4. NAN: the protagonist here, if the index is a whole, ending a non-zero, it indicates that this va

+ ------ + ---------------- + ------------------------- ------ + | 1bit | 8bit | 23bit | + ------ + ---------------- + ----------- -------------------- +
4. NAN: the protagonist here, if the index is a whole, ending a non-zero, it indicates that this value is not a true value (Not A Number). NAN is divided into two categories: QNAN (Quiet NAN) and SNAN (Singaling NAN). QNAN SNAN differs from that of the highest bit mantissa part QNAN defined as 1, SNAN MSB is defined as 0; QNAN generally expressed undefined arithmetic result, the most common way to divide by zero operation; SNAN generally used mark uninitialized value, in order to catch the exception.