001/*
002 * Copyright 2008 ZXing authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.itextpdf.text.pdf.qrcode;
018
019import java.util.ArrayList;
020
021/**
022 * <p>Implements Reed-Solomon enbcoding, as the name implies.</p>
023 *
024 * @author Sean Owen
025 * @author William Rucklidge
026 * @since 5.0.2
027 */
028public final class ReedSolomonEncoder {
029
030  private final GF256 field;
031  private final ArrayList<GF256Poly> cachedGenerators;
032
033  public ReedSolomonEncoder(GF256 field) {
034    if (!GF256.QR_CODE_FIELD.equals(field)) {
035      throw new IllegalArgumentException("Only QR Code is supported at this time");
036    }
037    this.field = field;
038    this.cachedGenerators = new ArrayList<GF256Poly>();
039    cachedGenerators.add(new GF256Poly(field, new int[] { 1 }));
040  }
041
042  private GF256Poly buildGenerator(int degree) {
043    if (degree >= cachedGenerators.size()) {
044      GF256Poly lastGenerator = cachedGenerators.get(cachedGenerators.size() - 1);
045      for (int d = cachedGenerators.size(); d <= degree; d++) {
046        GF256Poly nextGenerator = lastGenerator.multiply(new GF256Poly(field, new int[] { 1, field.exp(d - 1) }));
047        cachedGenerators.add(nextGenerator);
048        lastGenerator = nextGenerator;
049      }
050    }
051    return (GF256Poly) cachedGenerators.get(degree);
052  }
053
054  public void encode(int[] toEncode, int ecBytes) {
055    if (ecBytes == 0) {
056      throw new IllegalArgumentException("No error correction bytes");
057    }
058    int dataBytes = toEncode.length - ecBytes;
059    if (dataBytes <= 0) {
060      throw new IllegalArgumentException("No data bytes provided");
061    }
062    GF256Poly generator = buildGenerator(ecBytes);
063    int[] infoCoefficients = new int[dataBytes];
064    System.arraycopy(toEncode, 0, infoCoefficients, 0, dataBytes);
065    GF256Poly info = new GF256Poly(field, infoCoefficients);
066    info = info.multiplyByMonomial(ecBytes, 1);
067    GF256Poly remainder = info.divide(generator)[1];
068    int[] coefficients = remainder.getCoefficients();
069    int numZeroCoefficients = ecBytes - coefficients.length;
070    for (int i = 0; i < numZeroCoefficients; i++) {
071      toEncode[dataBytes + i] = 0;
072    }
073    System.arraycopy(coefficients, 0, toEncode, dataBytes + numZeroCoefficients, coefficients.length);
074  }
075
076}