zxing/csharp/oned/EAN13Reader.cs

/*
* 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();
          }

    
    
    }
}