1/*
2 * Copyright 2017 Timothy Arceri
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
21 * SOFTWARE.
22 *
23 */
24
25#if defined(__linux__)
26#include <sys/file.h>
27#include <unistd.h>
28#include <fcntl.h>
29#else
30#include <time.h>
31#endif
32
33#include "rand_xor.h"
34
35/* Super fast random number generator.
36 *
37 * This rand_xorshift128plus function by Sebastiano Vigna belongs
38 * to the public domain.
39 */
40uint64_t
41rand_xorshift128plus(uint64_t *seed)
42{
43   uint64_t *s = seed;
44
45   uint64_t s1 = s[0];
46   const uint64_t s0 = s[1];
47   s[0] = s0;
48   s1 ^= s1 << 23;
49   s[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5);
50
51   return s[1] + s0;
52}
53
54void
55s_rand_xorshift128plus(uint64_t *seed, bool randomised_seed)
56{
57   if (!randomised_seed)
58      goto fixed_seed;
59
60#if defined(__linux__)
61   int fd = open("/dev/urandom", O_RDONLY);
62   if (fd < 0)
63      goto fixed_seed;
64
65   size_t seed_size = sizeof(uint64_t) * 2;
66   if (read(fd, seed, seed_size) != seed_size) {
67      close(fd);
68      goto fixed_seed;
69   }
70
71   close(fd);
72   return;
73
74#else
75   seed[0] = 0x3bffb83978e24f88;
76   seed[1] = time(NULL);
77
78   return;
79#endif
80
81fixed_seed:
82
83   /* Fallback to a fixed seed */
84   seed[0] = 0x3bffb83978e24f88;
85   seed[1] = 0x9238d5d56c71cd35;
86}
87