Add a spacing saving heuristic to deque's extend methods
diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index e782b99..ae1de9a 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -543,8 +543,8 @@
check = self.check_sizeof
check(deque(), basesize + blocksize)
check(deque('a'), basesize + blocksize)
- check(deque('a' * (BLOCKLEN // 2)), basesize + blocksize)
- check(deque('a' * (BLOCKLEN // 2 + 1)), basesize + 2 * blocksize)
+ check(deque('a' * (BLOCKLEN - 1)), basesize + blocksize)
+ check(deque('a' * BLOCKLEN), basesize + 2 * blocksize)
check(deque('a' * (42 * BLOCKLEN)), basesize + 43 * blocksize)
class TestVariousIteratorArgs(unittest.TestCase):
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index 9924b63..67ff55b 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -332,6 +332,14 @@
return result;
}
+ /* Space saving heuristic. Start filling from the left */
+ if (Py_SIZE(deque) == 0) {
+ assert(deque->leftblock == deque->rightblock);
+ assert(deque->leftindex == deque->rightindex+1);
+ deque->leftindex = 1;
+ deque->rightindex = 0;
+ }
+
it = PyObject_GetIter(iterable);
if (it == NULL)
return NULL;
@@ -385,6 +393,14 @@
return result;
}
+ /* Space saving heuristic. Start filling from the right */
+ if (Py_SIZE(deque) == 0) {
+ assert(deque->leftblock == deque->rightblock);
+ assert(deque->leftindex == deque->rightindex+1);
+ deque->leftindex = BLOCKLEN - 1;
+ deque->rightindex = BLOCKLEN - 2;
+ }
+
it = PyObject_GetIter(iterable);
if (it == NULL)
return NULL;