This patch addresses two main issues: (1) There exist some non-fatal errors in some of the hash algorithms. For exmaple, in float_hash and complex_hash a certain part of the value is not included in the hash calculation. See Tim's, Guido's, and my discussion of this on python-dev in May under the title "fix float_hash and complex_hash for 64-bit *nix" (2) The hash algorithms that use pointers (e.g. func_hash, code_hash) are universally not correct on Win64 (they assume that sizeof(long) == sizeof(void*)) As well, this patch significantly cleans up the hash code. It adds the two function _Py_HashDouble and _PyHash_VoidPtr that the various hashing routine are changed to use. These help maintain the hash function invariant: (a==b) => (hash(a)==hash(b))) I have added Lib/test/test_hash.py and Lib/test/output/test_hash to test this for some cases.

--- a/Objects/classobject.c	Thu Jun 29 18:50:59 2000 +0000
+++ b/Objects/classobject.c	Thu Jun 29 19:17:04 2000 +0000
@@ -864,10 +864,7 @@
 		func = instance_getattr(inst, cmpstr);
 		if (func == NULL) {
 			PyErr_Clear();
-			outcome = (long)inst;
-			if (outcome == -1)
-				outcome = -2;
-			return outcome;
+			return _Py_HashPointer(inst);
 		}
 		PyErr_SetString(PyExc_TypeError, "unhashable instance");
 		return -1;