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<?php
/**
* This file is part of FPDI
*
* @package setasign\Fpdi
* @copyright Copyright (c) 2020 Setasign GmbH & Co. KG (https://www.setasign.com)
* @license http://opensource.org/licenses/mit-license The MIT License
*/
namespace setasign\Fpdi\PdfParser\Filter;
/**
* Class for handling LZW encoded data
*/
class Lzw implements FilterInterface
{
/**
* @var null|string
*/
protected $data;
/**
* @var array
*/
protected $sTable = [];
/**
* @var int
*/
protected $dataLength = 0;
/**
* @var int
*/
protected $tIdx;
/**
* @var int
*/
protected $bitsToGet = 9;
/**
* @var int
*/
protected $bytePointer;
/**
* @var int
*/
protected $nextData = 0;
/**
* @var int
*/
protected $nextBits = 0;
/**
* @var array
*/
protected $andTable = [511, 1023, 2047, 4095];
/**
* Method to decode LZW compressed data.
*
* @param string $data The compressed data
* @return string The uncompressed data
* @throws LzwException
*/
public function decode($data)
{
if ($data[0] === "\x00" && $data[1] === "\x01") {
throw new LzwException(
'LZW flavour not supported.',
LzwException::LZW_FLAVOUR_NOT_SUPPORTED
);
}
$this->initsTable();
$this->data = $data;
$this->dataLength = \strlen($data);
// Initialize pointers
$this->bytePointer = 0;
$this->nextData = 0;
$this->nextBits = 0;
$oldCode = 0;
$uncompData = '';
while (($code = $this->getNextCode()) !== 257) {
if ($code === 256) {
$this->initsTable();
$code = $this->getNextCode();
if ($code === 257) {
break;
}
$uncompData .= $this->sTable[$code];
$oldCode = $code;
} else {
if ($code < $this->tIdx) {
$string = $this->sTable[$code];
$uncompData .= $string;
$this->addStringToTable($this->sTable[$oldCode], $string[0]);
$oldCode = $code;
} else {
$string = $this->sTable[$oldCode];
$string .= $string[0];
$uncompData .= $string;
$this->addStringToTable($string);
$oldCode = $code;
}
}
}
return $uncompData;
}
/**
* Initialize the string table.
*/
protected function initsTable()
{
$this->sTable = [];
for ($i = 0; $i < 256; $i++) {
$this->sTable[$i] = \chr($i);
}
$this->tIdx = 258;
$this->bitsToGet = 9;
}
/**
* Add a new string to the string table.
*
* @param string $oldString
* @param string $newString
*/
protected function addStringToTable($oldString, $newString = '')
{
$string = $oldString . $newString;
// Add this new String to the table
$this->sTable[$this->tIdx++] = $string;
if ($this->tIdx === 511) {
$this->bitsToGet = 10;
} elseif ($this->tIdx === 1023) {
$this->bitsToGet = 11;
} elseif ($this->tIdx === 2047) {
$this->bitsToGet = 12;
}
}
/**
* Returns the next 9, 10, 11 or 12 bits.
*
* @return integer
*/
protected function getNextCode()
{
if ($this->bytePointer === $this->dataLength) {
return 257;
}
$this->nextData = ($this->nextData << 8) | (\ord($this->data[$this->bytePointer++]) & 0xff);
$this->nextBits += 8;
if ($this->nextBits < $this->bitsToGet) {
$this->nextData = ($this->nextData << 8) | (\ord($this->data[$this->bytePointer++]) & 0xff);
$this->nextBits += 8;
}
$code = ($this->nextData >> ($this->nextBits - $this->bitsToGet)) & $this->andTable[$this->bitsToGet - 9];
$this->nextBits -= $this->bitsToGet;
return $code;
}
}
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