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<?php
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/**
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 * This file is part of FPDI
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 *
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 * @package   setasign\Fpdi
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 * @copyright Copyright (c) 2023 Setasign GmbH & Co. KG (https://www.setasign.com)
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 * @license   http://opensource.org/licenses/mit-license The MIT License
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 */
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namespace setasign\Fpdi\PdfParser\Filter;
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/**
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 * Class for handling ASCII base-85 encoded data
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 */
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class Ascii85 implements FilterInterface
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{
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    /**
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     * Decode ASCII85 encoded string.
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     *
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     * @param string $data The input string
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     * @return string
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     * @throws Ascii85Exception
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     */
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    public function decode($data)
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    {
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        $out = '';
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        $state = 0;
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        $chn = null;
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        $data = \preg_replace('/\s/', '', $data);
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        $l = \strlen($data);
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        /** @noinspection ForeachInvariantsInspection */
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        for ($k = 0; $k < $l; ++$k) {
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            $ch = \ord($data[$k]) & 0xff;
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            //Start <~
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            if ($k === 0 && $ch === 60 && isset($data[$k + 1]) && (\ord($data[$k + 1]) & 0xFF) === 126) {
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                $k++;
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                continue;
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            }
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            //End ~>
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            if ($ch === 126 && isset($data[$k + 1]) && (\ord($data[$k + 1]) & 0xFF) === 62) {
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                break;
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            }
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            if ($ch === 122 /* z */ && $state === 0) {
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                $out .= \chr(0) . \chr(0) . \chr(0) . \chr(0);
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                continue;
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            }
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            if ($ch < 33 /* ! */ || $ch > 117 /* u */) {
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                throw new Ascii85Exception(
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                    'Illegal character found while ASCII85 decode.',
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                    Ascii85Exception::ILLEGAL_CHAR_FOUND
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                );
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            }
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            $chn[$state] = $ch - 33;/* ! */
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            $state++;
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            if ($state === 5) {
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                $state = 0;
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                $r = 0;
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                for ($j = 0; $j < 5; ++$j) {
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                    /** @noinspection UnnecessaryCastingInspection */
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                    $r = (int)($r * 85 + $chn[$j]);
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                }
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                $out .= \chr($r >> 24)
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                    . \chr($r >> 16)
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                    . \chr($r >> 8)
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                    . \chr($r);
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            }
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        }
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        if ($state === 1) {
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            throw new Ascii85Exception(
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                'Illegal length while ASCII85 decode.',
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                Ascii85Exception::ILLEGAL_LENGTH
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            );
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        }
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        if ($state === 2) {
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            $r = $chn[0] * 85 * 85 * 85 * 85 + ($chn[1] + 1) * 85 * 85 * 85;
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            $out .= \chr($r >> 24);
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        } elseif ($state === 3) {
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            $r = $chn[0] * 85 * 85 * 85 * 85 + $chn[1] * 85 * 85 * 85 + ($chn[2] + 1) * 85 * 85;
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            $out .= \chr($r >> 24);
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            $out .= \chr($r >> 16);
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        } elseif ($state === 4) {
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            $r = $chn[0] * 85 * 85 * 85 * 85 + $chn[1] * 85 * 85 * 85 + $chn[2] * 85 * 85 + ($chn[3] + 1) * 85;
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            $out .= \chr($r >> 24);
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            $out .= \chr($r >> 16);
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            $out .= \chr($r >> 8);
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        }
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        return $out;
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    }
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}