my $l = $r->_blind_len($in);
my $mask = $r->_random(($l+1)>>1);
$mask = substr $mask, 0, $l;
my $blound = $r->_blind_combine($in, $mask);
my $l = $r->_blind_len($in);
my $mask = $r->_random(($l+1)>>1);
$mask = substr $mask, 0, $l;
my $blound = $r->_blind_combine($in, $mask);