/*
* Copyright 2006 Jeremias Maerki.
*
* 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.datamatrix.encoder;
/**
* Error Correction Code for ECC200.
*/
public final class ErrorCorrection {
/**
* Lookup table which factors to use for which number of error correction
* codewords. See FACTORS.
*/
private static final int[] FACTOR_SETS = { 5, 7, 10, 11, 12, 14, 18, 20,
24, 28, 36, 42, 48, 56, 62, 68 };
/**
* Precomputed polynomial factors for ECC 200.
*/
private static final int[][] FACTORS = {
{ 228, 48, 15, 111, 62 },
{ 23, 68, 144, 134, 240, 92, 254 },
{ 28, 24, 185, 166, 223, 248, 116, 255, 110, 61 },
{ 175, 138, 205, 12, 194, 168, 39, 245, 60, 97, 120 },
{ 41, 153, 158, 91, 61, 42, 142, 213, 97, 178, 100, 242 },
{ 156, 97, 192, 252, 95, 9, 157, 119, 138, 45, 18, 186, 83, 185 },
{ 83, 195, 100, 39, 188, 75, 66, 61, 241, 213, 109, 129, 94, 254,
225, 48, 90, 188 },
{ 15, 195, 244, 9, 233, 71, 168, 2, 188, 160, 153, 145, 253, 79,
108, 82, 27, 174, 186, 172 },
{ 52, 190, 88, 205, 109, 39, 176, 21, 155, 197, 251, 223, 155, 21,
5, 172, 254, 124, 12, 181, 184, 96, 50, 193 },
{ 211, 231, 43, 97, 71, 96, 103, 174, 37, 151, 170, 53, 75, 34,
249, 121, 17, 138, 110, 213, 141, 136, 120, 151, 233, 168,
93, 255 },
{ 245, 127, 242, 218, 130, 250, 162, 181, 102, 120, 84, 179, 220,
251, 80, 182, 229, 18, 2, 4, 68, 33, 101, 137, 95, 119,
115, 44, 175, 184, 59, 25, 225, 98, 81, 112 },
{ 77, 193, 137, 31, 19, 38, 22, 153, 247, 105, 122, 2, 245, 133,
242, 8, 175, 95, 100, 9, 167, 105, 214, 111, 57, 121, 21,
1, 253, 57, 54, 101, 248, 202, 69, 50, 150, 177, 226, 5, 9,
5 },
{ 245, 132, 172, 223, 96, 32, 117, 22, 238, 133, 238, 231, 205,
188, 237, 87, 191, 106, 16, 147, 118, 23, 37, 90, 170, 205,
131, 88, 120, 100, 66, 138, 186, 240, 82, 44, 176, 87, 187,
147, 160, 175, 69, 213, 92, 253, 225, 19 },
{ 175, 9, 223, 238, 12, 17, 220, 208, 100, 29, 175, 170, 230, 192,
215, 235, 150, 159, 36, 223, 38, 200, 132, 54, 228, 146,
218, 234, 117, 203, 29, 232, 144, 238, 22, 150, 201, 117,
62, 207, 164, 13, 137, 245, 127, 67, 247, 28, 155, 43, 203,
107, 233, 53, 143, 46 },
{ 242, 93, 169, 50, 144, 210, 39, 118, 202, 188, 201, 189, 143,
108, 196, 37, 185, 112, 134, 230, 245, 63, 197, 190, 250,
106, 185, 221, 175, 64, 114, 71, 161, 44, 147, 6, 27, 218,
51, 63, 87, 10, 40, 130, 188, 17, 163, 31, 176, 170, 4,
107, 232, 7, 94, 166, 224, 124, 86, 47, 11, 204 },
{ 220, 228, 173, 89, 251, 149, 159, 56, 89, 33, 147, 244, 154, 36,
73, 127, 213, 136, 248, 180, 234, 197, 158, 177, 68, 122,
93, 213, 15, 160, 227, 236, 66, 139, 153, 185, 202, 167,
179, 25, 220, 232, 96, 210, 231, 136, 223, 239, 181, 241,
59, 52, 172, 25, 49, 232, 211, 189, 64, 54, 108, 153, 132,
63, 96, 103, 82, 186 } };
private static final int MODULO_VALUE = 0x12D;
private static final int[] LOG;
private static final int[] ALOG;
static {
// Create log and antilog table
LOG = new int[256];
ALOG = new int[255];
int p = 1;
for (int i = 0; i < 255; i++) {
ALOG[i] = p;
LOG[p] = i;
p *= 2;
if (p >= 256) {
p ^= MODULO_VALUE;
}
}
}
private ErrorCorrection() {
}
/**
* Creates the ECC200 error correction for an encoded message.
