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lzih_file_compression.pl
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lzih_file_compression.pl
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#!/usr/bin/perl
# Author: Trizen
# Date: 15 December 2022
# Edit: 13 June 2023
# https://github.com/trizen
# Compress/decompress files using LZ77 compression + fixed-width integers encoding + Huffman coding.
use 5.020;
use strict;
use warnings;
use experimental qw(signatures);
use Getopt::Std qw(getopts);
use File::Basename qw(basename);
use List::Util qw(max);
use constant {
PKGNAME => 'LZIH',
VERSION => '0.04',
FORMAT => 'lzih',
CHUNK_SIZE => 1 << 16, # higher value = better compression
};
# Container signature
use constant SIGNATURE => uc(FORMAT) . chr(4);
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 "$0: don't know what to do...\n";
usage(1);
}
}
sub lz77_compression ($str, $uncompressed, $indices, $lengths) {
my $la = 0;
my $prefix = '';
my @chars = split(//, $str);
my $end = $#chars;
while ($la <= $end) {
my $n = 1;
my $p = length($prefix);
my $tmp;
my $token = $chars[$la];
while ( $n < 255
and $la + $n <= $end
and ($tmp = rindex($prefix, $token, $p)) >= 0) {
$p = $tmp;
$token .= $chars[$la + $n];
++$n;
}
--$n;
push @$indices, $la - $p;
push @$lengths, $n;
push @$uncompressed, ord($chars[$la + $n]);
$la += $n + 1;
$prefix .= $token;
}
return;
}
sub lz77_decompression ($uncompressed, $indices, $lengths) {
my $chunk = '';
my $offset = 0;
foreach my $i (0 .. $#{$uncompressed}) {
$chunk .= substr($chunk, $offset - $indices->[$i], $lengths->[$i]) . $uncompressed->[$i];
$offset += $lengths->[$i] + 1;
}
return $chunk;
}
sub read_bit ($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) {
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';
}
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) {
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;
}
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, $prev;
}
return \@acc;
}
sub encode_integers ($integers) {
my @counts;
my $count = 0;
my $bits_width = 1;
my $bits_max_symbol = 1 << $bits_width;
my $processed_len = 0;
foreach my $k (@$integers) {
while ($k >= $bits_max_symbol) {
if ($count > 0) {
push @counts, [$bits_width, $count];
$processed_len += $count;
}
$count = 0;
$bits_max_symbol *= 2;
$bits_width += 1;
}
++$count;
}
push @counts, grep { $_->[1] > 0 } [$bits_width, scalar(@$integers) - $processed_len];
my $compressed = delta_encode([(map { $_->[0] } @counts), (map { $_->[1] } @counts)]);
my $bits = '';
foreach my $pair (@counts) {
my ($blen, $len) = @$pair;
foreach my $symbol (splice(@$integers, 0, $len)) {
$bits .= sprintf("%0*b", $blen, $symbol);
}
}
$compressed .= pack('B*', $bits);
return $compressed;
}
sub decode_integers ($fh) {
my $ints = delta_decode($fh);
my $half = scalar(@$ints) >> 1;
my @counts;
foreach my $i (0 .. ($half - 1)) {
push @counts, [$ints->[$i], $ints->[$half + $i]];
}
my $bits_len = 0;
foreach my $pair (@counts) {
my ($blen, $len) = @$pair;
$bits_len += $blen * $len;
}
my $bits = read_bits($fh, $bits_len);
my @integers;
foreach my $pair (@counts) {
my ($blen, $len) = @$pair;
foreach my $chunk (unpack(sprintf('(a%d)*', $blen), substr($bits, 0, $blen * $len, ''))) {
push @integers, oct('0b' . $chunk);
}
}
return \@integers;
}
# produce encode and decode dictionary from a tree
sub walk ($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 $" = '|';
$bits =~ s/(@{[sort { length($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 $max_symbol = max(keys %freq) // 0;
my @freqs;
foreach my $i (0 .. $max_symbol) {
push @freqs, $freq{$i} // 0;
}
print $out_fh delta_encode(\@freqs);
print $out_fh pack("N", length($enc));
print $out_fh pack("B*", $enc);
}
sub decode_huffman_entry ($fh) {
my @freqs = @{delta_decode($fh)};
my %freq;
foreach my $i (0 .. $#freqs) {
if ($freqs[$i]) {
$freq{$i} = $freqs[$i];
}
}
my (undef, $rev_dict) = mktree_from_freq(\%freq);
foreach my $k (keys %$rev_dict) {
$rev_dict->{$k} = chr($rev_dict->{$k});
}
my $enc_len = unpack('N', join('', map { getc($fh) // die "error" } 1 .. 4));
if ($enc_len > 0) {
return huffman_decode(read_bits($fh, $enc_len), $rev_dict);
}
return '';
}
# Compress file
sub compress_file ($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 $chunk), CHUNK_SIZE)) {
my (@uncompressed, @indices, @lengths);
lz77_compression($chunk, \@uncompressed, \@indices, \@lengths);
my $est_ratio = length($chunk) / (4 * scalar(@uncompressed));
say(scalar(@uncompressed), ' -> ', $est_ratio);
create_huffman_entry(\@uncompressed, $out_fh);
create_huffman_entry(\@lengths, $out_fh);
print $out_fh encode_integers(\@indices);
}
# 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)) {
my @uncompressed = split(//, decode_huffman_entry($fh));
my @lengths = unpack('C*', decode_huffman_entry($fh));
my $indices = decode_integers($fh);
print $out_fh lz77_decompression(\@uncompressed, $indices, \@lengths);
}
# Close the file
close $fh;
close $out_fh;
}
main();
exit(0);