the quick brown fox
brownbrownbrownbrown
..........00000.....

##</code><code>##

xxxyyxxy
yyyxyxxyyyxyxx
....0000...... False match

abcdefga
abcdefgabcdefg
00000000...... False match

##</code><code>##

sub lcssN (\$\$;$) {
    my( $ref1, $ref2, $min ) = @_;
    my( $swapped, $l1, $l2 ) = ( 0, map length( $$_ ), $ref1, $ref2 );
    ( $l2, $ref2, $l1, $ref1, $swapped ) = ( $l1, $ref1, $l2, $ref2, 1 ) if $l1 > $l2;
    $min = 1 unless defined $min;

    my $mask = $$ref1 x ( int( $l2 / $l1 ) + 1 );

    my @match = '';
    for my $start ( 0 .. $l1-1 ) {
        my $masked = substr( $mask, $start, $l2 ) ^ $$ref2;
        while( $masked =~ m[\0{$min,}]go ) {
            my $l = $+[ 0 ] - $-[ 0 ];
            my $match = substr( $$ref2, $-[ 0 ], $l );
            next unless 1+index $$ref1, $match;
            @match = (
                $match,
                ( $-[ 0 ]+$start ) % $l1,
                $-[ 0 ]
            ) if $l > length $match[ 0 ];
        }
    }
    @match[ 2, 1 ] = @match[ 1, 2 ] if $swapped;
    return unless $match[ 0 ];
    return wantarray ? @match : $match[ 0 ];
}

##</code><code>##

sub lcssN (\$\$;$) {
    my( $ref1, $ref2, $min ) = @_;
    my( $swapped, $l1, $l2 ) = ( 0, map length( $$_ ), $ref1, $ref2 );
    ( $l2, $ref2, $l1, $ref1, $swapped ) = ( $l1, $ref1, $l2, $ref2, 1 ) if $l1 > $l2;
    $min = 1 unless defined $min;

    my $mask = $$ref1 x ( int( $l2 / $l1 ) );

    my @match = '';
    for my $start ( 0 .. $l1-1 ) {
        my $masked = substr( $mask, $start, $l2 ) ^ $$ref2;
        while( $masked =~ m[\0{$min,}]go ) {
            my $l = $+[ 0 ] - $-[ 0 ];
            my $match = substr( $$ref2, $-[ 0 ], $l );
            @match = (
                $match,
                ( $-[ 0 ]+$start ) % $l1,
                $-[ 0 ]
            ) if $l > length $match[ 0 ];
        }
    }
    @match[ 2, 1 ] = @match[ 1, 2 ] if $swapped;
    return unless $match[ 0 ];
    return wantarray ? @match : $match[ 0 ];
}