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168 lines (126 loc) · 4.44 KB
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#!/usr/bin/perl
# Implementation of Run-length + Elias coding, for encoding arbitrary non-negative integers.
# References:
# Data Compression (Summer 2023) - Lecture 5 - Basic Techniques
# https://youtube.com/watch?v=TdFWb8mL5Gk
#
# Data Compression (Summer 2023) - Lecture 6 - Delta Compression and Prediction
# https://youtube.com/watch?v=-3H_eDbWNEU
use 5.036;
sub read_bit ($fh, $bitstring) {
if (($$bitstring // '') eq '') {
$$bitstring = unpack('b*', getc($fh) // return undef);
}
chop($$bitstring);
}
sub run_length ($arr) {
@$arr || return [];
my @result = [$arr->[0], 1];
my $prev_value = $arr->[0];
foreach my $i (1 .. $#{$arr}) {
my $curr_value = $arr->[$i];
if ($curr_value eq $prev_value) {
++$result[-1][1];
}
else {
push(@result, [$curr_value, 1]);
}
$prev_value = $curr_value;
}
return \@result;
}
sub RLEE_encoding ($integers, $double = 0) {
my @symbols = (scalar(@$integers), @$integers);
my $bitstring = '';
my $rle = run_length(\@symbols);
foreach my $cv (@$rle) {
my ($c, $v) = @$cv;
if ($c == 0) {
$bitstring .= '0';
}
elsif ($double) {
my $t = sprintf('%b', abs($c) + 1);
my $l = sprintf('%b', length($t));
$bitstring .= '1' . ('1' x (length($l) - 1)) . '0' . substr($l, 1) . substr($t, 1);
}
else {
my $t = sprintf('%b', abs($c));
$bitstring .= '1' . ('1' x (length($t) - 1)) . '0' . substr($t, 1);
}
if ($v == 1) {
$bitstring .= '0';
}
else {
my $t = sprintf('%b', $v);
$bitstring .= join('', '1' x (length($t) - 1), '0', substr($t, 1));
}
}
pack('B*', $bitstring);
}
sub RLEE_decoding ($bitstring, $double = 0) {
open my $fh, '<:raw', \$bitstring;
my @values;
my $buffer = '';
my $len = 0;
for (my $k = 0 ; $k <= $len ; ++$k) {
my $bit = read_bit($fh, \$buffer) // last;
if ($bit eq '0') {
push @values, 0;
}
elsif ($double) {
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 @values, $int - 1;
}
else {
my $n = 0;
++$n while (read_bit($fh, \$buffer) eq '1');
my $d = oct('0b1' . join('', map { read_bit($fh, \$buffer) } 1 .. $n));
push @values, $d;
}
my $bl = 0;
while (read_bit($fh, \$buffer) == 1) {
++$bl;
}
if ($bl > 0) {
my $run = oct('0b1' . join('', map { read_bit($fh, \$buffer) } 1 .. $bl)) - 1;
$k += $run;
push @values, ($values[-1]) x $run;
}
if ($k == 0) {
$len = pop(@values);
}
}
return \@values;
}
my @symbols = (
6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 1, 1, 3, 3, 1, 2, 3, 0, 0, 1, 2, 4, 2, 1, 0, 1, 2, 1, 1, 0, 0, 1
);
my $enc = RLEE_encoding([@symbols]);
my $dec = RLEE_decoding($enc);
say unpack('B*', $enc);
say "@$dec";
"@$dec" eq "@symbols" or die "error";
do {
my @integers = map { int(rand($_)) } 1 .. 1000;
my $str = RLEE_encoding([@integers], 1);
say "Encoded length: ", length($str);
say "Rawdata length: ", length(join(' ', @integers));
my $decoded = RLEE_decoding($str, 1);
join(' ', @integers) eq join(' ', @$decoded) or die "Decoding error";
{
open my $fh, '<:raw', __FILE__;
my $str = do { local $/; <$fh> };
my $encoded = RLEE_encoding([unpack('C*', $str)], 1);
my $decoded = RLEE_decoding($encoded, 1);
$str eq pack('C*', @$decoded) or die "error";
}
}
__END__
111111100110010111010001111110000000110100010100110110010011000110100100100110001110000110001000010011000101000100100000
6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 1 1 3 3 1 2 3 0 0 1 2 4 2 1 0 1 2 1 1 0 0 1
Encoded length: 1867
Rawdata length: 3606