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