lib/reed_solomon/encode_rs.c

   1 /*
   2  * lib/reed_solomon/encode_rs.c
   3  *
   4  * Overview:
   5  *   Generic Reed Solomon encoder / decoder library
   6  *
   7  * Copyright 2002, Phil Karn, KA9Q
   8  * May be used under the terms of the GNU General Public License (GPL)
   9  *
  10  * Adaption to the kernel by Thomas Gleixner (tglx@linutronix.de)
  11  *
  12  * $Id: encode_rs.c,v 1.4 2004/10/22 15:41:47 gleixner Exp $
  13  *
  14  */
  15
  16 /* Generic data width independent code which is included by the
  17  * wrappers.
  18  * int encode_rsX (struct rs_control *rs, uintX_t *data, int len, uintY_t *par)
  19  */
  20 {
  21         int i, j, pad;
  22         int nn = rs->nn;
  23         int nroots = rs->nroots;
  24         uint16_t *alpha_to = rs->alpha_to;
  25         uint16_t *index_of = rs->index_of;
  26         uint16_t *genpoly = rs->genpoly;
  27         uint16_t fb;
  28         uint16_t msk = (uint16_t) rs->nn;
  29
  30         /* Check length parameter for validity */
  31         pad = nn - nroots - len;
  32         if (pad < 0 || pad >= nn)
  33                 return -ERANGE;
  34
  35         for (i = 0; i < len; i++) {
  36                 fb = index_of[((((uint16_t) data[i])^invmsk) & msk) ^ par[0]];
  37                 /* feedback term is non-zero */
  38                 if (fb != nn) {
  39                         for (j = 1; j < nroots; j++) {
  40                                 par[j] ^= alpha_to[rs_modnn(rs, fb +
  41                                                          genpoly[nroots - j])];
  42                         }
  43                 }
  44                 /* Shift */
  45                 memmove(&par[0], &par[1], sizeof(uint16_t) * (nroots - 1));
  46                 if (fb != nn) {
  47                         par[nroots - 1] = alpha_to[rs_modnn(rs,
  48                                                             fb + genpoly[0])];
  49                 } else {
  50                         par[nroots - 1] = 0;
  51                 }
  52         }
  53         return 0;
  54 }