Add a comment explaining the compare-and-swap loop

lib/storage.hh

@@ -327,6 +327,13 @@ public:
             }
 
             // increase count, no checking for overflow
+            // current_tbl and new_tbl are the current and new bit packed values
+            // for the idx'th byte of the table.
+            // compare_exchange_weak will update the value of table[idx] if
+            // current_tbl is the current value (hasn't been changed by a
+            // different thread) if they differ the value actually stored
+            // in table[idx] is written to current_tbl so this is a
+            // compare-and-swap loop
             uint8_t new_count = (current_count + 1) << shift;
             uint8_t new_tbl = (current_tbl & ~mask) | (new_count & mask);
 

tests/test_countgraph.py

@@ -209,8 +209,8 @@ def test_get_raw_tables():
 
 
 def test_get_raw_tables_smallcountgraph():
-    # smallcountgraphs store individual counts packed into a byte, the raw tables
-    # probably do not give users what they expect (something that can be
+    # smallcountgraphs store individual counts packed into a byte, the raw
+    # tables probably do not give users what they expect (something that can be
     # given to numpy.frombuffer)
     ht = khmer.SmallCountgraph(20, 1e5, 4)
     assert not hasattr(ht, 'get_raw_tables')