/* There are three kinds of entries in the table:
-1. Unused: key == NULL
-2. Active: key != NULL and key != dummy
-3. Dummy: key == dummy
+1. Unused: key == NULL and hash == 0
+2. Dummy: key == dummy and hash == -1
+3. Active: key != NULL and key != dummy and hash != -1
-The hash field of Unused slots have no meaning.
-The hash field of Dummny slots are set to -1
+The hash field of Unused slots is always zero.
+
+The hash field of Dummy slots are set to -1
meaning that dummy entries can be detected by
either entry->key==dummy or by entry->hash==-1.
*/