pythongh-117999: fixed invalid small integer powers of real±0j

Author: skirpichev

Lib/test/test_complex.py

@@ -330,6 +330,13 @@ def test_pow_with_small_integer_exponents(self):
                     self.assertEqual(str(float_pow), str(int_pow))
                     self.assertEqual(str(complex_pow), str(int_pow))
 
+        self.assertFloatsAreIdentical(pow(complex(1,+0.0), 0).imag, +0.0)
+        self.assertFloatsAreIdentical(pow(complex(1,-0.0), 0).imag, +0.0)
+        self.assertFloatsAreIdentical(pow(complex(1,+0.0), 2).imag, +0.0)
+        self.assertFloatsAreIdentical(pow(complex(1,-0.0), 2).imag, -0.0)
+        self.assertFloatsAreIdentical(pow(complex(1,+0.0), -3).imag, -0.0)
+        self.assertFloatsAreIdentical(pow(complex(1,-0.0), -3).imag, +0.0)
+
     def test_boolcontext(self):
         for i in range(100):
             self.assertTrue(complex(random() + 1e-6, random() + 1e-6))

Misc/NEWS.d/next/Core and Builtins/2024-04-17-19-39-30.gh-issue-117999.oCJkud.rst

@@ -0,0 +1,2 @@
+Fixed invalid small integer powers for complex numbers with ``±0.0`` in
+imaginary component.  Patch by Sergey B Kirpichev.

Objects/complexobject.c

@@ -162,6 +162,8 @@ c_powu(Py_complex x, long n)
     Py_complex r, p;
     long mask = 1;
     r = c_1;
+    if (n)
+        r.imag = copysign(0.0, x.imag);
     p = x;
     while (mask > 0 && n >= mask) {
         if (n & mask)
@@ -177,9 +179,10 @@ c_powi(Py_complex x, long n)
 {
     if (n > 0)
         return c_powu(x,n);
-    else
+    else {
+        c_1.imag = -copysign(0.0, x.imag);
         return _Py_c_quot(c_1, c_powu(x,-n));
-
+    }
 }
 
 double