encode.c

#include <string.h>

#include "Headers/array.h"
#include "Headers/op.h"

struct Array* array2(uint8_t a, uint8_t b)
{
    struct Array *p = malloc(sizeof(struct Array));
    initArray(p, 3);
    p->array[0] = a;
    p->array[1] = b;
    p->used = 2;
    return p;
}

/*Generate an irreducible generator polynomial (necessary to encode a message into Reed-Solomon)*/
struct Array* rs_generator_poly(uint8_t nsym, struct gf_tables *gf_table)
{
  struct Array *g = malloc(sizeof(struct Array));
  initArray(g, nsym);
  g->array[0] = 1;
  insertArray(g);
  for(uint8_t i = 0; i < nsym; i++)
    g = gf_poly_mul(g, array2(1, gf_pow(2, i, gf_table)), gf_table);
  return g;
}

/*Reed-Solomon main encoding function*/
struct Array* rs_encode_msg(struct Array* msg_in, uint8_t nsym, struct gf_tables *gf_table)
{
  if(msg_in->used + nsym > 255){
    fprintf(stderr, "Message too long, %lu is the size when 255 is the max", msg_in->used + nsym);
    exit(EXIT_FAILURE);
  }
  size_t len_gen = nsym * 2;
  struct Array *gen = malloc(sizeof(struct Array));
  initArray(gen, len_gen);

  gen = rs_generator_poly(nsym, gf_table);

  struct Array *msg_out = malloc(sizeof(struct Array));

  initZArray(msg_out, msg_in->used + gen->used -1);
  memmove(msg_out->array, msg_in->array, msg_in->used);

  for(size_t i = 0; i < msg_in->used; i++){
    uint8_t coef = msg_out->array[i];
    if (coef != 0){
      for(size_t j = 1; j < gen->used; j++){
        msg_out->array[i+j] ^= gf_mul(gen->array[j], coef, gf_table);
      }
    }
  }
  msg_out->used = gen->used + msg_in->used-1;

  memmove(msg_out->array, msg_in->array, msg_in->used);
  freeArray(gen);
  return msg_out;
}