Adding upstream version 2:2.6.1.upstream/2%2.6.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 201 insertions, 0 deletions

diff --git a/lib/verity/rs_decode_char.c b/lib/verity/rs_decode_char.c
new file mode 100644
index 0000000..4473202
--- /dev/null
+++ b/lib/verity/rs_decode_char.c
@@ -0,0 +1,201 @@
+/*
+ * Reed-Solomon decoder, based on libfec
+ *
+ * Copyright (C) 2002, Phil Karn, KA9Q
+ * libcryptsetup modifications
+ *   Copyright (C) 2017-2023 Red Hat, Inc. All rights reserved.
+ *
+ * This file is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This file is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this file; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <string.h>
+#include <stdlib.h>
+
+#include "rs.h"
+
+#define MAX_NR_BUF 256
+
+int decode_rs_char(struct rs* rs, data_t* data)
+{
+	int deg_lambda, el, deg_omega, syn_error, count;
+	int i, j, r, k;
+	data_t q, tmp, num1, num2, den, discr_r;
+	data_t lambda[MAX_NR_BUF], s[MAX_NR_BUF]; /* Err+Eras Locator poly and syndrome poly */
+	data_t b[MAX_NR_BUF], t[MAX_NR_BUF], omega[MAX_NR_BUF];
+	data_t root[MAX_NR_BUF], reg[MAX_NR_BUF], loc[MAX_NR_BUF];
+
+	if (rs->nroots >= MAX_NR_BUF)
+		return -1;
+
+	memset(s, 0, rs->nroots * sizeof(data_t));
+	memset(b, 0, (rs->nroots + 1) * sizeof(data_t));
+
+	/* form the syndromes; i.e., evaluate data(x) at roots of g(x) */
+	for (i = 0; i < rs->nroots; i++)
+		s[i] = data[0];
+
+	for (j = 1; j < rs->nn - rs->pad; j++) {
+		for (i = 0; i < rs->nroots; i++) {
+			if (s[i] == 0) {
+				s[i] = data[j];
+			} else {
+				s[i] = data[j] ^ rs->alpha_to[modnn(rs, rs->index_of[s[i]] + (rs->fcr + i) * rs->prim)];
+			}
+		}
+	}
+
+	/* Convert syndromes to index form, checking for nonzero condition */
+	syn_error = 0;
+	for (i = 0; i < rs->nroots; i++) {
+		syn_error |= s[i];
+		s[i] = rs->index_of[s[i]];
+	}
+
+	/*
+	 * if syndrome is zero, data[] is a codeword and there are no
+	 * errors to correct. So return data[] unmodified
+	 */
+	if (!syn_error)
+		return 0;
+
+	memset(&lambda[1], 0, rs->nroots * sizeof(lambda[0]));
+	lambda[0] = 1;
+
+	for (i   = 0; i < rs->nroots + 1; i++)
+		b[i] = rs->index_of[lambda[i]];
+
+	/*
+	 * Begin Berlekamp-Massey algorithm to determine error+erasure
+	 * locator polynomial
+	 */
+	r  = 0;
+	el = 0;
+	while (++r <= rs->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] != A0)) {
+				discr_r ^= rs->alpha_to[modnn(rs, rs->index_of[lambda[i]] + s[r - i - 1])];
+			}
+		}
+		discr_r = rs->index_of[discr_r]; /* Index form */
+		if (discr_r == A0) {
+			/* 2 lines below: B(x) <-- x*B(x) */
+			memmove(&b[1], b, rs->nroots * sizeof(b[0]));
+			b[0] = A0;
+		} else {
+			/* 7 lines below: T(x) <-- lambda(x) - discr_r*x*b(x) */
+			t[0] = lambda[0];
+			for (i = 0; i < rs->nroots; i++) {
+				if (b[i] != A0)
+					t[i + 1] = lambda[i + 1] ^ rs->alpha_to[modnn(rs, discr_r + b[i])];
+				else
+					t[i + 1] = lambda[i + 1];
+			}
+			if (2 * el <= r - 1) {
+				el = r - el;
+				/*
+				 * 2 lines below: B(x) <-- inv(discr_r) *
+				 * lambda(x)
+				 */
+				for (i   = 0; i <= rs->nroots; i++)
+					b[i] = (lambda[i] == 0) ? A0 : modnn(rs, rs->index_of[lambda[i]] - discr_r + rs->nn);
+			} else {
+				/* 2 lines below: B(x) <-- x*B(x) */
+				memmove(&b[1], b, rs->nroots * sizeof(b[0]));
+				b[0] = A0;
+			}
+			memcpy(lambda, t, (rs->nroots + 1) * sizeof(t[0]));
+		}
+	}
+
+	/* Convert lambda to index form and compute deg(lambda(x)) */
+	deg_lambda = 0;
+	for (i = 0; i < rs->nroots + 1; i++) {
+		lambda[i] = rs->index_of[lambda[i]];
+		if (lambda[i] != A0)
+			deg_lambda = i;
+	}
+	/* Find roots of the error+erasure locator polynomial by Chien search */
+	memcpy(&reg[1], &lambda[1], rs->nroots * sizeof(reg[0]));
+	count = 0; /* Number of roots of lambda(x) */
+	for (i = 1, k = rs->iprim - 1; i <= rs->nn; i++, k = modnn(rs, k + rs->iprim)) {
+		q = 1; /* lambda[0] is always 0 */
+		for (j = deg_lambda; j > 0; j--) {
+			if (reg[j] != A0) {
+				reg[j] = modnn(rs, reg[j] + j);
+				q ^= rs->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;
+	}
+
+	/*
+	 * deg(lambda) unequal to number of roots => uncorrectable
+	 * error detected
+	 */
+	if (deg_lambda != count)
+		return -1;
+
+	/*
+	 * Compute err+eras evaluator poly omega(x) = s(x)*lambda(x) (modulo
+	 * x**rs->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] != A0) && (lambda[j] != A0))
+				tmp ^= rs->alpha_to[modnn(rs, s[i - j] + lambda[j])];
+		}
+		omega[i] = rs->index_of[tmp];
+	}
+
+	/*
+	 * Compute error values in poly-form. num1 = omega(inv(X(l))), num2 =
+	 * inv(X(l))**(rs->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] != A0)
+				num1 ^= rs->alpha_to[modnn(rs, omega[i] + i * root[j])];
+		}
+		num2 = rs->alpha_to[modnn(rs, root[j] * (rs->fcr - 1) + rs->nn)];
+		den  = 0;
+
+		/* lambda[i+1] for i even is the formal derivative lambda_pr of lambda[i] */
+		for (i = RS_MIN(deg_lambda, rs->nroots - 1) & ~1; i >= 0; i -= 2) {
+			if (lambda[i + 1] != A0)
+				den ^= rs->alpha_to[modnn(rs, lambda[i + 1] + i * root[j])];
+		}
+
+		/* Apply error to data */
+		if (num1 != 0 && loc[j] >= rs->pad) {
+			data[loc[j] - rs->pad] ^= rs->alpha_to[modnn(rs, rs->index_of[num1] +
+						  rs->index_of[num2] + rs->nn - rs->index_of[den])];
+		}
+	}
+
+	return count;
+}