bpo-44698: Fix undefined behaviour in complex exponentiation. (GH-27278) (#27366)
(cherry picked from commit 1d582bbc969e05896addf97844ddf17ce9830e5e)
Co-authored-by: T. Wouters <thomas@python.org>
diff --git a/Objects/complexobject.c b/Objects/complexobject.c
index 91e06a8..05cae32 100644
--- a/Objects/complexobject.c
+++ b/Objects/complexobject.c
@@ -514,8 +514,6 @@ static PyObject *
complex_pow(PyObject *v, PyObject *w, PyObject *z)
{
Py_complex p;
- Py_complex exponent;
- long int_exponent;
Py_complex a, b;
TO_COMPLEX(v, a);
TO_COMPLEX(w, b);
@@ -525,12 +523,21 @@ complex_pow(PyObject *v, PyObject *w, PyObject *z)
return NULL;
}
errno = 0;
- exponent = b;
- int_exponent = (long)exponent.real;
- if (exponent.imag == 0. && exponent.real == int_exponent)
- p = c_powi(a, int_exponent);
- else
- p = _Py_c_pow(a, exponent);
+ // Check if w is an integer value that fits inside a C long, so we can
+ // use a faster algorithm. TO_COMPLEX(w, b), above, already handled the
+ // conversion from larger longs, as well as other types.
+ if (PyLong_Check(w)) {
+ int overflow = 0;
+ long int_exponent = PyLong_AsLongAndOverflow(w, &overflow);
+ if (int_exponent == -1 && PyErr_Occurred())
+ return NULL;
+ if (overflow == 0)
+ p = c_powi(a, int_exponent);
+ else
+ p = _Py_c_pow(a, b);
+ } else {
+ p = _Py_c_pow(a, b);
+ }
Py_ADJUST_ERANGE2(p.real, p.imag);
if (errno == EDOM) {