New strop_joinfields implementation, highly optimized for Lists. All

other sequences use the Sequence protocol from the abstract API.  The
algorithm has changed so that only one pass through the sequences are
made.

Modules/stropmodule.c

@@ -168,11 +168,13 @@ strop_joinfields(self, args)
 	PyObject *self; /* Not used */
 	PyObject *args;
 {
-	PyObject *seq, *item, *res;
-	char *p, *sep = NULL;
-	int seqlen, reslen, itemlen, i, seplen = 0;
-	int ownrefs = 0;
-	PyObject* (*getitemfunc) Py_PROTO((PyObject*, int));
+	PyObject *seq;
+	char *sep = NULL;
+	int seqlen, seplen = 0;
+	int i, reslen = 0, slen = 0, sz = 100;
+	PyObject *res = NULL;
+	char* p = NULL;
+	intargfunc getitemfunc;
 
 	if (!PyArg_ParseTuple(args, "O|s#", &seq, &sep, &seplen))
 		return NULL;
@@ -180,84 +182,104 @@ strop_joinfields(self, args)
 		sep = " ";
 		seplen = 1;
 	}
-	/* do it this way to optimize for the common cases, but also
-	 * support the more general sequence protocol
-	 */
-	if (PyList_Check(seq)) {
-		getitemfunc = PyList_GetItem;
-		seqlen = PyList_Size(seq);
-	}
-	else if (PyTuple_Check(seq)) {
-		getitemfunc = PyTuple_GetItem;
-		seqlen = PyTuple_Size(seq);
-	}
-	else if (PySequence_Check(seq)) {
-		getitemfunc = PySequence_GetItem;
+
 	seqlen = PySequence_Length(seq);
-		ownrefs = 1;
-	}
-	else {
-		PyErr_SetString(PyExc_TypeError,
-				"first argument must be a sequence");
-		return NULL;
-	}
 	if (seqlen < 0 && PyErr_Occurred())
 		return NULL;
 
-	reslen = 0;
-	for (i = 0; i < seqlen; i++) {
-		if (!(item = getitemfunc(seq, i)))
+	if (seqlen == 1) {
+		/* Optimization if there's only one item */
+		PyObject *item = PySequence_GetItem(seq, 0);
+		if (item && !PyString_Check(item))
+			PyErr_SetString(PyExc_TypeError,
+				 "first argument must be sequence of strings");
+		return item;
+	}
+
+	if (!(res = PyString_FromStringAndSize((char*)NULL, sz)))
 		return NULL;
+	p = PyString_AsString(res);
 
+	/* optimize for lists, since it's the most common case.  all others
+	 * (tuples and arbitrary sequences) just use the sequence abstract
+	 * interface.
+	 */
+	if (PyList_Check(seq)) {
+		for (i = 0; i < seqlen; i++) {
+			PyObject *item = PyList_GET_ITEM(seq, i);
 			if (!PyString_Check(item)) {
 				PyErr_SetString(PyExc_TypeError,
 				"first argument must be sequence of strings");
-			if (ownrefs)
-				Py_DECREF(item);
+				Py_DECREF(res);
 				return NULL;
 			}
-		if (i > 0)
+			slen = PyString_GET_SIZE(item);
+			while (reslen + slen + seplen >= sz) {
+				if (_PyString_Resize(&res, sz * 2)) {
+					Py_DECREF(res);
+					return NULL;
+				}
+				sz *= 2;
+				p = PyString_AsString(res) + reslen;
+			}
+			if (i > 0) {
+				memcpy(p, sep, seplen);
+				p += seplen;
 				reslen += seplen;
-		reslen += PyString_Size(item);
-		if (ownrefs)
-			Py_DECREF(item);
 			}
-	if (seqlen == 1) {
-		/* Optimization if there's only one item */
-		item = getitemfunc(seq, 0);
-		if (!ownrefs)
-			Py_XINCREF(item);
-		return item;
+			memcpy(p, PyString_AS_STRING(item), slen);
+			p += slen;
+			reslen += slen;
 		}
-
-	res = PyString_FromStringAndSize((char *)NULL, reslen);
-	if (res == NULL)
+		if (_PyString_Resize(&res, reslen)) {
+			Py_DECREF(res);
+			res = NULL;
+		}
+		return res;
+	}
+	else if (!PySequence_Check(seq)) {
+		PyErr_SetString(PyExc_TypeError,
+				"first argument must be a sequence");
 		return NULL;
-	p = PyString_AsString(res);
+	}
+	/* type safe */
+	getitemfunc = seq->ob_type->tp_as_sequence->sq_item;
 	for (i = 0; i < seqlen; i++) {
-		if (!(item = getitemfunc(seq, i))) {
+		PyObject *item = getitemfunc(seq, i);
+		if (!item || !PyString_Check(item)) {
+			PyErr_SetString(PyExc_TypeError,
+				 "first argument must be sequence of strings");
 			Py_DECREF(res);
+			Py_XDECREF(item);
 			return NULL;
 		}
+		slen = PyString_GET_SIZE(item);
+		while (reslen + slen + seplen >= sz) {
+			if (_PyString_Resize(&res, sz * 2)) {
+				Py_DECREF(res);
+				Py_DECREF(item);
+				return NULL;
+			}
+			sz *= 2;
+			p = PyString_AsString(res) + reslen;
+		}
 		if (i > 0) {
 			memcpy(p, sep, seplen);
 			p += seplen;
+			reslen += seplen;
 		}
-		itemlen = PyString_Size(item);
-		memcpy(p, PyString_AsString(item), itemlen);
-		p += itemlen;
-		if (ownrefs)
+		memcpy(p, PyString_AS_STRING(item), slen);
+		p += slen;
+		reslen += slen;
 		Py_DECREF(item);
 	}
-	if (p != PyString_AsString(res) + reslen) {
-		PyErr_SetString(PyExc_SystemError,
-                                "strop.joinfields: assertion failed");
-		return NULL;
+	if (_PyString_Resize(&res, reslen)) {
+		Py_DECREF(res);
+		res = NULL;
 	}
 	return res;
 }
 
-
 static PyObject *
 strop_find(self, args)
 	PyObject *self; /* Not used */