String interning.

Objects/dictobject.c

@@ -87,6 +87,9 @@ typedef struct {
 	int ma_fill;
 	int ma_used;
 	int ma_size;
+#ifdef INTERN_STRINGS
+	int ma_fast;
+#endif
 	mappingentry *ma_table;
 } mappingobject;
 
@@ -106,6 +109,9 @@ newmappingobject()
 	mp->ma_table = NULL;
 	mp->ma_fill = 0;
 	mp->ma_used = 0;
+#ifdef INTERN_STRINGS
+	mp->ma_fast = 1;
+#endif
 	return (object *)mp;
 }
 
@@ -163,17 +169,40 @@ lookmapping(mp, key, hash)
 	unsigned long sum;
 	int incr;
 	int size;
+#ifdef INTERN_STRINGS
+	int fast;
+#endif
 
 	ep = &mp->ma_table[(unsigned long)hash%mp->ma_size];
 	ekey = ep->me_key;
 	if (ekey == NULL)
 		return ep;
+#ifdef INTERN_STRINGS
+	if ((fast = mp->ma_fast)) {
+		object *ikey;
+		if (!is_stringobject(key) ||
+		    (ikey = ((stringobject *)key)->ob_sinterned) == NULL)
+			fast = 0;
+		else
+			key = ikey;
+	}
+#endif
 	if (ekey == dummy)
 		freeslot = ep;
-	else if (ep->me_hash == hash && cmpobject(ekey, key) == 0)
-		return ep;
-	else
+	else {
+#ifdef INTERN_STRINGS
+		if (fast) {
+			if (ekey == key)
+				return ep;
+		}
+		else
+#endif
+		{
+			if (ep->me_hash == hash && cmpobject(ekey, key) == 0)
+				return ep;
+		}
 		freeslot = NULL;
+	}
 
 	size = mp->ma_size;
 	sum = hash;
@@ -184,6 +213,36 @@ lookmapping(mp, key, hash)
 
 	end = mp->ma_table + size;
 
+#ifdef INTERN_STRINGS
+	if (fast) {
+		if (freeslot == NULL) {
+			for (;;) {
+				ep += incr;
+				if (ep >= end)
+					ep -= size;
+				ekey = ep->me_key;
+				if (ekey == NULL || ekey == key)
+					return ep;
+				if (ekey == dummy) {
+					freeslot = ep;
+					break;
+				}
+			}
+		}
+
+		for (;;) {
+			ep += incr;
+			if (ep >= end)
+				ep -= size;
+			ekey = ep->me_key;
+			if (ekey == NULL)
+				return freeslot;
+			if (ekey == key)
+				return ep;
+		}
+	}
+#endif
+
 	if (freeslot == NULL) {
 		for (;;) {
 			ep += incr;
@@ -339,13 +398,35 @@ mappinginsert(op, key, value)
 		err_badcall();
 		return -1;
 	}
+	mp = (mappingobject *)op;
 #ifdef CACHE_HASH
-	if (!is_stringobject(key) || (hash = ((stringobject *) key)->ob_shash) == -1)
+	if (is_stringobject(key)) {
+#ifdef INTERN_STRINGS
+		if (((stringobject *)key)->ob_sinterned != NULL) {
+			key = ((stringobject *)key)->ob_sinterned;
+			hash = ((stringobject *)key)->ob_shash;
+		}
+		else
 #endif
-	hash = hashobject(key);
-	if (hash == -1)
-		return -1;
-	mp = (mappingobject *)op;
+		{
+			hash = ((stringobject *)key)->ob_shash;
+			if (hash == -1)
+				hash = hashobject(key);
+#ifdef INTERN_STRINGS
+			mp->ma_fast = 0;
+#endif
+		}
+	}
+	else
+#endif
+	{
+		hash = hashobject(key);
+		if (hash == -1)
+			return -1;
+#ifdef INTERN_STRINGS
+		mp->ma_fast = 0;
+#endif
+	}
 	/* if fill >= 2/3 size, resize */
 	if (mp->ma_fill*3 >= mp->ma_size*2) {
 		if (mappingresize(mp) != 0) {
@@ -907,16 +988,22 @@ setattro(v, name, value)
 	object *name;
 	object *value;
 {
+	int err;
+	INCREF(name);
+	PyString_InternInPlace(&name);
 	if (v->ob_type->tp_setattro != NULL)
-		return (*v->ob_type->tp_setattro)(v, name, value);
-
-	if (name != last_name_object) {
-		XDECREF(last_name_object);
-		INCREF(name);
-		last_name_object = name;
-		last_name_char = getstringvalue(name);
+		err = (*v->ob_type->tp_setattro)(v, name, value);
+	else {
+		if (name != last_name_object) {
+			XDECREF(last_name_object);
+			INCREF(name);
+			last_name_object = name;
+			last_name_char = getstringvalue(name);
+		}
+		err = setattr(v, last_name_char, value);
 	}
-	return setattr(v, last_name_char, value);
+	DECREF(name);
+	return err;
 }
 
 object *
@@ -931,6 +1018,7 @@ dictlookup(v, key)
 			last_name_char = NULL;
 			return NULL;
 		}
+		PyString_InternInPlace(&last_name_object);
 		last_name_char = getstringvalue(last_name_object);
 	}
 	return mappinglookup(v, last_name_object);
@@ -949,6 +1037,7 @@ dictinsert(v, key, item)
 			last_name_char = NULL;
 			return -1;
 		}
+		PyString_InternInPlace(&last_name_object);
 		last_name_char = getstringvalue(last_name_object);
 	}
 	return mappinginsert(v, last_name_object, item);

