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/*
 * 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.google.zxing.common.reedsolomon;

import java.util.Vector;

/**
 * 

Implements Reed-Solomon enbcoding, as the name implies.

* * @author Sean Owen * @author William Rucklidge */ public final class ReedSolomonEncoder { private final GF256 field; private final Vector 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 Vector(); cachedGenerators.addElement(new GF256Poly(field, new int[] { 1 })); } private GF256Poly buildGenerator(int degree) { if (degree >= cachedGenerators.size()) { GF256Poly lastGenerator = (GF256Poly) cachedGenerators.elementAt(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.addElement(nextGenerator); lastGenerator = nextGenerator; } } return (GF256Poly) cachedGenerators.elementAt(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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