diff options
| -rw-r--r-- | Misc/NEWS | 3 | ||||
| -rw-r--r-- | Objects/object.c | 22 |
2 files changed, 10 insertions, 15 deletions
@@ -12,6 +12,9 @@ What's New in Python 3.1 alpha 0 Core and Builtins ----------------- +- Issue #5186: Reduce hash collisions for objects with no __hash__ method by + rotating the object pointer by 4 bits to the right. + - Issue #4575: Fix Py_IS_INFINITY macro to work correctly on x87 FPUs: it now forces its argument to double before testing for infinity. diff --git a/Objects/object.c b/Objects/object.c index ee18bc3..8583797 100644 --- a/Objects/object.c +++ b/Objects/object.c @@ -699,23 +699,15 @@ _Py_HashDouble(double v) long _Py_HashPointer(void *p) { -#if SIZEOF_LONG >= SIZEOF_VOID_P - return (long)p; -#else - /* convert to a Python long and hash that */ - PyObject* longobj; long x; - - if ((longobj = PyLong_FromVoidPtr(p)) == NULL) { - x = -1; - goto finally; - } - x = PyObject_Hash(longobj); - -finally: - Py_XDECREF(longobj); + size_t y = (size_t)p; + /* bottom 3 or 4 bits are likely to be 0; rotate y by 4 to avoid + excessive hash collisions for dicts and sets */ + y = (y >> 4) | (y << (8 * SIZEOF_VOID_P - 4)); + x = (long)y; + if (x == -1) + x = -2; return x; -#endif } long |