code: def _mantissa(dval):
      
  
      bb = _double_as_bytes(dval)
      mantissa =  bb[1] & 0x0f << 48
      mantissa += bb[2] << 40
      mantissa += bb[3] << 32
      mantissa += bb[4]
      return mantissa
docs: Extract the _mantissa bits from a double-precision floating
      point value.