lib/random.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
   3  *
   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:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  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.
  15  */
  16
  17 #include <config.h>
  18 #include "random.h"
  19
  20 #include <errno.h>
  21 #include <stdlib.h>
  22 #include <sys/time.h>
  23
  24 #include "entropy.h"
  25 #include "hash.h"
  26 #include "ovs-thread.h"
  27 #include "timeval.h"
  28 #include "util.h"
  29
  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.
  33  *
  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.
  37  *
  38  * This random number generator is intended for purposes that do not require
  39  * cryptographic-quality randomness. */
  40
  41 /* Current random state. */
  42 DEFINE_STATIC_PER_THREAD_DATA(uint32_t, seed, 0);
  43
  44 static uint32_t random_next(void);
  45
  46 void
  47 random_init(void)
  48 {
  49     uint32_t *seedp = seed_get();
  50     while (!*seedp) {
  51         struct timeval tv;
  52         uint32_t entropy;
  53         pthread_t self;
  54
  55         xgettimeofday(&tv);
  56         get_entropy_or_die(&entropy, 4);
  57         self = pthread_self();
  58
  59         *seedp = (tv.tv_sec ^ tv.tv_usec ^ entropy
  60                   ^ hash_bytes(&self, sizeof self, 0));
  61     }
  62 }
  63
  64 void
  65 random_set_seed(uint32_t seed_)
  66 {
  67     ovs_assert(seed_);
  68     *seed_get() = seed_;
  69 }
  70
  71 void
  72 random_bytes(void *p_, size_t n)
  73 {
  74     uint8_t *p = p_;
  75
  76     random_init();
  77
  78     for (; n > 4; p += 4, n -= 4) {
  79         uint32_t x = random_next();
  80         memcpy(p, &x, 4);
  81     }
  82
  83     if (n) {
  84         uint32_t x = random_next();
  85         memcpy(p, &x, n);
  86     }
  87 }
  88
  89
  90 uint32_t
  91 random_uint32(void)
  92 {
  93     random_init();
  94     return random_next();
  95 }
  96
  97 uint64_t
  98 random_uint64(void)
  99 {
 100     uint64_t x;
 101
 102     random_init();
 103
 104     x = random_next();
 105     x |= (uint64_t) random_next() << 32;
 106     return x;
 107 }
 108
 109 static uint32_t
 110 random_next(void)
 111 {
 112     uint32_t *seedp = seed_get_unsafe();
 113
 114     *seedp ^= *seedp << 13;
 115     *seedp ^= *seedp >> 17;
 116     *seedp ^= *seedp << 5;
 117
 118     return *seedp;
 119 }