352 lines
6.4 KiB
C#
352 lines
6.4 KiB
C#
namespace MessagingToolkit.QRCode.Codec.Ecc;
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public class ReedSolomon
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{
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internal int[] y;
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internal int[] gexp = new int[512];
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internal int[] glog = new int[256];
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internal int NPAR;
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internal int MAXDEG;
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internal int[] synBytes;
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internal int[] Lambda;
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internal int[] Omega;
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internal int[] ErrorLocs = new int[256];
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internal int NErrors;
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internal int[] ErasureLocs = new int[256];
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internal int NErasures = 0;
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internal bool correctionSucceeded = true;
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public virtual bool CorrectionSucceeded => correctionSucceeded;
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public virtual int NumCorrectedErrors => NErrors;
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public ReedSolomon(int[] source, int NPAR)
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{
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initializeGaloisTables();
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y = source;
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this.NPAR = NPAR;
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MAXDEG = NPAR * 2;
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synBytes = new int[MAXDEG];
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Lambda = new int[MAXDEG];
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Omega = new int[MAXDEG];
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}
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internal virtual void initializeGaloisTables()
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{
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int num2;
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int num3;
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int num4;
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int num5;
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int num6;
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int num7;
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int num = (num2 = (num3 = (num4 = (num5 = (num6 = (num7 = 0))))));
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int num8 = 1;
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gexp[0] = 1;
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gexp[255] = gexp[0];
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glog[0] = 0;
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for (int i = 1; i < 256; i++)
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{
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int num9 = num7;
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num7 = num6;
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num6 = num5;
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num5 = num4;
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num4 = num3 ^ num9;
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num3 = num2 ^ num9;
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num2 = num ^ num9;
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num = num8;
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num8 = num9;
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gexp[i] = num8 + num * 2 + num2 * 4 + num3 * 8 + num4 * 16 + num5 * 32 + num6 * 64 + num7 * 128;
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gexp[i + 255] = gexp[i];
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}
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for (int i = 1; i < 256; i++)
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{
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for (int j = 0; j < 256; j++)
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{
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if (gexp[j] == i)
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{
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glog[i] = j;
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break;
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}
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}
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}
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}
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internal virtual int gmult(int a, int b)
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{
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if (a == 0 || b == 0)
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{
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return 0;
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}
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int num = glog[a];
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int num2 = glog[b];
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return gexp[num + num2];
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}
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internal virtual int ginv(int elt)
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{
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return gexp[255 - glog[elt]];
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}
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internal virtual void decode_data(int[] data)
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{
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for (int i = 0; i < MAXDEG; i++)
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{
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int num = 0;
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for (int j = 0; j < data.Length; j++)
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{
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num = data[j] ^ gmult(gexp[i + 1], num);
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}
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synBytes[i] = num;
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}
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}
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public virtual void correct()
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{
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decode_data(y);
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correctionSucceeded = true;
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bool flag = false;
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for (int i = 0; i < synBytes.Length; i++)
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{
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if (synBytes[i] != 0)
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{
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flag = true;
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}
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}
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if (flag)
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{
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correctionSucceeded = correct_errors_erasures(y, y.Length, 0, new int[1]);
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}
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}
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internal virtual void Modified_Berlekamp_Massey()
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{
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int[] array = new int[MAXDEG];
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int[] array2 = new int[MAXDEG];
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int[] array3 = new int[MAXDEG];
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int[] array4 = new int[MAXDEG];
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init_gamma(array4);
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copy_poly(array3, array4);
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mul_z_poly(array3);
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copy_poly(array, array4);
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int num = -1;
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int num2 = NErasures;
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for (int i = NErasures; i < 8; i++)
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{
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int num3 = compute_discrepancy(array, synBytes, num2, i);
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if (num3 != 0)
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{
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for (int j = 0; j < MAXDEG; j++)
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{
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array2[j] = array[j] ^ gmult(num3, array3[j]);
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}
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if (num2 < i - num)
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{
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int num4 = i - num;
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num = i - num2;
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for (int j = 0; j < MAXDEG; j++)
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{
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array3[j] = gmult(array[j], ginv(num3));
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}
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num2 = num4;
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}
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for (int j = 0; j < MAXDEG; j++)
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{
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array[j] = array2[j];
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}
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}
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mul_z_poly(array3);
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}
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for (int j = 0; j < MAXDEG; j++)
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{
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Lambda[j] = array[j];
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}
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compute_modified_omega();
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}
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internal virtual void compute_modified_omega()
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{
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int[] array = new int[MAXDEG * 2];
