31612d576602e5361c67c51f1f90577a17c21ed0
[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 <sys/file.h>
30 #include <unistd.h>
31 #include <fcntl.h>
32 #else
33 #include <time.h>
34 #endif
35
36 #include "rand_xor.h"
37
38 /* Super fast random number generator.
39 *
40 * This rand_xorshift128plus function by Sebastiano Vigna belongs
41 * to the public domain.
42 */
43 uint64_t
44 rand_xorshift128plus(uint64_t *seed)
45 {
46 uint64_t *s = seed;
47
48 uint64_t s1 = s[0];
49 const uint64_t s0 = s[1];
50 s[0] = s0;
51 s1 ^= s1 << 23;
52 s[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5);
53
54 return s[1] + s0;
55 }
56
57 void
58 s_rand_xorshift128plus(uint64_t *seed, bool randomised_seed)
59 {
60 if (!randomised_seed)
61 goto fixed_seed;
62
63 #if defined(__linux__)
64 size_t seed_size = sizeof(uint64_t) * 2;
65
66 #if defined(HAVE_GETRANDOM)
67 ssize_t ret = getrandom(seed, seed_size, GRND_NONBLOCK);
68 if (ret == seed_size)
69 return;
70 #endif
71
72 int fd = open("/dev/urandom", O_RDONLY);
73 if (fd < 0)
74 goto fixed_seed;
75
76 if (read(fd, seed, seed_size) != seed_size) {
77 close(fd);
78 goto fixed_seed;
79 }
80
81 close(fd);
82 return;
83
84 #else
85 seed[0] = 0x3bffb83978e24f88;
86 seed[1] = time(NULL);
87
88 return;
89 #endif
90
91 fixed_seed:
92
93 /* Fallback to a fixed seed */
94 seed[0] = 0x3bffb83978e24f88;
95 seed[1] = 0x9238d5d56c71cd35;
96 }