mirror of
https://github.com/servalproject/serval-dna.git
synced 2024-12-23 15:02:27 +00:00
107 lines
2.6 KiB
C
107 lines
2.6 KiB
C
/* 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 > (int)(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:;
|
|
|
|
}
|