use strict;
use warnings;

my $seq='ACGGGAGGACGGGAAAATTACTACGGCATTAGC';
my $rev='';
my $n = length $seq; while( $n-- ){ $rev .= $_ for map chr($_&2?$_^4:$_^21), ord substr $seq, $n, 1 }
print "$seq\n$rev\n";

##</code><code>##

use strict;
use warnings;

my $seq='ACGGGAGGACGGGAAAATTACTACGGCATTAGC';
my $rev='';
$rev = "$_$rev" for map chr($_&2?$_^4:$_^21), map ord, split//,$seq;
print "$seq\n$rev\n";