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gh-111389: Add PyHASH_MULTIPLIER constant #119214

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Merged
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May 21, 2024
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gh-111389: Add PyHASH_MULTIPLIER constant #119214

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6 changes: 6 additions & 0 deletions Doc/c-api/hash.rst
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Expand Up @@ -29,6 +29,12 @@ See also the :c:member:`PyTypeObject.tp_hash` member and :ref:`numeric-hash`.

.. versionadded:: 3.13

.. c:macro:: PyHASH_MULTIPLIER

Prime multiplier used in string and various other hashes.

.. versionadded:: 3.13

.. c:macro:: PyHASH_INF

The hash value returned for a positive infinity.
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5 changes: 3 additions & 2 deletions Include/cpython/pyhash.h
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Expand Up @@ -3,7 +3,7 @@
#endif

/* Prime multiplier used in string and various other hashes. */
#define _PyHASH_MULTIPLIER 1000003UL /* 0xf4243 */
#define PyHASH_MULTIPLIER 1000003UL /* 0xf4243 */

/* Parameters used for the numeric hash implementation. See notes for
_Py_HashDouble in Python/pyhash.c. Numeric hashes are based on
Expand All @@ -17,9 +17,10 @@

#define PyHASH_MODULUS (((size_t)1 << _PyHASH_BITS) - 1)
#define PyHASH_INF 314159
#define PyHASH_IMAG _PyHASH_MULTIPLIER
#define PyHASH_IMAG PyHASH_MULTIPLIER

/* Aliases kept for backward compatibility with Python 3.12 */
#define _PyHASH_MULTIPLIER PyHASH_MULTIPLIER
#define _PyHASH_BITS PyHASH_BITS
#define _PyHASH_MODULUS PyHASH_MODULUS
#define _PyHASH_INF PyHASH_INF
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/C API/2024-05-20-10-35-22.gh-issue-111389.a6axBk.rst
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@@ -0,0 +1,2 @@
Add :c:macro:`PyHASH_MULTIPLIER` constant: prime multiplier used in string
and various other hashes. Patch by Victor Stinner.
2 changes: 1 addition & 1 deletion Objects/codeobject.c
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Expand Up @@ -2020,7 +2020,7 @@ code_hash(PyCodeObject *co)
Py_uhash_t uhash = 20221211;
#define SCRAMBLE_IN(H) do { \
uhash ^= (Py_uhash_t)(H); \
uhash *= _PyHASH_MULTIPLIER; \
uhash *= PyHASH_MULTIPLIER; \
} while (0)
#define SCRAMBLE_IN_HASH(EXPR) do { \
Py_hash_t h = PyObject_Hash(EXPR); \
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2 changes: 1 addition & 1 deletion Python/optimizer.c
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Expand Up @@ -1496,7 +1496,7 @@ address_to_hash(void *ptr) {
uintptr_t addr = (uintptr_t)ptr;
for (int i = 0; i < SIZEOF_VOID_P; i++) {
uhash ^= addr & 255;
uhash *= (uint64_t)_PyHASH_MULTIPLIER;
uhash *= (uint64_t)PyHASH_MULTIPLIER;
addr >>= 8;
}
return uhash;
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4 changes: 2 additions & 2 deletions Python/pyhash.c
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Expand Up @@ -263,12 +263,12 @@ fnv(const void *src, Py_ssize_t len)
x ^= (Py_uhash_t) *p << 7;
while (blocks--) {
PY_UHASH_CPY(block.bytes, p);
x = (_PyHASH_MULTIPLIER * x) ^ block.value;
x = (PyHASH_MULTIPLIER * x) ^ block.value;
p += SIZEOF_PY_UHASH_T;
}
/* add remainder */
for (; remainder > 0; remainder--)
x = (_PyHASH_MULTIPLIER * x) ^ (Py_uhash_t) *p++;
x = (PyHASH_MULTIPLIER * x) ^ (Py_uhash_t) *p++;
x ^= (Py_uhash_t) len;
x ^= (Py_uhash_t) _Py_HashSecret.fnv.suffix;
if (x == (Py_uhash_t) -1) {
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2 changes: 1 addition & 1 deletion Python/tracemalloc.c
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Expand Up @@ -312,7 +312,7 @@ traceback_hash(traceback_t *traceback)
/* code based on tuplehash() of Objects/tupleobject.c */
Py_uhash_t x, y; /* Unsigned for defined overflow behavior. */
int len = traceback->nframe;
Py_uhash_t mult = _PyHASH_MULTIPLIER;
Py_uhash_t mult = PyHASH_MULTIPLIER;
frame_t *frame;

x = 0x345678UL;
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