Function Vector_slerp

source/blender/python/mathutils/mathutils_Vector.cc:1431–1501

    "   :return: The interpolated vector.\n"
    "   :rtype: :class:`Vector`\n");
static PyObject *Vector_slerp(VectorObject *self, PyObject *args)
{
  const int vec_num = self->vec_num;
  PyObject *value = nullptr;
  float fac, cosom, w[2];
  float self_vec[3], other_vec[3], ret_vec[3];
  float self_len_sq, other_len_sq;
  int x;
  PyObject *fallback = nullptr;

  if (!PyArg_ParseTuple(args, "Of|O:slerp", &value, &fac, &fallback)) {
    return nullptr;
  }

  if (BaseMath_ReadCallback(self) == -1) {
    return nullptr;
  }

  if (self->vec_num > 3) {
    PyErr_SetString(PyExc_ValueError, "Vector must be 2D or 3D");
    return nullptr;
  }

  if (mathutils_array_parse(
          other_vec, vec_num, vec_num, value, "Vector.slerp(other), invalid 'other' arg") == -1)
  {
    return nullptr;
  }

  self_len_sq = normalize_vn_vn(self_vec, self->vec, vec_num);
  other_len_sq = normalize_vn(other_vec, vec_num);

  /* use fallbacks for zero length vectors */
  if (UNLIKELY((self_len_sq < FLT_EPSILON) || (other_len_sq < FLT_EPSILON))) {
    /* avoid exception */
    if (fallback) {
      Py_INCREF(fallback);
      return fallback;
    }

    PyErr_SetString(PyExc_ValueError,
                    "Vector.slerp(): "
                    "zero length vectors unsupported");
    return nullptr;
  }

  /* We have sane state, execute slerp */
  cosom = float(dot_vn_vn(self_vec, other_vec, vec_num));

  /* direct opposite, can't slerp */
  if (UNLIKELY(cosom < (-1.0f + FLT_EPSILON))) {
    /* avoid exception */
    if (fallback) {
      Py_INCREF(fallback);
      return fallback;
    }

    PyErr_SetString(PyExc_ValueError,