mirror of https://github.com/NekoX-Dev/NekoX.git
167 lines
4.7 KiB
Java
Executable File
167 lines
4.7 KiB
Java
Executable File
/*
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* Copyright 2007 ZXing authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.zxing.common.reedsolomon;
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/**
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* <p>This class contains utility methods for performing mathematical operations over
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* the Galois Fields. Operations use a given primitive polynomial in calculations.</p>
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*
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* <p>Throughout this package, elements of the GF are represented as an {@code int}
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* for convenience and speed (but at the cost of memory).
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* </p>
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*
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* @author Sean Owen
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* @author David Olivier
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*/
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public final class GenericGF {
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public static final GenericGF AZTEC_DATA_12 = new GenericGF(0x1069, 4096, 1); // x^12 + x^6 + x^5 + x^3 + 1
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public static final GenericGF AZTEC_DATA_10 = new GenericGF(0x409, 1024, 1); // x^10 + x^3 + 1
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public static final GenericGF AZTEC_DATA_6 = new GenericGF(0x43, 64, 1); // x^6 + x + 1
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public static final GenericGF AZTEC_PARAM = new GenericGF(0x13, 16, 1); // x^4 + x + 1
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public static final GenericGF QR_CODE_FIELD_256 = new GenericGF(0x011D, 256, 0); // x^8 + x^4 + x^3 + x^2 + 1
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public static final GenericGF DATA_MATRIX_FIELD_256 = new GenericGF(0x012D, 256, 1); // x^8 + x^5 + x^3 + x^2 + 1
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public static final GenericGF AZTEC_DATA_8 = DATA_MATRIX_FIELD_256;
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public static final GenericGF MAXICODE_FIELD_64 = AZTEC_DATA_6;
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private final int[] expTable;
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private final int[] logTable;
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private final GenericGFPoly zero;
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private final GenericGFPoly one;
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private final int size;
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private final int primitive;
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private final int generatorBase;
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/**
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* Create a representation of GF(size) using the given primitive polynomial.
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*
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* @param primitive irreducible polynomial whose coefficients are represented by
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* the bits of an int, where the least-significant bit represents the constant
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* coefficient
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* @param size the size of the field
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* @param b the factor b in the generator polynomial can be 0- or 1-based
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* (g(x) = (x+a^b)(x+a^(b+1))...(x+a^(b+2t-1))).
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* In most cases it should be 1, but for QR code it is 0.
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*/
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public GenericGF(int primitive, int size, int b) {
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this.primitive = primitive;
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this.size = size;
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this.generatorBase = b;
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expTable = new int[size];
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logTable = new int[size];
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int x = 1;
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for (int i = 0; i < size; i++) {
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expTable[i] = x;
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x *= 2; // we're assuming the generator alpha is 2
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if (x >= size) {
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x ^= primitive;
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x &= size - 1;
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}
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}
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for (int i = 0; i < size - 1; i++) {
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logTable[expTable[i]] = i;
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}
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// logTable[0] == 0 but this should never be used
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zero = new GenericGFPoly(this, new int[]{0});
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one = new GenericGFPoly(this, new int[]{1});
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}
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GenericGFPoly getZero() {
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return zero;
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}
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GenericGFPoly getOne() {
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return one;
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}
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/**
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* @return the monomial representing coefficient * x^degree
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*/
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GenericGFPoly buildMonomial(int degree, int coefficient) {
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if (degree < 0) {
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throw new IllegalArgumentException();
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}
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if (coefficient == 0) {
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return zero;
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}
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int[] coefficients = new int[degree + 1];
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coefficients[0] = coefficient;
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return new GenericGFPoly(this, coefficients);
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}
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/**
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* Implements both addition and subtraction -- they are the same in GF(size).
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*
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* @return sum/difference of a and b
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*/
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static int addOrSubtract(int a, int b) {
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return a ^ b;
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}
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/**
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* @return 2 to the power of a in GF(size)
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*/
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int exp(int a) {
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return expTable[a];
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}
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/**
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* @return base 2 log of a in GF(size)
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*/
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int log(int a) {
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if (a == 0) {
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throw new IllegalArgumentException();
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}
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return logTable[a];
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}
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/**
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* @return multiplicative inverse of a
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*/
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int inverse(int a) {
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if (a == 0) {
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throw new ArithmeticException();
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}
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return expTable[size - logTable[a] - 1];
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}
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/**
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* @return product of a and b in GF(size)
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*/
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int multiply(int a, int b) {
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if (a == 0 || b == 0) {
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return 0;
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}
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return expTable[(logTable[a] + logTable[b]) % (size - 1)];
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}
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public int getSize() {
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return size;
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}
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public int getGeneratorBase() {
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return generatorBase;
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}
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@Override
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public String toString() {
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return "GF(0x" + Integer.toHexString(primitive) + ',' + size + ')';
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}
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}
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