1 files changed, 272 insertions, 0 deletions

diff --git a/lib/reed_solomon/decode_rs.c b/lib/reed_solomon/decode_rs.c
new file mode 100644
index 000000000000..d401decd6289
--- /dev/null
+++ b/lib/reed_solomon/decode_rs.c
@@ -0,0 +1,272 @@
+/* 
+ * lib/reed_solomon/decode_rs.c
+ *
+ * Overview:
+ *   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@linutronix.de)
+ *
+ * $Id: decode_rs.c,v 1.6 2004/10/22 15:41:47 gleixner Exp $
+ *
+ */
+
+/* Generic data width independent code which is included by the 
+ * wrappers.
+ */
+{ 
+        int deg_lambda, el, deg_omega;
+        int i, j, r, k, pad;
+        int nn = rs->nn;
+        int nroots = rs->nroots;
+        int fcr = rs->fcr;
+        int prim = rs->prim;
+        int iprim = rs->iprim;
+        uint16_t *alpha_to = rs->alpha_to;
+        uint16_t *index_of = rs->index_of;
+        uint16_t u, q, tmp, num1, num2, den, discr_r, syn_error;
+        /* Err+Eras Locator poly and syndrome poly The maximum value
+         * of nroots is 8. So the necessary stack size will be about
+         * 220 bytes max.
+         */
+        uint16_t lambda[nroots + 1], syn[nroots];
+        uint16_t b[nroots + 1], t[nroots + 1], omega[nroots + 1];
+        uint16_t root[nroots], reg[nroots + 1], loc[nroots];
+        int count = 0;
+        uint16_t msk = (uint16_t) rs->nn;
+
+        /* Check length parameter for validity */
+        pad = nn - nroots - len;
+        if (pad < 0 || pad >= nn)
+                return -ERANGE;
+                
+        /* Does the caller provide the syndrome ? */
+        if (s != NULL) 
+                goto decode;
+
+        /* form the syndromes; i.e., evaluate data(x) at roots of
+         * g(x) */
+        for (i = 0; i < nroots; i++)
+                syn[i] = (((uint16_t) data[0]) ^ invmsk) & msk;
+
+        for (j = 1; j < len; j++) {
+                for (i = 0; i < nroots; i++) {
+                        if (syn[i] == 0) {
+                                syn[i] = (((uint16_t) data[j]) ^ 
+                                          invmsk) & msk;
+                        } else {
+                                syn[i] = ((((uint16_t) data[j]) ^
+                                           invmsk) & msk) ^ 
+                                        alpha_to[rs_modnn(rs, index_of[syn[i]] +
+                                                       (fcr + i) * prim)];
+                        }
+                }
+        }
+
+        for (j = 0; j < nroots; j++) {
+                for (i = 0; i < nroots; i++) {
+                        if (syn[i] == 0) {
+                                syn[i] = ((uint16_t) par[j]) & msk;
+                        } else {
+                                syn[i] = (((uint16_t) par[j]) & msk) ^ 
+                                        alpha_to[rs_modnn(rs, index_of[syn[i]] +
+                                                       (fcr+i)*prim)];
+                        }
+                }
+        }
+        s = syn;
+
+        /* Convert syndromes to index form, checking for nonzero condition */
+        syn_error = 0;
+        for (i = 0; i < nroots; i++) {
+                syn_error |= s[i];
+                s[i] = index_of[s[i]];
+        }
+
+        if (!syn_error) {
+                /* if syndrome is zero, data[] is a codeword and there are no
+                 * errors to correct. So return data[] unmodified
+                 */
+                count = 0;
+                goto finish;
+        }
+
+ decode:
+        memset(&lambda[1], 0, nroots * sizeof(lambda[0]));
+        lambda[0] = 1;
+
+        if (no_eras > 0) {
+                /* Init lambda to be the erasure locator polynomial */
+                lambda[1] = alpha_to[rs_modnn(rs, 
+                                              prim * (nn - 1 - eras_pos[0]))];
+                for (i = 1; i < no_eras; i++) {
+                        u = rs_modnn(rs, prim * (nn - 1 - eras_pos[i]));
+                        for (j = i + 1; j > 0; j--) {
+                                tmp = index_of[lambda[j - 1]];
+                                if (tmp != nn) {
+                                        lambda[j] ^= 
+                                                alpha_to[rs_modnn(rs, u + tmp)];
+                                }
+                        }
+                }
+        }
+
+        for (i = 0; i < nroots + 1; i++)
+                b[i] = index_of[lambda[i]];
+
+        /*
+         * Begin Berlekamp-Massey algorithm to determine error+erasure
+         * locator polynomial
+         */
+        r = no_eras;
+        el = no_eras;
+        while (++r <= nroots) { /* r is the step number */
+                /* Compute discrepancy at the r-th step in poly-form */
+                discr_r = 0;
+                for (i = 0; i < r; i++) {
+                        if ((lambda[i] != 0) && (s[r - i - 1] != nn)) {
+                                discr_r ^= 
+                                        alpha_to[rs_modnn(rs, 
+                                                          index_of[lambda[i]] +
+                                                          s[r - i - 1])];
+                        }
+                }
+                discr_r = index_of[discr_r];    /* Index form */
+                if (discr_r == nn) {
+                        /* 2 lines below: B(x) <-- x*B(x) */
+                        memmove (&b[1], b, nroots * sizeof (b[0]));
+                        b[0] = nn;
+                } else {
+                        /* 7 lines below: T(x) <-- lambda(x)-discr_r*x*b(x) */
+                        t[0] = lambda[0];
+                        for (i = 0; i < nroots; i++) {
+                                if (b[i] != nn) {
