[Python-checkins] cpython: Move the active entry multiplication to later in the hash calculation

[raymond.hettinger]

https://hg.python.org/cpython/rev/2c124e30a324
changeset:   97315:2c124e30a324
user:        Raymond Hettinger <python at rcn.com>
date:        Fri Aug 07 00:43:39 2015 -0700
summary:
  Move the active entry multiplication to later in the hash calculation

files:
  Objects/setobject.c |  8 ++++----
  1 files changed, 4 insertions(+), 4 deletions(-)


diff --git a/Objects/setobject.c b/Objects/setobject.c
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -760,15 +760,12 @@
 frozenset_hash(PyObject *self)
 {
     PySetObject *so = (PySetObject *)self;
-    Py_uhash_t hash = 1927868237UL;
+    Py_uhash_t hash = 0;
     setentry *entry;
 
     if (so->hash != -1)
         return so->hash;
 
-    /* Initial dispersion based on the number of active entries */
-    hash *= (Py_uhash_t)PySet_GET_SIZE(self) + 1;
-
     /* Xor-in shuffled bits from every entry's hash field because xor is
        commutative and a frozenset hash should be independent of order.
 
@@ -790,6 +787,9 @@
     if ((so->fill - so->used) & 1)
         hash ^= _shuffle_bits(-1);
 
+    /* Factor in the number of active entries */
+    hash ^= ((Py_uhash_t)PySet_GET_SIZE(self) + 1) * 1927868237UL;
+
     /* Disperse patterns arising in nested frozensets */
     hash = hash * 69069U + 907133923UL;
 

-- 
Repository URL: https://hg.python.org/cpython