Add another guard on calculate_containing_cube_coordinate.

diff --git a/src/Grid.hs b/src/Grid.hs
index 8bf83828e9f23a97de57360ffeded92ebb92ccd2..7325d2b5b0968f5860834e21b809e9b67995dba8 100644 (file)
--- a/src/Grid.hs
+++ b/src/Grid.hs
@@ -96,6 +96,7 @@ calculate_containing_cube_coordinate g coord
     -- returns cube #1 if we would have returned cube #0 and cube #1
     -- exists.
     | coord == offset && (xsize > 0 && ysize > 0 && zsize > 0) = 1
+    | coord < offset = 0
     | otherwise = (ceiling ( (coord + offset) / cube_width )) - 1
     where
       (xsize, ysize, zsize) = dims (function_values g)