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<?php |
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namespace Faytekin\LZW; |
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class LZW |
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{ |
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public function compress(string $uncompress): string |
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{ |
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$dictSize = 256; |
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$dictionary = []; |
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for ($i = 0; $i < 256; $i++) { |
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$dictionary[$this->uniChr($i)] = $i; |
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} |
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$w = ''; |
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$result = []; |
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for ($i = 0; $i < strlen($uncompress); $i++) { |
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$c = $this->charAt($uncompress, $i); |
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$wc = $w.$c; |
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if (isset($dictionary[$wc])) { |
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$w = $wc; |
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} else { |
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array_push($result, $dictionary[$w]); |
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$dictionary[$wc] = $dictSize++; |
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$w = strval($c); |
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} |
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} |
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if ($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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public function decompress(string $compressed): ?string |
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{ |
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$compressed = explode(',', $compressed); |
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$dictSize = 256; |
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$dictionary = []; |
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for ($i = 1; $i < $dictSize; $i++) { |
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$dictionary[$i] = $this->uniChr($i); |
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} |
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$w = $this->uniChr($compressed[0]); |
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$result = $w; |
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for ($i = 1; $i < count($compressed); $i++) { |
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$k = $compressed[$i]; |
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if (isset($dictionary[$k])) { |
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$entry = $dictionary[$k]; |
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} elseif ($k == $dictSize) { |
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$entry = $w.$this->charAt($w, 0); |
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} else { |
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return null; |
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} |
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$result .= $entry; |
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$dictionary[$dictSize++] = $w.$this->charAt($entry, 0); |
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$w = $entry; |
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} |
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return $result; |
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} |
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public function charAt(string $string, int $index): ?string |
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{ |
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if ($index < mb_strlen($string)) { |
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return mb_substr($string, $index, 1, 'UTF-8'); |
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} |
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return null; |
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} |
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public function uniChr(int $u): string |
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{ |
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return mb_convert_encoding('&#'.intval($u).';', 'UTF-8', 'HTML-ENTITIES'); |
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84
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} |
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} |
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faytekin /
lzw
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