Initial import

1 files changed, 271 insertions, 0 deletions

diff --git a/lib/reed_solomon/decode_rs.c b/lib/reed_solomon/decode_rs.c
new file mode 100644
index 000000000..0ec3f257f
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+++ b/lib/reed_solomon/decode_rs.c
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+/*
+ * 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 1.7 2005/11/07 11:14:59 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;
+	BUG_ON(pad < 0 || pad >= nn);
+
+	/* 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 = -EBADMSG;
+		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;
+
+}