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+/*
+ * Copyright (c) 2015 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/*
+  Copyright (c) 2001, 2002, 2003 Eliot Dresselhaus
+
+  Permission is hereby granted, free of charge, to any person obtaining
+  a copy of this software and associated documentation files (the
+  "Software"), to deal in the Software without restriction, including
+  without limitation the rights to use, copy, modify, merge, publish,
+  distribute, sublicense, and/or sell copies of the Software, and to
+  permit persons to whom the Software is furnished to do so, subject to
+  the following conditions:
+
+  The above copyright notice and this permission notice shall be
+  included in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+#ifndef included_random_h
+#define included_random_h
+
+#include <vppinfra/clib.h>
+#include <vppinfra/vec.h>	/* for vec_resize */
+#include <vppinfra/format.h>	/* for unformat_input_t */
+
+/** \file
+    Linear Congruential Random Number Generator
+
+    This specific random number generator is described in
+    "Numerical Recipes in C", 2nd edition, page 284. If you need
+    random numbers with really excellent statistics, take a look
+    at Chapter 7...
+
+    By definition, a linear congruential random number generator
+    is of the form: rand[i+1] = a*rand[i] + c (mod m) for specific
+    values of (a,c,m).
+
+    In this case, choose m = 2**32 and use the low-order 32-bits of
+    the 64-bit product a*N[i]. Knuth suggests the use of a=1664525,
+    H.W. Lewis has tested C=1013904223 extensively. This routine is
+    reputedly as good as any 32-bit LCRN, and costs only a single
+    multiply-add.
+
+    Several variants: 32/64-bit, machine word width,
+    f64 on the closed interval [0,1].
+*/
+
+/** \brief 32-bit random number generator */
+always_inline u32
+random_u32 (u32 * seed)
+{
+  *seed = (1664525 * *seed) + 1013904223;
+  return *seed;
+}
+
+/* External test routine. */
+int test_random_main (unformat_input_t * input);
+
+/** \brief Maximum value returned by random_u32() */
+always_inline u32
+random_u32_max (void)
+{
+  return 0xffffffff;
+}
+
+#ifdef CLIB_UNIX
+
+#include <unistd.h>		/* for getpid */
+
+/** \brief Default random seed (unix/linux user-mode) */
+always_inline uword
+random_default_seed (void)
+{
+  return getpid ();
+}
+
+#endif
+
+#ifdef CLIB_LINUX_KERNEL
+
+#include <linux/sched.h>	/* for jiffies */
+
+/** \brief Default random seed (Linux kernel) */
+always_inline uword
+random_default_seed (void)
+{
+  return jiffies;
+}
+
+#endif
+
+#ifdef CLIB_STANDALONE
+extern u32 standalone_random_default_seed;
+
+always_inline u32
+random_default_seed (void)
+{
+  return standalone_random_default_seed;
+}
+#endif
+
+/** \brief 64-bit random number generator
+ * Again, constants courtesy of Donald Knuth.
+ *
+ */
+always_inline u64
+random_u64 (u64 * seed)
+{
+  *seed = 6364136223846793005ULL * *seed + 1442695040888963407ULL;
+  return *seed;
+}
+
+/** \brief machine word size random number generator */
+
+always_inline uword
+random_uword (u32 * seed)
+{
+  if (sizeof (uword) == sizeof (u64))
+    return random_u64 ((u64 *) seed);
+  else
+    return random_u32 (seed);
+}
+
+/** \brief Generate f64 random number in the interval [0,1] */
+always_inline f64
+random_f64 (u32 * seed)
+{
+  return (f64) random_u32 (seed) / (f64) random_u32_max ();
+}
+
+/** \brief Generate random character vector
+
+    From the alphabet a-z, lower case.
+    Returns a vector of the supplied length which is NOT guaranteed to be
+    NULL-terminated. FIXME?
+*/
+always_inline u8 *
+random_string (u32 * seed, uword len)
+{
+  u8 *alphabet = (u8 *) "abcdefghijklmnopqrstuvwxyz";
+  u8 *s = 0;
+  word i;
+
+  vec_resize (s, len);
+  for (i = 0; i < len; i++)
+    s[i] = alphabet[random_u32 (seed) % 26];
+
+  return s;
+}
+
+#endif /* included_random_h */
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */