65 lines
1.7 KiB
PHP
65 lines
1.7 KiB
PHP
class LZW
|
|
{
|
|
function compress($unc) {
|
|
$i;$c;$wc;
|
|
$w = "";
|
|
$dictionary = array();
|
|
$result = array();
|
|
$dictSize = 256;
|
|
for ($i = 0; $i < 256; $i += 1) {
|
|
$dictionary[chr($i)] = $i;
|
|
}
|
|
for ($i = 0; $i < strlen($unc); $i++) {
|
|
$c = $unc[$i];
|
|
$wc = $w.$c;
|
|
if (array_key_exists($w.$c, $dictionary)) {
|
|
$w = $w.$c;
|
|
} else {
|
|
array_push($result,$dictionary[$w]);
|
|
$dictionary[$wc] = $dictSize++;
|
|
$w = (string)$c;
|
|
}
|
|
}
|
|
if ($w !== "") {
|
|
array_push($result,$dictionary[$w]);
|
|
}
|
|
return implode(",",$result);
|
|
}
|
|
|
|
function decompress($com) {
|
|
$com = explode(",",$com);
|
|
$i;$w;$k;$result;
|
|
$dictionary = array();
|
|
$entry = "";
|
|
$dictSize = 256;
|
|
for ($i = 0; $i < 256; $i++) {
|
|
$dictionary[$i] = chr($i);
|
|
}
|
|
$w = chr($com[0]);
|
|
$result = $w;
|
|
for ($i = 1; $i < count($com);$i++) {
|
|
$k = $com[$i];
|
|
if ($dictionary[$k]) {
|
|
$entry = $dictionary[$k];
|
|
} else {
|
|
if ($k === $dictSize) {
|
|
$entry = $w.$w[0];
|
|
} else {
|
|
return null;
|
|
}
|
|
}
|
|
$result .= $entry;
|
|
$dictionary[$dictSize++] = $w . $entry[0];
|
|
$w = $entry;
|
|
}
|
|
return $result;
|
|
}
|
|
}
|
|
|
|
//How to use
|
|
$str = 'TOBEORNOTTOBEORTOBEORNOT';
|
|
$lzw = new LZW();
|
|
$com = $lzw->compress($str);
|
|
$dec = $lzw->decompress($com);
|
|
echo $com . "<br>" . $dec;
|