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Commit ffbdae1

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vstinnervstinner
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gh-111545: Add Py_HashPointer() function
* Implement _Py_HashPointerRaw() as a static inline function. * Add Py_HashPointer() tests to test_capi.test_hash. * Keep _Py_HashPointer() function as an alias to Py_HashPointer().
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‎Doc/c-api/hash.rst

Copy file name to clipboardExpand all lines: Doc/c-api/hash.rst
+9Lines changed: 9 additions & 0 deletions
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@@ -46,3 +46,12 @@ See also the :c:member:`PyTypeObject.tp_hash` member.
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Get the hash function definition.
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.. versionadded:: 3.4
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.. c:function:: Py_hash_t Py_HashPointer(const void *ptr)
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Hash a pointer.
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The function cannot fail: it cannot return ``-1``.
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.. versionadded:: 3.13

‎Doc/whatsnew/3.13.rst

Copy file name to clipboardExpand all lines: Doc/whatsnew/3.13.rst
+3Lines changed: 3 additions & 0 deletions
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@@ -1230,6 +1230,9 @@ New Features
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:exc:`KeyError` if the key missing.
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(Contributed by Stefan Behnel and Victor Stinner in :gh:`111262`.)
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* Add :c:func:`Py_HashPointer` function to hash a pointer.
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(Contributed by Victor Stinner in :gh:`111545`.)
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Porting to Python 3.13
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----------------------

‎Include/cpython/pyhash.h

Copy file name to clipboardExpand all lines: Include/cpython/pyhash.h
+2Lines changed: 2 additions & 0 deletions
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@@ -33,3 +33,5 @@ typedef struct {
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} PyHash_FuncDef;
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PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
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PyAPI_FUNC(Py_hash_t) Py_HashPointer(const void *ptr);

‎Include/internal/pycore_pyhash.h

Copy file name to clipboardExpand all lines: Include/internal/pycore_pyhash.h
+18-2Lines changed: 18 additions & 2 deletions
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@@ -5,8 +5,24 @@
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# error "this header requires Py_BUILD_CORE define"
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#endif
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// Similar to _Py_HashPointer(), but don't replace -1 with -2
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extern Py_hash_t _Py_HashPointerRaw(const void*);
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// Similar to Py_HashPointer(), but don't return -1 with -2.
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static inline Py_hash_t
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_Py_HashPointerRaw(const void *ptr)
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{
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uintptr_t x = (uintptr_t)ptr;
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Py_BUILD_ASSERT(sizeof(x) == sizeof(ptr));
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// Bottom 3 or 4 bits are likely to be 0; rotate x by 4 to the right
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// to avoid excessive hash collisions for dicts and sets.
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x = (x >> 4) | (x << (8 * SIZEOF_UINTPTR_T - 4));
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Py_BUILD_ASSERT(sizeof(x) == sizeof(Py_hash_t));
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return (Py_hash_t)x;
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}
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// Kept for backward compatibility
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#define _Py_HashPointer Py_HashPointer
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// Export for '_datetime' shared extension
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PyAPI_FUNC(Py_hash_t) _Py_HashBytes(const void*, Py_ssize_t);

