FASTIMUL         Optimized IMUL                                     Extension

  FASTIMUL destination_reg, source_r/m, value

    Generates code that multiplies source register or memory address by
    value (a fixed, signed constant), and puts it into destination register.

    This function (which is available even if the 8086 processor has been
    selected) changes the contents of source_r/m, and leaves the processor
    flags in an indeterminate state. FASTIMUL uses a combination of IMUL,
    MOV, NEG, SHL, ADD, and SUB instructions to perform its function.

    Example:    P8086
                fastimul dx,cx,10

                ; will generate this code:
                shl     cx,1
                mov     dx,cx
                shl     cx,1
                shl     cx,1
                add     dx,cx