Fix mirror sampling in trunk. Fixes issue 135.

src/nvimage/FloatImage.cpp

@@ -21,10 +21,13 @@ namespace
 {
     static int mirror(int x, int w)
     {
+        if (w == 1) return 0;
+
         x = abs(x);
         while (x >= w) {
-            x = 2 * w - x - 2;
+            x = abs(w + w - x - 2);
         }
+
         return x;
     }
 }