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<?php |
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namespace Mfonte\Base62x\Compression\Huffman\Binary; |
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/** |
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* a simple, fixed-size bit array, backed internally by a string. |
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*/ |
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class BitArray implements \ArrayAccess |
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{ |
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private $data = ''; |
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private $size = 0; |
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/** |
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* create a new bit array of the given size. |
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*/ |
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public function __construct($size) |
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{ |
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$this->size = $size; |
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$this->init(); |
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} |
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/** |
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* create a new BitArray from the bytes in the supplied string. |
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*/ |
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public static function load($data) |
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{ |
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$array = new self(mb_strlen($data) * 8); |
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$array->data = $data; |
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return $array; |
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} |
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/** |
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* retrieve the internal string representation of the binary data. |
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*/ |
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public function getData() |
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{ |
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return $this->data; |
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} |
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/** |
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* whether the given offset exists: ArrayAccess. |
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*/ |
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public function offsetExists($offset): bool |
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{ |
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if (!\is_int($offset)) { |
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return false; |
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} |
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return $offset >= 0 && $offset < $this->size; |
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} |
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/** |
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* get the value at the given offset: ArrayAccess. |
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*/ |
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#[\ReturnTypeWillChange] |
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public function offsetGet($offset) |
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{ |
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list($index, $bit) = $this->getPosition($offset); |
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return ($this->getNumericValueAt($index) & (1 << $bit)) ? 1 : 0; |
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} |
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/** |
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* set the value at the given offset: ArrayAccess. |
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*/ |
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public function offsetSet($offset, $value): void |
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{ |
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$Xor = false; |
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if (!$value) { |
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if ($this->offsetGet($offset)) { |
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// later, we'll flip that bit using XOR |
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$Xor = true; |
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} else { |
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// it's already 0. we're done |
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return; |
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} |
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} |
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list($index, $bit) = $this->getPosition($offset); |
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$byte = $this->getNumericValueAt($index); |
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$byte = ($Xor) |
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? $byte ^ (1 << $bit) |
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: $byte | (1 << $bit); |
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$this->data[$index] = pack('C*', $byte); |
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} |
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/** |
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* unset given offset: ArrayAccess |
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* NOTE: This deviates a little from the true ArrayAccess meaning, |
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* b/c we have a value (0 or 1) at every bit no matter what. unsetting sets to 0. |
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*/ |
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public function offsetUnset($offset): void |
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{ |
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$this->offsetSet($offset, 0); |
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} |
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/** |
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* get the one-byte character that contains the given offset. |
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*/ |
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private function getPosition($offset) |
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{ |
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$quotient = (int) ($offset / 8); |
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$bit = $offset % 8; |
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return [$quotient, $bit]; |
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} |
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/** |
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* get the current numeric value of a byte in our string. |
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*/ |
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private function getNumericValueAt($index) |
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{ |
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$bytes = unpack('C*', $this->data[$index]); |
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return $bytes[1]; |
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} |
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/** |
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* initialize the array with 0 for all bits. |
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*/ |
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private function init() |
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{ |
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$this->data = str_repeat("\0", (int) (ceil($this->size / 8))); |
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} |
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} |
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mauriziofonte /
php-base62x
