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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.
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
Include/object.h
View File

@ -293,6 +293,10 @@ extern DL_IMPORT(void) Py_ReprLeave Py_PROTO((PyObject *));
/* tstate dict key for PyObject_Compare helper */
extern PyObject *_PyCompareState_Key;
/* Helpers for hash functions */
extern DL_IMPORT(long) _Py_HashDouble Py_PROTO((double));
extern DL_IMPORT(long) _Py_HashPointer Py_PROTO((void*));
/* Flag bits for printing: */
#define Py_PRINT_RAW 1 /* No string quotes etc. */

1
Lib/test/output/test_hash Normal file
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@ -0,0 +1 @@
test_hash

26
Lib/test/test_hash.py Normal file
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@ -0,0 +1,26 @@
# test the invariant that
# iff a==b then hash(a)==hash(b)
#
import test_support
def same_hash(*objlist):
# hash each object given an raise TestFailed if
# the hash values are not all the same
hashed = map(hash, objlist)
for h in hashed[1:]:
if h != hashed[0]:
raise TestFailed, "hashed values differ: %s" % `objlist`
same_hash(1, 1L, 1.0, 1.0+0.0j)
same_hash(int(1), long(1), float(1), complex(1))
same_hash(long(1.23e300), float(1.23e300))
same_hash(float(0.5), complex(0.5, 0.0))

5
Objects/classobject.c
View File

@ -864,10 +864,7 @@ instance_hash(inst)
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;

37
Objects/complexobject.c
View File

@ -285,8 +285,7 @@ complex_hash(v)
PyComplexObject *v;
{
double intpart, fractpart;
int expo;
long hipart, x;
long x;
/* This is designed so that Python numbers with the same
value hash to the same value, otherwise comparisons
of mapping keys will turn out weird */
@ -302,7 +301,7 @@ complex_hash(v)
#endif
if (fractpart == 0.0 && v->cval.imag == 0.0) {
if (intpart > 0x7fffffffL || -intpart > 0x7fffffffL) {
if (intpart > LONG_MAX || -intpart > LONG_MAX) {
/* Convert to long int and use its hash... */
PyObject *w = PyLong_FromDouble(v->cval.real);
if (w == NULL)
@ -314,36 +313,18 @@ complex_hash(v)
x = (long)intpart;
}
else {
fractpart = frexp(fractpart, &expo);
fractpart = fractpart * 2147483648.0; /* 2**31 */
hipart = (long)fractpart; /* Take the top 32 bits */
fractpart = (fractpart - (double)hipart) * 2147483648.0;
/* Get the next 32 bits */
x = hipart + (long)fractpart + (long)intpart + (expo << 15);
/* Combine everything */
x = _Py_HashDouble(v->cval.real);
if (x == -1)
return -1;
if (v->cval.imag != 0.0) { /* Hash the imaginary part */
/* XXX Note that this hashes complex(x, y)
to the same value as complex(y, x).
Still better than it used to be :-) */
#ifdef MPW
{
extended e;
fractpart = modf(v->cval.imag, &e);
intpart = e;
}
#else
fractpart = modf(v->cval.imag, &intpart);
#endif
fractpart = frexp(fractpart, &expo);
fractpart = fractpart * 2147483648.0; /* 2**31 */
hipart = (long)fractpart; /* Take the top 32 bits */
fractpart =
(fractpart - (double)hipart) * 2147483648.0;
/* Get the next 32 bits */
x ^= hipart + (long)fractpart +
(long)intpart + (expo << 15);
/* Combine everything */
long y = _Py_HashDouble(v->cval.imag);
if (y == -1)
return -1;
x += y;
}
}
if (x == -1)

21
Objects/floatobject.c
View File

@ -59,7 +59,13 @@ PERFORMANCE OF THIS SOFTWARE.
#endif
#ifndef LONG_MAX
#if SIZEOF_LONG == 4
#define LONG_MAX 0X7FFFFFFFL
#elif SIZEOF_LONG == 8
#define LONG_MAX 0X7FFFFFFFFFFFFFFFL
#else
#error "could not set LONG_MAX"
#endif
#endif
#ifndef LONG_MIN
@ -357,12 +363,12 @@ float_compare(v, w)
return (i < j) ? -1 : (i > j) ? 1 : 0;
}
static long
float_hash(v)
PyFloatObject *v;
{
double intpart, fractpart;
int expo;
long x;
/* This is designed so that Python numbers with the same
value hash to the same value, otherwise comparisons
@ -379,7 +385,7 @@ float_hash(v)
#endif
if (fractpart == 0.0) {
if (intpart > 0x7fffffffL || -intpart > 0x7fffffffL) {
if (intpart > LONG_MAX || -intpart > LONG_MAX) {
/* Convert to long int and use its hash... */
PyObject *w = PyLong_FromDouble(v->ob_fval);
if (w == NULL)
@ -393,14 +399,9 @@ float_hash(v)
else {
/* Note -- if you change this code, also change the copy
in complexobject.c */
long hipart;
fractpart = frexp(fractpart, &expo);
fractpart = fractpart * 2147483648.0; /* 2**31 */
hipart = (long)fractpart; /* Take the top 32 bits */
fractpart = (fractpart - (double)hipart) * 2147483648.0;
/* Get the next 32 bits */
x = hipart + (long)fractpart + (long)intpart + (expo << 15);
/* Combine everything */
x = _Py_HashDouble(v->ob_fval);
if (x == -1)
return -1;
}
if (x == -1)
x = -2;

6
Objects/funcobject.c
View File

@ -231,10 +231,12 @@ static long
func_hash(f)
PyFunctionObject *f;
{
long h;
long h,x;
h = PyObject_Hash(f->func_code);
if (h == -1) return h;
h = h ^ (long)f->func_globals;
x = _Py_HashPointer(f->func_globals);
if (x == -1) return x;
h ^= x;
if (h == -1) h = -2;
return h;
}

10
Objects/methodobject.c
View File

@ -172,7 +172,7 @@ static long
meth_hash(a)
PyCFunctionObject *a;
{
long x;
long x,y;
if (a->m_self == NULL)
x = 0;
else {
@ -180,7 +180,13 @@ meth_hash(a)
if (x == -1)
return -1;
}
return x ^ (long) a->m_ml->ml_meth;
y = _Py_HashPointer(a->m_ml->ml_meth);
if (y == -1)
return -1;
x ^= y;
if (x == -1)
x = -2;
return x;
}
PyTypeObject PyCFunction_Type = {

63
Objects/object.c
View File

@ -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;

2
PC/_winreg.c
View File

@ -423,7 +423,7 @@ PyHKEY_hashFunc(PyObject *ob)
/* Just use the address.
XXX - should we use the handle value?
*/
return (long)ob;
return _Py_HashPointer(ob);
}