1 /* Common code for intializing a Reed-Solomon control block (char or int symbols) 2 * Copyright 2004 Phil Karn, KA9Q 3 * May be used under the terms of the GNU Lesser General Public License (LGPL) 4 */ 5 #undef NULL 6 #define NULL ((void *)0) 7 8 { 9 int i, j, sr,root,iprim; 10 11 rs = NULL; 12 /* Check parameter ranges */ 13 if(symsize < 0 || symsize > 8*(int)sizeof(data_t)){ 14 goto done; 15 } 16 17 if(fcr < 0 || fcr >= (1<<symsize)) 18 goto done; 19 if(prim <= 0 || prim >= (1<<symsize)) 20 goto done; 21 if(nroots < 0 || nroots >= (1<<symsize)) 22 goto done; /* Can't have more roots than symbol values! */ 23 if(pad < 0 || pad >= ((1<<symsize) -1 - nroots)) 24 goto done; /* Too much padding */ 25 26 rs = (struct rs *)calloc(1,sizeof(struct rs)); 27 if(rs == NULL) 28 goto done; 29 30 rs->mm = symsize; 31 rs->nn = (1<<symsize)-1; 32 rs->pad = pad; 33 34 rs->alpha_to = (data_t *)malloc(sizeof(data_t)*(rs->nn+1)); 35 if(rs->alpha_to == NULL){ 36 free(rs); 37 rs = NULL; 38 goto done; 39 } 40 rs->index_of = (data_t *)malloc(sizeof(data_t)*(rs->nn+1)); 41 if(rs->index_of == NULL){ 42 free(rs->alpha_to); 43 free(rs); 44 rs = NULL; 45 goto done; 46 } 47 48 /* Generate Galois field lookup tables */ 49 rs->index_of[0] = A0; /* log(zero) = -inf */ 50 rs->alpha_to[A0] = 0; /* alpha**-inf = 0 */ 51 sr = 1; 52 for(i=0;i<rs->nn;i++){ 53 rs->index_of[sr] = i; 54 rs->alpha_to[i] = sr; 55 sr <<= 1; 56 if(sr & (1<<symsize)) 57 sr ^= gfpoly; 58 sr &= rs->nn; 59 } 60 if(sr != 1){ 61 /* field generator polynomial is not primitive! */ 62 free(rs->alpha_to); 63 free(rs->index_of); 64 free(rs); 65 rs = NULL; 66 goto done; 67 } 68 69 /* Form RS code generator polynomial from its roots */ 70 rs->genpoly = (data_t *)malloc(sizeof(data_t)*(nroots+1)); 71 if(rs->genpoly == NULL){ 72 free(rs->alpha_to); 73 free(rs->index_of); 74 free(rs); 75 rs = NULL; 76 goto done; 77 } 78 rs->fcr = fcr; 79 rs->prim = prim; 80 rs->nroots = nroots; 81 82 /* Find prim-th root of 1, used in decoding */ 83 for(iprim=1;(iprim % prim) != 0;iprim += rs->nn) 84 ; 85 rs->iprim = iprim / prim; 86 87 rs->genpoly[0] = 1; 88 for (i = 0,root=fcr*prim; i < nroots; i++,root += prim) { 89 rs->genpoly[i+1] = 1; 90 91 /* Multiply rs->genpoly[] by @**(root + x) */ 92 for (j = i; j > 0; j--){ 93 if (rs->genpoly[j] != 0) 94 rs->genpoly[j] = rs->genpoly[j-1] ^ rs->alpha_to[modnn(rs,rs->index_of[rs->genpoly[j]] + root)]; 95 else 96 rs->genpoly[j] = rs->genpoly[j-1]; 97 } 98 /* rs->genpoly[0] can never be zero */ 99 rs->genpoly[0] = rs->alpha_to[modnn(rs,rs->index_of[rs->genpoly[0]] + root)]; 100 } 101 /* convert rs->genpoly[] to index form for quicker encoding */ 102 for (i = 0; i <= nroots; i++) 103 rs->genpoly[i] = rs->index_of[rs->genpoly[i]]; 104 done:; 105 106 } 107
