Optimize slice assignments.

* Replace sprintf message with a constant message string -- this error
  message ran on every invocation except straight deletions but it was
  only needed when the rhs was not iterable.  The message was also
  out-of-date and did not reflect that iterable arguments were allowed.

* For inner loops that do not make ref count adjustments, use memmove()
  for fast copying and better readability.

* For inner loops that do make ref count adjustments, speed them up by
  factoring out the constant structure reference and using vitem[] instead.

diff --git a/Objects/listobject.c b/Objects/listobject.c
index f5a9c7b087cc148434bf2f1c9771e02485b2bb59..fd0dc70438c0ea2e4fd5978ab6831f3ef62b2fce 100644 (file)
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -460,6 +460,7 @@ list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
           list. :-( */
        PyObject **recycle, **p;
        PyObject **item;
+       PyObject **vitem = NULL;
        PyObject *v_as_SF = NULL; /* PySequence_Fast(v) */
        int n; /* Size of replacement list */
        int d; /* Change in size */
@@ -469,7 +470,6 @@ list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
        if (v == NULL)
                n = 0;
        else {
-               char msg[256];
                if (a == b) {
                        /* Special case "a[i:j] = a" -- copy b first */
                        int ret;
@@ -480,15 +480,16 @@ list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
                        Py_DECREF(v);
                        return ret;
                }
-
-               PyOS_snprintf(msg, sizeof(msg),
-                             "must assign sequence"
-                             " (not \"%.200s\") to slice",
-                             v->ob_type->tp_name);
-               v_as_SF = PySequence_Fast(v, msg);
+               v_as_SF = PySequence_Fast(v, "can only assign an iterable");
                if(v_as_SF == NULL)
                        return -1;
                n = PySequence_Fast_GET_SIZE(v_as_SF);
+               if (PyList_Check(v_as_SF))
+                       vitem = ((PyListObject *)v_as_SF)->ob_item;
+               else {
+                       assert (PyTuple_Check(v_as_SF));
+                       vitem = ((PyTupleObject *)v_as_SF)->ob_item;
+               }
        }
        if (ilow < 0)
                ilow = 0;
@@ -510,11 +511,11 @@ list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
        else
                p = recycle = NULL;
        if (d <= 0) { /* Delete -d items; recycle ihigh-ilow items */
-               for (k = ilow; k < ihigh; k++)
-                       *p++ = item[k];
+               memmove(p, &item[ilow], (ihigh - ilow)*sizeof(PyObject *));
+               p += ihigh - ilow;
                if (d < 0) {
-                       for (/*k = ihigh*/; k < a->ob_size; k++)
-                               item[k+d] = item[k];
+                       memmove(&item[ihigh+d], &item[ihigh], 
+                               (a->ob_size - ihigh)*sizeof(PyObject *));
                        list_resize(a, a->ob_size + d);
                        item = a->ob_item;
                }
@@ -527,13 +528,13 @@ list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
                        return -1;
                }
                item = a->ob_item;
-               for (k = s; --k >= ihigh; )
-                       item[k+d] = item[k];
-               for (/*k = ihigh-1*/; k >= ilow; --k)
-                       *p++ = item[k];
+               memmove(&item[ihigh+d], &item[ihigh],
+                       (s - ihigh)*sizeof(PyObject *));
+               memmove(p, &item[ilow], (ihigh - ilow)*sizeof(PyObject *));
+               p += ihigh - ilow;
        }
        for (k = 0; k < n; k++, ilow++) {
-               PyObject *w = PySequence_Fast_GET_ITEM(v_as_SF, k);
+               PyObject *w = vitem[k];
                Py_XINCREF(w);
                item[ilow] = w;
        }