Objects/mappingobject.c

@@ -87,6 +87,9 @@ typedef struct {
 	int ma_fill;
 	int ma_used;
 	int ma_size;
+#ifdef INTERN_STRINGS
+	int ma_fast;
+#endif
 	mappingentry *ma_table;
 } mappingobject;
 
@@ -106,6 +109,9 @@ newmappingobject()
 	mp->ma_table = NULL;
 	mp->ma_fill = 0;
 	mp->ma_used = 0;
+#ifdef INTERN_STRINGS
+	mp->ma_fast = 1;
+#endif
 	return (object *)mp;
 }
 
@@ -163,17 +169,40 @@ lookmapping(mp, key, hash)
 	unsigned long sum;
 	int incr;
 	int size;
+#ifdef INTERN_STRINGS
+	int fast;
+#endif
 
 	ep = &mp->ma_table[(unsigned long)hash%mp->ma_size];
 	ekey = ep->me_key;
 	if (ekey == NULL)
 		return ep;
+#ifdef INTERN_STRINGS
+	if ((fast = mp->ma_fast)) {
+		object *ikey;
+		if (!is_stringobject(key) ||
+		    (ikey = ((stringobject *)key)->ob_sinterned) == NULL)
+			fast = 0;
+		else
+			key = ikey;
+	}
+#endif
 	if (ekey == dummy)
 		freeslot = ep;
-	else if (ep->me_hash == hash && cmpobject(ekey, key) == 0)
-		return ep;
-	else
+	else {
+#ifdef INTERN_STRINGS
+		if (fast) {
+			if (ekey == key)
+				return ep;
+		}
+		else
+#endif
+		{
+			if (ep->me_hash == hash && cmpobject(ekey, key) == 0)
+				return ep;
+		}
 		freeslot = NULL;
+	}
 
 	size = mp->ma_size;
 	sum = hash;
@@ -184,6 +213,36 @@ lookmapping(mp, key, hash)
 
 	end = mp->ma_table + size;
 
+#ifdef INTERN_STRINGS
+	if (fast) {
+		if (freeslot == NULL) {
+			for (;;) {
+				ep += incr;
+				if (ep >= end)
+					ep -= size;
+				ekey = ep->me_key;
+				if (ekey == NULL || ekey == key)
+					return ep;
+				if (ekey == dummy) {
+					freeslot = ep;
+					break;
+				}
+			}
+		}
+
+		for (;;) {
+			ep += incr;
+			if (ep >= end)
+				ep -= size;
+			ekey = ep->me_key;
+			if (ekey == NULL)
+				return freeslot;
+			if (ekey == key)
+				return ep;
+		}
+	}
+#endif
+
 	if (freeslot == NULL) {
 		for (;;) {
 			ep += incr;
@@ -339,13 +398,35 @@ mappinginsert(op, key, value)
 		err_badcall();
 		return -1;
 	}
+	mp = (mappingobject *)op;
 #ifdef CACHE_HASH
-	if (!is_stringobject(key) || (hash = ((stringobject *) key)->ob_shash) == -1)
+	if (is_stringobject(key)) {
+#ifdef INTERN_STRINGS
+		if (((stringobject *)key)->ob_sinterned != NULL) {
+			key = ((stringobject *)key)->ob_sinterned;
+			hash = ((stringobject *)key)->ob_shash;
+		}
+		else
 #endif
-	hash = hashobject(key);
-	if (hash == -1)
-		return -1;
-	mp = (mappingobject *)op;
+		{
+			hash = ((stringobject *)key)->ob_shash;
+			if (hash == -1)
+				hash = hashobject(key);
+#ifdef INTERN_STRINGS
+			mp->ma_fast = 0;
+#endif
+		}
+	}
+	else
+#endif
+	{
+		hash = hashobject(key);
+		if (hash == -1)
+			return -1;
+#ifdef INTERN_STRINGS
+		mp->ma_fast = 0;
+#endif
+	}
 	/* if fill >= 2/3 size, resize */
 	if (mp->ma_fill*3 >= mp->ma_size*2) {
 		if (mappingresize(mp) != 0) {
@@ -907,16 +988,22 @@ setattro(v, name, value)
 	object *name;
 	object *value;
 {
+	int err;
+	INCREF(name);
+	PyString_InternInPlace(&name);
 	if (v->ob_type->tp_setattro != NULL)
-		return (*v->ob_type->tp_setattro)(v, name, value);
-
-	if (name != last_name_object) {
-		XDECREF(last_name_object);
-		INCREF(name);
-		last_name_object = name;
-		last_name_char = getstringvalue(name);
+		err = (*v->ob_type->tp_setattro)(v, name, value);
+	else {
+		if (name != last_name_object) {
+			XDECREF(last_name_object);
+			INCREF(name);
+			last_name_object = name;
+			last_name_char = getstringvalue(name);
+		}
+		err = setattr(v, last_name_char, value);
 	}
-	return setattr(v, last_name_char, value);
+	DECREF(name);
+	return err;
 }
 
