text: /*
   * Copyright (C) 2004, 2005, 2007, 2009, 2013, 2014  Internet Systems Consortium, Inc. ("ISC")
   * Copyright (C) 1999-2003  Internet Software Consortium.
   *
   * Permission to use, copy, modify, and/or distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
   * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
   * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
   * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
   * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
   * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
   * PERFORMANCE OF THIS SOFTWARE.
   */
  
  /* $Id: random.c,v 1.28 2009/07/16 05:52:46 marka Exp $ */
  
  /*! \file */
  
  #include <config.h>
  
  #include <stdlib.h>
  #include <time.h>		/* Required for time(). */
  #ifdef HAVE_SYS_TYPES_H
  #include <sys/types.h>
  #endif
  #ifdef HAVE_UNISTD_H
  #include <unistd.h>
  #endif
  
  #include <isc/mutex.h>
  #include <isc/once.h>
  #include <isc/random.h>
  #include <isc/string.h>
  #include <isc/util.h>
  
  static isc_once_t once = ISC_ONCE_INIT;
  
  static void
  initialize_rand(void)
  {
  #ifndef HAVE_ARC4RANDOM
  	unsigned int pid = getpid();
  
  	/*
  	 * The low bits of pid generally change faster.
  	 * Xor them with the high bits of time which change slowly.
  	 */
  	pid = ((pid << 16) & 0xffff0000) | ((pid >> 16) & 0xffff);
  
  	srand((unsigned)time(NULL) ^ pid);
  #endif
  }
  
  static void
  initialize(void)
  {
  	RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS);
  }
  
  void
  isc_random_seed(isc_uint32_t seed)
  {
  	initialize();
  
  #ifndef HAVE_ARC4RANDOM
  	srand(seed);
  #elif defined(HAVE_ARC4RANDOM_ADDRANDOM)
  	arc4random_addrandom((u_char *) &seed, sizeof(isc_uint32_t));
  #else
  	/*
  	 * If arcrandom() is available and no corresponding seeding
  	 * function arc4random_addrandom() is available, no seeding is
  	 * done on such platforms (e.g., OpenBSD 5.5). This is because
  	 * the OS itself is supposed to seed the RNG and it is assumed
  	 * that no explicit seeding is required.
  	 */
  #endif
  }
  
  void
  isc_random_get(isc_uint32_t *val)
  {
  	REQUIRE(val != NULL);
  
  	initialize();
  
  #ifndef HAVE_ARC4RANDOM
  	/*
  	 * rand()'s lower bits are not random.
  	 * rand()'s upper bit is zero.
  	 */
  #if RAND_MAX >= 0xfffff
  	/* We have at least 20 bits.  Use lower 16 excluding lower most 4 */
  	*val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000);
  #elif RAND_MAX >= 0x7fff
  	/* We have at least 15 bits.  Use lower 10/11 excluding lower most 4 */
  	*val = ((rand() >> 4) & 0x000007ff) | ((rand() << 7) & 0x003ff800) |
  		((rand() << 18) & 0xffc00000);
  #else
  #error RAND_MAX is too small
  #endif
  #else
  	*val = arc4random();
  #endif
  }
  
  isc_uint32_t
  isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) {
  	isc_uint32_t rnd;
  
  	REQUIRE(jitter < max || (jitter == 0 && max == 0));
  
  	if (jitter == 0)
  		return (max);
  
  	isc_random_get(&rnd);
  	return (max - rnd % jitter);
  }
  