LXR linux/lib/reed_solomon/encode

   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 1.5 2005/11/07 11:14:59 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}
  55