bool Reed_solomon_code::chien_search(int length,uint8_t* sigma,int sigma_len,uint8_t* res,int& res_len){
int jisu=sigma_len-1;
uint8_t wa=sigma[1];
uint8_t seki=sigma[jisu];
if(jisu==1){
if(shared_galois.log_tbl[wa]>=length)return false;
res[0]=wa;
res_len=1;
return true;
}
if(jisu==2){
res_len=2;
return chien_search(length,0,wa,seki,res[0],res[1]);
}
res_len=jisu;
int pos_idx=jisu-1;
for(int i=0,z=255;i<length;i++,z--){
uint8_t wk=1;
for(int j=1,wz=z;j<=jisu;j++,wz=(wz+z)%255)
wk^=shared_galois.mul_exp(sigma[j],wz);
if(wk==0){
uint8_t pv=shared_galois.exp_tbl[i];
wa^=pv;
seki=shared_galois.div(seki,pv);
res[pos_idx--]=pv;
if(pos_idx==1){
return chien_search(length,i+1,wa,seki,res[0],res[1]);
}
}
}
return false;
}
// Top level decoder module
void rs_decode (unsigned char n, unsigned char t, unsigned char in_d[nn],
unsigned char *k, unsigned char out_d[kk])
{
unsigned char temp_k = n - 2*t;
unsigned char s[2*tt];
unsigned char c[tt+2];
unsigned char w[tt+2];
unsigned char lambda[tt];
unsigned char omega[tt];
unsigned char err_no;
unsigned char err_loc[kk];
unsigned char alpha_inv[tt];
unsigned char err[kk];
unsigned char in_data[kk];
unsigned char in_d_2[nn];
Simple_rs1: for (int i = 0; i < nn; i++)
in_d_2[i] = in_d[i];
*k = temp_k;
rs_fifo(temp_k, in_d, in_data);
syndrome(temp_k, t, in_d_2, s);
berlekamp(t, s, lambda, omega);
chien_search(kk, tt, lambda, &err_no, err_loc, alpha_inv);
error_mag(kk, lambda, omega, err_no, err_loc, alpha_inv, err);
error_correct(temp_k, in_data, err, out_d);
}
uint8_t* Reed_solomon_code::decode(uint8_t* input){
uint8_t syn[255];
if(shared_galois.calc_syndrome(input,n,syn,npar))return input;
uint8_t sigma[256];
int sigma_len;
if(calc_sigma_mbm(syn,sigma,sigma_len)==NULL)return NULL;
uint8_t pos[256];
int pos_len;
if(!chien_search(n,sigma,sigma_len,pos,pos_len))return NULL;
uint8_t omega[256];
shared_galois.mul_poly(syn,npar,sigma,sigma_len,omega,sigma_len-1);
do_forney(input,n,pos,pos_len,sigma,sigma_len,omega,sigma_len-1);
return input;
}