Fast distance computation for BRouter

App.java

class App {
    public static void main(String [ ] args)
    {
        int N_TESTS = 10000000;
        double R = 6371000.;
        double rad = Math.PI / 180;

        double[] latlng1 = {48.8124, 2.3158};
        double[] latlng2 = {48.8204, 2.3210};

        double lon1, lon2, lat1, lat2, l, l2, l4, coslat, coslat6, dlat, dlon, sinDLat, sinDLon, a, c;
        double distance = 0.;

        System.out.println("Leaflet implementation:");
        long time = System.currentTimeMillis();
        for (int i = 0; i < N_TESTS; i++) {
            lat1 = latlng1[0] * rad;
            lat2 = latlng2[0] * rad;
            sinDLat = Math.sin((latlng2[0] - latlng1[0]) * rad / 2);
            sinDLon = Math.sin((latlng2[1] - latlng1[1]) * rad / 2);
            a = sinDLat * sinDLat + Math.cos(lat1) * Math.cos(lat2) * sinDLon * sinDLon;
            c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
            distance = R * c;

        }
        System.out.println((System.currentTimeMillis() - time) / 1000.);
        System.out.println(distance);

        System.out.println("Current BRouter implementation:");
        time = System.currentTimeMillis();
        for (int i = 0; i < N_TESTS; i++) {
            lon1 = latlng1[1] * 1e6;
            lat1 = latlng1[0] * 1e6;
            lon2 = latlng2[1] * 1e6;
            lat2 = latlng2[0] * 1e6;

            l = (lat2 - 90000000) * 0.00000001234134;
            l2 = l * l;
            l4 = l2 * l2;
            coslat = 1. - l2 + l4 / 6.;

            dlat = ( lat2 - lat1 );
            dlon = ( lon2 - lon1 ) * coslat;
            distance = Math.sqrt( dlat * dlat + dlon * dlon ) * 0.110984; //  6378000. / 57.3;
            distance = (int) ( distance + 1.0 );
        }
        System.out.println((System.currentTimeMillis() - time) / 1000.);
        System.out.println(distance);

        System.out.println("Mapbox CheapRuler implementation:");
        time = System.currentTimeMillis();
        MathHelper mh = new MathHelper();
        for (int i = 0; i < N_TESTS; i++) {
            double cos = mh.cos(latlng1[0] * Math.PI / 180);
            double cos2 = 2 * cos * cos - 1;
            double cos3 = 2 * cos * cos2 - cos;
            double cos4 = 2 * cos * cos3 - cos2;
            double cos5 = 2 * cos * cos4 - cos3;
            // multipliers for converting longitude and latitude degrees into distance (http://1.usa.gov/1Wb1bv7)
            double kx = (111.41513 * cos - 0.09455 * cos3 + 0.00012 * cos5);
            double ky = (111.13209 - 0.56605 * cos2 + 0.0012 * cos4);

            dlat = (latlng1[0] - latlng2[0]) * ky;
            dlon = (latlng1[1] - latlng2[1]) * kx;
            distance = Math.sqrt(dlat * dlat + dlon * dlon);  // in km
        }
        System.out.println((System.currentTimeMillis() - time) / 1000.);
        System.out.println(distance * 1000);
    }
}

MathHelper.java

// This code is coming from
// https://github.com/Bukkit/mc-dev/blob/master/net/minecraft/server/MathHelper.java
// and is therefore under Mojang copyright.
public class MathHelper {
    private static double[] a = new double[65536];

    public static final double sin(double f) {
        return a[(int) (f * 10430.378F) & '\uffff'];
    }

    public static final double cos(double f) {
        return a[(int) (f * 10430.378F + 16384.0F) & '\uffff'];
    }

    static {
        for (int i = 0; i < 65536; ++i) {
            a[i] = Math.sin((double) i * 3.141592653589793D * 2.0D / 65536.0D);
        }
    }
}