zxing/csharp/qrcode/decoder/FormatInformation.cs

/*
* Copyright 2007 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.
*/
using System;
using com.google.zxing;
using com.google.zxing.common;

namespace com.google.zxing.qrcode.decoder
{
    public sealed class FormatInformation
    { 
          private static int FORMAT_INFO_MASK_QR = 0x5412;
          /**
           * See ISO 18004:2006, Annex C, Table C.1
           */
          private static readonly int[][] FORMAT_INFO_DECODE_LOOKUP = new int[][] { new int[] { 0x5412, 0x00 }, new int[] { 0x5125, 0x01 }, new int[] { 0x5E7C, 0x02 }, new int[] { 0x5B4B, 0x03 }, new int[] { 0x45F9, 0x04 }, new int[] { 0x40CE, 0x05 }, new int[] { 0x4F97, 0x06 }, new int[] { 0x4AA0, 0x07 }, new int[] { 0x77C4, 0x08 }, new int[] { 0x72F3, 0x09 }, new int[] { 0x7DAA, 0x0A }, new int[] { 0x789D, 0x0B }, new int[] { 0x662F, 0x0C }, new int[] { 0x6318, 0x0D }, new int[] { 0x6C41, 0x0E }, new int[] { 0x6976, 0x0F }, new int[] { 0x1689, 0x10 }, new int[] { 0x13BE, 0x11 }, new int[] { 0x1CE7, 0x12 }, new int[] { 0x19D0, 0x13 }, new int[] { 0x0762, 0x14 }, new int[] { 0x0255, 0x15 }, new int[] { 0x0D0C, 0x16 }, new int[] { 0x083B, 0x17 }, new int[] { 0x355F, 0x18 }, new int[] { 0x3068, 0x19 }, new int[] { 0x3F31, 0x1A }, new int[] { 0x3A06, 0x1B }, new int[] { 0x24B4, 0x1C }, new int[] { 0x2183, 0x1D }, new int[] { 0x2EDA, 0x1E }, new int[] { 0x2BED, 0x1F } };
		
          /**
           * Offset i holds the number of 1 bits in the binary representation of i
           */
          private static int[] BITS_SET_IN_HALF_BYTE =
              {0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};

          private ErrorCorrectionLevel errorCorrectionLevel;
          private byte dataMask;

          private FormatInformation(int formatInfo) {
            // Bits 3,4
            errorCorrectionLevel = ErrorCorrectionLevel.forBits((formatInfo >> 3) & 0x03);
            // Bottom 3 bits
            dataMask = (byte) (formatInfo & 0x07);
          }

          public static int numBitsDiffering(int a, int b) {
              a ^= b; // a now has a 1 bit exactly where its bit differs with b's
              // Count bits set quickly with a series of lookups:
              return BITS_SET_IN_HALF_BYTE[a & 0x0F] + BITS_SET_IN_HALF_BYTE[(SupportClass.URShift(a, 4) & 0x0F)] + BITS_SET_IN_HALF_BYTE[(SupportClass.URShift(a, 8) & 0x0F)] + BITS_SET_IN_HALF_BYTE[(SupportClass.URShift(a, 12) & 0x0F)] + BITS_SET_IN_HALF_BYTE[(SupportClass.URShift(a, 16) & 0x0F)] + BITS_SET_IN_HALF_BYTE[(SupportClass.URShift(a, 20) & 0x0F)] + BITS_SET_IN_HALF_BYTE[(SupportClass.URShift(a, 24) & 0x0F)] + BITS_SET_IN_HALF_BYTE[(SupportClass.URShift(a, 28) & 0x0F)];
          }

          /**
           * @param rawFormatInfo
           * @return
           */
          public static FormatInformation decodeFormatInformation(int rawFormatInfo){
              try{
                FormatInformation formatInfo = doDecodeFormatInformation(rawFormatInfo);
                if (formatInfo != null) {
                  return formatInfo;
                }
                // Should return null, but, some QR codes apparently
                // do not mask this info. Try again, first masking the raw bits so
                // the function will unmask
                return doDecodeFormatInformation(rawFormatInfo ^ FORMAT_INFO_MASK_QR);
              }catch(Exception e){
                  throw new ReaderException(e.Message);
              }            
          }

          private static FormatInformation doDecodeFormatInformation(int rawFormatInfo) {
            // Unmask:
            int unmaskedFormatInfo = rawFormatInfo ^ FORMAT_INFO_MASK_QR;
            // Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing
            int bestDifference = int.MaxValue;
            int bestFormatInfo = 0;
            for (int i = 0; i < FORMAT_INFO_DECODE_LOOKUP.Length; i++) {
              int[] decodeInfo = FORMAT_INFO_DECODE_LOOKUP[i];
              int targetInfo = decodeInfo[0];
              if (targetInfo == unmaskedFormatInfo) {
                // Found an exact match
                return new FormatInformation(decodeInfo[1]);
              }
              int bitsDifference = numBitsDiffering(unmaskedFormatInfo, targetInfo);
              if (bitsDifference < bestDifference) {
                bestFormatInfo = decodeInfo[1];
                bestDifference = bitsDifference;
              }
            }
            if (bestDifference <= 3) {
              return new FormatInformation(bestFormatInfo);
            }
            return null;
          }

          public ErrorCorrectionLevel getErrorCorrectionLevel() {
            return errorCorrectionLevel;
          }

          public byte getDataMask() {
            return dataMask;
          }

          public int hashCode() {
            return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
          }

          public bool equals(Object o) {
            if (!(o.GetType() == typeof(FormatInformation))){
              return false;
            }
            FormatInformation other = (FormatInformation) o;
            return this.errorCorrectionLevel == other.errorCorrectionLevel &&
                this.dataMask == other.dataMask;
          }
    
    }
}