effectivearea: force qsort to always return the same ordering when comparing identica...

git-svn-id: http://svn.osgeo.org/postgis/trunk@13423 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/liblwgeom/effectivearea.c b/liblwgeom/effectivearea.c
index b89fd2cb3bdef72011c3d7695491bdbe1939f6a7..ddcd19cbb3697b94625156f3441f84228cc79bed 100644 (file)
--- a/liblwgeom/effectivearea.c
+++ b/liblwgeom/effectivearea.c
@@ -90,10 +90,15 @@ We create the minheap by ordering the minheap array by the areas in the areanode
 */
 static int cmpfunc (const void * a, const void * b)
 {
-//     LWDEBUG(2, "cmpfunc entered");
        double v1 =  (*(areanode**)a)->area;
        double v2 = (*(areanode**)b)->area;
-       return  (v1>v2 ) ? 1 : -1;
+       /*qsort gives unpredictable results when comaping identical values. 
+       If two values is the same we force returning the last point in hte point array.
+       That way we get the same ordering on diffreent machines and pllatforms*/
+       if (v1==v2)
+               return (*(areanode**)a)-(*(areanode**)b);
+       else
+               return  (v1>v2 ) ? 1 : -1;
 }
 
 
@@ -246,6 +251,7 @@ static void tune_areas(EFFECTIVE_AREAS *ea, int avoid_collaps, int set_area, dou
        for (i=0;i<npoints;i++)
        {
                 ((areanode*) tree.key_array[i])->treeindex=i;
+               LWDEBUGF(4,"Check ordering qsort gives, area=%lf and belong to point %d",((areanode*) tree.key_array[i])->area, tree.key_array[i]-ea->initial_arealist);
        }
        /*Ok, now we have a minHeap, just need to keep it*/