Make the zero delta a global singleton.

python · encukou · May 23, 2024 · May 23, 2024 · May 23, 2024 · May 23, 2024
commit 773ddca3846e9b0d93a823ab614646ad23f9416c
@@ -1178,6 +1178,8 @@ new_time_subclass_fold_ex(int hour, int minute, int second, int usecond,
    return t;
 }

+static PyDateTime_Delta * look_up_delta(int, int, int, PyTypeObject *);
+
 /* Create a timedelta instance.  Normalize the members iff normalize is
 * true.  Passing false is a speed optimization, if you know for sure
 * that seconds and microseconds are already in their proper ranges.  In any
@@ -1198,6 +1200,12 @@ new_delta_ex(int days, int seconds, int microseconds, int normalize,
    if (check_delta_day_range(days) < 0)
        return NULL;

+    self = look_up_delta(days, seconds, microseconds, type);
+    if (self != NULL) {
+        return (PyObject *)self;
+    }
+    assert(!PyErr_Occurred());
+
    self = (PyDateTime_Delta *) (type->tp_alloc(type, 0));
    if (self != NULL) {
        self->hashcode = -1;
@@ -2892,6 +2900,25 @@ static PyTypeObject PyDateTime_DeltaType = {
    0,                                                  /* tp_free */
 };

+// XXX Can we make this const?
+static PyDateTime_Delta zero_delta = {
+    PyObject_HEAD_INIT(&PyDateTime_DeltaType)
+    /* Letting this be set lazily is a benign race. */
+    .hashcode = -1,
+};
+
+static PyDateTime_Delta *
+look_up_delta(int days, int seconds, int microseconds, PyTypeObject *type)
+{
+    if (days == 0 && seconds == 0 && microseconds == 0
+            && type == zero_delta.ob_base.ob_type)
+    {
+        return &zero_delta;
+    }
+    return NULL;
+}
+
+
 /*
 * PyDateTime_Date implementation.
 */