source-class-Com.Tecnick.Pdf.Filter.Type.Lzw

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<?php
/**
 * Lzw.php
 *
 * @since       2011-05-23
 * @category    Library
 * @package     PdfFilter
 * @author      Nicola Asuni <info@tecnick.com>
 * @copyright   2011-2015 Nicola Asuni - Tecnick.com LTD
 * @license     http://www.gnu.org/copyleft/lesser.html GNU-LGPL v3 (see LICENSE.TXT)
 * @link        https://github.com/tecnickcom/tc-lib-pdf-filter
 *
 * This file is part of tc-lib-pdf-filter software library.
 */

namespace Com\Tecnick\Pdf\Filter\Type;

use \Com\Tecnick\Pdf\Filter\Exception as PPException;

/**
 * Com\Tecnick\Pdf\Filter\Type\Lzw
 *
 * LZWDecode
 * Decompresses data encoded using the LZW (Lempel-Ziv-Welch) adaptive compression method,
 * reproducing the original text or binary data.
 *
 * @since       2011-05-23
 * @category    Library
 * @package     PdfFilter
 * @author      Nicola Asuni <info@tecnick.com>
 * @copyright   2011-2015 Nicola Asuni - Tecnick.com LTD
 * @license     http://www.gnu.org/copyleft/lesser.html GNU-LGPL v3 (see LICENSE.TXT)
 * @link        https://github.com/tecnickcom/tc-lib-pdf-filter
 */
class Lzw
{
    /**
     * Decode the data
     *
     * @param string $data Data to decode.
     *
     * @return string Decoded data string.
     */
    public function decode($data)
    {
        // initialize string to return
        $decoded = '';
        // data length
        $data_length = strlen($data);
        // convert string to binary string
        $bitstring = '';
        for ($i = 0; $i < $data_length; ++$i) {
            $bitstring .= sprintf('%08b', ord($data[$i]));
        }
        // get the number of bits
        $data_length = strlen($bitstring);
        // initialize code length in bits
        $bitlen = 9;
        // initialize dictionary index
        $dix = 258;
        // initialize the dictionary (with the first 256 entries).
        $dictionary = array();
        for ($i = 0; $i < 256; ++$i) {
            $dictionary[$i] = chr($i);
        }
        // previous val
        $prev_index = 0;
        // while we encounter EOD marker (257), read code_length bits
        while (($data_length > 0) && (($index = bindec(substr($bitstring, 0, $bitlen))) != 257)) {
            $this->process($decoded, $bitstring, $bitlen, $data_length, $index, $dictionary, $dix, $prev_index);
        }
        return $decoded;
    }

    /**
     * Internal processing
     *
     * @param string $decoded
     * @param string $bitstring
     * @param int    $bitlen
     * @param int    $data_length
     * @param int    $index
     * @param array  $dictionary
     * @param int    $dix
     * @param int    $prev_index
     */
    protected function process(
        &$decoded,
        &$bitstring,
        &$bitlen,
        &$data_length,
        &$index,
        &$dictionary,
        &$dix,
        &$prev_index
    ) {
        // remove read bits from string
        $bitstring = substr($bitstring, $bitlen);
        // update number of bits
        $data_length -= $bitlen;
        if ($index == 256) { // clear-table marker
            // reset code length in bits
            $bitlen = 9;
            // reset dictionary index
            $dix = 258;
            $prev_index = 256;
            // reset the dictionary (with the first 256 entries).
            $dictionary = array();
            for ($i = 0; $i < 256; ++$i) {
                $dictionary[$i] = chr($i);
            }
        } elseif ($prev_index == 256) {
            // first entry
            $decoded .= $dictionary[$index];
            $prev_index = $index;
        } else {
            // check if index exist in the dictionary
            if ($index < $dix) {
                // index exist on dictionary
                $decoded .= $dictionary[$index];
                $dic_val = $dictionary[$prev_index].$dictionary[$index][0];
                // store current index
                $prev_index = $index;
            } else {
                // index do not exist on dictionary
                $dic_val = $dictionary[$prev_index].$dictionary[$prev_index][0];
                $decoded .= $dic_val;
            }
            // update dictionary
            $dictionary[$dix] = $dic_val;
            ++$dix;
            // change bit length by case
            if ($dix == 2047) {
                $bitlen = 12;
            } elseif ($dix == 1023) {
                $bitlen = 11;
            } elseif ($dix == 511) {
                $bitlen = 10;
            }
        }
    }
}
 

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