zxing/csharp/oned/EAN13Reader.cs

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/*
* 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.
*/
namespace com.google.zxing.oned
{
/**
* <p>Implements decoding of the EAN-13 format.</p>
*
* @author dswitkin@google.com (Daniel Switkin)
* @author Sean Owen
* @author alasdair@google.com (Alasdair Mackintosh)
*/
using System.Text;
using com.google.zxing.common;
public sealed class EAN13Reader : AbstractUPCEANReader
{
// For an EAN-13 barcode, the first digit is represented by the parities used
// to encode the next six digits, according to the table below. For example,
// if the barcode is 5 123456 789012 then the value of the first digit is
// signified by using odd for '1', even for '2', even for '3', odd for '4',
// odd for '5', and even for '6'. See http://en.wikipedia.org/wiki/EAN-13
//
// Parity of next 6 digits
// Digit 0 1 2 3 4 5
// 0 Odd Odd Odd Odd Odd Odd
// 1 Odd Odd Even Odd Even Even
// 2 Odd Odd Even Even Odd Even
// 3 Odd Odd Even Even Even Odd
// 4 Odd Even Odd Odd Even Even
// 5 Odd Even Even Odd Odd Even
// 6 Odd Even Even Even Odd Odd
// 7 Odd Even Odd Even Odd Even
// 8 Odd Even Odd Even Even Odd
// 9 Odd Even Even Odd Even Odd
//
// Note that the encoding for '0' uses the same parity as a UPC barcode. Hence
// a UPC barcode can be converted to an EAN-13 barcode by prepending a 0.
//
// The encodong is represented by the following array, which is a bit pattern
// using Odd = 0 and Even = 1. For example, 5 is represented by:
//
// Odd Even Even Odd Odd Even
// in binary:
// 0 1 1 0 0 1 == 0x19
//
private static int[] FIRST_DIGIT_ENCODINGS = {
0x00, 0x0B, 0x0D, 0xE, 0x13, 0x19, 0x1C, 0x15, 0x16, 0x1A
};
private int[] decodeMiddleCounters;
public EAN13Reader() {
decodeMiddleCounters = new int[4];
}
protected override int decodeMiddle(BitArray row, int[] startRange, StringBuilder resultString) {
int[] counters = decodeMiddleCounters;
counters[0] = 0;
counters[1] = 0;
counters[2] = 0;
counters[3] = 0;
int end = row.getSize();
int rowOffset = startRange[1];
int lgPatternFound = 0;
for (int x = 0; x < 6 && rowOffset < end; x++) {
int bestMatch = decodeDigit(row, counters, rowOffset, L_AND_G_PATTERNS);
resultString.Append((char) ('0' + bestMatch % 10));
for (int i = 0; i < counters.Length; i++) {
rowOffset += counters[i];
}
if (bestMatch >= 10) {
lgPatternFound |= 1 << (5 - x);
}
}
determineFirstDigit(resultString, lgPatternFound);
int[] middleRange = findGuardPattern(row, rowOffset, true, MIDDLE_PATTERN);
rowOffset = middleRange[1];
for (int x = 0; x < 6 && rowOffset < end; x++) {
int bestMatch = decodeDigit(row, counters, rowOffset, L_PATTERNS);
resultString.Append((char) ('0' + bestMatch));
for (int i = 0; i < counters.Length; i++) {
rowOffset += counters[i];
}
}
return rowOffset;
}
public override BarcodeFormat getBarcodeFormat() {
return BarcodeFormat.EAN_13;
}
/**
* Based on pattern of odd-even ('L' and 'G') patterns used to encoded the explicitly-encoded digits
* in a barcode, determines the implicitly encoded first digit and adds it to the result string.
*
* @param resultString string to insert decoded first digit into
* @param lgPatternFound int whose bits indicates the pattern of odd/even L/G patterns used to
* encode digits
* @throws ReaderException if first digit cannot be determined
*/
private static void determineFirstDigit(StringBuilder resultString, int lgPatternFound) {
for (int d = 0; d < 10; d++) {
if (lgPatternFound == FIRST_DIGIT_ENCODINGS[d]) {
resultString.Insert(0, (char) ('0' + d));
return;
}
}
throw new ReaderException();
}
}
}