/IEEE_MODE

    /IEEE_MODE=option
    /IEEE_MODE=DENORM_RESULTS (D)

 Selects the IEEE floating-point mode to be used.

 Options:

  FAST              During program execution, only finite values (no
                    infinities, NaNs, or denorms) are created.
                    Exceptional conditions, such as floating point
                    overflow and divide by zero, are fatal.

  UNDERFLOW_TO_ZERO Generate infinities and NaNs.  Flush
                    denormalized results and underflow to zero
                    without exceptions.

  DENORM_RESULTS    Same as UNDERFLOW_TO_ZERO, except that denorms
                    are generated.  This is the default for I64
                    systems.

  INEXACT           Same as DENORM_RESULTS, except that inexact
                    values are trapped.  This is the slowest mode.

 On Alpha sytems, the /IEEE_MODE qualifier generally has its
 greatest effect on the generated code of a compilation.  When calls
 are made between functions compiled with different /IEEE_MODE
 qualifiers, each function produces the /IEEE_MODE behavior with
 which it was compiled.

 On I64 systems, the /IEEE_MODE qualifier primarily affects only the
 setting of a hardware register at program startup.  In general, the
 /IEEE_MODE behavior for a given function is controlled by the
 /IEEE_MODE option specified on the compilation that produced the
 main program:  the startup code for the main program sets the
 hardware register according the command-line qualifiers used to
 compile the main program.

 When applied to a compilation that does not contain a main program,
 the /IEEE_MODE qualifier does have some effect:  it might affect
 the evaluation of floating-point constant expressions, and it is
 used to set the EXCEPTION_MODE used by the math library for calls
 from that compilation.  But the qualifier has no effect on the
 exceptional behavior of floating-point calculations generated as
 inline code for that compilation.  Therefore, if floating-point
 exceptional behavior is important to an application, all of its
 compilations, including the one containing the main program, should
 be compiled with the same /IEEE_MODE setting.

 Even on Alpha systems, the particular setting of
 /IEEE_MODE=UNDERFLOW_TO_ZERO has this characteristic:  its primary
 effect requires the setting of a runtime status register, and so it
 needs to be specified on the compilation containing the main
 program in order to be effective in other compilations.