FindHull Integer overrun about aforge

[GoogleCodeExporter]

It would be nice if you provide sample list, which reproduces the issue (you 
can attach it as a code file). "slightly less than 2E9" is a bit vague. Also 
you don't tell anything about the number of points.

Original comment by [email protected] on 2 Oct 2014 at 7:06

[GoogleCodeExporter]

1) Provide list with 4 or more x,y list points where all values are 2E9 - 1. 

2) Try: 2,000,000,000. - 1. 
Given that, we've found issues with values much more reduced... 
We're not presently dedicated to this issue-- just trying to help you. 
We've found success & failures with values @ (.5 * Int32.MaxValue). 
We're in the field running real field data and not purposed @ debugging your 
code. 

3) The number of points is ~believed not critical, but obviously you need to 
get into the process... ie, >3. 
-------

Somewhat irritated by the tongue lash, 
spending a few hours after our immediate above, 
we believe we've found the problem: 

1) 
Within AForge's 2.2.5.0 AForge.Math.DLL @ method "public List<IntPoint> 
FindHull(List<IntPoint> points)", the following source line appears to be the 
issue: 
"if ((newPoint.X - prevPoint.X) * (lastPoint.Y - newPoint.Y) - (lastPoint.X - 
newPoint.X) * (newPoint.Y - prevPoint.Y) < 0)". 

2)This line, when loaded as previously described (ie, large Int32 magnitudes), 
May throw exception: 
 "...'System.ArgumentOutOfRangeException' occurred in MSCORLIB.DLL". 

3) Further investigation shows possibility of ~ (8 * Int32.MaxValue^2). 

4) Solution, we ~think:  Change the subject line so as to process LONG values; 
ex:

//-------------------------------------------------
                // check if current point is on the left side from two last points

                //test:
                long sub1 = newPoint.X - prevPoint.X;
                long sub2 = lastPoint.Y - newPoint.Y;
                long sub3 = lastPoint.X - newPoint.X;
                long sub4 = newPoint.Y - prevPoint.Y;
                long mult1 = sub1 * sub2;
                long mult2 = sub3 * sub4;
                long diff = mult1 - mult2;
                if (diff < 0)
                    //if ((newPoint.X - prevPoint.X) * (lastPoint.Y - newPoint.Y) - (lastPoint.X - newPoint.X) * (newPoint.Y - prevPoint.Y) < 0)
                    {
                        // add the point to the hull
                        convexHullTemp.Add(newPoint);
                        // and remove it from the list of points to process
                        pointsToProcess.RemoveAt(0);

                        prevPoint = lastPoint;
                        lastPoint = newPoint;
                    }
                    else
                    {
                        // remove the last point from the hull
                        convexHullTemp.RemoveAt(convexHullTemp.Count - 1);

                        lastPoint = prevPoint;
                        prevPoint = convexHullTemp[convexHullTemp.Count - 2];
                    }
//-------------------------------------------------

That's our 2cents, Vaguely. 
:-)

If you desire converse, please eme directly at "[email protected]" .
We're working in the gulf & google connect not regularly available. 
Bests, RJF. 

Original comment by [email protected] on 2 Oct 2014 at 9:18