The Floating-Point Underflow Detection routine enables or
    disables floating-point underflow detection for the calling
    routine activation. The previous setting is returned as a
    function value.

    This routine is available on OpenVMS Alpha and I64 systems in
    translated form and is applicable to translated VAX images only.

    Format

      LIB$FLT_UNDER  new-setting

1  –  Returns

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

    The old floating-point underflow enable setting (the previous
    contents of the SF$W_PSW[PSW$V_FU] in the caller's frame).

2  –  Argument

 new-setting

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    New floating-point underflow enable setting. The new-setting
    argument is the address of an unsigned byte containing the
    new setting. Bit 0 set to 1 means enable; bit 0 set to 0 means
    disable.