Add commentary about the hash function

link-grammar/connectors.h

@@ -313,10 +313,25 @@ typedef uint32_t connector_hash_t;
 
 static inline connector_hash_t connector_hash(const Connector *c)
 {
+	// The use of (c->desc->lc_mask & 1) during hashing is important;
+	// See pull req #1487 for details. This raises other questions
+	// about hashing. Two forms are attempted below. They appear to
+	// be equivalent, in terms of measured elapsed-time performance.
+	// (I did not look at the quality of the distribution.)
+	// The second form uses some mixing bitshifts:
+	// 266281 == sum of 1 8 32 4096 (256*1024) It is a prime number
+	// 524429 == sum of 1 4 8 128 (512*1024) and it is a prime number
+#ifdef SIMPLE_HASH
 	return c->desc->uc_num +
 		(c->multi << 19) +
 		(((connector_hash_t)c->desc->lc_mask & 1) << 20) +
 		(connector_hash_t)c->desc->lc_letters;
+#else
+	return c->desc->uc_num +
+		c->multi * 266281 +
+		(((connector_hash_t)c->desc->lc_mask & 1) * 524429) +
+		((connector_hash_t)c->desc->lc_letters) * 101;
+#endif
 }
 
 /**