my $obj = bless {datahash => \%datahash, ...};

$obj->sub1 ();
$obj->sub2 ();
...

sub sub1 {
    my $self = shift;

    $self->sub3 (wibble => 3);
}

...

sub sub3 {
    my ($self, %params) = @_;

    for my $key (keys %{$self->{datahash}}) {
        my $value = $self->{datahash}{$key} * $params->{wibble};
        ...
    }
}