FSCALE          Scale by a power of 2                Exceptions: I O U
                                                     C3 C2 C1 C0: ? ? * ?
FSCALE

        Logic   ST ← ST * 2**ST(1)

    FSCALE interprets the contents of ST(1) as an integer, and uses it
    as an exponent of 2 with which to multiply the contents of ST. Thus,
    FSCALE provides a quick way to multiply or divide by a power of 2.

    The number in ST(1) must be -2**15 <= ST(1) < 2**15. It is truncated
    before the operation is performed. If 0 < ST(1) < 1, the result is
    undefined (and no exception is generated).


    Opcode      Format
    D9 FD       FSCALE


    Timing
    Operand       8087         287        387      486     Pentium
    -            32-38        32-38      67-86    30-32    20-31   NP