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Filename : RsItem.php
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<?php

namespace QR_Code\Encoder\ErrorCorrection;

/**
 * Class RsItem
 *
 * Reed-Solomon error correction support
 *
 * Copyright (C) 2002, 2003, 2004, 2006 Phil Karn, KA9Q
 * (libfec is released under the GNU Lesser General Public License.)
 *
 * Based on libqrencode C library distributed under LGPL 2.1
 * Copyright (C) 2006, 2007, 2008, 2009 Kentaro Fukuchi <fukuchi@megaui.net>
 *
 * Based on PHP QR Code distributed under LGPL 3
 * Copyright (C) 2010 Dominik Dzienia <deltalab at poczta dot fm>
 *
 * QR Code Generator for PHP is distributed under MIT
 * Copyright (C) 2018 Bruno Vaula Werneck <brunovaulawerneck at gmail dot com>
 *
 * @package QR_Code\Encoder\ErrorCorrection
 */
class RsItem
{
    public $mm;                  // Bits per symbol
    public $nn;                  // Symbols per block (= (1<<mm)-1)
    public $alpha_to = [];  // log lookup table
    public $index_of = [];  // Antilog lookup table
    public $genpoly  = [];   // Generator polynomial
    public $nroots;              // Number of generator roots = number of parity symbols
    public $fcr;                 // First consecutive root, index form
    public $prim;                // Primitive element, index form
    public $iprim;               // prim-th root of 1, index form
    public $pad;                 // Padding bytes in shortened block
    public $gfpoly;

    /**
     * @param $x
     * @return int
     */
    public function modnn ($x)
    {
        while ($x >= $this->nn) {
            $x -= $this->nn;
            $x = ($x >> $this->mm) + ($x & $this->nn);
        }

        return $x;
    }

    /**
     * @param $symsize
     * @param $gfpoly
     * @param $fcr
     * @param $prim
     * @param $nroots
     * @param $pad
     * @return null|\QR_Code\Encoder\ErrorCorrection\RsItem
     */
    public static function init_rs_char ($symsize, $gfpoly, $fcr, $prim, $nroots, $pad)
    {
        // Common code for intializing a Reed-Solomon control block (char or int symbols)
        // Copyright 2004 Phil Karn, KA9Q
        // May be used under the terms of the GNU Lesser General Public License (LGPL)

        $rs = null;

        // Check parameter ranges
        if ($symsize < 0 || $symsize > 8) return $rs;
        if ($fcr < 0 || $fcr >= (1 << $symsize)) return $rs;
        if ($prim <= 0 || $prim >= (1 << $symsize)) return $rs;
        if ($nroots < 0 || $nroots >= (1 << $symsize)) return $rs; // Can't have more roots than symbol values!
        if ($pad < 0 || $pad >= ((1 << $symsize) - 1 - $nroots)) return $rs; // Too much padding

        $rs = new RsItem();
        $rs->mm = $symsize;
        $rs->nn = (1 << $symsize) - 1;
        $rs->pad = $pad;

        $rs->alpha_to = array_fill(0, $rs->nn + 1, 0);
        $rs->index_of = array_fill(0, $rs->nn + 1, 0);

        // PHP style macro replacement ;)
        $NN =& $rs->nn;
        $A0 =& $NN;

        // Generate Galois field lookup tables
        $rs->index_of[0] = $A0; // log(zero) = -inf
        $rs->alpha_to[$A0] = 0; // alpha**-inf = 0
        $sr = 1;

        for ($i = 0; $i < $rs->nn; $i++) {
            $rs->index_of[$sr] = $i;
            $rs->alpha_to[$i] = $sr;
            $sr <<= 1;
            if ($sr & (1 << $symsize)) {
                $sr ^= $gfpoly;
            }
            $sr &= $rs->nn;
        }

        if ($sr != 1) {
            // field generator polynomial is not primitive!
            $rs = null;
            return $rs;
        }

        /* Form RS code generator polynomial from its roots */
        $rs->genpoly = array_fill(0, $nroots + 1, 0);

        $rs->fcr = $fcr;
        $rs->prim = $prim;
        $rs->nroots = $nroots;
        $rs->gfpoly = $gfpoly;

        /* Find prim-th root of 1, used in decoding */
        $iprim = 1;
        while (($iprim % $prim) != 0) {
            $iprim += $rs->nn;
        }

        $rs->iprim = (int) ($iprim / $prim);
        $rs->genpoly[0] = 1;

        for ($i = 0, $root = $fcr * $prim; $i < $nroots; $i++, $root += $prim) {
            $rs->genpoly[$i + 1] = 1;

            // Multiply rs->genpoly[] by  @**(root + x)
            for ($j = $i; $j > 0; $j--) {
                if ($rs->genpoly[$j] != 0) {
                    $rs->genpoly[$j] = $rs->genpoly[$j - 1] ^ $rs->alpha_to[$rs->modnn($rs->index_of[$rs->genpoly[$j]] + $root)];
                } else {
                    $rs->genpoly[$j] = $rs->genpoly[$j - 1];
                }
            }
            // rs->genpoly[0] can never be zero
            $rs->genpoly[0] = $rs->alpha_to[$rs->modnn($rs->index_of[$rs->genpoly[0]] + $root)];
        }

        // convert rs->genpoly[] to index form for quicker encoding
        for ($i = 0; $i <= $nroots; $i++)
            $rs->genpoly[$i] = $rs->index_of[$rs->genpoly[$i]];

        return $rs;
    }

    /**
     * @param $data
     * @param $parity
     */
    public function encode_rs_char ($data, &$parity)
    {
        $MM =& $this->mm;
        $NN =& $this->nn;
        $ALPHA_TO =& $this->alpha_to;
        $INDEX_OF =& $this->index_of;
        $GENPOLY =& $this->genpoly;
        $NROOTS =& $this->nroots;
        $FCR =& $this->fcr;
        $PRIM =& $this->prim;
        $IPRIM =& $this->iprim;
        $PAD =& $this->pad;
        $A0 =& $NN;

        $parity = array_fill(0, $NROOTS, 0);

        for ($i = 0; $i < ($NN - $NROOTS - $PAD); $i++) {

            $feedback = $INDEX_OF[$data[$i] ^ $parity[0]];
            if ($feedback != $A0) {
                // feedback term is non-zero

                // This line is unnecessary when GENPOLY[NROOTS] is unity, as it must
                // always be for the polynomials constructed by init_rs()
                $feedback = $this->modnn($NN - $GENPOLY[$NROOTS] + $feedback);

                for ($j = 1; $j < $NROOTS; $j++) {
                    $parity[$j] ^= $ALPHA_TO[$this->modnn($feedback + $GENPOLY[$NROOTS - $j])];
                }
            }

            // Shift
            array_shift($parity);
            if ($feedback != $A0) {
                array_push($parity, $ALPHA_TO[$this->modnn($feedback + $GENPOLY[0])]);
            } else {
                array_push($parity, 0);
            }
        }
    }
}