Skip to content

Commit

Permalink
gh-111545: Add PyHash_Double() function
Browse files Browse the repository at this point in the history
* Add again the private _PyHASH_NAN constant.
* Add tests: Modules/_testcapi/hash.c and
  Lib/test/test_capi/test_hash.py.
  • Loading branch information
vstinner committed Nov 27, 2023
1 parent 7ac49e7 commit ae3843d
Show file tree
Hide file tree
Showing 9 changed files with 134 additions and 9 deletions.
29 changes: 29 additions & 0 deletions Doc/c-api/hash.rst
Original file line number Diff line number Diff line change
Expand Up @@ -5,12 +5,16 @@ PyHash API

See also the :c:member:`PyTypeObject.tp_hash` member.

Types
^^^^^

.. c:type:: Py_hash_t
Hash value type: signed integer.

.. versionadded:: 3.2


.. c:type:: Py_uhash_t
Hash value type: unsigned integer.
Expand Down Expand Up @@ -41,8 +45,33 @@ See also the :c:member:`PyTypeObject.tp_hash` member.
.. versionadded:: 3.4


Functions
^^^^^^^^^

.. c:function:: int PyHash_Double(double value, Py_hash_t *result)
Hash a C double number.
* Set *\*result* to the hash and return ``1`` if *value* is finite or is
infinity.
* Set *\*result* to :data:`sys.hash_info.nan <sys.hash_info>` (``0``) and
return ``0`` if *value* is not-a-number (NaN).
*result* must not be ``NULL``.
.. note::
Only rely on the function return value to distinguish the "not-a-number"
case. *\*result* can be ``0`` if *value* is finite. For example,
``PyHash_Double(0.0, &result)`` sets *\*result* to 0.
.. versionadded:: 3.13
.. c:function:: PyHash_FuncDef* PyHash_GetFuncDef(void)
Get the hash function definition.
.. seealso::
:pep:`456` "Secure and interchangeable hash algorithm".
.. versionadded:: 3.4
8 changes: 7 additions & 1 deletion Doc/library/sys.rst
Original file line number Diff line number Diff line change
Expand Up @@ -1034,7 +1034,13 @@ always available.

.. attribute:: hash_info.nan

(This attribute is no longer used)
The hash value returned for not-a-number (NaN).

This hash value is only used by the :c:func:`PyHash_Double` C function if
the argument is not-a-number (NaN).

.. versionchanged:: 3.10
This hash value is no longer used to hash numbers in Python.

.. attribute:: hash_info.imag

Expand Down
3 changes: 3 additions & 0 deletions Doc/whatsnew/3.13.rst
Original file line number Diff line number Diff line change
Expand Up @@ -1196,6 +1196,9 @@ New Features
:exc:`KeyError` if the key missing.
(Contributed by Stefan Behnel and Victor Stinner in :gh:`111262`.)

* Add :c:func:`PyHash_Double` function to hash a C double number.
(Contributed by Victor Stinner in :gh:`111545`.)


Porting to Python 3.13
----------------------
Expand Down
3 changes: 3 additions & 0 deletions Include/cpython/pyhash.h
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@

#define _PyHASH_MODULUS (((size_t)1 << _PyHASH_BITS) - 1)
#define _PyHASH_INF 314159
#define _PyHASH_NAN 0
#define _PyHASH_IMAG _PyHASH_MULTIPLIER

/* Helpers for hash functions */
Expand All @@ -33,3 +34,5 @@ typedef struct {
} PyHash_FuncDef;

PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);

PyAPI_FUNC(int) PyHash_Double(double value, Py_hash_t *result);
44 changes: 44 additions & 0 deletions Lib/test/test_capi/test_hash.py
Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
import math
import sys
import unittest
from test.support import import_helper
Expand Down Expand Up @@ -31,3 +32,46 @@ def test_hash_getfuncdef(self):
self.assertEqual(func_def.name, hash_info.algorithm)
self.assertEqual(func_def.hash_bits, hash_info.hash_bits)
self.assertEqual(func_def.seed_bits, hash_info.seed_bits)

def test_hash_double(self):
# Test PyHash_Double()
hash_double = _testcapi.hash_double

def check_number(value, expected):
self.assertEqual(hash_double(value), (1, expected))

