b486a53343cc40c0ef8bc48969856e8b3063e731
[mesa.git] / src / util / rand_xor.c
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 #if defined(HAVE_GETRANDOM)
27 #include <sys/random.h>
28 #endif
29 #include <unistd.h>
30 #include <fcntl.h>
31 #else
32 #include <time.h>
33 #endif
34
35 #include "rand_xor.h"
36
37 /* Super fast random number generator.
38 *
39 * This rand_xorshift128plus function by Sebastiano Vigna belongs
40 * to the public domain.
41 */
42 uint64_t
43 rand_xorshift128plus(uint64_t seed[2])
44 {
45 uint64_t *s = seed;
46
47 uint64_t s1 = s[0];
48 const uint64_t s0 = s[1];
49 s[0] = s0;
50 s1 ^= s1 << 23;
51 s[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5);
52
53 return s[1] + s0;
54 }
55
56 void
57 s_rand_xorshift128plus(uint64_t seed[2], bool randomised_seed)
58 {
59 if (!randomised_seed)
60 goto fixed_seed;
61
62 #if defined(__linux__)
63 size_t seed_size = sizeof(uint64_t) * 2;
64
65 #if defined(HAVE_GETRANDOM)
66 ssize_t ret = getrandom(seed, seed_size, GRND_NONBLOCK);
67 if (ret == seed_size)
68 return;
69 #endif
70
71 int fd = open("/dev/urandom", O_RDONLY);
72 if (fd < 0)
73 goto fixed_seed;
74
75 if (read(fd, seed, seed_size) != seed_size) {
76 close(fd);
77 goto fixed_seed;
78 }
79
80 close(fd);
81 return;
82
83 #else
84 seed[0] = 0x3bffb83978e24f88;
85 seed[1] = time(NULL);
86
87 return;
88 #endif
89
90 fixed_seed:
91
92 /* Fallback to a fixed seed */
93 seed[0] = 0x3bffb83978e24f88;
94 seed[1] = 0x9238d5d56c71cd35;
95 }