F2XM1           Compute 2 to the Xth power - 1       Exceptions: P U D I S
                                                     (operands not checked)
F2XM1                                                C3 C2 C1 C0: ? ? * ?

        Logic   ST ← 2**ST - 1

    F2MX1 calculates 2 to the power X and subtracts 1 from the result.
    X is taken from ST and must be 0 < X < .5 on the 8087 and 80287,
    or -1.0 < X < 1.0 on the 387+. If X is outside the acceptable range,
    F2XM1 produces an unpredictable result.

    This instruction provides increased accuracy over 2**X when X is
    near 0 (for example, when calculating hyperbolic trignometric
    functions).


    Opcode      Format
    D9 F0       F2XM1


    Timing
    Operand       8087         287        387      486     Pentium
    -           310-630      310-630    211-476  140-279   13-57   NP