Matthew Schulkind (Google)
Matt York (LifeMarks)
Paul Hackenberger
+sanfordsquires (?)
Sean Owen (Google)
Vince Francis (LifeMarks)
*
* @author srowen@google.com (Sean Owen)
* @author William Rucklidge
+ * @author sanfordsquires
*/
public final class ReedSolomonDecoder {
*
* @param received data and error-correction codewords
* @param twoS number of error-correction codewords available
- * @param dataMatrix if true, then uses a calculation that matches the Data Matrix
- * standard rather than the one used in QR Code
* @throws ReedSolomonException if decoding fails for any reason
*/
- public void decode(int[] received, int twoS, boolean dataMatrix) throws ReedSolomonException {
+ public void decode(int[] received, int twoS) throws ReedSolomonException {
GF256Poly poly = new GF256Poly(field, received);
int[] syndromeCoefficients = new int[twoS];
+ boolean dataMatrix = field.equals(GF256.DATA_MATRIX_FIELD);
boolean noError = true;
for (int i = 0; i < twoS; i++) {
- // This difference in syndrome calculation appears to be correct, but then causes issues below
+ // Thanks to sanfordsquires for this fix:
int eval = poly.evaluateAt(field.exp(dataMatrix ? i + 1 : i));
syndromeCoefficients[syndromeCoefficients.length - 1 - i] = eval;
if (eval != 0) {
return;
}
GF256Poly syndrome = new GF256Poly(field, syndromeCoefficients);
- if (dataMatrix) {
- // TODO Not clear this is correct for DataMatrix, but it gives almost-correct behavior;
- // works except when number of errors is the maximum allowable.
- syndrome = syndrome.multiply(field.buildMonomial(1, 1));
- }
GF256Poly[] sigmaOmega =
runEuclideanAlgorithm(field.buildMonomial(twoS, 1), syndrome, twoS);
GF256Poly sigma = sigmaOmega[0];
GF256Poly omega = sigmaOmega[1];
int[] errorLocations = findErrorLocations(sigma);
- int[] errorMagnitudes = findErrorMagnitudes(omega, errorLocations);
+ int[] errorMagnitudes = findErrorMagnitudes(omega, errorLocations, dataMatrix);
for (int i = 0; i < errorLocations.length; i++) {
int position = received.length - 1 - field.log(errorLocations[i]);
+ if (position < 0) {
+ throw new ReedSolomonException("Bad error location");
+ }
received[position] = GF256.addOrSubtract(received[position], errorMagnitudes[i]);
}
}
return result;
}
- private int[] findErrorMagnitudes(GF256Poly errorEvaluator, int[] errorLocations) {
+ private int[] findErrorMagnitudes(GF256Poly errorEvaluator, int[] errorLocations, boolean dataMatrix) {
// This is directly applying Forney's Formula
int s = errorLocations.length;
int[] result = new int[s];
}
result[i] = field.multiply(errorEvaluator.evaluateAt(xiInverse),
field.inverse(denominator));
+ // Thanks to sanfordsquires for this fix:
+ if (dataMatrix) {
+ result[i] = field.multiply(result[i], xiInverse);
+ }
}
return result;
}
}\r
int numECCodewords = codewordBytes.length - numDataCodewords;\r
try {\r
- rsDecoder.decode(codewordsInts, numECCodewords, true);\r
+ rsDecoder.decode(codewordsInts, numECCodewords);\r
} catch (ReedSolomonException rse) {\r
throw new ReaderException(rse.toString());\r
}\r
}\r
int numECCodewords = codewordBytes.length - numDataCodewords;\r
try {\r
- rsDecoder.decode(codewordsInts, numECCodewords, false);\r
+ rsDecoder.decode(codewordsInts, numECCodewords);\r
} catch (ReedSolomonException rse) {\r
throw new ReaderException(rse.toString());\r
}\r
--- /dev/null
+/*
+ * 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 junit.framework.TestCase;
