FUCOM             Unordered Compare (80387)   Exception Flags: I D S

FUCOM [register]

       Logic:      sets condition codes in the status word:

                   C3 C2 C1 C0    Means
                   -- -- -- --    -----------
                   0  0  ?  0     ST > source
                   0  0  ?  1     ST < source
                   1  0  ?  0     ST = source
                   1  1  ?  1     unordered

     FUCOM compares two registers and leaves the result encoded in the
     status word as shown above. If no register is specified, ST(1)
     is compared to ST. Otherwise, register is compared to ST.

     FUCOM is like FCOM except that it does not cause an invalid
     operation exception if one of the operands is a NAN. Instead, it
     sets the condition codes to give an unordered result.

  --------------------------------------------------------------------------
   Operands            Clocks         Bytes           Example
   FUCOM reg           24               3             FUCOM ST(1)
  --------------------------------------------------------------------------

        Note:          Use JP to test for an unordered comparison.