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Core barcode encoding/decoding library
/*
* Copyright 2010 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.aztec.decoder;
import com.google.zxing.FormatException;
import com.google.zxing.aztec.AztecDetectorResult;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.common.DecoderResult;
import com.google.zxing.common.reedsolomon.GenericGF;
import com.google.zxing.common.reedsolomon.ReedSolomonDecoder;
import com.google.zxing.common.reedsolomon.ReedSolomonException;
import java.util.Arrays;
/**
* The main class which implements Aztec Code decoding -- as opposed to locating and extracting
* the Aztec Code from an image.
*
* @author David Olivier
*/
public final class Decoder {
private enum Table {
UPPER,
LOWER,
MIXED,
DIGIT,
PUNCT,
BINARY
}
private static final String[] UPPER_TABLE = {
"CTRL_PS", " ", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P",
"Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "CTRL_LL", "CTRL_ML", "CTRL_DL", "CTRL_BS"
};
private static final String[] LOWER_TABLE = {
"CTRL_PS", " ", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p",
"q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "CTRL_US", "CTRL_ML", "CTRL_DL", "CTRL_BS"
};
private static final String[] MIXED_TABLE = {
"CTRL_PS", " ", "\1", "\2", "\3", "\4", "\5", "\6", "\7", "\b", "\t", "\n",
"\13", "\f", "\r", "\33", "\34", "\35", "\36", "\37", "@", "\\", "^", "_",
"`", "|", "~", "\177", "CTRL_LL", "CTRL_UL", "CTRL_PL", "CTRL_BS"
};
private static final String[] PUNCT_TABLE = {
"", "\r", "\r\n", ". ", ", ", ": ", "!", "\"", "#", "$", "%", "&", "'", "(", ")",
"*", "+", ",", "-", ".", "/", ":", ";", "<", "=", ">", "?", "[", "]", "{", "}", "CTRL_UL"
};
private static final String[] DIGIT_TABLE = {
"CTRL_PS", " ", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", ",", ".", "CTRL_UL", "CTRL_US"
};
private AztecDetectorResult ddata;
public DecoderResult decode(AztecDetectorResult detectorResult) throws FormatException {
ddata = detectorResult;
BitMatrix matrix = detectorResult.getBits();
boolean[] rawbits = extractBits(matrix);
boolean[] correctedBits = correctBits(rawbits);
String result = getEncodedData(correctedBits);
return new DecoderResult(null, result, null, null);
}
// This method is used for testing the high-level encoder
public static String highLevelDecode(boolean[] correctedBits) {
return getEncodedData(correctedBits);
}
/**
* Gets the string encoded in the aztec code bits
*
* @return the decoded string
*/
private static String getEncodedData(boolean[] correctedBits) {
int endIndex = correctedBits.length;
Table latchTable = Table.UPPER; // table most recently latched to
Table shiftTable = Table.UPPER; // table to use for the next read
StringBuilder result = new StringBuilder(20);
int index = 0;
while (index < endIndex) {
if (shiftTable == Table.BINARY) {
if (endIndex - index < 5) {
break;
}
int length = readCode(correctedBits, index, 5);
index += 5;
if (length == 0) {
if (endIndex - index < 11) {
break;
}
length = readCode(correctedBits, index, 11) + 31;
index += 11;
}
for (int charCount = 0; charCount < length; charCount++) {
if (endIndex - index < 8) {
index = endIndex; // Force outer loop to exit
break;
}
int code = readCode(correctedBits, index, 8);
result.append((char) code);
index += 8;
}
// Go back to whatever mode we had been in
shiftTable = latchTable;
} else {
int size = shiftTable == Table.DIGIT ? 4 : 5;
if (endIndex - index < size) {
break;
}
int code = readCode(correctedBits, index, size);
index += size;
String str = getCharacter(shiftTable, code);
if (str.startsWith("CTRL_")) {
// Table changes
shiftTable = getTable(str.charAt(5));
if (str.charAt(6) == 'L') {
latchTable = shiftTable;
}
} else {
result.append(str);
// Go back to whatever mode we had been in
shiftTable = latchTable;
}
}
}
return result.toString();
}
/**
* gets the table corresponding to the char passed
*/
private static Table getTable(char t) {
switch (t) {
case 'L':
return Table.LOWER;
case 'P':
return Table.PUNCT;
case 'M':
return Table.MIXED;
case 'D':
return Table.DIGIT;
case 'B':
return Table.BINARY;
case 'U':
default:
return Table.UPPER;
}
}
/**
* Gets the character (or string) corresponding to the passed code in the given table
*
* @param table the table used
* @param code the code of the character
*/
private static String getCharacter(Table table, int code) {
switch (table) {
case UPPER:
return UPPER_TABLE[code];
case LOWER:
return LOWER_TABLE[code];
case MIXED:
return MIXED_TABLE[code];
case PUNCT:
return PUNCT_TABLE[code];
case DIGIT:
return DIGIT_TABLE[code];
default:
// Should not reach here.
throw new IllegalStateException("Bad table");
}
}
/**
* Performs RS error correction on an array of bits.