+
+import java.util.BitSet;
+import java.util.Random;
+
+/**
+ * @author srowen@google.com (Sean Owen)
+ */
+abstract class AbstractReedSolomonTestCase extends TestCase {
+
+ static void corrupt(int[] received, int howMany, Random random) {
+ BitSet corrupted = new BitSet(received.length);
+ for (int j = 0; j < howMany; j++) {
+ int location = random.nextInt(received.length);
+ if (corrupted.get(location)) {
+ j--;
+ } else {
+ corrupted.set(location);
+ received[location] = (received[location] + 1 + random.nextInt(255)) & 0xFF;
+ }
+ }
+ }
+
+}
\ No newline at end of file
package com.google.zxing.common.reedsolomon;
-import junit.framework.TestCase;
-
-import java.util.BitSet;
import java.util.Random;
/**
* @author srowen@google.com (Sean Owen)
+ * @author sanfordsquires
*/
-public final class ReedSolomonDecoderDataMatrixTestCase extends TestCase {
+public final class ReedSolomonDecoderDataMatrixTestCase extends AbstractReedSolomonTestCase {
private static final int[] DM_CODE_TEST = { 142, 164, 186 };
private static final int[] DM_CODE_TEST_WITH_EC = { 142, 164, 186, 114, 25, 5, 88, 102 };
Random random = new Random(0xDEADBEEFL);
for (int i = 0; i < DM_CODE_TEST.length; i++) { // # iterations is kind of arbitrary
System.arraycopy(DM_CODE_TEST_WITH_EC, 0, received, 0, received.length);
- // TODO we aren't testing max errors really since there is a known bug here
- corrupt(received, DM_CODE_CORRECTABLE - 1, random);
+ corrupt(received, DM_CODE_CORRECTABLE, random);
checkQRRSDecode(received);
}
}
}
private void checkQRRSDecode(int[] received) throws ReedSolomonException {
- dmRSDecoder.decode(received, 2 * DM_CODE_CORRECTABLE, true);
+ dmRSDecoder.decode(received, 2 * DM_CODE_CORRECTABLE);
for (int i = 0; i < DM_CODE_TEST.length; i++) {
assertEquals(received[i], DM_CODE_TEST[i]);
}
}
- private static void corrupt(int[] received, int howMany, Random random) {
- BitSet corrupted = new BitSet(received.length);
- for (int j = 0; j < howMany; j++) {
- int location = random.nextInt(received.length);
- if (corrupted.get(location)) {
- j--;
- } else {
- corrupted.set(location);
- int newByte = random.nextInt(256);
- received[location] = newByte;
- }
- }
- }
}
\ No newline at end of file
package com.google.zxing.common.reedsolomon;
-import junit.framework.TestCase;
-
-import java.util.BitSet;
import java.util.Random;
/**
* @author srowen@google.com (Sean Owen)
*/
-public final class ReedSolomonDecoderQRCodeTestCase extends TestCase {
+public final class ReedSolomonDecoderQRCodeTestCase extends AbstractReedSolomonTestCase {
/** See ISO 18004, Appendix I, from which this example is taken. */
private static final int[] QR_CODE_TEST =
}
private void checkQRRSDecode(int[] received) throws ReedSolomonException {
- qrRSDecoder.decode(received, 2*QR_CODE_CORRECTABLE, false);
+ qrRSDecoder.decode(received, 2*QR_CODE_CORRECTABLE);
for (int i = 0; i < QR_CODE_TEST.length; i++) {
assertEquals(received[i], QR_CODE_TEST[i]);
}
}
- private static void corrupt(int[] received, int howMany, Random random) {
- BitSet corrupted = new BitSet(received.length);
- for (int j = 0; j < howMany; j++) {
- int location = random.nextInt(received.length);
- if (corrupted.get(location)) {
- j--;
- } else {
- corrupted.set(location);
- int newByte = random.nextInt(256);
- received[location] = newByte;
- }
- }
- }
}
\ No newline at end of file
projects / zxing.git / commitdiff