calculate 2**N in PY_LONG_LONG if it's larger than long and the value fits

Cython/Utility/Optimize.c

@@ -470,6 +470,9 @@ static PyObject* __Pyx__PyNumber_PowerOf2(PyObject *two, PyObject *exp, PyObject
         if ((size_t)shiftby <= sizeof(long) * 8 - 2) {
             long value = 1L << shiftby;
             return PyInt_FromLong(value);
+        } else if ((size_t)shiftby <= sizeof(unsigned PY_LONG_LONG) * 8 - 1) {
+            unsigned PY_LONG_LONG value = ((unsigned PY_LONG_LONG)1) << shiftby;
+            return PyLong_FromUnsignedLongLong(value);
         } else {
             PyObject *one = PyInt_FromLong(1L);
             if (unlikely(!one)) return NULL;

tests/run/powop.pyx

@@ -107,6 +107,10 @@ def optimised_pow2(n):
     1073741824
     >>> print(repr(optimised_pow2(32)).rstrip('L'))
     4294967296
+    >>> print(repr(optimised_pow2(60)).rstrip('L'))
+    1152921504606846976
+    >>> print(repr(optimised_pow2(64)).rstrip('L'))
+    18446744073709551616
     >>> print(repr(optimised_pow2(100)).rstrip('L'))
     1267650600228229401496703205376
     >>> optimised_pow2(30000) == 2 ** 30000