Prevent integer overflow when checking stencil position

git-svn-id: http://svn.aei.mpg.de/numrel/AEIThorns/AEILocalInterp/trunk@27 0f49ee68-0e4f-0410-9b9c-b2c123ded7ef

1 files changed, 4 insertions, 2 deletions

diff --git a/src/molecule_posn.c b/src/molecule_posn.c
index 1eb4eeb..efa04d9 100644
--- a/src/molecule_posn.c
+++ b/src/molecule_posn.c
@@ -216,12 +216,14 @@ fp fp_i_center = IS_EVEN(molecule_size)	/* ... as a floating-point number */
 int int_i_center = (int) fp_i_center;	/* ... as an integer */
 
 /* then clamp the molecule at the grid boundaries */
-if (int_i_center - mr_minus < grid_i_min)
+if (int_i_center < grid_i_min) int_i_center = grid_i_min;
+if (int_i_center < grid_i_min + mr_minus)
    then {
 	int_i_center = grid_i_min + mr_minus;
 	fp_i_center = (fp) int_i_center;
 	}
-if (int_i_center + mr_plus > grid_i_max)
+if (int_i_center > grid_i_max) int_i_center = grid_i_max;
+if (int_i_center > grid_i_max - mr_plus)
    then {
 	int_i_center = grid_i_max - mr_plus;
 	fp_i_center = (fp) int_i_center;