cnf-qrcode/src/lib/core/reed-solomon-encoder.js

generate qrcode,support svg base64 utf8

import Buffer from '../utils/buffer';
import * as Polynomial from './polynomial';

function ReedSolomonEncoder(degree) {
  this.genPoly = undefined;
  this.degree = degree;

  if (this.degree) this.initialize(this.degree);
}

/**
 * Initialize the encoder.
 * The input param should correspond to the number of error correction codewords.
 *
 * @param  {Number} degree
 */
ReedSolomonEncoder.prototype.initialize = function initialize(degree) {
  // create an irreducible generator polynomial
  this.degree = degree;
  this.genPoly = Polynomial.generateECPolynomial(this.degree);
};

/**
 * Encodes a chunk of data
 *
 * @param  {Buffer} data Buffer containing input data
 * @return {Buffer}      Buffer containing encoded data
 */
ReedSolomonEncoder.prototype.encode = function encode(data) {
  if (!this.genPoly) {
    throw new Error('Encoder not initialized');
  }

  // Calculate EC for this data block
  // extends data size to data+genPoly size
  const pad = new Buffer(this.degree);
  pad.fill(0);
  const paddedData = Buffer.concat([data, pad], data.length + this.degree);

  // The error correction codewords are the remainder after dividing the data codewords
  // by a generator polynomial
  const remainder = Polynomial.mod(paddedData, this.genPoly);

  // return EC data blocks (last n byte, where n is the degree of genPoly)
  // If coefficients number in remainder are less than genPoly degree,
  // pad with 0s to the left to reach the needed number of coefficients
  const start = this.degree - remainder.length;
  if (start > 0) {
    const buff = new Buffer(this.degree);
    buff.fill(0);
    remainder.copy(buff, start);

    return buff;
  }

  return remainder;
};

export default ReedSolomonEncoder;