gh-113841: fix possible undefined division by 0 in _Py_c_pow() (GH-127211)

`x**y == 1/x**-y ` thus changing `/=` to `*=` by negating the exponent.

3 files changed, 8 insertions, 1 deletions

diff --git a/Lib/test/test_complex.py b/Lib/test/test_complex.py
index ecc9731..c51327c 100644
--- a/Lib/test/test_complex.py
+++ b/Lib/test/test_complex.py
@@ -338,6 +338,11 @@ class ComplexTest(ComplexesAreIdenticalMixin, unittest.TestCase):
                     except OverflowError:
                         pass
 
+        # gh-113841: possible undefined division by 0 in _Py_c_pow()
+        x, y = 9j, 33j**3
+        with self.assertRaises(OverflowError):
+            x**y
+
     def test_pow_with_small_integer_exponents(self):
         # Check that small integer exponents are handled identically
         # regardless of their type.
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-11-24-07-01-28.gh-issue-113841.WFg-Bu.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-11-24-07-01-28.gh-issue-113841.WFg-Bu.rst
new file mode 100644
index 0000000..2b07fdf
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2024-11-24-07-01-28.gh-issue-113841.WFg-Bu.rst
@@ -0,0 +1,2 @@
+Fix possible undefined behavior division by zero in :class:`complex`'s
+:c:func:`_Py_c_pow`.
diff --git a/Objects/complexobject.c b/Objects/complexobject.c
index 7b4948f..9faa575 100644
--- a/Objects/complexobject.c
+++ b/Objects/complexobject.c
@@ -168,7 +168,7 @@ _Py_c_pow(Py_complex a, Py_complex b)
         at = atan2(a.imag, a.real);
         phase = at*b.real;
         if (b.imag != 0.0) {
-            len /= exp(at*b.imag);
+            len *= exp(-at*b.imag);
             phase += b.imag*log(vabs);
         }
         r.real = len*cos(phase);