[Python-checkins] cpython: Precomputing the number iterations allows the inner-loop to be vectorizable.

[raymond.hettinger]

https://hg.python.org/cpython/rev/821eca6e5a33
changeset:   98283:821eca6e5a33
user:        Raymond Hettinger <python at rcn.com>
date:        Sat Sep 26 02:14:50 2015 -0700
summary:
  Precomputing the number iterations allows the inner-loop to be vectorizable.

files:
  Modules/_collectionsmodule.c |  8 ++++++--
  1 files changed, 6 insertions(+), 2 deletions(-)


diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -557,7 +557,7 @@
 static PyObject *
 deque_inplace_repeat(dequeobject *deque, Py_ssize_t n)
 {
-    Py_ssize_t i, size;
+    Py_ssize_t i, m, size;
     PyObject *seq;
     PyObject *rv;
 
@@ -598,7 +598,11 @@
                 MARK_END(b->rightlink);
                 deque->rightindex = -1;
             }
-            for ( ; i < n-1 && deque->rightindex != BLOCKLEN - 1 ; i++) {
+            m = n - 1 - i;
+            if (m > BLOCKLEN - 1 - deque->rightindex)
+                m = BLOCKLEN - 1 - deque->rightindex;
+            i += m;
+            while (m--) {
                 deque->rightindex++;
                 Py_INCREF(item);
                 deque->rightblock->data[deque->rightindex] = item;

-- 
Repository URL: https://hg.python.org/cpython