lzb2_file_compression.pl

#!/usr/bin/perl

# Author: Trizen
# Date: 11 May 2024
# Edit: 02 June 2024
# https://github.com/trizen

# Compress/decompress files using LZ77 compression (LZSS variant with hash tables), using a byte-aligned encoding, similar to LZ4.

# References:
#   https://github.com/lz4/lz4/blob/dev/doc/lz4_Frame_format.md
#   https://github.com/lz4/lz4/blob/dev/doc/lz4_Block_format.md

use 5.036;
use Getopt::Std    qw(getopts);
use File::Basename qw(basename);

use constant {
    PKGNAME => 'LZB2',
    VERSION => '0.01',
    FORMAT  => 'lzb2',

    MIN_MATCH_LEN  => 4,                # minimum match length
    MAX_MATCH_LEN  => ~0,               # maximum match length
    MAX_MATCH_DIST => (1 << 16) - 1,    # maximum match distance
    MAX_CHAIN_LEN  => 48,               # higher value = better compression

    CHUNK_SIZE => 1 << 18,
};

# 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 lzss_encode($str) {

    my $la = 0;

    my @symbols = unpack('C*', $str);
    my $end     = $#symbols;

    my $min_len       = MIN_MATCH_LEN;     # minimum match length
    my $max_len       = MAX_MATCH_LEN;     # maximum match length
    my $max_dist      = MAX_MATCH_DIST;    # maximum match distance
    my $max_chain_len = MAX_CHAIN_LEN;     # how many recent positions to keep track of

    my (@literals, @distances, @lengths, %table);

    while ($la <= $end) {

        my $best_n = 1;
        my $best_p = $la;

        my $lookahead = substr($str, $la, $min_len);

        if (exists($table{$lookahead})) {

            foreach my $p (@{$table{$lookahead}}) {

                last if ($la - $p > $max_dist);

                my $n = $min_len;

                while ($n <= $max_len and $la + $n <= $end and $symbols[$la + $n - 1] == $symbols[$p + $n - 1]) {
                    ++$n;
                }

                if ($n > $best_n) {
                    $best_p = $p;
                    $best_n = $n;
                }
            }

            my $matched = substr($str, $la, $best_n);

            foreach my $i (0 .. length($matched) - $min_len) {

                my $key = substr($matched, $i, $min_len);
                unshift @{$table{$key}}, $la + $i;

                if (scalar(@{$table{$key}}) > $max_chain_len) {
                    pop @{$table{$key}};
                }
            }
        }

        if ($best_n == 1) {
            $table{$lookahead} = [$la];
        }

        if ($best_n > $min_len) {

            push @lengths,   $best_n - 1;
            push @distances, $la - $best_p;
            push @literals,  undef;

            $la += $best_n - 1;
        }
        else {

            push @lengths,   (0) x $best_n;
            push @distances, (0) x $best_n;
            push @literals, @symbols[$best_p .. $best_p + $best_n - 1];

            $la += $best_n;
        }
    }

    return (\@literals, \@distances, \@lengths);
}

sub compression($chunk, $out_fh) {
    my ($literals, $distances, $lengths) = lzss_encode($chunk);

    my $literals_end = $#{$literals};

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

        my @uncompressed;
        while ($i <= $literals_end and defined($literals->[$i])) {
            push @uncompressed, $literals->[$i];
            ++$i;
        }

        my $literals_string = pack('C*', @uncompressed);
        my $literals_length = scalar(@uncompressed);

        my $dist      = $distances->[$i] // 0;
        my $match_len = $lengths->[$i]   // 0;

        my $len_byte = 0;

        $len_byte |= ($literals_length >= 7 ? 7  : $literals_length) << 5;
        $len_byte |= ($match_len >= 31      ? 31 : $match_len);

        $literals_length -= 7;
        $match_len       -= 31;

        print $out_fh chr($len_byte);

        while ($literals_length >= 0) {
            print $out_fh chr($literals_length >= 255 ? 255 : $literals_length);
            $literals_length -= 255;
        }

        print $out_fh $literals_string;

        while ($match_len >= 0) {
            print $out_fh chr($match_len >= 255 ? 255 : $match_len);
            $match_len -= 255;
        }

        if ($dist >= 1 << 16) {
            die "Too large distance: $dist";
        }

        print $out_fh pack('B*', sprintf('%016b', $dist));
    }

}

sub decompression($fh, $out_fh) {

    my $search_window = '';

    while (!eof($fh)) {

        my $len_byte = ord(getc($fh));

        my $literals_length = $len_byte >> 5;
        my $match_len       = $len_byte & 0b11111;

        if ($literals_length == 7) {
            while (1) {
                my $byte_len = ord(getc($fh));
                $literals_length += $byte_len;
                last if $byte_len != 255;
            }
        }

        my $literals = '';
        if ($literals_length > 0) {
            read($fh, $literals, $literals_length);
        }

        if ($match_len == 31) {
            while (1) {
                my $byte_len = ord(getc($fh));
                $match_len += $byte_len;
                last if $byte_len != 255;
            }
        }

        my $offset = oct('0b' . unpack('B*', getc($fh) . getc($fh)));

        $search_window .= $literals;

        if ($offset == 1) {
            $search_window .= substr($search_window, -1) x $match_len;
        }
        elsif ($offset >= $match_len) {    # non-overlapping matches
            $search_window .= substr($search_window, length($search_window) - $offset, $match_len);
        }
        else {                             # overlapping matches
            foreach my $i (1 .. $match_len) {
                $search_window .= substr($search_window, length($search_window) - $offset, 1);
            }
        }

        print $out_fh substr($search_window, -($match_len + $literals_length));
        $search_window = substr($search_window, -MAX_MATCH_DIST) if (length($search_window) > 2 * MAX_MATCH_DIST);
    }
}

# 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);