FABS            Absolute value                       Exceptions: I
                                                     C3 C2 C1 C0: ? ? * ?
FABS

        Logic   ST ← abs(ST)

    FABS replaces the contents of ST with its absolute value, i.e.
    forces it to a positive value by clearing its sign bit.


    Opcode      Format
    D9 E1       FABS


    Timing
    Operand       8087         287        387      486     Pentium
    -            10-17        10-17       22        3       1      FX