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

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