Small optimizations for list_slice() and list_extend_internal().

* Using addition instead of substraction on array indices allows the
  compiler to use a fast addressing mode.  Saves about 10%.

* Using PyTuple_GET_ITEM and PyList_SET_ITEM is about 7% faster than
  PySequenceFast_GET_ITEM which has to make a list check on every pass.

diff --git a/Objects/listobject.c b/Objects/listobject.c
index 162efa0ce3f405a66e89f84ceeab8d910430a7ee..0508d37b0061a0eb08e7c01a66ea38db47b10219 100644 (file)
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -342,7 +342,7 @@ static PyObject *
 list_slice(PyListObject *a, int ilow, int ihigh)
 {
        PyListObject *np;
-       int i;
+       int i, len;
        if (ilow < 0)
                ilow = 0;
        else if (ilow > a->ob_size)
@@ -351,13 +351,15 @@ list_slice(PyListObject *a, int ilow, int ihigh)
                ihigh = ilow;
        else if (ihigh > a->ob_size)
                ihigh = a->ob_size;
-       np = (PyListObject *) PyList_New(ihigh - ilow);
+       len = ihigh - ilow;
+       np = (PyListObject *) PyList_New(len);
        if (np == NULL)
                return NULL;
-       for (i = ilow; i < ihigh; i++) {
-               PyObject *v = a->ob_item[i];
+
+       for (i = 0; i < len; i++) {
+               PyObject *v = a->ob_item[i+ilow];
                Py_INCREF(v);
-               np->ob_item[i - ilow] = v;
+               np->ob_item[i] = v;
        }
        return (PyObject *)np;
 }
@@ -676,10 +678,19 @@ listextend_internal(PyListObject *self, PyObject *b)
        }
 
        /* populate the end of self with b's items */
-       for (i = 0; i < blen; i++) {
-               PyObject *o = PySequence_Fast_GET_ITEM(b, i);
-               Py_INCREF(o);
-               PyList_SET_ITEM(self, i+selflen, o);
+       if (PyList_Check(b)) {
+               for (i = 0; i < blen; i++) {
+                       PyObject *o = PyList_GET_ITEM(b, i);
+                       Py_INCREF(o);
+                       PyList_SET_ITEM(self, i+selflen, o);
+               }
+       } else {
+               assert (PyTuple_Check(b));
+               for (i = 0; i < blen; i++) {
+                       PyObject *o = PyTuple_GET_ITEM(b, i);
+                       Py_INCREF(o);
+                       PyList_SET_ITEM(self, i+selflen, o);
+               }
        }
        Py_DECREF(b);
        return 0;