/* 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:; }