Error compiling Cython file:
      ------------------------------------------------------------
      ...
              while len(self.pages) > 0 and self.pages[-1].count == 0:
                  self.pages.pop()

          cpdef add(self, usize_t number):
              """Add a positive integer to the bitfield"""
              cdef usize_t page = number / PAGE_FULL_COUNT
                                         ^
      ------------------------------------------------------------

      cimpl/field.pyx:463:35: Cannot assign type 'double' to 'usize_t'

      Error compiling Cython file:
      ------------------------------------------------------------
      ...
              the_page.add(page_index)

          cpdef remove(Bitfield self, usize_t number):
              """Remove a positive integer from the bitfield
              If the integer does not exist in the field, raise a KeyError"""
              cdef usize_t page_no = number / PAGE_FULL_COUNT
                                            ^
      ------------------------------------------------------------

      cimpl/field.pyx:472:38: Cannot assign type 'double' to 'usize_t'

      Error compiling Cython file:
      ------------------------------------------------------------
      ...
                  raise KeyError()

          cpdef discard(Bitfield self, usize_t number):
              """Remove a positive integer from the bitfield if it is a member.
              If the element is not a member, do nothing."""
              cdef usize_t page = number / PAGE_FULL_COUNT
                                         ^
      ------------------------------------------------------------

      cimpl/field.pyx:486:35: Cannot assign type 'double' to 'usize_t'