2 * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at:
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
26 #include "ovs-thread.h"
30 /* This is the 32-bit PRNG recommended in G. Marsaglia, "Xorshift RNGs",
31 * _Journal of Statistical Software_ 8:14 (July 2003). According to the paper,
32 * it has a period of 2**32 - 1 and passes almost all tests of randomness.
34 * We use this PRNG instead of libc's rand() because rand() varies in quality
35 * and because its maximum value also varies between 32767 and INT_MAX, whereas
36 * we often want random numbers in the full range of uint32_t.
38 * This random number generator is intended for purposes that do not require
39 * cryptographic-quality randomness. */
41 /* Current random state. */
42 DEFINE_STATIC_PER_THREAD_DATA(uint32_t, seed, 0);
44 static uint32_t random_next(void);
49 uint32_t *seedp = seed_get();
56 get_entropy_or_die(&entropy, 4);
57 self = pthread_self();
59 *seedp = (tv.tv_sec ^ tv.tv_usec ^ entropy
60 ^ hash_bytes(&self, sizeof self, 0));
65 random_set_seed(uint32_t seed_)
72 random_bytes(void *p_, size_t n)
78 for (; n > 4; p += 4, n -= 4) {
79 uint32_t x = random_next();
84 uint32_t x = random_next();
105 x |= (uint64_t) random_next() << 32;
112 uint32_t *seedp = seed_get_unsafe();
114 *seedp ^= *seedp << 13;
115 *seedp ^= *seedp >> 17;
116 *seedp ^= *seedp << 5;