mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-11-14 16:11:50 -05:00
121 lines
3.1 KiB
C
121 lines
3.1 KiB
C
/* Initialize a RS codec
|
|
*
|
|
* Copyright 2002 Phil Karn, KA9Q
|
|
* May be used under the terms of the GNU General Public License (GPL)
|
|
*/
|
|
#include <stdlib.h>
|
|
|
|
#ifdef CCSDS
|
|
#include "ccsds.h"
|
|
#elif defined(BIGSYM)
|
|
#include "int.h"
|
|
#else
|
|
#include "char.h"
|
|
#endif
|
|
|
|
void FREE_RS(void *p){
|
|
struct rs *rs = (struct rs *)p;
|
|
|
|
free(rs->alpha_to);
|
|
free(rs->index_of);
|
|
free(rs->genpoly);
|
|
free(rs);
|
|
}
|
|
|
|
/* Initialize a Reed-Solomon codec
|
|
* symsize = symbol size, bits (1-8)
|
|
* gfpoly = Field generator polynomial coefficients
|
|
* fcr = first root of RS code generator polynomial, index form
|
|
* prim = primitive element to generate polynomial roots
|
|
* nroots = RS code generator polynomial degree (number of roots)
|
|
*/
|
|
void *INIT_RS(unsigned int symsize,unsigned int gfpoly,unsigned fcr,unsigned prim,
|
|
unsigned int nroots){
|
|
struct rs *rs;
|
|
int i, j, sr,root,iprim;
|
|
|
|
/* Check parameter ranges */
|
|
if(symsize < 0 || symsize > (int)(8*sizeof(DTYPE)))
|
|
return NULL; /* Need version with ints rather than chars */
|
|
|
|
if(fcr >= (1<<symsize))
|
|
return NULL;
|
|
if(prim == 0 || prim >= (1<<symsize))
|
|
return NULL;
|
|
if(nroots >= (1<<symsize))
|
|
return NULL; /* Can't have more roots than symbol values! */
|
|
|
|
rs = (struct rs *)calloc(1,sizeof(struct rs));
|
|
rs->mm = symsize;
|
|
rs->nn = (1<<symsize)-1;
|
|
|
|
rs->alpha_to = (DTYPE *)malloc(sizeof(DTYPE)*(rs->nn+1));
|
|
if(rs->alpha_to == NULL){
|
|
free(rs);
|
|
return NULL;
|
|
}
|
|
rs->index_of = (DTYPE *)malloc(sizeof(DTYPE)*(rs->nn+1));
|
|
if(rs->index_of == NULL){
|
|
free(rs->alpha_to);
|
|
free(rs);
|
|
return NULL;
|
|
}
|
|
|
|
/* 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);
|
|
return NULL;
|
|
}
|
|
|
|
/* Form RS code generator polynomial from its roots */
|
|
rs->genpoly = (DTYPE *)malloc(sizeof(DTYPE)*(nroots+1));
|
|
if(rs->genpoly == NULL){
|
|
free(rs->alpha_to);
|
|
free(rs->index_of);
|
|
free(rs);
|
|
return NULL;
|
|
}
|
|
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]];
|
|
|
|
return rs;
|
|
}
|