mirror of
https://github.com/libretro/beetle-pce-fast-libretro.git
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138 lines
4.0 KiB
C++
138 lines
4.0 KiB
C++
/* dvdisaster: Additional error correction for optical media.
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* Copyright (C) 2004-2007 Carsten Gnoerlich.
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* Project home page: http://www.dvdisaster.com
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* Email: carsten@dvdisaster.com -or- cgnoerlich@fsfe.org
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*
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* The Reed-Solomon error correction draws a lot of inspiration - and even code -
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* from Phil Karn's excellent Reed-Solomon library: http://www.ka9q.net/code/fec/
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA,
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* or direct your browser at http://www.gnu.org.
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*/
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#include "dvdisaster.h"
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#include "galois-inlines.h"
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/***
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*** Galois field arithmetic.
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***
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* Calculations are done over the extension field GF(2**n).
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* Be careful not to overgeneralize these arithmetics;
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* they only work for the case of GF(p**n) with p being prime.
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*/
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/* Initialize the Galois field tables */
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GaloisTables* CreateGaloisTables(int32_t gf_generator)
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{
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GaloisTables *gt = (GaloisTables *)calloc(1, sizeof(GaloisTables));
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int32_t b,log;
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/* Allocate the tables.
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The encoder uses a special version of alpha_to which has the mod_fieldmax()
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folded into the table. */
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gt->gfGenerator = gf_generator;
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gt->indexOf = (int32_t *)calloc(GF_FIELDSIZE, sizeof(int32_t));
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gt->alphaTo = (int32_t *)calloc(GF_FIELDSIZE, sizeof(int32_t));
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gt->encAlphaTo = (int32_t *)calloc(2*GF_FIELDSIZE, sizeof(int32_t));
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/* create the log/ilog values */
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for(b=1, log=0; log<GF_FIELDMAX; log++)
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{ gt->indexOf[b] = log;
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gt->alphaTo[log] = b;
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b = b << 1;
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if(b & GF_FIELDSIZE)
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b = b ^ gf_generator;
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}
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/* we're even closed using infinity (makes things easier) */
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gt->indexOf[0] = GF_ALPHA0; /* log(0) = inf */
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gt->alphaTo[GF_ALPHA0] = 0; /* and the other way around */
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for(b=0; b<2*GF_FIELDSIZE; b++)
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gt->encAlphaTo[b] = gt->alphaTo[mod_fieldmax(b)];
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return gt;
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}
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void FreeGaloisTables(GaloisTables *gt)
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{
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if(gt->indexOf) free(gt->indexOf);
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if(gt->alphaTo) free(gt->alphaTo);
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if(gt->encAlphaTo) free(gt->encAlphaTo);
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free(gt);
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}
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/***
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*** Create the the Reed-Solomon generator polynomial
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*** and some auxiliary data structures.
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*/
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ReedSolomonTables *CreateReedSolomonTables(GaloisTables *gt,
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int32_t first_consecutive_root,
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int32_t prim_elem,
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int nroots_in)
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{ ReedSolomonTables *rt = (ReedSolomonTables *)calloc(1, sizeof(ReedSolomonTables));
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int32_t i,j,root;
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rt->gfTables = gt;
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rt->fcr = first_consecutive_root;
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rt->primElem = prim_elem;
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rt->nroots = nroots_in;
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rt->ndata = GF_FIELDMAX - rt->nroots;
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rt->gpoly = (int32_t *)calloc((rt->nroots+1), sizeof(int32_t));
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/* Create the RS code generator polynomial */
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rt->gpoly[0] = 1;
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for(i=0, root=first_consecutive_root*prim_elem; i<rt->nroots; i++, root+=prim_elem)
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{ rt->gpoly[i+1] = 1;
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/* Multiply gpoly by alpha**(root+x) */
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for(j=i; j>0; j--)
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{
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if(rt->gpoly[j] != 0)
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rt->gpoly[j] = rt->gpoly[j-1] ^ gt->alphaTo[mod_fieldmax(gt->indexOf[rt->gpoly[j]] + root)];
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else
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rt->gpoly[j] = rt->gpoly[j-1];
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}
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rt->gpoly[0] = gt->alphaTo[mod_fieldmax(gt->indexOf[rt->gpoly[0]] + root)];
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}
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/* Store the polynomials index for faster encoding */
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for(i=0; i<=rt->nroots; i++)
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rt->gpoly[i] = gt->indexOf[rt->gpoly[i]];
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return rt;
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}
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void FreeReedSolomonTables(ReedSolomonTables *rt)
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{
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if(rt->gpoly) free(rt->gpoly);
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free(rt);
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}
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