FCHS            Change sign                          Exceptions: I
                                                     C3 C2 C1 C0: ? ? * ?
FCHS

        Logic   ST ← -1 * ST

    FCHS inverts the sign bit of ST. Thus, it converts a positive number
    into a negative number, or vice versa.


    Opcode      Format
    D9 E0       FCHS


    Timing
    Operand       8087         287        387      486     Pentium
    -            10-17        10-17      24-25      6       1      FX