-#define SHIFT_BIT (3)
-#define SHIFT_BYTE (2)
-#define SHIFT_WORD (SHIFT_BIT+SHIFT_BYTE)
-#define SHIFT_MEGABYTE (20)
-#define SHIFT_MEGAWORD (SHIFT_MEGABYTE-SHIFT_BYTE)
+#define SHIFT_BIT (3)
+#define SHIFT_BYTE (2)
+#define SHIFT_WORD (SHIFT_BIT+SHIFT_BYTE)
+#define SHIFT_MEGABYTE (20)
+#define SHIFT_MEGAWORD (SHIFT_MEGABYTE-SHIFT_BYTE)
+
+/*
+ * Using virtual memory can cause thrashing. This should be the largest
+ * number that is supported without a large amount of disk activity --
+ * that would increase the run time from hours to days or weeks!
+ */
+#define LARGE_MINIMUM (8UL) /* megabytes */
+
+/*
+ * Do not increase this number beyond the unsigned integer bit size.
+ * Due to a multiple of 4, it must be LESS than 128 (yielding 2**30 bits).
+ */
+#define LARGE_MAXIMUM (127UL) /* megabytes */