Issue #8188: Introduce a new scheme for computing hashes of numbers

(instances of int, float, complex, decimal.Decimal and
fractions.Fraction) that makes it easy to maintain the invariant that
hash(x) == hash(y) whenever x and y have equal value.

1 files changed, 56 insertions, 0 deletions

diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 77b120f..4c87d54 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -570,6 +570,57 @@ sys_setrecursionlimit(PyObject *self, PyObject *args)
     return Py_None;
 }
 
+static PyTypeObject Hash_InfoType;
+
+PyDoc_STRVAR(hash_info_doc,
+"hash_info\n\
+\n\
+A struct sequence providing parameters used for computing\n\
+numeric hashes.  The attributes are read only.");
+
+static PyStructSequence_Field hash_info_fields[] = {
+    {"width", "width of the type used for hashing, in bits"},
+    {"modulus", "prime number giving the modulus on which the hash "
+                "function is based"},
+    {"inf", "value to be used for hash of a positive infinity"},
+    {"nan", "value to be used for hash of a nan"},
+    {"imag", "multiplier used for the imaginary part of a complex number"},
+    {NULL, NULL}
+};
+
+static PyStructSequence_Desc hash_info_desc = {
+    "sys.hash_info",
+    hash_info_doc,
+    hash_info_fields,
+    5,
+};
+
+PyObject *
+get_hash_info(void)
+{
+    PyObject *hash_info;
+    int field = 0;
+    hash_info = PyStructSequence_New(&Hash_InfoType);
+    if (hash_info == NULL)
+        return NULL;
+    PyStructSequence_SET_ITEM(hash_info, field++,
+                              PyLong_FromLong(8*sizeof(long)));
+    PyStructSequence_SET_ITEM(hash_info, field++,
+                              PyLong_FromLong(_PyHASH_MODULUS));
+    PyStructSequence_SET_ITEM(hash_info, field++,
+                              PyLong_FromLong(_PyHASH_INF));
+    PyStructSequence_SET_ITEM(hash_info, field++,
+                              PyLong_FromLong(_PyHASH_NAN));
+    PyStructSequence_SET_ITEM(hash_info, field++,
+                              PyLong_FromLong(_PyHASH_IMAG));
+    if (PyErr_Occurred()) {
+        Py_CLEAR(hash_info);
+        return NULL;
+    }
+    return hash_info;
+}
+
+
 PyDoc_STRVAR(setrecursionlimit_doc,
 "setrecursionlimit(n)\n\
 \n\
@@ -1482,6 +1533,11 @@ _PySys_Init(void)
                         PyFloat_GetInfo());
     SET_SYS_FROM_STRING("int_info",
                         PyLong_GetInfo());
+    /* initialize hash_info */
+    if (Hash_InfoType.tp_name == 0)
+        PyStructSequence_InitType(&Hash_InfoType, &hash_info_desc);
+    SET_SYS_FROM_STRING("hash_info",
+                        get_hash_info());
     SET_SYS_FROM_STRING("maxunicode",
                         PyLong_FromLong(PyUnicode_GetMax()));
     SET_SYS_FROM_STRING("builtin_module_names",