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This patch addresses two main issues: (1) There exist some non-fatal

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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.
This commit is contained in:
Fred Drake 2000-06-29 19:17:04 +00:00
parent b46696c0ed
commit 13634cf7a4
10 changed files with 126 additions and 49 deletions
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63
Objects/object.c
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@ -33,6 +33,8 @@ PERFORMANCE OF THIS SOFTWARE.
#include "Python.h"
#include "mymath.h"
/* just for trashcan: */
#include "compile.h"
#include "frameobject.h"
@ -507,6 +509,62 @@ PyObject_Compare(v, w)
return result;
}
/* Set of hash utility functions to help maintaining the invariant that
iff a==b then hash(a)==hash(b)
All the utility functions (_Py_Hash*()) return "-1" to signify an error.
*/
long
_Py_HashDouble(v)
double v;
{
/* Use frexp to get at the bits in the double.
* Since the VAX D double format has 56 mantissa bits, which is the
* most of any double format in use, each of these parts may have as
* many as (but no more than) 56 significant bits.
* So, assuming sizeof(long) >= 4, each part can be broken into two longs;
* frexp and multiplication are used to do that.
* Also, since the Cray double format has 15 exponent bits, which is the
* most of any double format in use, shifting the exponent field left by
* 15 won't overflow a long (again assuming sizeof(long) >= 4).
*/
int expo;
long hipart;
v = frexp(v, &expo);
v = v * 2147483648.0; /* 2**31 */
hipart = (long)v; /* Take the top 32 bits */
v = (v - (double)hipart) * 2147483648.0; /* Get the next 32 bits */
return hipart + (long)v + (expo << 15); /* Combine everything */
}
long
_Py_HashPointer(p)
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);
return x;
#endif
}
long
PyObject_Hash(v)
PyObject *v;
@ -514,8 +572,9 @@ PyObject_Hash(v)
PyTypeObject *tp = v->ob_type;
if (tp->tp_hash != NULL)
return (*tp->tp_hash)(v);
if (tp->tp_compare == NULL)
return (long) v; /* Use address as hash value */
if (tp->tp_compare == NULL) {
return _Py_HashPointer(v); /* Use address as hash value */
}
/* If there's a cmp but no hash defined, the object can't be hashed */
PyErr_SetString(PyExc_TypeError, "unhashable type");
return -1;