Improve deque iteration.

* The default __reversed__ performed badly, so reintroduced a custom
  reverse iterator.
* Added length transparency to improve speed with map(), list(), etc.

diff --git a/Modules/collectionsmodule.c b/Modules/collectionsmodule.c
index ddc6f88461b60ce9c5bda48e844a9ce9e586b13f..cf474f7e21ee77f5543d16ba7e844bdbdbab482b 100644 (file)
--- a/Modules/collectionsmodule.c
+++ b/Modules/collectionsmodule.c
@@ -645,6 +645,9 @@ static PySequenceMethods deque_as_sequence = {
 /* deque object ********************************************************/
 
 static PyObject *deque_iter(dequeobject *deque);
+static PyObject *deque_reviter(dequeobject *deque);
+PyDoc_STRVAR(reversed_doc, 
+       "D.__reversed__() -- return a reverse iterator over the deque");
 
 static PyMethodDef deque_methods[] = {
        {"append",              (PyCFunction)deque_append,      
@@ -665,6 +668,8 @@ static PyMethodDef deque_methods[] = {
                METH_NOARGS,     popleft_doc},
        {"__reduce__",  (PyCFunction)deque_reduce,      
                METH_NOARGS,     reduce_doc},
+       {"__reversed__",        (PyCFunction)deque_reviter,     
+               METH_NOARGS,     reversed_doc},
        {"rotate",              (PyCFunction)deque_rotate,      
                METH_VARARGS,   rotate_doc},
        {NULL,          NULL}   /* sentinel */
@@ -727,6 +732,7 @@ typedef struct {
        block *b;
        dequeobject *deque;
        int len;
+       int counter;
 } dequeiterobject;
 
 PyTypeObject dequeiter_type;
@@ -744,6 +750,7 @@ deque_iter(dequeobject *deque)
        Py_INCREF(deque);
        it->deque = deque;
        it->len = deque->len;
+       it->counter = deque->len;
        return (PyObject *)it;
 }
 
@@ -774,10 +781,22 @@ dequeiter_next(dequeiterobject *it)
                it->b = it->b->rightlink;
                it->index = 0;
        }
+       it->counter--;
        Py_INCREF(item);
        return item;
 }
 
+static int
+dequeiter_len(dequeiterobject *it)
+{
+       return it->counter;
+}
+
+static PySequenceMethods dequeiter_as_sequence = {
+       (inquiry)dequeiter_len,         /* sq_length */
+       0,                              /* sq_concat */
+};
+
 PyTypeObject dequeiter_type = {
        PyObject_HEAD_INIT(NULL)
        0,                                      /* ob_size */
@@ -792,7 +811,7 @@ PyTypeObject dequeiter_type = {
        0,                                      /* tp_compare */
        0,                                      /* tp_repr */
        0,                                      /* tp_as_number */
-       0,                                      /* tp_as_sequence */
+       &dequeiter_as_sequence,                 /* tp_as_sequence */
        0,                                      /* tp_as_mapping */
        0,                                      /* tp_hash */
        0,                                      /* tp_call */
@@ -811,6 +830,85 @@ PyTypeObject dequeiter_type = {
        0,
 };
 
+/*********************** Deque Reverse Iterator **************************/
+
+PyTypeObject dequereviter_type;
+
+static PyObject *
+deque_reviter(dequeobject *deque)
+{
+       dequeiterobject *it;
+
+       it = PyObject_New(dequeiterobject, &dequereviter_type);
+       if (it == NULL)
+               return NULL;
+       it->b = deque->rightblock;
+       it->index = deque->rightindex;
+       Py_INCREF(deque);
+       it->deque = deque;
+       it->len = deque->len;
+       it->counter = deque->len;
+       return (PyObject *)it;
+}
+
+static PyObject *
+dequereviter_next(dequeiterobject *it)
+{
+       PyObject *item;
+       if (it->b == it->deque->leftblock && it->index < it->deque->leftindex)
+               return NULL;
+
+       if (it->len != it->deque->len) {
+               it->len = -1; /* Make this state sticky */
+               PyErr_SetString(PyExc_RuntimeError,
+                               "deque changed size during iteration");
+               return NULL;
+       }
+
+       item = it->b->data[it->index];
+       it->index--;
+       if (it->index == -1 && it->b->leftlink != NULL) {
+               it->b = it->b->leftlink;
+               it->index = BLOCKLEN - 1;
+       }
+       it->counter--;
+       Py_INCREF(item);
+       return item;
+}
+
+PyTypeObject dequereviter_type = {
+       PyObject_HEAD_INIT(NULL)
+       0,                                      /* ob_size */
+       "deque_reverse_iterator",               /* tp_name */
+       sizeof(dequeiterobject),                /* tp_basicsize */
+       0,                                      /* tp_itemsize */
+       /* methods */
+       (destructor)dequeiter_dealloc,          /* tp_dealloc */
+       0,                                      /* tp_print */
+       0,                                      /* tp_getattr */
+       0,                                      /* tp_setattr */
+       0,                                      /* tp_compare */
+       0,                                      /* tp_repr */
+       0,                                      /* tp_as_number */
+       &dequeiter_as_sequence,                 /* tp_as_sequence */
+       0,                                      /* tp_as_mapping */
+       0,                                      /* tp_hash */
+       0,                                      /* tp_call */
+       0,                                      /* tp_str */
+       PyObject_GenericGetAttr,                /* tp_getattro */
+       0,                                      /* tp_setattro */
+       0,                                      /* tp_as_buffer */
+       Py_TPFLAGS_DEFAULT,                     /* tp_flags */
+       0,                                      /* tp_doc */
+       0,                                      /* tp_traverse */
+       0,                                      /* tp_clear */
+       0,                                      /* tp_richcompare */
+       0,                                      /* tp_weaklistoffset */
+       PyObject_SelfIter,                      /* tp_iter */
+       (iternextfunc)dequereviter_next,        /* tp_iternext */
+       0,
+};
+
 /* module level code ********************************************************/
 
 PyDoc_STRVAR(module_doc,
@@ -832,5 +930,8 @@ initcollections(void)
        if (PyType_Ready(&dequeiter_type) < 0)
                return; 
 
+       if (PyType_Ready(&dequereviter_type) < 0)
+               return;
+
        return;
 }