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Core barcode encoding/decoding library
/*
* Copyright 2012 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.pdf417.decoder.ec;
import com.google.zxing.pdf417.PDF417Common;
/**
* A field based on powers of a generator integer, modulo some modulus.
*
* @author Sean Owen
* @see com.google.zxing.common.reedsolomon.GenericGF
*/
public final class ModulusGF {
public static final ModulusGF PDF417_GF = new ModulusGF(PDF417Common.NUMBER_OF_CODEWORDS, 3);
private final int[] expTable;
private final int[] logTable;
private final ModulusPoly zero;
private final ModulusPoly one;
private final int modulus;
private ModulusGF(int modulus, int generator) {
this.modulus = modulus;
expTable = new int[modulus];
logTable = new int[modulus];
int x = 1;
for (int i = 0; i < modulus; i++) {
expTable[i] = x;
x = (x * generator) % modulus;
}
for (int i = 0; i < modulus - 1; i++) {
logTable[expTable[i]] = i;
}
// logTable[0] == 0 but this should never be used
zero = new ModulusPoly(this, new int[]{0});
one = new ModulusPoly(this, new int[]{1});
}
ModulusPoly getZero() {
return zero;
}
ModulusPoly getOne() {
return one;
}
ModulusPoly buildMonomial(int degree, int coefficient) {
if (degree < 0) {
throw new IllegalArgumentException();
}
if (coefficient == 0) {
return zero;
}
int[] coefficients = new int[degree + 1];
coefficients[0] = coefficient;
return new ModulusPoly(this, coefficients);
}
int add(int a, int b) {
return (a + b) % modulus;
}
int subtract(int a, int b) {
return (modulus + a - b) % modulus;
}
int exp(int a) {
return expTable[a];
}
int log(int a) {
if (a == 0) {
throw new IllegalArgumentException();
}
return logTable[a];
}
int inverse(int a) {
if (a == 0) {
throw new ArithmeticException();
}
return expTable[modulus - logTable[a] - 1];
}
int multiply(int a, int b) {
if (a == 0 || b == 0) {
return 0;
}
return expTable[(logTable[a] + logTable[b]) % (modulus - 1)];
}
int getSize() {
return modulus;
}
}