public static double atan2()

in commons-math-core/src/main/java/org/apache/commons/math4/core/jdkmath/AccurateMath.java [2640:2726]
61 lines of code
22 McCabe index (conditional complexity)

    public static double atan2(double y, double x) {
        if (Double.isNaN(x) || Double.isNaN(y)) {
            return Double.NaN;
        }

        if (y == 0) {
            final double invx = 1d / x;

            if (invx == 0) { // X is infinite
                if (x > 0) {
                    return y; // return +/- 0.0
                }
                return copySign(Math.PI, y);
            }

            if (x < 0 || invx < 0) {
                return copySign(Math.PI, y);
            }
            return x * y;
        }

        // y cannot now be zero

        if (y == Double.POSITIVE_INFINITY) {
            if (x == Double.POSITIVE_INFINITY) {
                return Math.PI * F_1_4;
            }

            if (x == Double.NEGATIVE_INFINITY) {
                return Math.PI * F_3_4;
            }

            return Math.PI * F_1_2;
        }

        if (y == Double.NEGATIVE_INFINITY) {
            if (x == Double.POSITIVE_INFINITY) {
                return -Math.PI * F_1_4;
            }

            if (x == Double.NEGATIVE_INFINITY) {
                return -Math.PI * F_3_4;
            }

            return -Math.PI * F_1_2;
        }

        if (x == Double.POSITIVE_INFINITY) {
            return y > 0 ? 0d : -0d;
        }

        if (x == Double.NEGATIVE_INFINITY) {
            return y > 0 ? Math.PI : -Math.PI;
        }

        // Neither y nor x can be infinite or NAN here

        if (x == 0) {
            return y > 0 ? Math.PI * F_1_2 : -Math.PI * F_1_2;
        }

        // Compute ratio r = y/x
        final double r = y / x;
        if (Double.isInfinite(r)) { // bypass calculations that can create NaN
            return atan(r, 0, x < 0);
        }

        double ra = doubleHighPart(r);
        double rb = r - ra;

        // Split x
        final double xa = doubleHighPart(x);
        final double xb = x - xa;

        rb += (y - ra * xa - ra * xb - rb * xa - rb * xb) / x;

        final double temp = ra + rb;
        rb = -(temp - ra - rb);
        ra = temp;

        if (ra == 0) { // Fix up the sign so atan works correctly
            ra = copySign(0d, y);
        }

        // Call atan
        return atan(ra, rb, x < 0);
    }