/*
* Copyright 2008 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.itextpdf.text.pdf.qrcode;
import java.util.ArrayList;
/**
* <p>Implements Reed-Solomon enbcoding, as the name implies.</p>
*
* @author Sean Owen
* @author William Rucklidge
* @since 5.0.2
*/
public final class ReedSolomonEncoder {
private final GF256 field;
private final ArrayList<GF256Poly> cachedGenerators;
public ReedSolomonEncoder(GF256 field) {
if (!GF256.QR_CODE_FIELD.equals(field)) {
throw new IllegalArgumentException("Only QR Code is supported at this time");
}
this.field = field;
this.cachedGenerators = new ArrayList<GF256Poly>();
cachedGenerators.add(new GF256Poly(field, new int[] { 1 }));
}
private GF256Poly buildGenerator(int degree) {
if (degree >= cachedGenerators.size()) {
GF256Poly lastGenerator = cachedGenerators.get(cachedGenerators.size() - 1);
for (int d = cachedGenerators.size(); d <= degree; d++) {
GF256Poly nextGenerator = lastGenerator.multiply(new GF256Poly(field, new int[] { 1, field.exp(d - 1) }));
cachedGenerators.add(nextGenerator);
lastGenerator = nextGenerator;
}
}
return (GF256Poly) cachedGenerators.get(degree);
}
public void encode(int[] toEncode, int ecBytes) {
if (ecBytes == 0) {
throw new IllegalArgumentException("No error correction bytes");
}
int dataBytes = toEncode.length - ecBytes;
if (dataBytes <= 0) {
throw new IllegalArgumentException("No data bytes provided");
}
GF256Poly generator = buildGenerator(ecBytes);
int[] infoCoefficients = new int[dataBytes];
System.arraycopy(toEncode, 0, infoCoefficients, 0, dataBytes);
GF256Poly info = new GF256Poly(field, infoCoefficients);
info = info.multiplyByMonomial(ecBytes, 1);
GF256Poly remainder = info.divide(generator)[1];
int[] coefficients = remainder.getCoefficients();
int numZeroCoefficients = ecBytes - coefficients.length;
for (int i = 0; i < numZeroCoefficients; i++) {
toEncode[dataBytes + i] = 0;
}
System.arraycopy(coefficients, 0, toEncode, dataBytes + numZeroCoefficients, coefficients.length);
}
}
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