n - i + 1) * x / (i * y);
                    result += term;
                }
            }
        }

        return result;
    }