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mult_polys(array, Lambda, synBytes);
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zero_poly(Omega);
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for (int i = 0; i < NPAR; i++)
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{
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Omega[i] = array[i];
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}
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}
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internal virtual void mult_polys(int[] dst, int[] p1, int[] p2)
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{
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int[] array = new int[MAXDEG * 2];
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for (int i = 0; i < MAXDEG * 2; i++)
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{
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dst[i] = 0;
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}
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for (int i = 0; i < MAXDEG; i++)
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{
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for (int j = MAXDEG; j < MAXDEG * 2; j++)
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{
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array[j] = 0;
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}
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for (int j = 0; j < MAXDEG; j++)
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{
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array[j] = gmult(p2[j], p1[i]);
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}
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for (int j = MAXDEG * 2 - 1; j >= i; j--)
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{
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array[j] = array[j - i];
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}
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for (int j = 0; j < i; j++)
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{
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array[j] = 0;
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}
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for (int j = 0; j < MAXDEG * 2; j++)
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{
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dst[j] ^= array[j];
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}
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}
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}
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internal virtual void init_gamma(int[] gamma)
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{
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int[] array = new int[MAXDEG];
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zero_poly(gamma);
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zero_poly(array);
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gamma[0] = 1;
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for (int i = 0; i < NErasures; i++)
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{
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copy_poly(array, gamma);
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scale_poly(gexp[ErasureLocs[i]], array);
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mul_z_poly(array);
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add_polys(gamma, array);
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}
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}
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internal virtual void compute_next_omega(int d, int[] A, int[] dst, int[] src)
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{
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for (int i = 0; i < MAXDEG; i++)
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{
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dst[i] = src[i] ^ gmult(d, A[i]);
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}
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}
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internal virtual int compute_discrepancy(int[] lambda, int[] S, int L, int n)
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{
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int num = 0;
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for (int i = 0; i <= L; i++)
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{
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num ^= gmult(lambda[i], S[n - i]);
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}
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return num;
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}
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internal virtual void add_polys(int[] dst, int[] src)
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{
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for (int i = 0; i < MAXDEG; i++)
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{
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dst[i] ^= src[i];
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}
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}
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internal virtual void copy_poly(int[] dst, int[] src)
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{
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for (int i = 0; i < MAXDEG; i++)
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{
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dst[i] = src[i];
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}
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}
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internal virtual void scale_poly(int k, int[] poly)
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{
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for (int i = 0; i < MAXDEG; i++)
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{
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poly[i] = gmult(k, poly[i]);
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}
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}
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internal virtual void zero_poly(int[] poly)
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{
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for (int i = 0; i < MAXDEG; i++)
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{
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poly[i] = 0;
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}
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}
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internal virtual void mul_z_poly(int[] src)
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{
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for (int num = MAXDEG - 1; num > 0; num--)
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{
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src[num] = src[num - 1];
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}
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src[0] = 0;
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}
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internal virtual void Find_Roots()
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{
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NErrors = 0;
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for (int i = 1; i < 256; i++)
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{
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int num = 0;
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for (int j = 0; j < NPAR + 1; j++)
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{
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num ^= gmult(gexp[j * i % 255], Lambda[j]);
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}
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if (num == 0)
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{
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ErrorLocs[NErrors] = 255 - i;
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NErrors++;
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}
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}
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}
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internal virtual bool correct_errors_erasures(int[] codeword, int csize, int nerasures, int[] erasures)
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{
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NErasures = nerasures;
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for (int i = 0; i < NErasures; i++)
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{
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ErasureLocs[i] = erasures[i];
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}
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Modified_Berlekamp_Massey();
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Find_Roots();
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if (NErrors <= NPAR || NErrors > 0)
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{
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for (int j = 0; j < NErrors; j++)
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{
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if (ErrorLocs[j] >= csize)
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{
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return false;
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}
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}
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for (int j = 0; j < NErrors; j++)
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{
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int i = ErrorLocs[j];
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int num = 0;
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for (int k = 0; k < MAXDEG; k++)
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{
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num ^= gmult(Omega[k], gexp[(255 - i) * k % 255]);
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}
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int num2 = 0;
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for (int k = 1; k < MAXDEG; k += 2)
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{
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num2 ^= gmult(Lambda[k], gexp[(255 - i) * (k - 1) % 255]);
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}
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int num3 = gmult(num, ginv(num2));
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codeword[csize - i - 1] ^= num3;
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}
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return true;
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}
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return false;
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}
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}
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