gh-120010: fix invalid (nan+nanj) results in _Py_c_prod()

Lib/test/test_complex.py

@@ -299,6 +299,22 @@ def test_mul(self):
  self.assertRaises(TypeError, operator.mul, 1j, None)
  self.assertRaises(TypeError, operator.mul, None, 1j)
 
+ for z, w, r in [(1e300+1j, complex(INF, INF), complex(NAN, INF)),
+ (1e300+1j, complex(NAN, INF), complex(-INF, INF)),
+ (1e300+1j, complex(INF, NAN), complex(INF, INF)),
+ (complex(INF, 1), complex(NAN, INF), complex(NAN, INF)),
+ (complex(INF, 1), complex(INF, NAN), complex(INF, NAN)),
+ (complex(NAN, 1), complex(1, INF), complex(-INF, NAN)),
+ (complex(1, NAN), complex(1, INF), complex(NAN, INF)),
+ (complex(1e200, NAN), complex(1e200, NAN), complex(INF, NAN)),
+ (complex(1e200, NAN), complex(NAN, 1e200), complex(NAN, INF)),
+ (complex(NAN, 1e200), complex(1e200, NAN), complex(NAN, INF)),
+ (complex(NAN, 1e200), complex(NAN, 1e200), complex(-INF, NAN)),
+ (complex(NAN, NAN), complex(NAN, NAN), complex(NAN, NAN))]:
+ with self.subTest(z=z, w=w, r=r):
+ self.assertComplexesAreIdentical(z * w, r)
+ self.assertComplexesAreIdentical(w * z, r)
+
  def test_mod(self):
  # % is no longer supported on complex numbers
  with self.assertRaises(TypeError):
@@ -340,6 +356,7 @@ def test_pow(self):
  self.assertAlmostEqual(pow(1j, 200), 1)
  self.assertRaises(ValueError, pow, 1+1j, 1+1j, 1+1j)
  self.assertRaises(OverflowError, pow, 1e200+1j, 1e200+1j)
+ self.assertRaises(OverflowError, pow, 1e200+1j, 5)
  self.assertRaises(TypeError, pow, 1j, None)
  self.assertRaises(TypeError, pow, None, 1j)
  self.assertAlmostEqual(pow(1j, 0.5), 0.7071067811865476+0.7071067811865475j)

Misc/NEWS.d/next/Core_and_Builtins/2024-06-04-08-26-25.gh-issue-120010._z-AWz.rst

@@ -0,0 +1,2 @@
+Correct invalid corner cases which resulted in ``(nan+nanj)`` output in complex
+multiplication, e.g., ``(1e300+1j)*(nan+infj)``. Patch by Sergey B Kirpichev.

Objects/complexobject.c

@@ -85,11 +85,63 @@ _Py_c_neg(Py_complex a)
 }
 
 Py_complex
-_Py_c_prod(Py_complex a, Py_complex b)
+_Py_c_prod(Py_complex z, Py_complex w)
 {
- Py_complex r;
- r.real = a.real*b.real - a.imag*b.imag;
- r.imag = a.real*b.imag + a.imag*b.real;
+ double a = z.real, b = z.imag, c = w.real, d = w.imag;
+ double ac = a*c, bd = b*d, ad = a*d, bc = b*c;
+ Py_complex r ={ac - bd, ad + bc};
+
+ /* Recover infinities that computed as nan+nanj. See e.g. the C11,
+ Annex G.5.1, routine _Cmultd(). */
+ if (isnan(r.real) && isnan(r.imag)){
+ int recalc = 0;
+
+ if (isinf(a) || isinf(b)){/* z is infinite */
+ /* "Box" the infinity and change nans in the other factor to 0 */
+ a = copysign(isinf(a) ? 1.0 : 0.0, a);
+ b = copysign(isinf(b) ? 1.0 : 0.0, b);
+ if (isnan(c)){
+ c = copysign(0.0, c);
+ }
+ if (isnan(d)){
+ d = copysign(0.0, d);
+ }
+ recalc = 1;
+ }
+ if (isinf(c) || isinf(d)){/* w is infinite */
+ /* "Box" the infinity and change nans in the other factor to 0 */
+ c = copysign(isinf(c) ? 1.0 : 0.0, c);
+ d = copysign(isinf(d) ? 1.0 : 0.0, d);
+ if (isnan(a)){
+ a = copysign(0.0, a);
+ }
+ if (isnan(b)){
+ b = copysign(0.0, b);
+ }
+ recalc = 1;
+ }
+ if (!recalc && (isinf(ac) || isinf(bd) || isinf(ad) || isinf(bc))){
+ /* Recover infinities from overflow by changing nans to 0 */
+ if (isnan(a)){
+ a = copysign(0.0, a);
+ }
+ if (isnan(b)){
+ b = copysign(0.0, b);
+ }
+ if (isnan(c)){
+ c = copysign(0.0, c);
+ }
+ if (isnan(d)){
+ d = copysign(0.0, d);
+ }
+ recalc = 1;
+ }
+ if (recalc){
+ r.real = Py_INFINITY*(a*c - b*d);
+ r.imag = Py_INFINITY*(a*d + b*c);
+ }
+ }
+
  return r;
 }