/*

 * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 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 "hash.h"

#include "ovs-thread.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. */

DEFINE_STATIC_PER_THREAD_DATA(uint32_t, seed, 0);

static uint32_t random_next(void);

void

random_init(void)

{

    uint32_t *seedp = seed_get();

    while (!*seedp) {

        struct timeval tv;

        uint32_t entropy;

        pthread_t self;

        xgettimeofday(&tv);

        get_entropy_or_die(&entropy, 4);

        self = pthread_self();

        *seedp = (tv.tv_sec ^ tv.tv_usec ^ entropy

                  ^ hash_bytes(&self, sizeof self, 0));

    }

}

void

random_set_seed(uint32_t seed_)

{

    ovs_assert(seed_);

    *seed_get() = 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);

    }

}

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;

}

static uint32_t

random_next(void)

{

    uint32_t *seedp = seed_get_unsafe();

    *seedp ^= *seedp << 13;

    *seedp ^= *seedp >> 17;

    *seedp ^= *seedp << 5;

    return *seedp;

}