diplodocus.org Git - nmh/blob - sbr/m_rand.c

   1 /*
   2  * m_rand -- provides pseudorandom bytes
   3  *
   4  * This code is Copyright (c) 2012, by the authors of nmh.  See the
   5  * COPYRIGHT file in the root directory of the nmh distribution for
   6  * complete copyright information.
   7  */
   8
   9 #include <stdlib.h>  /* for abs(), srand(), rand(), arc4random() */
  10 #include <stdio.h>   /* for fopen(), fread(), fclose() */
  11 #include <unistd.h>  /* for getpid() */
  12 #include <time.h>    /* for time() */
  13
  14 #include <config.h>
  15
  16 #if !HAVE_ARC4RANDOM
  17 static int seeded = 0;
  18 #endif
  19
  20
  21 int
  22 m_rand (unsigned char *buf, size_t n) {
  23 #if !HAVE_ARC4RANDOM
  24   if (! seeded) {
  25     FILE *devurandom;
  26     unsigned int seed;
  27
  28     if ((devurandom = fopen ("/dev/urandom", "r"))) {
  29       if (fread (&seed, sizeof (seed), 1, devurandom) == 1) seeded = 1;
  30       fclose (devurandom);
  31     }
  32
  33     if (! seeded) {
  34       /* This seed calculation is from Helmut G. Katzgraber, "Random
  35          Numbers in Scientific Computing:  An Introduction",
  36          arXiv:1005.4117v1 [physics.comp-ph], 22 May 2010, p. 19.
  37          time() and getpid() shouldn't fail on POSIX platforms. */
  38       seed = abs ((int) ((time (0) * 181 * ((getpid ()-83) * 359)) % 104729));
  39       seeded = 1;
  40     }
  41
  42     srand (seed);
  43   }
  44
  45   while (n > 0) {
  46     int rnd = rand ();
  47     unsigned char *rndp = (unsigned char *) &rnd;
  48     unsigned int i;
  49
  50     for (i = 0; i < sizeof rnd  &&  n > 0;  ++i, --n) {
  51       *buf++ = *rndp++;
  52     }
  53   }
  54 #else
  55   arc4random_buf(buf, n);
  56 #endif
  57
  58   return 0;
  59 }