int_lshift(): Simplified/sped overflow-checking.

tim-one · tim-one · commit da1a2212c8dd · 2002-08-11T17:54:42.000Z
diff --git a/Objects/intobject.c b/Objects/intobject.c
@@ -675,15 +675,13 @@ int_lshift(PyIntObject *v, PyIntObject *w)
 			return NULL;
 		return PyInt_FromLong(0L);
 	}
-	c = a < 0 ? ~a : a;
-	c >>= LONG_BIT - 1 - b;
-	if (c) {
+	c = a << b;
+	if (a != Py_ARITHMETIC_RIGHT_SHIFT(long, c, b)) {
 		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);
 }
 

Original file line number	Diff line number	Diff line change
`@@ -675,15 +675,13 @@ int_lshift(PyIntObject v, PyIntObject w)`
`675`	`675`	`return NULL;`
`676`	`676`	`return PyInt_FromLong(0L);`
`677`	`677`	`}`
`678`		`- c = a < 0 ? ~a : a;`
`679`		`- c >>= LONG_BIT - 1 - b;`
`680`		`- if (c) {`
	`678`	`+ c = a << b;`
	`679`	`+ if (a != Py_ARITHMETIC_RIGHT_SHIFT(long, c, b)) {`
`681`	`680`	`if (PyErr_Warn(PyExc_DeprecationWarning,`
`682`	`681`	`"x<<y losing bits or changing sign "`
`683`	`682`	`"will return a long in Python 2.4 and up") < 0)`
`684`	`683`	`return NULL;`
`685`	`684`	`}`
`686`		`- c = (long)((unsigned long)a << b);`
`687`	`685`	`return PyInt_FromLong(c);`
`688`	`686`	`}`
`689`	`687`