cpython/Include/setobject.h

/* Set object interface */

#ifndef Py_SETOBJECT_H
#define Py_SETOBJECT_H
#ifdef __cplusplus
extern "C" {
#endif


/*
There are three kinds of slots in the table:

1. Unused:  key == NULL
2. Active:  key != NULL and key != dummy
3. Dummy:   key == dummy

Note: .pop() abuses the hash field of an Unused or Dummy slot to
hold a search finger.  The hash field of Unused or Dummy slots has
no meaning otherwise.
*/

#define PySet_MINSIZE 8

typedef struct {
	long hash;      /* cached hash code for the entry key */
	PyObject *key;
} setentry;


/*
This data structure is shared by set and frozenset objects.
*/

typedef struct _setobject PySetObject;
struct _setobject {
	PyObject_HEAD

	int fill;  /* # Active + # Dummy */
	int used;  /* # Active */

	/* The table contains mask + 1 slots, and that's a power of 2.
	 * We store the mask instead of the size because the mask is more
	 * frequently needed.
	 */
	int mask;

	/* table points to smalltable for small tables, else to
	 * additional malloc'ed memory.  table is never NULL!  This rule
	 * saves repeated runtime null-tests.
	 */
	setentry *table;
	setentry *(*lookup)(PySetObject *so, PyObject *key, long hash);
	setentry smalltable[PySet_MINSIZE];

	long hash;		/* only used by frozenset objects */
	PyObject *weakreflist;	/* List of weak references */
};

PyAPI_DATA(PyTypeObject) PySet_Type;
PyAPI_DATA(PyTypeObject) PyFrozenSet_Type;

/* Invariants for frozensets only:
 *     data is immutable.
 *     hash is the hash of the frozenset or -1 if not computed yet.
 */

#define PyFrozenSet_CheckExact(ob) ((ob)->ob_type == &PyFrozenSet_Type)
#define PyAnySet_Check(ob) \
	((ob)->ob_type == &PySet_Type || (ob)->ob_type == &PyFrozenSet_Type || \
	  PyType_IsSubtype((ob)->ob_type, &PySet_Type) || \
	  PyType_IsSubtype((ob)->ob_type, &PyFrozenSet_Type))

#ifdef __cplusplus
}
#endif
#endif /* !Py_SETOBJECT_H */