rlh_file_compression.pl

#!/usr/bin/perl

# Author: Trizen
# Date: 13 August 2023
# https://github.com/trizen

# Compress/decompress files using Run-length encoding + Huffman coding.

use 5.036;

use Getopt::Std    qw(getopts);
use File::Basename qw(basename);
use List::Util     qw(max uniq);

use constant {
    PKGNAME => 'RLH',
    VERSION => '0.01',
    FORMAT  => 'rlh',

    CHUNK_SIZE => 1 << 15,
};

# Container signature
use constant SIGNATURE => uc(FORMAT) . chr(1);

sub usage {
    my ($code) = @_;
    print <<"EOH";
usage: $0 [options] [input file] [output file]

options:
        -e            : extract
        -i <filename> : input filename
        -o <filename> : output filename
        -r            : rewrite output

        -v            : version number
        -h            : this message

examples:
         $0 document.txt
         $0 document.txt archive.${\FORMAT}
         $0 archive.${\FORMAT} document.txt
         $0 -e -i archive.${\FORMAT} -o document.txt

EOH

    exit($code // 0);
}

sub version {
    printf("%s %s\n", PKGNAME, VERSION);
    exit;
}

sub valid_archive {
    my ($fh) = @_;

    if (read($fh, (my $sig), length(SIGNATURE), 0) == length(SIGNATURE)) {
        $sig eq SIGNATURE || return;
    }

    return 1;
}

sub main {
    my %opt;
    getopts('ei:o:vhr', \%opt);

    $opt{h} && usage(0);
    $opt{v} && version();

    my ($input, $output) = @ARGV;
    $input  //= $opt{i} // usage(2);
    $output //= $opt{o};

    my $ext = qr{\.${\FORMAT}\z}io;
    if ($opt{e} || $input =~ $ext) {

        if (not defined $output) {
            ($output = basename($input)) =~ s{$ext}{}
              || die "$0: no output file specified!\n";
        }

        if (not $opt{r} and -e $output) {
            print "'$output' already exists! -- Replace? [y/N] ";
            <STDIN> =~ /^y/i || exit 17;
        }

        decompress_file($input, $output)
          || die "$0: error: decompression failed!\n";
    }
    elsif ($input !~ $ext || (defined($output) && $output =~ $ext)) {
        $output //= basename($input) . '.' . FORMAT;
        compress_file($input, $output)
          || die "$0: error: compression failed!\n";
    }
    else {
        warn "$0: don't know what to do...\n";
        usage(1);
    }
}

sub read_bit ($fh, $bitstring) {

    if (($$bitstring // '') eq '') {
        $$bitstring = unpack('b*', getc($fh) // return undef);
    }

    chop($$bitstring);
}

sub read_bits ($fh, $bits_len) {

    my $data = '';
    read($fh, $data, $bits_len >> 3);
    $data = unpack('B*', $data);

    while (length($data) < $bits_len) {
        $data .= unpack('B*', getc($fh) // return undef);
    }

    if (length($data) > $bits_len) {
        $data = substr($data, 0, $bits_len);
    }

    return $data;
}

sub delta_encode ($integers, $double = 0) {

    my @deltas;
    my $prev = 0;

    unshift(@$integers, scalar(@$integers));

    while (@$integers) {
        my $curr = shift(@$integers);
        push @deltas, $curr - $prev;
        $prev = $curr;
    }

    my $bitstring = '';

    foreach my $d (@deltas) {
        if ($d == 0) {
            $bitstring .= '0';
        }
        elsif ($double) {
            my $t = sprintf('%b', abs($d) + 1);
            my $l = sprintf('%b', length($t));
            $bitstring .= '1' . (($d < 0) ? '0' : '1') . ('1' x (length($l) - 1)) . '0' . substr($l, 1) . substr($t, 1);
        }
        else {
            my $t = sprintf('%b', abs($d));
            $bitstring .= '1' . (($d < 0) ? '0' : '1') . ('1' x (length($t) - 1)) . '0' . substr($t, 1);
        }
    }

    pack('B*', $bitstring);
}

sub delta_decode ($fh, $double = 0) {

    my @deltas;
    my $buffer = '';
    my $len    = 0;

    for (my $k = 0 ; $k <= $len ; ++$k) {
        my $bit = read_bit($fh, \$buffer);

        if ($bit eq '0') {
            push @deltas, 0;
        }
        elsif ($double) {
            my $bit = read_bit($fh, \$buffer);

            my $bl = 0;
            ++$bl while (read_bit($fh, \$buffer) eq '1');

            my $bl2 = oct('0b1' . join('', map { read_bit($fh, \$buffer) } 1 .. $bl));
            my $int = oct('0b1' . join('', map { read_bit($fh, \$buffer) } 1 .. ($bl2 - 1)));

            push @deltas, ($bit eq '1' ? 1 : -1) * ($int - 1);
        }
        else {
            my $bit = read_bit($fh, \$buffer);
            my $n   = 0;
            ++$n while (read_bit($fh, \$buffer) eq '1');
            my $d = oct('0b1' . join('', map { read_bit($fh, \$buffer) } 1 .. $n));
            push @deltas, ($bit eq '1' ? $d : -$d);
        }

        if ($k == 0) {
            $len = pop(@deltas);
        }
    }

    my @acc;
    my $prev = $len;

