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/*
* Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira, Inc.
*
* 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.
*/
#include <config.h>
#include "random.h"
#include <errno.h>
#include <stdlib.h>
#include <sys/time.h>
#include "entropy.h"
#include "timeval.h"
#include "util.h"
/* This is the 32-bit PRNG recommended in G. Marsaglia, "Xorshift RNGs",
* _Journal of Statistical Software_ 8:14 (July 2003). According to the paper,
* it has a period of 2**32 - 1 and passes almost all tests of randomness.
*
* We use this PRNG instead of libc's rand() because rand() varies in quality
* and because its maximum value also varies between 32767 and INT_MAX, whereas
* we often want random numbers in the full range of uint32_t.
*
* This random number generator is intended for purposes that do not require
* cryptographic-quality randomness. */
/* Current random state. */
static uint32_t seed;
static uint32_t random_next(void);
void
random_init(void)
{
while (!seed) {
struct timeval tv;
uint32_t entropy;
xgettimeofday(&tv);
get_entropy_or_die(&entropy, 4);
seed = tv.tv_sec ^ tv.tv_usec ^ entropy;
}
}
void
random_set_seed(uint32_t seed_)
{
ovs_assert(seed_);
seed = seed_;
}
void
random_bytes(void *p_, size_t n)
{
uint8_t *p = p_;
random_init();
for (; n > 4; p += 4, n -= 4) {
uint32_t x = random_next();
memcpy(p, &x, 4);
}
if (n) {
uint32_t x = random_next();
memcpy(p, &x, n);
}
}
uint8_t
random_uint8(void)
{
return random_uint32();
}
uint16_t
random_uint16(void)
{
return random_uint32();
}
uint32_t
random_uint32(void)
{
random_init();
return random_next();
}
uint64_t
random_uint64(void)
{
uint64_t x;
random_init();
x = random_next();
x |= (uint64_t) random_next() << 32;
return x;
}
int
random_range(int max)
{
return random_uint32() % max;
}
static uint32_t
random_next(void)
{
seed ^= seed << 13;
seed ^= seed >> 17;
seed ^= seed << 5;
return seed;
}
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