// SPDX-License-Identifier: GPL-2.0
/*
 * Generic Reed Solomon encoder / decoder library
 *
 * Copyright 2002, Phil Karn, KA9Q
 * May be used under the terms of the GNU General Public License (GPL)
 *
 * Adaption to the kernel by Thomas Gleixner (tglx@kernel.org)
 *
 * Generic data width independent code which is included by the wrappers.
 */
{
        struct rs_codec *rs = rsc->codec;
        int i, j, pad;
        int nn = rs->nn;
        int nroots = rs->nroots;
        uint16_t *alpha_to = rs->alpha_to;
        uint16_t *index_of = rs->index_of;
        uint16_t *genpoly = rs->genpoly;
        uint16_t fb;
        uint16_t msk = (uint16_t) rs->nn;

        /* Check length parameter for validity */
        pad = nn - nroots - len;
        if (pad < 0 || pad >= nn)
                return -ERANGE;

        for (i = 0; i < len; i++) {
                fb = index_of[((((uint16_t) data[i])^invmsk) & msk) ^ par[0]];
                /* feedback term is non-zero */
                if (fb != nn) {
                        for (j = 1; j < nroots; j++) {
                                par[j] ^= alpha_to[rs_modnn(rs, fb +
                                                         genpoly[nroots - j])];
                        }
                }
                /* Shift */
                memmove(&par[0], &par[1], sizeof(uint16_t) * (nroots - 1));
                if (fb != nn) {
                        par[nroots - 1] = alpha_to[rs_modnn(rs,
                                                            fb + genpoly[0])];
                } else {
                        par[nroots - 1] = 0;
                }
        }
        return 0;
}