Additional special-case handling for math.pow.

Windows/VS2008 doesn't like (-1)**(+-inf).

diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index a78b6988dcbed2c2652545c9fbde6b4832a3b24e..bb97a2c1023f15b1fd9e975ea7c44ed8245e6087 100644 (file)
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -521,9 +521,19 @@ math_pow(PyObject *self, PyObject *args)
        y = PyFloat_AsDouble(oy);
        if ((x == -1.0 || y == -1.0) && PyErr_Occurred())
                return NULL;
-       /* 1**x and x**0 return 1., even if x is a NaN or infinity. */
-       if (x == 1.0 || y == 0.0)
+
+       /* deal directly with various special cases, to cope with problems on
+          various platforms whose semantics don't exactly match C99 */
+
+       /* 1**x, x**0, and (-1)**(+-infinity) return 1., even if x is NaN or
+          an infinity. */
+       if (x == 1. || y == 0. || (x == -1. && Py_IS_INFINITY(y)))
                return PyFloat_FromDouble(1.);
+       /* otherwise, return a NaN if either input was a NaN */
+       if (Py_IS_NAN(x))
+               return PyFloat_FromDouble(x);
+       if (Py_IS_NAN(y))
+               return PyFloat_FromDouble(y);
        /* inf ** (nonzero, non-NaN) is one of +-0, +-infinity */
        if (Py_IS_INFINITY(x) && !Py_IS_NAN(y)) {
                y_is_odd = Py_IS_FINITE(y) && fmod(fabs(y), 2.0) == 1.0;
@@ -539,10 +549,7 @@ math_pow(PyObject *self, PyObject *args)
        r = pow(x, y);
        PyFPE_END_PROTECT(r);
        if (Py_IS_NAN(r)) {
-               if (!Py_IS_NAN(x) && !Py_IS_NAN(y))
-                       errno = EDOM;
-               else
-                       errno = 0;
+               errno = EDOM;
        }
        /* an infinite result arises either from: