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;
namespace com.google.zxing.qrcode.decoder
{
	
	/// <summary> <p>Encapsulates a QR Code's format information, including the data mask used and
	/// error correction level.</p>
	/// 
	/// </summary>
	/// <author>  Sean Owen
	/// </author>
	/// <author>www.Redivivus.in (suraj.supekar@redivivus.in) - Ported from ZXING Java Source 
	/// </author>
	/// <seealso cref="DataMask">
	/// </seealso>
	/// <seealso cref="ErrorCorrectionLevel">
	/// </seealso>
	sealed class FormatInformation
	{
		internal ErrorCorrectionLevel ErrorCorrectionLevel
		{
			get
			{
				return errorCorrectionLevel;
			}
			
		}
		internal sbyte DataMask
		{
			get
			{
				return dataMask;
			}
			
		}
		
		private const int FORMAT_INFO_MASK_QR = 0x5412;
		
		/// <summary> See ISO 18004:2006, Annex C, Table C.1</summary>
		//UPGRADE_NOTE: Final was removed from the declaration of 'FORMAT_INFO_DECODE_LOOKUP'. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
		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}};
		
		/// <summary> Offset i holds the number of 1 bits in the binary representation of i</summary>
		//UPGRADE_NOTE: Final was removed from the declaration of 'BITS_SET_IN_HALF_BYTE'. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
		private static readonly int[] BITS_SET_IN_HALF_BYTE = new int[]{0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};
		
		//UPGRADE_NOTE: Final was removed from the declaration of 'errorCorrectionLevel '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
		private ErrorCorrectionLevel errorCorrectionLevel;
		//UPGRADE_NOTE: Final was removed from the declaration of 'dataMask '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
		private sbyte dataMask;
		
		private FormatInformation(int formatInfo)
		{
			// Bits 3,4
			errorCorrectionLevel = ErrorCorrectionLevel.forBits((formatInfo >> 3) & 0x03);
			// Bottom 3 bits
			dataMask = (sbyte) (formatInfo & 0x07);
		}
		
		internal 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 name="maskedFormatInfo">format info indicator, with mask still applied
		/// </param>
		/// <returns> information about the format it specifies, or <code>null</code>
		/// if doesn't seem to match any known pattern
		/// </returns>
		internal static FormatInformation decodeFormatInformation(int maskedFormatInfo)
		{
			FormatInformation formatInfo = doDecodeFormatInformation(maskedFormatInfo);
			if (formatInfo != null)
			{
				return formatInfo;
			}
			// Should return null, but, some QR codes apparently
			// do not mask this info. Try again by actually masking the pattern
			// first
			return doDecodeFormatInformation(maskedFormatInfo ^ FORMAT_INFO_MASK_QR);
		}
		
		private static FormatInformation doDecodeFormatInformation(int maskedFormatInfo)
		{
			// Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing
			int bestDifference = System.Int32.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 == maskedFormatInfo)
				{
					// Found an exact match
					return new FormatInformation(decodeInfo[1]);
				}
				int bitsDifference = numBitsDiffering(maskedFormatInfo, targetInfo);
				if (bitsDifference < bestDifference)
				{
					bestFormatInfo = decodeInfo[1];
					bestDifference = bitsDifference;
				}
			}
			// Hamming distance of the 32 masked codes is 7, by construction, so <= 3 bits
			// differing means we found a match
			if (bestDifference <= 3)
			{
				return new FormatInformation(bestFormatInfo);
			}
			return null;
		}
		
		public override int GetHashCode()
		{
			return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
		}
		
		public  override bool Equals(System.Object o)
		{
			if (!(o is FormatInformation))
			{
				return false;
			}
			FormatInformation other = (FormatInformation) o;
			return this.errorCorrectionLevel == other.errorCorrectionLevel && this.dataMask == other.dataMask;
		}
	}
}