private static double sfExact()

in commons-statistics-inference/src/main/java/org/apache/commons/statistics/inference/KolmogorovSmirnovDistribution.java [189:224]

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

        private static double sfExact(double x, int n) {
            if (n * x * x >= 370 || x >= 1) {
                // p would underflow, or x is out of the domain
                return 0;
            }
            final double nx = x * n;
            if (nx <= 1) {
                // x <= 1/(2n)
                if (nx <= HALF) {
                    // Also detects x <= 0 (iff n is positive)
                    return 1;
                }
                if (n == 1) {
                    // Simplification of:
                    // 1 - (n! (2x - 1/n)^n) == 1 - (2x - 1)
                    return 2.0 - 2.0 * x;
                }
                // 1/(2n) < x <= 1/n
                // 1 - (n! (2x - 1/n)^n)
                final double f = 2 * x - 1.0 / n;
                // Switch threshold where (2x - 1/n)^n is sub-normal
                // Max factorial threshold is n=170
                final double logf = Math.log(f);
                if (n <= MAX_FACTORIAL && n * logf > LOG_MIN_NORMAL) {
                    return 1 - Factorial.doubleValue(n) * Math.pow(f, n);
                }
                return -Math.expm1(LogFactorial.create().value(n) + n * logf);
            }
            // 1 - 1/n <= x < 1
            if (n - 1 <= nx) {
                // 2 * (1-x)^n
                return 2 * Math.pow(1 - x, n);
            }

            return -1;
        }