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- #!/usr/bin/perl
- # File compression with rANS encoding, using big integers.
- # Reference:
- # Stanford EE274: Data Compression I 2023 I Lecture 7 - ANS
- # https://youtube.com/watch?v=5Hp4bnvSjng
- use 5.036;
- use Getopt::Std qw(getopts);
- use File::Basename qw(basename);
- use List::Util qw(max);
- use Math::GMPz;
- use constant {
- PKGNAME => 'rANS',
- VERSION => '0.01',
- FORMAT => 'rans',
- };
- # Container signature
- use constant SIGNATURE => uc(FORMAT) . chr(1);
- sub usage ($code = 0) {
- 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);
- }
- sub version {
- printf("%s %s\n", PKGNAME, VERSION);
- exit;
- }
- 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($input, $output)
- || die "$0: error: decompression failed!\n";
- }
- elsif ($input !~ $ext || (defined($output) && $output =~ $ext)) {
- $output //= basename($input) . '.' . FORMAT;
- compress($input, $output)
- || die "$0: error: compression failed!\n";
- }
- else {
- warn "$0: don't know what to do...\n";
- usage(1);
- }
- }
- sub valid_archive ($fh) {
- if (read($fh, (my $sig), length(SIGNATURE), 0) == length(SIGNATURE)) {
- $sig eq SIGNATURE || return;
- }
- return 1;
- }
- sub read_bit ($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) {
- 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, $prev;
- }
- return \@acc;
- }
- sub cumulative_freq ($freq) {
- my %cf;
- my $total = Math::GMPz->new(0);
- foreach my $c (sort keys %{$freq}) {
- $cf{$c} = $total;
- $total += $freq->{$c};
- }
- return %cf;
- }
- sub rans_base_enc($freq, $cumul, $M, $x_prev, $s, $block_id, $x) {
- Math::GMPz::Rmpz_div_ui($block_id, $x_prev, $freq->{$s});
- my $r = Math::GMPz::Rmpz_mod_ui($x, $x_prev, $freq->{$s});
- my $slot = $cumul->{$s} + $r;
- Math::GMPz::Rmpz_mul_ui($x, $block_id, $M);
- Math::GMPz::Rmpz_add_ui($x, $x, $slot);
- return $x;
- }
- sub encode($input, $freq, $cumul, $M) {
- my $x = Math::GMPz::Rmpz_init_set_ui(0);
- my $block_id = Math::GMPz::Rmpz_init();
- my $next_x = Math::GMPz::Rmpz_init();
- foreach my $s (@$input) {
- $x = rans_base_enc($freq, $cumul, $M, $x, $s, $block_id, $next_x);
- }
- return $x;
- }
- sub rans_base_dec($alphabet, $freq, $cumul, $M, $x, $block_id, $slot, $x_prev) {
- Math::GMPz::Rmpz_tdiv_qr_ui($block_id, $slot, $x, $M);
- my ($left, $right, $mid, $cmp) = (0, $#{$alphabet});
- while (1) {
- $mid = ($left + $right) >> 1;
- $cmp = ($cumul->{$alphabet->[$mid]} <=> $slot) || last;
- if ($cmp < 0) {
- $left = $mid + 1;
- $left > $right and last;
- }
- else {
- $right = $mid - 1;
- if ($left > $right) {
- $mid -= 1;
- last;
- }
- }
- }
- my $s = $alphabet->[$mid];
- Math::GMPz::Rmpz_mul_ui($x_prev, $block_id, $freq->{$s});
- Math::GMPz::Rmpz_add($x_prev, $x_prev, $slot);
- Math::GMPz::Rmpz_sub_ui($x_prev, $x_prev, $cumul->{$s});
- return ($s, $x_prev);
- }
- sub decode($x, $alphabet, $freq, $cumul, $M) {
- my @dec;
- my $s = undef;
- my $block_id = Math::GMPz::Rmpz_init();
- my $slot = Math::GMPz::Rmpz_init();
- my $x_prev = Math::GMPz::Rmpz_init();
- for (1 .. $M) {
- ($s, $x) = rans_base_dec($alphabet, $freq, $cumul, $M, $x, $block_id, $slot, $x_prev);
- push @dec, $s;
- }
- return [reverse @dec];
- }
- sub compress ($input, $output) {
- # Open the input file
- open my $fh, '<:raw', $input;
- # Open the output file and write the archive signature
- open my $out_fh, '>:raw', $output;
- print {$out_fh} SIGNATURE;
- my $str = do {
- local $/;
- scalar(<$fh>);
- };
- close $fh;
- my (%freq, %cumul);
- my @symbols = unpack('C*', $str);
- ++$freq{$_} for @symbols;
- my @alphabet = sort { $a <=> $b } keys %freq;
- my $t = 0;
- foreach my $s (@alphabet) {
- $cumul{$s} = $t;
- $t += $freq{$s};
- }
- my $M = $t;
- my $enc = encode(\@symbols, \%freq, \%cumul, $M);
- my $bin = Math::GMPz::Rmpz_get_str($enc, 2);
- my $max_symbol = max(keys %freq) // 0;
- my @freqs;
- foreach my $k (0 .. $max_symbol) {
- push @freqs, $freq{$k} // 0;
- }
- print {$out_fh} delta_encode(\@freqs);
- print {$out_fh} pack('N', length($bin));
- print {$out_fh} pack('B*', $bin);
- close $out_fh;
- }
- sub decompress ($input, $output) {
- # Open and validate the input file
- open my $fh, '<:raw', $input;
- valid_archive($fh) || die "$0: file `$input' is not a \U${\FORMAT}\E archive!\n";
- my @freqs = @{delta_decode($fh)};
- my $bits_len = unpack('N', join('', map { getc($fh) // die "error" } 1 .. 4));
- # Create the frequency table
- my %freq;
- foreach my $i (0 .. $#freqs) {
- if ($freqs[$i] > 0) {
- $freq{$i} = $freqs[$i];
- }
- }
- # Decode the bits into an integer
- my $enc = Math::GMPz->new(read_bits($fh, $bits_len), 2);
- # Open the output file
- open my $out_fh, '>:raw', $output;
- my @alphabet = sort { $a <=> $b } keys %freq;
- my $t = 0;
- my %cumul;
- foreach my $s (@alphabet) {
- $cumul{$s} = $t;
- $t += $freq{$s};
- }
- my $M = $t;
- my $symbols = decode($enc, \@alphabet, \%freq, \%cumul, $M);
- print $out_fh pack('C*', @$symbols);
- close $out_fh;
- }
- main();
- exit(0);
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