package Somename;
use Math::BigFloat;

sub new {
    my $class = shift;
    my $self = bless {};
    $self -> { underlying } = Math::BigFloat -> new( @_ );
    return ( $self, $class );
}

sub fsetround { # e.g. $obj -> fsetround( mode => 'FE_DOWNWARD' );
    my $self = shift;
    my %opt = @_;
    while ( my ( $k, $v ) = each %opt ) {
        $self -> { $k } = $v;
    }

    # set defaults here e.g. for round by default 
    # to 17 digits from the left
    $self -> { scale } ||= 17; 

}

sub fgetround
    my $self = shift;

    if ( $self -> { mode } eq 'FE_DOWNWARD' ) {
        my $bf = $self -> { underlying };
        return $bf -> ffround( -( $self -> { scale } ) );
    }
    # elsif ...
    # etc. for the other features of fenv 
}