text: /*
   * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
   *
   * 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 <assert.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_)
  {
      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();
  }
  
  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;
  }
  