Portability fix and a minor style fix

Author: mdickinson

Modules/mathmodule.c

@@ -3908,19 +3908,29 @@ math_nextafter_impl(PyObject *module, double x, double y, PyObject *steps)
  return NULL;
  }
 
- uint64_t usteps = PyLong_AsUnsignedLongLong(steps);
+ unsigned long long usteps_ull = PyLong_AsUnsignedLongLong(steps);
  // Conveniently, uint64_t and double have the same number of bits
  // on all the platforms we care about.
  // So if an overflow occurs, we can just use UINT64_MAX.
- if (usteps == (unsigned long long)-1 && PyErr_Occurred()) {
- if(!PyErr_ExceptionMatches(PyExc_OverflowError)) {
- Py_DECREF(steps);
- return NULL;
+ Py_DECREF(steps);
+ if (usteps_ull >= UINT64_MAX) {
+ // This branch includes the case where an error occurred, since
+ // (unsigned long long)(-1) = ULLONG_MAX >= UINT64_MAX. Note that
+ // usteps_ull can be strictly larger than UINT64_MAX on a machine
+ // where unsigned long long has width > 64 bits.
+ if (PyErr_Occurred()) {
+ if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
+ PyErr_Clear();
+ }
+ else {
+ return NULL;
+ }
  }
- PyErr_Clear();
- usteps = UINT64_MAX;
+ usteps_ull = UINT64_MAX;
  }
- Py_DECREF(steps);
+ assert(usteps_ull <= UINT64_MAX);
+ uint64_t usteps = (uint64_t)usteps_ull;
+
  if (usteps == 0) {
  return PyFloat_FromDouble(x);
  }
@@ -3937,7 +3947,7 @@ math_nextafter_impl(PyObject *module, double x, double y, PyObject *steps)
  // would be a "mixed-endian" double.)
  union pun {double f; uint64_t i;};
  union pun ux = {x}, uy = {y};
- if(ux.i == uy.i) {
+ if (ux.i == uy.i) {
  return PyFloat_FromDouble(x);
  }