| /* The guts of the Reed-Solomon encoder, meant to be #included |

| * into a function body with the following typedefs, macros and variables supplied |

| * according to the code parameters: |

| |

| * data_t - a typedef for the data symbol |

| * data_t data[] - array of NN-NROOTS-PAD and type data_t to be encoded |

| * data_t parity[] - an array of NROOTS and type data_t to be written with parity symbols |

| * NROOTS - the number of roots in the RS code generator polynomial, |

| * which is the same as the number of parity symbols in a block. |

| Integer variable or literal. |

| * |

| * NN - the total number of symbols in a RS block. Integer variable or literal. |

| * PAD - the number of pad symbols in a block. Integer variable or literal. |

| * ALPHA_TO - The address of an array of NN elements to convert Galois field |

| * elements in index (log) form to polynomial form. Read only. |

| * INDEX_OF - The address of an array of NN elements to convert Galois field |

| * elements in polynomial form to index (log) form. Read only. |

| * MODNN - a function to reduce its argument modulo NN. May be inline or a macro. |

| * GENPOLY - an array of NROOTS+1 elements containing the generator polynomial in index form |

| |

| * The memset() and memmove() functions are used. The appropriate header |

| * file declaring these functions (usually <string.h>) must be included by the calling |

| * program. |

| |

| * Copyright 2004, Phil Karn, KA9Q |

| * May be used under the terms of the GNU Lesser General Public License (LGPL) |

| */ |

| |

| |

| #undef A0 |

| #define A0 (NN) /* Special reserved value encoding zero in index form */ |

| |

| { |

| int i, j; |

| data_t feedback; |

| |

| memset(parity,0,NROOTS*sizeof(data_t)); |

| |

| for(i=0;i<NN-NROOTS-PAD;i++){ |

| feedback = INDEX_OF[data[i] ^ parity[0]]; |

| if(feedback != A0){ /* feedback term is non-zero */ |

| #ifdef UNNORMALIZED |

| /* This line is unnecessary when GENPOLY[NROOTS] is unity, as it must |

| * always be for the polynomials constructed by init_rs() |

| */ |

| feedback = MODNN(NN - GENPOLY[NROOTS] + feedback); |

| #endif |

| for(j=1;j<NROOTS;j++) |

| parity[j] ^= ALPHA_TO[MODNN(feedback + GENPOLY[NROOTS-j])]; |

| } |

| /* Shift */ |

| memmove(&parity[0],&parity[1],sizeof(data_t)*(NROOTS-1)); |

| if(feedback != A0) |

| parity[NROOTS-1] = ALPHA_TO[MODNN(feedback + GENPOLY[0])]; |

| else |

| parity[NROOTS-1] = 0; |

| } |

| } |