contrib/bind-9.2.4rc7/lib/isc/random.c

   1 /*
   2  * Copyright (C) 2004  Internet Systems Consortium, Inc. ("ISC")
   3  * Copyright (C) 1999-2001, 2003  Internet Software Consortium.
   4  *
   5  * Permission to use, copy, modify, and 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 1.15.2.5 2004/03/09 06:11:50 marka Exp $ */
  19
  20 #include <config.h>
  21
  22 #include <stdlib.h>
  23 #include <time.h>               /* Required for time(). */
  24 #ifdef HAVE_SYS_TYPES_H
  25 #include <sys/types.h>
  26 #endif
  27 #ifdef HAVE_UNISTD_H
  28 #include <unistd.h>
  29 #endif
  30
  31 #include <isc/mutex.h>
  32 #include <isc/once.h>
  33 #include <isc/random.h>
  34 #include <isc/string.h>
  35 #include <isc/util.h>
  36
  37 static isc_once_t once = ISC_ONCE_INIT;
  38
  39 static void
  40 initialize_rand(void)
  41 {
  42 #ifndef HAVE_ARC4RANDOM
  43         unsigned int pid = getpid();
  44
  45         /*
  46          * The low bits of pid generally change faster.
  47          * Xor them with the high bits of time which change slowly.
  48          */
  49         pid = ((pid << 16) & 0xffff0000) | ((pid >> 16) & 0xffff);
  50
  51         srand(time(NULL) ^ pid);
  52 #endif
  53 }
  54
  55 static void
  56 initialize(void)
  57 {
  58         RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS);
  59 }
  60
  61 void
  62 isc_random_seed(isc_uint32_t seed)
  63 {
  64         initialize();
  65
  66 #ifndef HAVE_ARC4RANDOM
  67         srand(seed);
  68 #else
  69         arc4random_addrandom((u_char *) &seed, sizeof(isc_uint32_t));
  70 #endif
  71 }
  72
  73 void
  74 isc_random_get(isc_uint32_t *val)
  75 {
  76         REQUIRE(val != NULL);
  77
  78         initialize();
  79
  80 #ifndef HAVE_ARC4RANDOM
  81         /*
  82          * rand()'s lower bits are not random.
  83          * rand()'s upper bit is zero.
  84          */
  85         *val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000) ;
  86 #else
  87         *val = arc4random();
  88 #endif
  89 }
  90
  91 isc_uint32_t
  92 isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) {
  93         REQUIRE(jitter < max);
  94         if (jitter == 0)
  95                 return (max);
  96         else
  97 #ifndef HAVE_ARC4RANDOM
  98                 return (max - rand() % jitter);
  99 #else
 100                 return (max - arc4random() % jitter);
 101 #endif
 102 }