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<?php |
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namespace CHMLib\Reader; |
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use Exception; |
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/** |
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* Read data from a raw string of bytes. |
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*/ |
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class BitReader extends StringReader |
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{ |
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/** |
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* The maximum size of the buffer in bits. |
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* |
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* @var int |
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*/ |
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const BUFFER_BITS = 32; |
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/** |
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* Pre-calculated mask to make sure we get. |
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* |
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* @var int[] |
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*/ |
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protected static $UNSIGNED_MASK = array( |
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0x0000, |
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0x0001, 0x0003, 0x0007, 0x000f, |
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0x001f, 0x003f, 0x007f, 0x00ff, |
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0x01ff, 0x03ff, 0x07ff, 0x0fff, |
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0x1fff, 0x3fff, 0x7fff, 0xffff, |
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); |
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/** |
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* The current bit buffer. |
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* |
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* @var int |
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*/ |
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protected $buffer; |
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/** |
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* The number of bits in the buffer. |
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* |
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* @var int |
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*/ |
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protected $bufferSize; |
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/** |
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* Initializes the instance. |
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* |
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* @param string $string The raw string containing the data to be read. |
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*/ |
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public function __construct($string) |
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{ |
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parent::__construct($string); |
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$this->buffer = 0; |
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$this->bufferSize = 0; |
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} |
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/** |
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* Make sure that there are at least $n (<=16) bits in the buffer. |
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* If less than $n bits are there, read a 16-bit little-endian word from the byte array. |
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* |
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* @param int $n The minimum number of bits that should be available in the remaining bit buffer. |
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* |
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* @return int Return the number of remaining bits in the buffer. |
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*/ |
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public function ensure($n) |
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{ |
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while ($this->bufferSize < $n) { |
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if (($this->length - $this->position) < 2) { |
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$this->position = $this->length; |
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break; |
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} |
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$word = $this->readUInt16(); |
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$this->buffer |= $word << (static::BUFFER_BITS - 16 - $this->bufferSize); |
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$this->bufferSize += 16; |
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} |
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return $this->bufferSize; |
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} |
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/** |
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* Peek n bits, may raise an EOF Exception if there are not enough bits and $suppressException is false. |
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* |
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* @param int $n The number of bits to peek. |
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* @param bool $suppressException Set to true to avoid raising an exception if there are not enough bits. |
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* |
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* @return int |
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*/ |
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public function peek($n, $suppressException = false) |
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{ |
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if ($this->ensure($n) < $n) { |
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if (!$suppressException) { |
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throw new Exception('EOF'); |
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} |
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} |
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return (($this->buffer >> (static::BUFFER_BITS - $n))) & static::$UNSIGNED_MASK[$n]; |
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} |
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/** |
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* Read no more than 16 bits (represented as a little endian integer). |
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* |
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* @param int $n The number of bits to retrieve. |
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* |
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* @return int |
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*/ |
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public function readLE($n) |
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{ |
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$result = $this->peek($n); |
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$this->buffer <<= $n; |
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$this->bufferSize -= $n; |
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return $result; |
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} |
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/** |
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* Reset the bits buffer and flush $n bytes. |
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* |
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* @param int $n The number of bytes to skip. |
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* |
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* @throws \Exception Throws an Exception in case of errors. |
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*/ |
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public function skip($n) |
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{ |
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$this->buffer = 0; |
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$this->bufferSize = 0; |
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$this->setPosition($this->position + $n); |
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} |
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/** |
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* Read a number of bytes and insert them in an array at a specified position. |
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* |
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* @param array $buffer The buffer where the data should be inserted. |
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* @param int $offset The offset at which the data should be inserted. |
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* @param int $length The number of bytes to read. |
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* |
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* @throws \Exception Throws an Exception in case of errors. |
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* |
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* @return array Return the $buffer array with filled-in bytes. |
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*/ |
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public function readFully($buffer, $offset, $length) |
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{ |
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if ($length === 0) { |
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$result = $buffer; |
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} else { |
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$bufferSize = count($buffer); |
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$postSize = $bufferSize - $offset - $length; |
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if ($postSize < 0) { |
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throw new Exception('Buffer too small'); |
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} |
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$pre = ($offset === 0) ? array() : array_slice($buffer, 0, $offset); |
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$mid = $this->readBytes($length); |
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$post = ($postSize === 0) ? array() : array_slice($buffer, -$postSize); |
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$result = array_merge($pre, $mid, $post); |
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} |
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return $result; |
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} |
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} |
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mlocati /
chm-lib
