@zxing/library
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TypeScript port of ZXing multi-format 1D/2D barcode image processing library.
201 lines (200 loc) • 8.49 kB
JavaScript
"use strict";
/*
* 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.
*/
var __values = (this && this.__values) || function(o) {
var s = typeof Symbol === "function" && Symbol.iterator, m = s && o[s], i = 0;
if (m) return m.call(o);
if (o && typeof o.length === "number") return {
next: function () {
if (o && i >= o.length) o = void 0;
return { value: o && o[i++], done: !o };
}
};
throw new TypeError(s ? "Object is not iterable." : "Symbol.iterator is not defined.");
};
Object.defineProperty(exports, "__esModule", { value: true });
// package com.google.zxing.pdf417.decoder.ec;
// import com.google.zxing.ChecksumException;
var ChecksumException_1 = require("../../../ChecksumException");
var ModulusPoly_1 = require("./ModulusPoly");
var ModulusGF_1 = require("./ModulusGF");
/**
* <p>PDF417 error correction implementation.</p>
*
* <p>This <a href="http://en.wikipedia.org/wiki/Reed%E2%80%93Solomon_error_correction#Example">example</a>
* is quite useful in understanding the algorithm.</p>
*
* @author Sean Owen
* @see com.google.zxing.common.reedsolomon.ReedSolomonDecoder
*/
var ErrorCorrection = /** @class */ (function () {
function ErrorCorrection() {
this.field = ModulusGF_1.default.PDF417_GF;
}
/**
* @param received received codewords
* @param numECCodewords number of those codewords used for EC
* @param erasures location of erasures
* @return number of errors
* @throws ChecksumException if errors cannot be corrected, maybe because of too many errors
*/
ErrorCorrection.prototype.decode = function (received, numECCodewords, erasures) {
var e_1, _a;
var poly = new ModulusPoly_1.default(this.field, received);
var S = new Int32Array(numECCodewords);
var error = false;
for (var i /*int*/ = numECCodewords; i > 0; i--) {
var evaluation = poly.evaluateAt(this.field.exp(i));
S[numECCodewords - i] = evaluation;
if (evaluation !== 0) {
error = true;
}
}
if (!error) {
return 0;
}
var knownErrors = this.field.getOne();
if (erasures != null) {
try {
for (var erasures_1 = __values(erasures), erasures_1_1 = erasures_1.next(); !erasures_1_1.done; erasures_1_1 = erasures_1.next()) {
var erasure = erasures_1_1.value;
var b = this.field.exp(received.length - 1 - erasure);
// Add (1 - bx) term:
var term = new ModulusPoly_1.default(this.field, new Int32Array([this.field.subtract(0, b), 1]));
knownErrors = knownErrors.multiply(term);
}
}
catch (e_1_1) { e_1 = { error: e_1_1 }; }
finally {
try {
if (erasures_1_1 && !erasures_1_1.done && (_a = erasures_1.return)) _a.call(erasures_1);
}
finally { if (e_1) throw e_1.error; }
}
}
var syndrome = new ModulusPoly_1.default(this.field, S);
// syndrome = syndrome.multiply(knownErrors);
var sigmaOmega = this.runEuclideanAlgorithm(this.field.buildMonomial(numECCodewords, 1), syndrome, numECCodewords);
var sigma = sigmaOmega[0];
var omega = sigmaOmega[1];
// sigma = sigma.multiply(knownErrors);
var errorLocations = this.findErrorLocations(sigma);
var errorMagnitudes = this.findErrorMagnitudes(omega, sigma, errorLocations);
for (var i /*int*/ = 0; i < errorLocations.length; i++) {
var position = received.length - 1 - this.field.log(errorLocations[i]);
if (position < 0) {
throw ChecksumException_1.default.getChecksumInstance();
}
received[position] = this.field.subtract(received[position], errorMagnitudes[i]);
}
return errorLocations.length;
};
/**
*
* @param ModulusPoly
* @param a
* @param ModulusPoly
* @param b
* @param int
* @param R
* @throws ChecksumException
*/
ErrorCorrection.prototype.runEuclideanAlgorithm = function (a, b, R) {
// Assume a's degree is >= b's
if (a.getDegree() < b.getDegree()) {
var temp = a;
a = b;
b = temp;
}
var rLast = a;
var r = b;
var tLast = this.field.getZero();
var t = this.field.getOne();
// Run Euclidean algorithm until r's degree is less than R/2
while (r.getDegree() >= Math.round(R / 2)) {
var rLastLast = rLast;
var tLastLast = tLast;
rLast = r;
tLast = t;
// Divide rLastLast by rLast, with quotient in q and remainder in r
if (rLast.isZero()) {
// Oops, Euclidean algorithm already terminated?
throw ChecksumException_1.default.getChecksumInstance();
}
r = rLastLast;
var q = this.field.getZero();
var denominatorLeadingTerm = rLast.getCoefficient(rLast.getDegree());
var dltInverse = this.field.inverse(denominatorLeadingTerm);
while (r.getDegree() >= rLast.getDegree() && !r.isZero()) {
var degreeDiff = r.getDegree() - rLast.getDegree();
var scale = this.field.multiply(r.getCoefficient(r.getDegree()), dltInverse);
q = q.add(this.field.buildMonomial(degreeDiff, scale));
r = r.subtract(rLast.multiplyByMonomial(degreeDiff, scale));
}
t = q.multiply(tLast).subtract(tLastLast).negative();
}
var sigmaTildeAtZero = t.getCoefficient(0);
if (sigmaTildeAtZero === 0) {
throw ChecksumException_1.default.getChecksumInstance();
}
var inverse = this.field.inverse(sigmaTildeAtZero);
var sigma = t.multiply(inverse);
var omega = r.multiply(inverse);
return [sigma, omega];
};
/**
*
* @param errorLocator
* @throws ChecksumException
*/
ErrorCorrection.prototype.findErrorLocations = function (errorLocator) {
// This is a direct application of Chien's search
var numErrors = errorLocator.getDegree();
var result = new Int32Array(numErrors);
var e = 0;
for (var i /*int*/ = 1; i < this.field.getSize() && e < numErrors; i++) {
if (errorLocator.evaluateAt(i) === 0) {
result[e] = this.field.inverse(i);
e++;
}
}
if (e !== numErrors) {
throw ChecksumException_1.default.getChecksumInstance();
}
return result;
};
ErrorCorrection.prototype.findErrorMagnitudes = function (errorEvaluator, errorLocator, errorLocations) {
var errorLocatorDegree = errorLocator.getDegree();
var formalDerivativeCoefficients = new Int32Array(errorLocatorDegree);
for (var i /*int*/ = 1; i <= errorLocatorDegree; i++) {
formalDerivativeCoefficients[errorLocatorDegree - i] =
this.field.multiply(i, errorLocator.getCoefficient(i));
}
var formalDerivative = new ModulusPoly_1.default(this.field, formalDerivativeCoefficients);
// This is directly applying Forney's Formula
var s = errorLocations.length;
var result = new Int32Array(s);
for (var i /*int*/ = 0; i < s; i++) {
var xiInverse = this.field.inverse(errorLocations[i]);
var numerator = this.field.subtract(0, errorEvaluator.evaluateAt(xiInverse));
var denominator = this.field.inverse(formalDerivative.evaluateAt(xiInverse));
result[i] = this.field.multiply(numerator, denominator);
}
return result;
};
return ErrorCorrection;
}());
exports.default = ErrorCorrection;