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Preparing for next version of CTDB
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chudov
159
CUETools.Parity/Parity2Syndrome.cs
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159
CUETools.Parity/Parity2Syndrome.cs
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using System;
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using System.Collections.Generic;
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using System.Text;
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namespace CUETools.Parity
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{
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public class ParityToSyndrome
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{
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private int[] erasures_pos;
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private int[] erasure_loc_pol;
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private int[] erasure_diff;
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private int npar;
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const int w = 16;
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const int max = (1 << w) - 1;
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public ParityToSyndrome(int npar)
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{
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this.npar = npar;
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this.InitTables();
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}
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private void InitTables()
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{
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var num_erasures = this.npar;
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// Compute the erasure locator polynomial:
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erasures_pos = new int[num_erasures];
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for (int x = 0; x < num_erasures; x++)
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erasures_pos[x] = x;
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//%Compute the erasure-locator polynomial
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// Optimized version
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var erasure_loc_pol_exp = new int[num_erasures + 1];
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erasure_loc_pol_exp[0] = 1;
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for (int i = 0; i < num_erasures; i++)
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for (int x = num_erasures; x > 0; x--)
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erasure_loc_pol_exp[x] ^= Galois16.instance.mulExp(erasure_loc_pol_exp[x - 1], erasures_pos[i]);
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erasure_loc_pol = Galois16.instance.toLog(erasure_loc_pol_exp);
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erasure_diff = Galois16.instance.gfdiff(erasure_loc_pol);
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}
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public static unsafe byte[] Syndrome2Parity(ushort[,] syndrome, byte[] parity = null)
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{
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var stride = syndrome.GetLength(0);
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var npar = syndrome.GetLength(1);
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var converter = new ParityToSyndrome(npar);
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if (parity == null)
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parity = new byte[npar * stride * 2];
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fixed (byte* bpar = parity)
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fixed (ushort* syn = syndrome)
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{
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ushort* par = (ushort*)bpar;
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for (int i = 0; i < stride; i++)
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converter.Syndrome2Parity(syn + i * npar, par + i * npar);
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}
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return parity;
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}
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public static unsafe ushort[,] Parity2Syndrome(int stride, int npar, int npar2, byte[] parity)
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{
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if (npar > npar2)
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throw new InvalidOperationException();
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var syndrome = new ushort[stride, npar];
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fixed (byte* pbpar = parity)
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fixed (ushort* psyn = syndrome, plog = Galois16.instance.LogTbl, pexp = Galois16.instance.ExpTbl)
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{
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ushort* ppar = (ushort*)pbpar;
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for (int y = 0; y < stride; y++)
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{
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ushort* syn = psyn + y * npar;
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ushort* par = ppar + y * npar2;
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for (int x1 = 0; x1 < npar2; x1++)
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{
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ushort lo = par[x1];
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if (lo != 0)
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{
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var llo = plog[lo] + 0xffff;
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for (int x = 0; x < npar; x++)
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syn[x] ^= pexp[llo - (1 + x1) * x];
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}
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}
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}
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}
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return syndrome;
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}
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public unsafe void Syndrome2Parity(ushort* syndrome, ushort* parity)
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{
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// Advance syndrome by npar zeroes (for npar 'erased' parity symbols)
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var S_pol = new int[npar + 1];
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S_pol[0] = -1;
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for (int i = 0; i < npar; i++)
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{
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if (syndrome[i] == 0)
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S_pol[i + 1] = -1;
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else
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{
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var exp = Galois16.instance.LogTbl[syndrome[i]] + npar * i;
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S_pol[i + 1] = (exp & max) + (exp >> w);
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}
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}
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var mod_syn = Galois16.instance.gfconv(erasure_loc_pol, S_pol, npar + 1);
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//%Calculate remaining errors (non-erasures)
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//
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//S_M = [];
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//for i = 1:h - num_erasures
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// S_M(i) = mod_syn(i + num_erasures + 1);
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//end
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//flag = 0;
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//if isempty(S_M) == 1
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// flag = 0;
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//else
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// for i = 1:length(S_M)
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// if (S_M(i) ~= -Inf)
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// flag = 1; %Other errors occured in conjunction with erasures
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// end
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// end
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//end
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//%Find error-location polynomial sigma (Berlekamp's iterative algorithm -
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//if (flag == 1)
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//{
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// ...
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//}
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//else
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//{
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// sigma = 0;
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// comp_error_locs = [];
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//}
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#if kjsljdf
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var sigma = new int[1] { 0 };
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var omega = gfconv(sigma, gfadd(mod_syn, 0), npar + 1);
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var tsi = gfconv(sigma, erasure_loc_pol);
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var tsi_diff = gfdiff(tsi);
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//var e_e_places = [erasures_pos comp_error_locs];
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#else
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var omega = mod_syn;
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var tsi_diff = erasure_diff;
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var e_e_places = erasures_pos;
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#endif
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//%Calculate the error magnitudes
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//%Substitute the inverse into sigma_diff
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//var ERR = new int[e_e_places.Length];
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for (int ii = 0; ii < e_e_places.Length; ii++)
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{
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var point = max - e_e_places[ii];
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var ERR_DEN = Galois16.instance.gfsubstitute(tsi_diff, point, tsi_diff.Length);
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var ERR_NUM = Galois16.instance.gfsubstitute(omega, point, omega.Length);
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// Additional +ii because we use slightly different syndrome
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var pow = ERR_NUM + e_e_places[ii] + ii + max - ERR_DEN;
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//ERR[ii] = ERR_NUM == -1 ? 0 : expTbl[(pow & max) + (pow >> w)];
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parity[npar - 1 - ii] = ERR_NUM == -1 ? (ushort)0 : Galois16.instance.ExpTbl[(pow & max) + (pow >> w)];
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}
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}
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}
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}
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