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/* Common code for intializing a Reed-Solomon control block (char or int symbols)
* Copyright 2004 Phil Karn, KA9Q
* May be used under the terms of the GNU Lesser General Public License (LGPL)
*/
#undef NULL
#define NULL ((void *)0)
{
int i, j, sr,root,iprim;
rs = NULL;
/* Check parameter ranges */
if(symsize < 0 || symsize > 8*sizeof(data_t)){
goto done;
}
if(fcr < 0 || fcr >= (1<<symsize))
goto done;
if(prim <= 0 || prim >= (1<<symsize))
goto done;
if(nroots < 0 || nroots >= (1<<symsize))
goto done; /* Can't have more roots than symbol values! */
if(pad < 0 || pad >= ((1<<symsize) -1 - nroots))
goto done; /* Too much padding */
rs = (struct rs *)calloc(1,sizeof(struct rs));
if(rs == NULL)
goto done;
rs->mm = symsize;
rs->nn = (1<<symsize)-1;
rs->pad = pad;
rs->alpha_to = (data_t *)malloc(sizeof(data_t)*(rs->nn+1));
if(rs->alpha_to == NULL){
free(rs);
rs = NULL;
goto done;
}
rs->index_of = (data_t *)malloc(sizeof(data_t)*(rs->nn+1));
if(rs->index_of == NULL){
free(rs->alpha_to);
free(rs);
rs = NULL;
goto done;
}
/* Generate Galois field lookup tables */
rs->index_of[0] = A0; /* log(zero) = -inf */
rs->alpha_to[A0] = 0; /* alpha**-inf = 0 */
sr = 1;
for(i=0;i<rs->nn;i++){
rs->index_of[sr] = i;
rs->alpha_to[i] = sr;
sr <<= 1;
if(sr & (1<<symsize))
sr ^= gfpoly;
sr &= rs->nn;
}
if(sr != 1){
/* field generator polynomial is not primitive! */
free(rs->alpha_to);
free(rs->index_of);
free(rs);
rs = NULL;
goto done;
}
/* Form RS code generator polynomial from its roots */
rs->genpoly = (data_t *)malloc(sizeof(data_t)*(nroots+1));
if(rs->genpoly == NULL){
free(rs->alpha_to);
free(rs->index_of);
free(rs);
rs = NULL;
goto done;
}
rs->fcr = fcr;
rs->prim = prim;
rs->nroots = nroots;
/* Find prim-th root of 1, used in decoding */
for(iprim=1;(iprim % prim) != 0;iprim += rs->nn)
;
rs->iprim = iprim / prim;
rs->genpoly[0] = 1;
for (i = 0,root=fcr*prim; i < nroots; i++,root += prim) {
rs->genpoly[i+1] = 1;
/* Multiply rs->genpoly[] by @**(root + x) */
for (j = i; j > 0; j--){
if (rs->genpoly[j] != 0)
rs->genpoly[j] = rs->genpoly[j-1] ^ rs->alpha_to[modnn(rs,rs->index_of[rs->genpoly[j]] + root)];
else
rs->genpoly[j] = rs->genpoly[j-1];
}
/* rs->genpoly[0] can never be zero */
rs->genpoly[0] = rs->alpha_to[modnn(rs,rs->index_of[rs->genpoly[0]] + root)];
}
/* convert rs->genpoly[] to index form for quicker encoding */
for (i = 0; i <= nroots; i++)
rs->genpoly[i] = rs->index_of[rs->genpoly[i]];
done:;
}
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