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diff --git a/tests/helpers/c/prng.c b/tests/helpers/c/prng.c
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+/*
+ * Very simple prng to allow for randomized tests with reproducable
+ * results.
+ *
+ * Copyright (C) 2012 by Open Source Routing.
+ * Copyright (C) 2012 by Internet Systems Consortium, Inc. ("ISC")
+ * Copyright (C) 2017 Christian Franke
+ *
+ * This file is part of Quagga
+ *
+ * Quagga is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2, or (at your option) any
+ * later version.
+ *
+ * Quagga 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
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; see the file COPYING; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <zebra.h>
+
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "prng.h"
+
+struct prng {
+ uint64_t state;
+};
+
+struct prng *prng_new(unsigned long long seed)
+{
+ struct prng *rv = calloc(sizeof(*rv), 1);
+ assert(rv);
+
+ rv->state = seed;
+
+ return rv;
+}
+
+/*
+ * This implementation has originally been provided to musl libc by
+ * Szabolcs Nagy <nsz at port70 dot net> in 2013 under the terms of
+ * the MIT license.
+ * It is a simple LCG which D.E. Knuth attributes to C.E. Haynes in
+ * TAOCP Vol2 3.3.4
+ */
+int prng_rand(struct prng *prng)
+{
+ prng->state = 6364136223846793005ULL * prng->state + 1;
+ return prng->state >> 33;
+}
+
+const char *prng_fuzz(struct prng *prng, const char *string,
+ const char *charset, unsigned int operations)
+{
+ static char buf[256];
+ unsigned int charset_len;
+ unsigned int i;
+ unsigned int offset;
+ unsigned int op;
+ unsigned int character;
+
+ assert(strlen(string) < sizeof(buf));
+
+ strncpy(buf, string, sizeof(buf));
+ charset_len = strlen(charset);
+
+ for (i = 0; i < operations; i++) {
+ offset = prng_rand(prng) % strlen(buf);
+ op = prng_rand(prng) % 3;
+
+ switch (op) {
+ case 0:
+ /* replace */
+ character = prng_rand(prng) % charset_len;
+ buf[offset] = charset[character];
+ break;
+ case 1:
+ /* remove */
+ memmove(buf + offset, buf + offset + 1,
+ strlen(buf) - offset);
+ break;
+ case 2:
+ /* insert */
+ assert(strlen(buf) + 1 < sizeof(buf));
+
+ memmove(buf + offset + 1, buf + offset,
+ strlen(buf) + 1 - offset);
+ character = prng_rand(prng) % charset_len;
+ buf[offset] = charset[character];
+ break;
+ }
+ }
+ return buf;
+}
+
+void prng_free(struct prng *prng)
+{
+ free(prng);
+}