 object *
@@ -931,6 +1018,7 @@ dictlookup(v, key)
 			last_name_char = NULL;
 			return NULL;
 		}
+		PyString_InternInPlace(&last_name_object);
 		last_name_char = getstringvalue(last_name_object);
 	}
 	return mappinglookup(v, last_name_object);
@@ -949,6 +1037,7 @@ dictinsert(v, key, item)
 			last_name_char = NULL;
 			return -1;
 		}
+		PyString_InternInPlace(&last_name_object);
 		last_name_char = getstringvalue(last_name_object);
 	}
 	return mappinginsert(v, last_name_object, item);

Objects/stringobject.c

@@ -97,6 +97,9 @@ newsizedstringobject(str, size)
 	op->ob_size = size;
 #ifdef CACHE_HASH
 	op->ob_shash = -1;
+#endif
+#ifdef INTERN_STRINGS
+	op->ob_sinterned = NULL;
 #endif
 	NEWREF(op);
 	if (str != NULL)
@@ -144,6 +147,9 @@ newstringobject(str)
 	op->ob_size = size;
 #ifdef CACHE_HASH
 	op->ob_shash = -1;
+#endif
+#ifdef INTERN_STRINGS
+	op->ob_sinterned = NULL;
 #endif
 	NEWREF(op);
 	strcpy(op->ob_sval, str);
@@ -303,6 +309,9 @@ string_concat(a, bb)
 	op->ob_size = size;
 #ifdef CACHE_HASH
 	op->ob_shash = -1;
+#endif
+#ifdef INTERN_STRINGS
+	op->ob_sinterned = NULL;
 #endif
 	NEWREF(op);
 	memcpy(op->ob_sval, a->ob_sval, (int) a->ob_size);
@@ -335,6 +344,9 @@ string_repeat(a, n)
 	op->ob_size = size;
 #ifdef CACHE_HASH
 	op->ob_shash = -1;
+#endif
+#ifdef INTERN_STRINGS
+	op->ob_sinterned = NULL;
 #endif
 	NEWREF(op);
 	for (i = 0; i < size; i += a->ob_size)
@@ -462,6 +474,13 @@ typeobject Stringtype = {
 	&string_as_sequence,	/*tp_as_sequence*/
 	0,		/*tp_as_mapping*/
 	(hashfunc)string_hash, /*tp_hash*/
+	0,		/*tp_call*/
+	0,		/*tp_str*/
+	0,		/*tp_getattro*/
+	0,		/*tp_setattro*/
+	0,		/*tp_xxx3*/
+	0,		/*tp_xxx4*/
+	0,		/*tp_doc*/
 };
 
 void
@@ -928,3 +947,59 @@ formatstring(format, args)
 		DECREF(args);
 	return NULL;
 }
+
+
+#ifdef INTERN_STRINGS
+
+static PyObject *interned;
+
+void
+PyString_InternInPlace(p)
+	PyObject **p;
+{
+	register PyStringObject *s = (PyStringObject *)(*p);
+	PyObject *t;
+	if (s == NULL || !PyString_Check(s))
+		Py_FatalError("PyString_InternInPlace: strings only please!");
+	if ((t = s->ob_sinterned) != NULL) {
+		if (t == (PyObject *)s)
+			return;
+		Py_INCREF(t);
+		*p = t;
+		Py_DECREF(s);
+		return;
+	}
+	if (interned == NULL) {
+		interned = PyDict_New();
+		if (interned == NULL)
+			return;
+		/* Force slow lookups: */
+		PyDict_SetItem(interned, Py_None, Py_None);
+	}
+	if ((t = PyDict_GetItem(interned, (PyObject *)s)) != NULL) {
+		Py_INCREF(t);
+		*p = s->ob_sinterned = t;
+		Py_DECREF(s);
+		return;
+	}
+	t = (PyObject *)s;
+	if (PyDict_SetItem(interned, t, t) == 0) {
+		s->ob_sinterned = t;
+		return;
+	}
+	PyErr_Clear();
+}
+
+
+PyObject *
+PyString_InternFromString(cp)
+	const char *cp;
+{
+	PyObject *s = PyString_FromString(cp);
+	if (s == NULL)
+		return NULL;
+	PyString_InternInPlace(&s);
+	return s;
+}
+
+#endif