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authorGuido van Rossum <guido@python.org>1998-05-26 14:33:37 (GMT)
committerGuido van Rossum <guido@python.org>1998-05-26 14:33:37 (GMT)
commitf753181272d9f69ec9cea4330cfd0af1fcabc935 (patch)
tree1284fe12ed5a9a6f5b5e477b8b1df252bf9b41cf /Objects/longobject.c
parent2028dd04236c9b960de5e2febd49abff039e665b (diff)
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Subject: Buglet in PyLong_AsLong
From: "Tim Peters" <tim_one@email.msn.com> To: "Guido van Rossum" <guido@CNRI.Reston.VA.US> Date: Sat, 23 May 1998 21:45:53 -0400 Guido, the overflow checking in PyLong_AsLong is off a little: 1) If the C in use sign-extends right shifts on signed longs, there's a spurious overflow error when converting the most-negative int: Python 1.5.1 (#0, Apr 13 1998, 20:22:04) [MSC 32 bit (Intel)] on win32 Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam >>> x = -1L << 31 >>> x -2147483648L >>> int(x) Traceback (innermost last): File "<stdin>", line 1, in ? OverflowError: long int too long to convert >>> 2) If C does not sign-extend, some genuine overflows won't be caught. The attached should repair both, and, because I installed a new disk and a C compiler today, it's even been compiled this time <wink>. Python 1.5.1 (#0, May 23 1998, 20:24:58) [MSC 32 bit (Intel)] on win32 Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam >>> x = -1L << 31 >>> x -2147483648L >>> int(x) -2147483648 >>> int(-x) Traceback (innermost last): File "<stdin>", line 1, in ? OverflowError: long int too long to convert >>> int(-x-1) 2147483647 >>> int(x-1) Traceback (innermost last): File "<stdin>", line 1, in ? OverflowError: long int too long to convert >>> end-casing-ly y'rs - tim
Diffstat (limited to 'Objects/longobject.c')
-rw-r--r--Objects/longobject.c28
1 files changed, 19 insertions, 9 deletions
diff --git a/Objects/longobject.c b/Objects/longobject.c
index becf1bc..9657c08 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -175,10 +175,11 @@ long
PyLong_AsLong(vv)
PyObject *vv;
{
+ /* This version by Tim Peters */
register PyLongObject *v;
- long x, prev;
+ unsigned long x, prev;
int i, sign;
-
+
if (vv == NULL || !PyLong_Check(vv)) {
PyErr_BadInternalCall();
return -1;
@@ -194,13 +195,22 @@ PyLong_AsLong(vv)
while (--i >= 0) {
prev = x;
x = (x << SHIFT) + v->ob_digit[i];
- if ((x >> SHIFT) != prev) {
- PyErr_SetString(PyExc_OverflowError,
- "long int too long to convert");
- return -1;
- }
- }
- return x * sign;
+ if ((x >> SHIFT) != prev)
+ goto overflow;
+ }
+ /* Haven't lost any bits, but if the sign bit is set we're in
+ * trouble *unless* this is the min negative number. So,
+ * trouble iff sign bit set && (positive || some bit set other
+ * than the sign bit).
+ */
+ if ((long)x < 0 && (sign > 0 || (x << 1) != 0))
+ goto overflow;
+ return (long)x * sign;
+
+ overflow:
+ PyErr_SetString(PyExc_OverflowError,
+ "long int too long to convert");
+ return -1;
}
/* Get a C long int from a long int object.