external/bsd/bind/dist/lib/isc/random.c

   1 /*      $NetBSD$        */
   2
   3 /*
   4  * Copyright (C) 2004, 2005, 2007, 2009  Internet Systems Consortium, Inc. ("ISC")
   5  * Copyright (C) 1999-2003  Internet Software Consortium.
   6  *
   7  * Permission to use, copy, modify, and/or distribute this software for any
   8  * purpose with or without fee is hereby granted, provided that the above
   9  * copyright notice and this permission notice appear in all copies.
  10  *
  11  * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
  12  * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
  13  * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
  14  * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
  15  * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
  16  * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
  17  * PERFORMANCE OF THIS SOFTWARE.
  18  */
  19
  20 /* Id: random.c,v 1.28 2009/07/16 05:52:46 marka Exp */
  21
  22 /*! \file */
  23
  24 #include <config.h>
  25
  26 #include <stdlib.h>
  27 #include <time.h>               /* Required for time(). */
  28 #ifdef HAVE_SYS_TYPES_H
  29 #include <sys/types.h>
  30 #endif
  31 #ifdef HAVE_UNISTD_H
  32 #include <unistd.h>
  33 #endif
  34
  35 #include <isc/mutex.h>
  36 #include <isc/once.h>
  37 #include <isc/random.h>
  38 #include <isc/string.h>
  39 #include <isc/util.h>
  40
  41 static isc_once_t once = ISC_ONCE_INIT;
  42
  43 static void
  44 initialize_rand(void)
  45 {
  46 #ifndef HAVE_ARC4RANDOM
  47         unsigned int pid = getpid();
  48
  49         /*
  50          * The low bits of pid generally change faster.
  51          * Xor them with the high bits of time which change slowly.
  52          */
  53         pid = ((pid << 16) & 0xffff0000) | ((pid >> 16) & 0xffff);
  54
  55         srand(time(NULL) ^ pid);
  56 #endif
  57 }
  58
  59 static void
  60 initialize(void)
  61 {
  62         RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS);
  63 }
  64
  65 void
  66 isc_random_seed(isc_uint32_t seed)
  67 {
  68         initialize();
  69
  70 #ifndef HAVE_ARC4RANDOM
  71         srand(seed);
  72 #else
  73         arc4random_addrandom((u_char *) &seed, sizeof(isc_uint32_t));
  74 #endif
  75 }
  76
  77 void
  78 isc_random_get(isc_uint32_t *val)
  79 {
  80         REQUIRE(val != NULL);
  81
  82         initialize();
  83
  84 #ifndef HAVE_ARC4RANDOM
  85         /*
  86          * rand()'s lower bits are not random.
  87          * rand()'s upper bit is zero.
  88          */
  89 #if RAND_MAX >= 0xfffff
  90         /* We have at least 20 bits.  Use lower 16 excluding lower most 4 */
  91         *val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000);
  92 #elif RAND_MAX >= 0x7fff
  93         /* We have at least 15 bits.  Use lower 10/11 excluding lower most 4 */
  94         *val = ((rand() >> 4) & 0x000007ff) | ((rand() << 7) & 0x003ff800) |
  95                 ((rand() << 18) & 0xffc00000);
  96 #else
  97 #error RAND_MAX is too small
  98 #endif
  99 #else
 100         *val = arc4random();
 101 #endif
 102 }
 103
 104 isc_uint32_t
 105 isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) {
 106         isc_uint32_t rnd;
 107
 108         REQUIRE(jitter < max || (jitter == 0 && max == 0));
 109
 110         if (jitter == 0)
 111                 return (max);
 112
 113         isc_random_get(&rnd);
 114         return (max - rnd % jitter);
 115 }