contrib/bind/lib/isc/random.c

   1 /*
   2  * Copyright (C) 2004, 2005, 2007, 2009  Internet Systems Consortium, Inc. ("ISC")
   3  * Copyright (C) 1999-2003  Internet Software Consortium.
   4  *
   5  * Permission to use, copy, modify, and/or distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
  10  * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
  11  * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
  12  * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
  13  * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
  14  * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
  15  * PERFORMANCE OF THIS SOFTWARE.
  16  */
  17
  18 /* $Id: random.c,v 1.25.128.2 2009/07/16 23:46:44 tbox Exp $ */
  19
  20 /*! \file */
  21
  22 #include <config.h>
  23
  24 #include <stdlib.h>
  25 #include <time.h>               /* Required for time(). */
  26 #ifdef HAVE_SYS_TYPES_H
  27 #include <sys/types.h>
  28 #endif
  29 #ifdef HAVE_UNISTD_H
  30 #include <unistd.h>
  31 #endif
  32
  33 #include <isc/mutex.h>
  34 #include <isc/once.h>
  35 #include <isc/random.h>
  36 #include <isc/string.h>
  37 #include <isc/util.h>
  38
  39 static isc_once_t once = ISC_ONCE_INIT;
  40
  41 static void
  42 initialize_rand(void)
  43 {
  44 #ifndef HAVE_ARC4RANDOM
  45         unsigned int pid = getpid();
  46
  47         /*
  48          * The low bits of pid generally change faster.
  49          * Xor them with the high bits of time which change slowly.
  50          */
  51         pid = ((pid << 16) & 0xffff0000) | ((pid >> 16) & 0xffff);
  52
  53         srand(time(NULL) ^ pid);
  54 #endif
  55 }
  56
  57 static void
  58 initialize(void)
  59 {
  60         RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS);
  61 }
  62
  63 void
  64 isc_random_seed(isc_uint32_t seed)
  65 {
  66         initialize();
  67
  68 #ifndef HAVE_ARC4RANDOM
  69         srand(seed);
  70 #else
  71         arc4random_addrandom((u_char *) &seed, sizeof(isc_uint32_t));
  72 #endif
  73 }
  74
  75 void
  76 isc_random_get(isc_uint32_t *val)
  77 {
  78         REQUIRE(val != NULL);
  79
  80         initialize();
  81
  82 #ifndef HAVE_ARC4RANDOM
  83         /*
  84          * rand()'s lower bits are not random.
  85          * rand()'s upper bit is zero.
  86          */
  87 #if RAND_MAX >= 0xfffff
  88         /* We have at least 20 bits.  Use lower 16 excluding lower most 4 */
  89         *val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000);
  90 #elif RAND_MAX >= 0x7fff
  91         /* We have at least 15 bits.  Use lower 10/11 excluding lower most 4 */
  92         *val = ((rand() >> 4) & 0x000007ff) | ((rand() << 7) & 0x003ff800) |
  93                 ((rand() << 18) & 0xffc00000);
  94 #else
  95 #error RAND_MAX is too small
  96 #endif
  97 #else
  98         *val = arc4random();
  99 #endif
 100 }
 101
 102 isc_uint32_t
 103 isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) {
 104         isc_uint32_t rnd;
 105
 106         REQUIRE(jitter < max);
 107
 108         if (jitter == 0)
 109                 return (max);
 110
 111         isc_random_get(&rnd);
 112         return (max - rnd % jitter);
 113 }