2 * Copyright (c) 2008, 2009, 2010, 2011, 2012 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.
29 /* This is the 32-bit PRNG recommended in G. Marsaglia, "Xorshift RNGs",
30 * _Journal of Statistical Software_ 8:14 (July 2003). According to the paper,
31 * it has a period of 2**32 - 1 and passes almost all tests of randomness.
33 * We use this PRNG instead of libc's rand() because rand() varies in quality
34 * and because its maximum value also varies between 32767 and INT_MAX, whereas
35 * we often want random numbers in the full range of uint32_t.
37 * This random number generator is intended for purposes that do not require
38 * cryptographic-quality randomness. */
40 /* Current random state. */
43 static uint32_t random_next(void);
53 get_entropy_or_die(&entropy, 4);
55 seed = tv.tv_sec ^ tv.tv_usec ^ entropy;
60 random_set_seed(uint32_t seed_)
67 random_bytes(void *p_, size_t n)
73 for (; n > 4; p += 4, n -= 4) {
74 uint32_t x = random_next();
79 uint32_t x = random_next();
87 return random_uint32();
93 return random_uint32();
100 return random_next();
111 x |= (uint64_t) random_next() << 32;
116 random_range(int max)
118 return random_uint32() % max;