*
* @return the corrected array
* @throws FormatException if the input contains too many errors
*/
private boolean[] correctBits(boolean[] rawbits) throws FormatException {
GenericGF gf;
int codewordSize;
if (ddata.getNbLayers() <= 2) {
codewordSize = 6;
gf = GenericGF.AZTEC_DATA_6;
} else if (ddata.getNbLayers() <= 8) {
codewordSize = 8;
gf = GenericGF.AZTEC_DATA_8;
} else if (ddata.getNbLayers() <= 22) {
codewordSize = 10;
gf = GenericGF.AZTEC_DATA_10;
} else {
codewordSize = 12;
gf = GenericGF.AZTEC_DATA_12;
}
int numDataCodewords = ddata.getNbDatablocks();
int numCodewords = rawbits.length / codewordSize;
if (numCodewords < numDataCodewords) {
throw FormatException.getFormatInstance();
}
int offset = rawbits.length % codewordSize;
int numECCodewords = numCodewords - numDataCodewords;
int[] dataWords = new int[numCodewords];
for (int i = 0; i < numCodewords; i++, offset += codewordSize) {
dataWords[i] = readCode(rawbits, offset, codewordSize);
}
try {
ReedSolomonDecoder rsDecoder = new ReedSolomonDecoder(gf);
rsDecoder.decode(dataWords, numECCodewords);
} catch (ReedSolomonException ignored) {
throw FormatException.getFormatInstance();
}
// Now perform the unstuffing operation.
// First, count how many bits are going to be thrown out as stuffing
int mask = (1 << codewordSize) - 1;
int stuffedBits = 0;
for (int i = 0; i < numDataCodewords; i++) {
int dataWord = dataWords[i];
if (dataWord == 0 || dataWord == mask) {
throw FormatException.getFormatInstance();
} else if (dataWord == 1 || dataWord == mask - 1) {
stuffedBits++;
}
}
// Now, actually unpack the bits and remove the stuffing
boolean[] correctedBits = new boolean[numDataCodewords * codewordSize - stuffedBits];
int index = 0;
for (int i = 0; i < numDataCodewords; i++) {
int dataWord = dataWords[i];
if (dataWord == 1 || dataWord == mask - 1) {
// next codewordSize-1 bits are all zeros or all ones
Arrays.fill(correctedBits, index, index + codewordSize - 1, dataWord > 1);
index += codewordSize - 1;
} else {
for (int bit = codewordSize - 1; bit >= 0; --bit) {
correctedBits[index++] = (dataWord & (1 << bit)) != 0;
}
}
}
return correctedBits;
}
/**
* Gets the array of bits from an Aztec Code matrix
*
* @return the array of bits
*/
boolean[] extractBits(BitMatrix matrix) {
boolean compact = ddata.isCompact();
int layers = ddata.getNbLayers();
int baseMatrixSize = compact ? 11 + layers * 4 : 14 + layers * 4; // not including alignment lines
int[] alignmentMap = new int[baseMatrixSize];
boolean[] rawbits = new boolean[totalBitsInLayer(layers, compact)];
if (compact) {
for (int i = 0; i < alignmentMap.length; i++) {
alignmentMap[i] = i;
}
} else {
int matrixSize = baseMatrixSize + 1 + 2 * ((baseMatrixSize / 2 - 1) / 15);
int origCenter = baseMatrixSize / 2;
int center = matrixSize / 2;
for (int i = 0; i < origCenter; i++) {
int newOffset = i + i / 15;
alignmentMap[origCenter - i - 1] = center - newOffset - 1;
alignmentMap[origCenter + i] = center + newOffset + 1;
}
}
for (int i = 0, rowOffset = 0; i < layers; i++) {
int rowSize = compact ? (layers - i) * 4 + 9 : (layers - i) * 4 + 12;
// The top-left most point of this layer is (not including alignment lines)
int low = i * 2;
// The bottom-right most point of this layer is (not including alignment lines)
int high = baseMatrixSize - 1 - low;
// We pull bits from the two 2 x rowSize columns and two rowSize x 2 rows
for (int j = 0; j < rowSize; j++) {
int columnOffset = j * 2;
for (int k = 0; k < 2; k++) {
// left column
rawbits[rowOffset + columnOffset + k] =
matrix.get(alignmentMap[low + k], alignmentMap[low + j]);
// bottom row
rawbits[rowOffset + 2 * rowSize + columnOffset + k] =
matrix.get(alignmentMap[low + j], alignmentMap[high - k]);
// right column
rawbits[rowOffset + 4 * rowSize + columnOffset + k] =
matrix.get(alignmentMap[high - k], alignmentMap[high - j]);
// top row
rawbits[rowOffset + 6 * rowSize + columnOffset + k] =
matrix.get(alignmentMap[high - j], alignmentMap[low + k]);
}
}
rowOffset += rowSize * 8;
}
return rawbits;
}
/**
* Reads a code of given length and at given index in an array of bits
*/
private static int readCode(boolean[] rawbits, int startIndex, int length) {
int res = 0;
for (int i = startIndex; i < startIndex + length; i++) {
res <<= 1;
if (rawbits[i]) {
res |= 0x01;
}
}
return res;
}
private static int totalBitsInLayer(int layers, boolean compact) {
return ((compact ? 88 : 112) + 16 * layers) * layers;
}
}
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