# test some integers
integers = [
*range(1, 30),
2**30 - 1,
2 ** 233,
int(sys.float_info.max),
]
for x in integers:
with self.subTest(x=x):
check_number(float(x), hash(x))
check_number(float(-x), hash(-x))

# test positive and negative zeros
check_number(float(0.0), 0)
check_number(float(-0.0), 0)

# test +inf and -inf
inf = float("inf")
check_number(inf, sys.hash_info.inf)
check_number(-inf, -sys.hash_info.inf)

# special float values: compare with Python hash() function
special_values = (
math.nextafter(0.0, 1.0), # smallest positive subnormal number
sys.float_info.min, # smallest positive normal number
sys.float_info.epsilon,
sys.float_info.max, # largest positive finite number
)
for x in special_values:
with self.subTest(x=x):
check_number(x, hash(x))
check_number(-x, hash(-x))

# test not-a-number (NaN)
self.assertEqual(hash_double(float('nan')), (0, sys.hash_info.nan))
Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Add :c:func:`PyHash_Double` function to hash a C double number. Patch by
Victor Stinner.
20 changes: 20 additions & 0 deletions Modules/_testcapi/hash.c
Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
#include "parts.h"
#include "util.h"


static PyObject *
hash_getfuncdef(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
{
Expand Down Expand Up @@ -44,8 +45,27 @@ hash_getfuncdef(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
return result;
}


static PyObject *
hash_double(PyObject *Py_UNUSED(module), PyObject *args)
{
double value;
if (!PyArg_ParseTuple(args, "d", &value)) {
return NULL;
}

Py_hash_t hash;
int res = PyHash_Double(value, &hash);
assert(hash != -1);

Py_BUILD_ASSERT(sizeof(long long) >= sizeof(hash));
return Py_BuildValue("iN", res, PyLong_FromLongLong(hash));
}


static PyMethodDef test_methods[] = {
{"hash_getfuncdef", hash_getfuncdef, METH_NOARGS},
{"hash_double", hash_double, METH_VARARGS},
{NULL},
};

Expand Down
32 changes: 25 additions & 7 deletions Python/pyhash.c
Original file line number Diff line number Diff line change
Expand Up @@ -85,18 +85,23 @@ static Py_ssize_t hashstats[Py_HASH_STATS_MAX + 1] = {0};

Py_hash_t _Py_HashPointer(const void *);

Py_hash_t
_Py_HashDouble(PyObject *inst, double v)
int
PyHash_Double(double v, Py_hash_t *result)
{
int e, sign;
double m;
Py_uhash_t x, y;

if (!Py_IS_FINITE(v)) {
if (Py_IS_INFINITY(v))
return v > 0 ? _PyHASH_INF : -_PyHASH_INF;
else
return _Py_HashPointer(inst);
if (Py_IS_INFINITY(v)) {
*result = (v > 0 ? _PyHASH_INF : -_PyHASH_INF);
return 1;
}
else {
assert(Py_IS_NAN(v));
*result = _PyHASH_NAN;
return 0;
}
}

m = frexp(v, &e);
Expand Down Expand Up @@ -128,7 +133,20 @@ _Py_HashDouble(PyObject *inst, double v)
x = x * sign;
if (x == (Py_uhash_t)-1)
x = (Py_uhash_t)-2;
return (Py_hash_t)x;
*result = (Py_hash_t)x;
return 1;
}

Py_hash_t
_Py_HashDouble(PyObject *obj, double v)
{
assert(obj != NULL);

Py_hash_t hash;
if (PyHash_Double(v, &hash) == 0) {
hash = _Py_HashPointer(obj);
}
return hash;
}

Py_hash_t
Expand Down
2 changes: 1 addition & 1 deletion Python/sysmodule.c
Original file line number Diff line number Diff line change
Expand Up @@ -1497,7 +1497,7 @@ get_hash_info(PyThreadState *tstate)
PyStructSequence_SET_ITEM(hash_info, field++,
PyLong_FromLong(_PyHASH_INF));
PyStructSequence_SET_ITEM(hash_info, field++,
PyLong_FromLong(0)); // This is no longer used
PyLong_FromLong(_PyHASH_NAN));
PyStructSequence_SET_ITEM(hash_info, field++,
PyLong_FromLong(_PyHASH_IMAG));
PyStructSequence_SET_ITEM(hash_info, field++,
Expand Down

0 comments on commit ae3843d

Please sign in to comment.