X-Git-Url: http://git.rot13.org/?a=blobdiff_plain;f=csharp%2Fcommon%2Freedsolomon%2FGF256.cs;fp=csharp%2Fcommon%2Freedsolomon%2FGF256.cs;h=d00663381d09ec104820446ff0ae317c28cf2d7a;hb=ec1d7dfa5fb34e69b0f65f936eec23c8a8b88b56;hp=0000000000000000000000000000000000000000;hpb=e8f7ac2a4615b772609002f4f903fda2e9474c5c;p=zxing.git

diff --git a/csharp/common/reedsolomon/GF256.cs b/csharp/common/reedsolomon/GF256.cs
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+/*
+* 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.common.reedsolomon
+{
+	
+	/// <summary> <p>This class contains utility methods for performing mathematical operations over
+	/// the Galois Field GF(256). Operations use a given primitive polynomial in calculations.</p>
+	/// 
+	/// <p>Throughout this package, elements of GF(256) are represented as an <code>int</code>
+	/// for convenience and speed (but at the cost of memory).
+	/// Only the bottom 8 bits are really used.</p>
+	/// 
+	/// </summary>
+	/// <author>  Sean Owen
+	/// </author>
+	/// <author>www.Redivivus.in (suraj.supekar@redivivus.in) - Ported from ZXING Java Source 
+	/// </author>
+	public sealed class GF256
+	{
+		internal GF256Poly Zero
+		{
+			get
+			{
+				return zero;
+			}
+			
+		}
+		internal GF256Poly One
+		{
+			get
+			{
+				return one;
+			}
+			
+		}
+		
+		//UPGRADE_NOTE: Final was removed from the declaration of 'QR_CODE_FIELD '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
+		public static readonly GF256 QR_CODE_FIELD = new GF256(0x011D); // x^8 + x^4 + x^3 + x^2 + 1
+		//UPGRADE_NOTE: Final was removed from the declaration of 'DATA_MATRIX_FIELD '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
+		public static readonly GF256 DATA_MATRIX_FIELD = new GF256(0x012D); // x^8 + x^5 + x^3 + x^2 + 1
+		
+		//UPGRADE_NOTE: Final was removed from the declaration of 'expTable '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
+		private int[] expTable;
+		//UPGRADE_NOTE: Final was removed from the declaration of 'logTable '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
+		private int[] logTable;
+		//UPGRADE_NOTE: Final was removed from the declaration of 'zero '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
+		private GF256Poly zero;
+		//UPGRADE_NOTE: Final was removed from the declaration of 'one '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
+		private GF256Poly one;
+		
+		/// <summary> Create a representation of GF(256) using the given primitive polynomial.
+		/// 
+		/// </summary>
+		/// <param name="primitive">irreducible polynomial whose coefficients are represented by
+		/// the bits of an int, where the least-significant bit represents the constant
+		/// coefficient
+		/// </param>
+		private GF256(int primitive)
+		{
+			expTable = new int[256];
+			logTable = new int[256];
+			int x = 1;
+			for (int i = 0; i < 256; i++)
+			{
+				expTable[i] = x;
+				x <<= 1; // x = x * 2; we're assuming the generator alpha is 2
+				if (x >= 0x100)
+				{
+					x ^= primitive;
+				}
+			}
+			for (int i = 0; i < 255; i++)
+			{
+				logTable[expTable[i]] = i;
+			}
+			// logTable[0] == 0 but this should never be used
+			zero = new GF256Poly(this, new int[]{0});
+			one = new GF256Poly(this, new int[]{1});
+		}
+		
+		/// <returns> the monomial representing coefficient * x^degree
+		/// </returns>
+		internal GF256Poly buildMonomial(int degree, int coefficient)
+		{
+			if (degree < 0)
+			{
+				throw new System.ArgumentException();
+			}
+			if (coefficient == 0)
+			{
+				return zero;
+			}
+			int[] coefficients = new int[degree + 1];
+			coefficients[0] = coefficient;
+			return new GF256Poly(this, coefficients);
+		}
+		
+		/// <summary> Implements both addition and subtraction -- they are the same in GF(256).
+		/// 
+		/// </summary>
+		/// <returns> sum/difference of a and b
+		/// </returns>
+		internal static int addOrSubtract(int a, int b)
+		{
+			return a ^ b;
+		}
+		
+		/// <returns> 2 to the power of a in GF(256)
+		/// </returns>
+		internal int exp(int a)
+		{
+			return expTable[a];
+		}
+		
+		/// <returns> base 2 log of a in GF(256)
+		/// </returns>
+		internal int log(int a)
+		{
+			if (a == 0)
+			{
+				throw new System.ArgumentException();
+			}
+			return logTable[a];
+		}
+		
+		/// <returns> multiplicative inverse of a
+		/// </returns>
+		internal int inverse(int a)
+		{
+			if (a == 0)
+			{
+				throw new System.ArithmeticException();
+			}
+			return expTable[255 - logTable[a]];
+		}
+		
+		/// <param name="a">
+		/// </param>
+		/// <param name="b">
+		/// </param>
+		/// <returns> product of a and b in GF(256)
+		/// </returns>
+		internal int multiply(int a, int b)
+		{
+			if (a == 0 || b == 0)
+			{
+				return 0;
+			}
+			if (a == 1)
+			{
+				return b;
+			}
+			if (b == 1)
+			{
+				return a;
+			}
+			return expTable[(logTable[a] + logTable[b]) % 255];
+		}
+	}
+}
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