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 <stdbool.h>
  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 #include "m_rand.h"
  16
  17 #if !HAVE_ARC4RANDOM
  18 static bool seeded = false;
  19 #endif
  20
  21
  22 int
  23 m_rand (unsigned char *buf, size_t n)
  24 {
  25 #if !HAVE_ARC4RANDOM
  26   if (! seeded) {
  27     FILE *devurandom;
  28     unsigned int seed;
  29
  30     if ((devurandom = fopen ("/dev/urandom", "r"))) {
  31       if (fread (&seed, sizeof (seed), 1, devurandom) == 1)
  32           seeded = true;
  33       fclose (devurandom);
  34     }
  35
  36     if (! seeded) {
  37       /* This seed calculation is from Helmut G. Katzgraber, "Random
  38          Numbers in Scientific Computing:  An Introduction",
  39          arXiv:1005.4117v1 [physics.comp-ph], 22 May 2010, p. 19.
  40          time() and getpid() shouldn't fail on POSIX platforms. */
  41       seed = abs ((int) ((time (0) * 181 * ((getpid ()-83) * 359)) % 104729));
  42       seeded = true;
  43     }
  44
  45     srand (seed);
  46   }
  47
  48   while (n > 0) {
  49     int rnd = rand ();
  50     unsigned char *rndp = (unsigned char *) &rnd;
  51     unsigned int i;
  52
  53     for (i = 0; i < sizeof rnd  &&  n > 0;  ++i, --n) {
  54       *buf++ = *rndp++;
  55     }
  56   }
  57 #else
  58   arc4random_buf(buf, n);
  59 #endif
  60
  61   return 0;
  62 }