‎Lib/test/test_capi/test_hash.py

Copy file name to clipboardExpand all lines: Lib/test/test_capi/test_hash.py
+47-1Lines changed: 47 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4,7 +4,8 @@
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_testcapi = import_helper.import_module('_testcapi')
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SIZEOF_PY_HASH_T = _testcapi.SIZEOF_VOID_P
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SIZEOF_VOID_P = _testcapi.SIZEOF_VOID_P
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SIZEOF_PY_HASH_T = SIZEOF_VOID_P
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class CAPITest(unittest.TestCase):
@@ -31,3 +32,48 @@ def test_hash_getfuncdef(self):
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self.assertEqual(func_def.name, hash_info.algorithm)
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self.assertEqual(func_def.hash_bits, hash_info.hash_bits)
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self.assertEqual(func_def.seed_bits, hash_info.seed_bits)
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def test_hash_pointer(self):
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# Test Py_HashPointer()
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hash_pointer = _testcapi.hash_pointer
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UHASH_T_MASK = ((2 ** (8 * SIZEOF_PY_HASH_T)) - 1)
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HASH_T_MAX = (2 ** (8 * SIZEOF_PY_HASH_T - 1) - 1)
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def python_hash_pointer(x):
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# Py_HashPointer() rotates the pointer bits by 4 bits to the right
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x = (x >> 4) | ((x & 15) << (8 * SIZEOF_VOID_P - 4))
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# Convert unsigned uintptr_t (Py_uhash_t) to signed Py_hash_t
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if HASH_T_MAX < x:
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x = (~x) + 1
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x &= UHASH_T_MASK
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x = (~x) + 1
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return x
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if SIZEOF_VOID_P == 8:
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values = (
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0xABCDEF1234567890,
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0x1234567890ABCDEF,
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0xFEE4ABEDD1CECA5E,
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)
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else:
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values = (
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0x12345678,
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0x1234ABCD,
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0xDEADCAFE,
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)
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for value in values:
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expected = python_hash_pointer(value)
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with self.subTest(value=value):
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self.assertEqual(hash_pointer(value), expected,
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f"hash_pointer({value:x}) = "
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f"{hash_pointer(value):x} != {expected:x}")
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# Py_HashPointer(NULL) returns 0
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self.assertEqual(hash_pointer(0), 0)
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# Py_HashPointer((void*)(uintptr_t)-1) doesn't return -1 but -2
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VOID_P_MAX = -1 & (2 ** (8 * SIZEOF_VOID_P) - 1)
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self.assertEqual(hash_pointer(VOID_P_MAX), -2)

‎Misc/NEWS.d/next/C API/2023-11-15-01-26-59.gh-issue-111545.iAoFtA.rst

Copy file name to clipboard
+2Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
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Add :c:func:`Py_HashPointer` function to hash a pointer. Patch by Victor
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Stinner.

‎Modules/_testcapi/hash.c

Copy file name to clipboardExpand all lines: Modules/_testcapi/hash.c
+16Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -44,8 +44,24 @@ hash_getfuncdef(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
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return result;
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}
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static PyObject *
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hash_pointer(PyObject *Py_UNUSED(module), PyObject *arg)
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{
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void *ptr = PyLong_AsVoidPtr(arg);
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if (ptr == NULL && PyErr_Occurred()) {
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return NULL;
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}
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Py_hash_t hash = Py_HashPointer(ptr);
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Py_BUILD_ASSERT(sizeof(long long) >= sizeof(hash));
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return PyLong_FromLongLong(hash);
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}
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static PyMethodDef test_methods[] = {
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{"hash_getfuncdef", hash_getfuncdef, METH_NOARGS},
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{"hash_pointer", hash_pointer, METH_O},
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{NULL},
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};
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‎Python/hashtable.c

Copy file name to clipboardExpand all lines: Python/hashtable.c
+1-1Lines changed: 1 addition & 1 deletion
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@@ -45,7 +45,7 @@
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*/
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#include "Python.h"
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#include "pycore_hashtable.h"
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#include "pycore_hashtable.h" // export _Py_hashtable_new()
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#include "pycore_pyhash.h" // _Py_HashPointerRaw()
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#define HASHTABLE_MIN_SIZE 16

‎Python/pyhash.c

Copy file name to clipboardExpand all lines: Python/pyhash.c
+5-17Lines changed: 5 additions & 17 deletions
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@@ -83,8 +83,6 @@ static Py_ssize_t hashstats[Py_HASH_STATS_MAX + 1] = {0};
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*/
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Py_hash_t _Py_HashPointer(const void *);
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Py_hash_t
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_Py_HashDouble(PyObject *inst, double v)
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{
@@ -132,23 +130,13 @@ _Py_HashDouble(PyObject *inst, double v)
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}
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Py_hash_t
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_Py_HashPointerRaw(const void *p)
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{
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size_t y = (size_t)p;
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/* bottom 3 or 4 bits are likely to be 0; rotate y by 4 to avoid
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excessive hash collisions for dicts and sets */
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y = (y >> 4) | (y << (8 * SIZEOF_VOID_P - 4));
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return (Py_hash_t)y;
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}
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Py_hash_t
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_Py_HashPointer(const void *p)
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Py_HashPointer(const void *ptr)
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{
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Py_hash_t x = _Py_HashPointerRaw(p);
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if (x == -1) {
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x = -2;
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Py_hash_t hash = _Py_HashPointerRaw(ptr);
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if (hash == -1) {
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hash = -2;
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}
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return x;
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return hash;
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}
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Py_hash_t

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