my $buf;
sub gen_salva2 {
    print "$buf\n";
    while (length $buf < $len) {
        $buf .= $set[rand @set] for (1..$len*100);
        $buf =~ s/(.)\1{$max_reps,}/$1 x $max_reps/ge;
    }
    substr($buf, -$len, $len, '');
}