tuple_hash

Author: mdboom

Objects/tupleobject.c

@@ -320,20 +320,40 @@ tuple_hash(PyObject *op)
     PyTupleObject *v = _PyTuple_CAST(op);
     Py_ssize_t len = Py_SIZE(v);
     PyObject **item = v->ob_item;
+    Py_uhash_t acc;
 
-    Py_uhash_t acc = _PyHASH_XXPRIME_5;
-    for (Py_ssize_t i = 0; i < len; i++) {
-        Py_uhash_t lane = PyObject_Hash(item[i]);
+    switch (len) {
+    case 0:
+        return _PyHASH_XXPRIME_5 ^ (_PyHASH_XXPRIME_5 ^ 3527539UL);
+
+    case 1:
+        Py_uhash_t lane = PyObject_Hash(item[0]);
         if (lane == (Py_uhash_t)-1) {
             return -1;
         }
+        acc = _PyHASH_XXPRIME_5;
         acc += lane * _PyHASH_XXPRIME_2;
         acc = _PyHASH_XXROTATE(acc);
         acc *= _PyHASH_XXPRIME_1;
-    }
+        acc += 1 ^ (_PyHASH_XXPRIME_5 ^ 3527539UL);
 
-    /* Add input length, mangled to keep the historical value of hash(()). */
-    acc += len ^ (_PyHASH_XXPRIME_5 ^ 3527539UL);
+        break;
+
+    default:
+        acc = _PyHASH_XXPRIME_5;
+        for (Py_ssize_t i = 0; i < len; i++) {
+            Py_uhash_t lane = PyObject_Hash(item[i]);
+            if (lane == (Py_uhash_t)-1) {
+                return -1;
+            }
+            acc += lane * _PyHASH_XXPRIME_2;
+            acc = _PyHASH_XXROTATE(acc);
+            acc *= _PyHASH_XXPRIME_1;
+        }
+
+        /* Add input length, mangled to keep the historical value of hash(()). */
+        acc += len ^ (_PyHASH_XXPRIME_5 ^ 3527539UL);
+    }
 
     if (acc == (Py_uhash_t)-1) {
         return 1546275796;