    foreach my $d (@deltas) {
        $prev += $d;
        push @acc, $prev;
    }

    return \@acc;
}

# produce encode and decode dictionary from a tree
sub walk ($node, $code, $h, $rev_h) {

    my $c = $node->[0] // return ($h, $rev_h);
    if (ref $c) { walk($c->[$_], $code . $_, $h, $rev_h) for ('0', '1') }
    else        { $h->{$c} = $code; $rev_h->{$code} = $c }

    return ($h, $rev_h);
}

# make a tree, and return resulting dictionaries
sub mktree_from_freq ($freq) {

    my @nodes = map { [$_, $freq->{$_}] } sort { $a <=> $b } keys %$freq;

    do {    # poor man's priority queue
        @nodes = sort { $a->[1] <=> $b->[1] } @nodes;
        my ($x, $y) = splice(@nodes, 0, 2);
        if (defined($x)) {
            if (defined($y)) {
                push @nodes, [[$x, $y], $x->[1] + $y->[1]];
            }
            else {
                push @nodes, [[$x], $x->[1]];
            }
        }
    } while (@nodes > 1);

    walk($nodes[0], '', {}, {});
}

sub huffman_encode ($bytes, $dict) {
    join('', @{$dict}{@$bytes});
}

sub huffman_decode ($bits, $hash) {
    local $" = '|';
    [split(' ', $bits =~ s/(@{[sort { length($a) <=> length($b) } keys %{$hash}]})/$hash->{$1} /gr)];    # very fast
}

sub create_huffman_entry ($bytes, $out_fh) {

    my %freq;
    ++$freq{$_} for @$bytes;

    my ($h, $rev_h) = mktree_from_freq(\%freq);
    my $enc = huffman_encode($bytes, $h);

    my @symbols = sort { $a <=> $b } keys(%freq);

    print $out_fh delta_encode([@symbols]);
    print $out_fh delta_encode([map { $freq{$_} } @symbols], 1);

    print $out_fh pack("N",  length($enc));
    print $out_fh pack("B*", $enc);
}

sub decode_huffman_entry ($fh) {

    my $symbols = delta_decode($fh);
    my $freqs   = delta_decode($fh, 1);

    my %freq;
    foreach my $i (0 .. $#{$symbols}) {
        $freq{$symbols->[$i]} = $freqs->[$i];
    }

    my (undef, $rev_dict) = mktree_from_freq(\%freq);

    my $enc_len = unpack('N', join('', map { getc($fh) // die "error" } 1 .. 4));
    say "Encoded length: $enc_len";

    if ($enc_len > 0) {
        return huffman_decode(read_bits($fh, $enc_len), $rev_dict);
    }

    return [];
}

sub rle4_encode ($bytes) {    # RLE1

    my @rle;
    my $end  = $#{$bytes};
    my $prev = -1;
    my $run  = 0;

    for (my $i = 0 ; $i <= $end ; ++$i) {

        if ($bytes->[$i] == $prev) {
            ++$run;
        }
        else {
            $run = 1;
        }

        push @rle, $bytes->[$i];
        $prev = $bytes->[$i];

        if ($run >= 4) {

            $run = 0;
            $i += 1;

            while ($i <= $end and $bytes->[$i] == $prev) {
                ++$run;
                ++$i;
            }

            push @rle, $run;
            $run = 1;

            if ($i <= $end) {
                $prev = $bytes->[$i];
                push @rle, $bytes->[$i];
            }
        }
    }

    return \@rle;
}

sub rle4_decode ($bytes) {    # RLE1

    my @dec  = $bytes->[0];
    my $end  = $#{$bytes};
    my $prev = $bytes->[0];
    my $run  = 1;

    for (my $i = 1 ; $i <= $end ; ++$i) {

        if ($bytes->[$i] == $prev) {
            ++$run;
        }
        else {
            $run = 1;
        }

        push @dec, $bytes->[$i];
        $prev = $bytes->[$i];

        if ($run >= 4) {
            if (++$i <= $end) {
                $run = $bytes->[$i];
                push @dec, (($prev) x $run);
            }

            $run = 0;
        }
    }

    return \@dec;
}

sub compression ($chunk, $out_fh) {
    my $bytes = [unpack('C*', $chunk)];
    $bytes = rle4_encode($bytes);
    create_huffman_entry($bytes, $out_fh);
}

sub decompression ($fh, $out_fh) {
    my $bytes = decode_huffman_entry($fh);
    $bytes = rle4_decode($bytes);
    print $out_fh pack('C*', @$bytes);
}

# Compress file
sub compress_file ($input, $output) {

    open my $fh, '<:raw', $input
      or die "Can't open file <<$input>> for reading: $!";

    my $header = SIGNATURE;

    # Open the output file for writing
    open my $out_fh, '>:raw', $output
      or die "Can't open file <<$output>> for write: $!";

    # Print the header
    print $out_fh $header;

    # Compress data
    while (read($fh, (my $chunk), CHUNK_SIZE)) {
        compression($chunk, $out_fh);
    }

    # Close the file
    close $out_fh;
}

# Decompress file
sub decompress_file ($input, $output) {

    # Open and validate the input file
    open my $fh, '<:raw', $input
      or die "Can't open file <<$input>> for reading: $!";

    valid_archive($fh) || die "$0: file `$input' is not a \U${\FORMAT}\E v${\VERSION} archive!\n";

    # Open the output file
    open my $out_fh, '>:raw', $output
      or die "Can't open file <<$output>> for writing: $!";

    while (!eof($fh)) {
        decompression($fh, $out_fh);
    }

    # Close the file
    close $fh;
    close $out_fh;
}

main();
exit(0);