static long fastPowScaled()

in commons-statistics-inference/src/main/java/org/apache/commons/statistics/inference/DD.java [1172:1205]

• 23 lines of code
• 7 McCabe index (conditional complexity)

    static long fastPowScaled(double x, double xx, int n, DD f) {
        // Edge cases.
        if (n == 0) {
            f.set(0.5, 0);
            return 1;
        }
        // IEEE result for non-finite or zero
        if (!Double.isFinite(x) || x == 0) {
            f.set(Math.pow(x, n), 0);
            return 0;
        }
        // Here the number is non-zero finite
        assert x == x + xx : NOT_NOMALIZED;
        long b = frexp(x, xx, f);
        // Handle exact powers of 2
        if (Math.abs(f.hi) == HALF && f.lo == 0) {
            // (f * 2^b)^n = (2f)^n * 2^(b-1)^n
            // Use Math.pow to create the sign.
            // Note the result must be scaled to the fractional representation
            // by multiplication by 0.5 and addition of 1 to the exponent.
            f.hi = 0.5 * Math.pow(2 * f.hi, n);
            // Propagate sign change (x*f.hi) to the zero
            f.lo = Math.copySign(0.0, x * f.hi * xx);
            return 1 + (b - 1) * n;
        }
        if (n < 0) {
            b = computeFastPowScaled(b, f.hi, f.lo, -n, f);
            // Result is a non-zero fraction part so inversion is safe
            inverse(f.hi, f.lo, f);
            // Rescale to [0.5, 1.0]
            return -b + frexp(f.hi, f.lo, f);
        }
        return computeFastPowScaled(b, f.hi, f.lo, n, f);
    }