FCOS            Cosine                               Exceptions: P U D I S
                                                     C3 C2 C1 C0: ? * * ?
FCOS                                                 FPU: 387+

        Logic   ST ← cos(ST)

    FCOS replaces ST with the value of its cosine. The absolute value of
    ST, expressed in radians, must be below 2**63. If it is not, C2 is
    set and ST remains unchanged.

    
    Note
    The 80486+ checks for interrupts while executing this instruction.
    It will abort FCOS to service an interrupt.


    Opcode      Format
    D9 FF       FCOS


    Timing
    Operand       8087         287        387      486     Pentium
    -              -            -       123-772  257-354   18-124  NP

        Additional cycles required if operand > pi/4 (~3.141/4 = ~.785)