gh-111389: expose PyHASH_INF/BITS/MODULUS/IMAG macros as public (#111418)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: 2 people

Doc/c-api/hash.rst

@@ -3,7 +3,7 @@
 PyHash API
 ----------
 
-See also the :c:member:`PyTypeObject.tp_hash` member.
+See also the :c:member:`PyTypeObject.tp_hash` member and :ref:`numeric-hash`.
 
 .. c:type:: Py_hash_t
 
@@ -17,6 +17,29 @@ See also the :c:member:`PyTypeObject.tp_hash` member.
 
    .. versionadded:: 3.2
 
+.. c:macro:: PyHASH_MODULUS
+
+   The `Mersenne prime <https://en.wikipedia.org/wiki/Mersenne_prime>`_ ``P = 2**n -1``, used for numeric hash scheme.
+
+   .. versionadded:: 3.13
+
+.. c:macro:: PyHASH_BITS
+
+   The exponent ``n`` of ``P`` in :c:macro:`PyHASH_MODULUS`.
+
+   .. versionadded:: 3.13
+
+.. c:macro:: PyHASH_INF
+
+   The hash value returned for a positive infinity.
+
+   .. versionadded:: 3.13
+
+.. c:macro:: PyHASH_IMAG
+
+   The multiplier used for the imaginary part of a complex number.
+
+   .. versionadded:: 3.13
 
 .. c:type:: PyHash_FuncDef
 

Include/cpython/pyhash.h

@@ -10,14 +10,20 @@
    reduction modulo the prime 2**_PyHASH_BITS - 1. */
 
 #if SIZEOF_VOID_P >= 8
-#  define _PyHASH_BITS 61
+#  define PyHASH_BITS 61
 #else
-#  define _PyHASH_BITS 31
+#  define PyHASH_BITS 31
 #endif
 
-#define _PyHASH_MODULUS (((size_t)1 << _PyHASH_BITS) - 1)
-#define _PyHASH_INF 314159
-#define _PyHASH_IMAG _PyHASH_MULTIPLIER
+#define PyHASH_MODULUS (((size_t)1 << _PyHASH_BITS) - 1)
+#define PyHASH_INF 314159
+#define PyHASH_IMAG _PyHASH_MULTIPLIER
+
+/* Aliases kept for backward compatibility with Python 3.12 */
+#define _PyHASH_BITS PyHASH_BITS
+#define _PyHASH_MODULUS PyHASH_MODULUS
+#define _PyHASH_INF PyHASH_INF
+#define _PyHASH_IMAG PyHASH_IMAG
 
 /* Helpers for hash functions */
 PyAPI_FUNC(Py_hash_t) _Py_HashDouble(PyObject *, double);

Misc/NEWS.d/next/C API/2023-11-15-09-24-51.gh-issue-111418.FYYetY.rst

@@ -0,0 +1,2 @@
+Add :c:macro:`PyHASH_MODULUS`, :c:macro:`PyHASH_BITS`, :c:macro:`PyHASH_INF`
+and :c:macro:`PyHASH_IMAG` C macros.  Patch by Sergey B Kirpichev.