From: Guido van Rossum <guido@python.org>
Date: Sun, 11 Aug 2002 14:04:13 +0000 (+0000)
Subject: Use a better check for overflow from a<<b.
X-Git-Tag: v2.3c1~4549
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=643d59cbd6f86516b083b958d76750b3626da3d6;p=python

Use a better check for overflow from a<<b.
---

diff --git a/Objects/intobject.c b/Objects/intobject.c
index 728f798a5b..40f38ba343 100644
--- a/Objects/intobject.c
+++ b/Objects/intobject.c
@@ -675,13 +675,15 @@ int_lshift(PyIntObject *v, PyIntObject *w)
 			return NULL;
 		return PyInt_FromLong(0L);
 	}
-	c = (long)((unsigned long)a << b);
-	if ((c >> b) != a || (c < 0 && a > 0)) {
+	c = a < 0 ? ~a : a;
+	c >>= LONG_BIT - 1 - b;
+	if (c) {
 		if (PyErr_Warn(PyExc_DeprecationWarning,
 			       "x<<y losing bits or changing sign "
 			       "will return a long in Python 2.4 and up") < 0)
 			return NULL;
 	}
+	c = (long)((unsigned long)a << b);
 	return PyInt_FromLong(c);
 }