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<?php |
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namespace Mfonte\Base62x\Compression\Huffman; |
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use Mfonte\Base62x\Exception\CompressionException; |
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/** |
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* Node in a huffman tree implementing a huffman coding. |
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*/ |
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class HuffmanNode |
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{ |
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private $weight = null; |
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private $symbol = null; |
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private $leftChild = null; |
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private $rightChild = null; |
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private $parent = null; |
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/** |
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* create a new leaf node. |
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*/ |
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public function __construct($symbol, $weight = null) |
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{ |
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$this->symbol = $symbol; |
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$this->weight = $weight; |
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} |
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/** |
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* create a new node whose children are the supplied nodes. |
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*/ |
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public static function join(self $left, self $right) |
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{ |
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$newParent = new self(null, $left->getWeight() + $right->getWeight()); |
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$newParent->leftChild = $left; |
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$newParent->rightChild = $right; |
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return $newParent; |
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} |
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/** |
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* perform a depth-first search to construct a. |
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*/ |
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public function getCodeHash(&$hashTable, $prefix = '') |
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{ |
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if ($this->isLeaf()) { |
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$hashTable[$this->symbol] = $prefix; |
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} else { |
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$this->leftChild->getCodeHash($hashTable, "{$prefix}0"); |
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$this->rightChild->getCodeHash($hashTable, "{$prefix}1"); |
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} |
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} |
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public function isLeaf() |
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{ |
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return $this->symbol !== null; |
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} |
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public function getWeight() |
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{ |
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return $this->weight; |
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} |
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public function getSymbol() |
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{ |
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return $this->symbol; |
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} |
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public function getRightChild() |
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{ |
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return $this->rightChild; |
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} |
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public function getLeftChild() |
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{ |
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return $this->leftChild; |
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} |
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public function getParent() |
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{ |
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return $this->parent; |
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} |
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/** |
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* read a node encoded using __toString. |
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*/ |
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private static function readEncodedNode(&$str) |
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{ |
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$retval = null; |
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$switch = $str[0]; |
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$str = mb_substr($str, 1); |
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switch ($switch) { |
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case '0': |
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$left = self::readEncodedNode($str); |
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$right = self::readEncodedNode($str); |
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$parent = new self(null); |
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$parent->leftChild = $left; |
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$parent->rightChild = $right; |
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$retval = $parent; |
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break; |
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case '1': |
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case '2': |
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$symbol = ($switch == 1) |
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? $str[0] : |
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HuffmanCoding::SYMBOL_EOF; |
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$str = mb_substr($str, 1); |
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$retval = new self($symbol); |
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break; |
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default: |
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throw new CompressionException('huffman', 'Encoding is out of sync.'); |
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} |
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return $retval; |
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} |
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/** |
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* opposite of __toString. |
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**/ |
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public static function loadFromString(&$str) |
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{ |
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return self::readEncodedNode($str); |
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} |
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/** |
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* create a string for compactly encoding this node (and its children). |
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*/ |
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public function __toString() |
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{ |
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if ($this->isLeaf()) { |
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if ($this->symbol === HuffmanCoding::SYMBOL_EOF) { |
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return '2~'; // ~ stands in BC HuffmanCoding::SYMBOL_EOF may be more than one byte |
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} else { |
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return '1'.$this->symbol; |
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} |
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} else { |
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return '0'.(string) $this->leftChild.(string) $this->rightChild; |
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} |
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} |
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} |
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mauriziofonte /
php-base62x