+                                        t[i + 1] = lambda[i + 1] ^ 
+                                                alpha_to[rs_modnn(rs, discr_r +
+                                                                  b[i])];
+                                } else
+                                        t[i + 1] = lambda[i + 1];
+                        }
+                        if (2 * el <= r + no_eras - 1) {
+                                el = r + no_eras - el;
+                                /*
+                                 * 2 lines below: B(x) <-- inv(discr_r) *
+                                 * lambda(x)
+                                 */
+                                for (i = 0; i <= nroots; i++) {
+                                        b[i] = (lambda[i] == 0) ? nn :
+                                                rs_modnn(rs, index_of[lambda[i]]
+                                                         - discr_r + nn);
+                                }
+                        } else {
+                                /* 2 lines below: B(x) <-- x*B(x) */
+                                memmove(&b[1], b, nroots * sizeof(b[0]));
+                                b[0] = nn;
+                        }
+                        memcpy(lambda, t, (nroots + 1) * sizeof(t[0]));
+                }
+        }
+
+        /* Convert lambda to index form and compute deg(lambda(x)) */
+        deg_lambda = 0;
+        for (i = 0; i < nroots + 1; i++) {
+                lambda[i] = index_of[lambda[i]];
+                if (lambda[i] != nn)
+                        deg_lambda = i;
+        }
+        /* Find roots of error+erasure locator polynomial by Chien search */
+        memcpy(&reg[1], &lambda[1], nroots * sizeof(reg[0]));
+        count = 0;              /* Number of roots of lambda(x) */
+        for (i = 1, k = iprim - 1; i <= nn; i++, k = rs_modnn(rs, k + iprim)) {
+                q = 1;          /* lambda[0] is always 0 */
+                for (j = deg_lambda; j > 0; j--) {
+                        if (reg[j] != nn) {
+                                reg[j] = rs_modnn(rs, reg[j] + j);
+                                q ^= alpha_to[reg[j]];
+                        }
+                }
+                if (q != 0)
+                        continue;       /* Not a root */
+                /* store root (index-form) and error location number */
+                root[count] = i;
+                loc[count] = k;
+                /* If we've already found max possible roots,
+                 * abort the search to save time
+                 */
+                if (++count == deg_lambda)
+                        break;
+        }
+        if (deg_lambda != count) {
+                /*
+                 * deg(lambda) unequal to number of roots => uncorrectable
+                 * error detected
+                 */
+                count = -1;
+                goto finish;
+        }
+        /*
+         * Compute err+eras evaluator poly omega(x) = s(x)*lambda(x) (modulo
+         * x**nroots). in index form. Also find deg(omega).
+         */
+        deg_omega = deg_lambda - 1;
+        for (i = 0; i <= deg_omega; i++) {
+                tmp = 0;
+                for (j = i; j >= 0; j--) {
+                        if ((s[i - j] != nn) && (lambda[j] != nn))
+                                tmp ^=
+                                    alpha_to[rs_modnn(rs, s[i - j] + lambda[j])];
+                }
+                omega[i] = index_of[tmp];
+        }
+
+        /*
+         * Compute error values in poly-form. num1 = omega(inv(X(l))), num2 =
+         * inv(X(l))**(fcr-1) and den = lambda_pr(inv(X(l))) all in poly-form
+         */
+        for (j = count - 1; j >= 0; j--) {
+                num1 = 0;
+                for (i = deg_omega; i >= 0; i--) {
+                        if (omega[i] != nn)
+                                num1 ^= alpha_to[rs_modnn(rs, omega[i] + 
+                                                        i * root[j])];
+                }
+                num2 = alpha_to[rs_modnn(rs, root[j] * (fcr - 1) + nn)];
+                den = 0;
+
+                /* lambda[i+1] for i even is the formal derivative
+                 * lambda_pr of lambda[i] */
+                for (i = min(deg_lambda, nroots - 1) & ~1; i >= 0; i -= 2) {
+                        if (lambda[i + 1] != nn) {
+                                den ^= alpha_to[rs_modnn(rs, lambda[i + 1] + 
+                                                       i * root[j])];
+                        }
+                }
+                /* Apply error to data */
+                if (num1 != 0 && loc[j] >= pad) {
+                        uint16_t cor = alpha_to[rs_modnn(rs,index_of[num1] + 
+                                                       index_of[num2] +
+                                                       nn - index_of[den])];
+                        /* Store the error correction pattern, if a
+                         * correction buffer is available */
+                        if (corr) {
+                                corr[j] = cor;
+                        } else {
+                                /* If a data buffer is given and the
+                                 * error is inside the message,
+                                 * correct it */
+                                if (data && (loc[j] < (nn - nroots)))
+                                        data[loc[j] - pad] ^= cor;
+                        }
+                }
+        }
+
+finish:
+        if (eras_pos != NULL) {
+                for (i = 0; i < count; i++)
+                        eras_pos[i] = loc[i] - pad;
+        }
+        return count;
+
+}