Name: yyT116575 Date: 05/21/2001


java version "1.3.1"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.1-b24)
Java HotSpot(TM) Server VM (build 1.3.1-b24, mixed mode)

There is a sample code computing an estimation of orthodromic distance between
two geographic points. Note that this computation involve 8 sin/cos/sqrt
operations and only one acos operation.

public class Ellipsoid {
  private double a = 6378137.0;
  private double b = 6378137.0*(1-1/298.257223563); // WGS 1984

  public double distance(double x1, double y1, double x2, double y2) {
    y1 = Math.toRadians(y1);
    y2 = Math.toRadians(y2);
    final double y = 0.5*(y1+y2);
    final double dx = Math.toRadians(Math.abs(x2-x1) % 360);
    final double ang = Math.sin(y1)*Math.sin(y2)
        + Math.cos(y1)*Math.cos(y2)*Math.cos(dx);
    final double ier = hypot(Math.sin(y)/a , Math.cos(y)/b);
    return Math.acos(ang)/ier;
  }

  private static double hypot(double x, double y) {
    return Math.sqrt(x*x + y*y);
  }

  public static void main(String[] args) {
    double sum=0;
    final Ellipsoid ell=new Ellipsoid();
    for (int i=0; i<20000000; i++) {
      double x1 = Math.random()*10+20; // 20 to 30?E
      double x2 = Math.random()*10+20; // 20 to 30?E
      double y1 = Math.random()*10+40; // 40 to 50?N
      double y2 = Math.random()*10+40; // 40 to 50?N
      double dx = ell.distance(x1,y1 , x2,y2);
      sum += dx;
    }
    System.out.println(sum/20000000);
  }
}



There is a portion of the profiling output (code was run with -server and
-Xprof options).

     Compiled + native Method
  8.9% 2746 + 0 Ellipsoid.main
  6.6% 2051 + 0 Ellipsoid.distance
  0.0% 3 + 0 adapters
 15.6% 4800 + 0 Total compiled

         Stub + native Method
 36.0% 81 + 11032 java.lang.StrictMath.acos
 36.0% 81 + 11032 Total stub

  Thread-local ticks:
  0.0% 5 Class loader
 48.1% 14839 Unknown: running frame
  0.1% 21 Unknown: thread_state



The JVM spend 36% of its time into the "acos" function, which is only about 12%
of all trigonometric functions. In my real program (which involve I/O,
searching, sorting and distances computation), this only "acos" call eat 32% of
my CPU time. Since my computation take a few hours, I would appreciate hardware
acceleration if it is possible.
(Review ID: 124713)
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