*
* @param codewords
* the codewords
* @param symbolInfo
* information about the symbol to be encoded
* @return the codewords with interleaved error correction.
*/
public static String encodeECC200(String codewords, SymbolInfo symbolInfo) {
if (codewords.length() != symbolInfo.getDataCapacity()) {
throw new IllegalArgumentException(
"The number of codewords does not match the selected symbol");
}
StringBuilder sb = new StringBuilder(symbolInfo.getDataCapacity()
+ symbolInfo.getErrorCodewords());
sb.append(codewords);
int blockCount = symbolInfo.getInterleavedBlockCount();
if (blockCount == 1) {
String ecc = createECCBlock(codewords,
symbolInfo.getErrorCodewords());
sb.append(ecc);
} else {
sb.setLength(sb.capacity());
int[] dataSizes = new int[blockCount];
int[] errorSizes = new int[blockCount];
int[] startPos = new int[blockCount];
for (int i = 0; i < blockCount; i++) {
dataSizes[i] = symbolInfo
.getDataLengthForInterleavedBlock(i + 1);
errorSizes[i] = symbolInfo
.getErrorLengthForInterleavedBlock(i + 1);
startPos[i] = 0;
if (i > 0) {
startPos[i] = startPos[i - 1] + dataSizes[i];
}
}
for (int block = 0; block < blockCount; block++) {
StringBuilder temp = new StringBuilder(dataSizes[block]);
for (int d = block; d < symbolInfo.getDataCapacity(); d += blockCount) {
temp.append(codewords.charAt(d));
}
String ecc = createECCBlock(temp.toString(), errorSizes[block]);
int pos = 0;
for (int e = block; e < errorSizes[block] * blockCount; e += blockCount) {
sb.setCharAt(symbolInfo.getDataCapacity() + e,
ecc.charAt(pos++));
}
}
}
return sb.toString();
}
private static String createECCBlock(CharSequence codewords, int numECWords) {
return createECCBlock(codewords, 0, codewords.length(), numECWords);
}
private static String createECCBlock(CharSequence codewords, int start,
int len, int numECWords) {
int table = -1;
for (int i = 0; i < FACTOR_SETS.length; i++) {
if (FACTOR_SETS[i] == numECWords) {
table = i;
break;
}
}
if (table < 0) {
throw new IllegalArgumentException(
"Illegal number of error correction codewords specified: "
+ numECWords);
}
int[] poly = FACTORS[table];
char[] ecc = new char[numECWords];
for (int i = 0; i < numECWords; i++) {
ecc[i] = 0;
}
for (int i = start; i < start + len; i++) {
int m = ecc[numECWords - 1] ^ codewords.charAt(i);
for (int k = numECWords - 1; k > 0; k--) {
if (m != 0 && poly[k] != 0) {
ecc[k] = (char) (ecc[k - 1] ^ ALOG[(LOG[m] + LOG[poly[k]]) % 255]);
} else {
ecc[k] = ecc[k - 1];
}
}
if (m != 0 && poly[0] != 0) {
ecc[0] = (char) ALOG[(LOG[m] + LOG[poly[0]]) % 255];
} else {
ecc[0] = 0;
}
}
char[] eccReversed = new char[numECWords];
for (int i = 0; i < numECWords; i++) {
eccReversed[i] = ecc[numECWords - i - 1];
}
return String.valueOf(eccReversed);
}
}