de05fa64b3cd898ecf555bcb19d0c92978698dd2
[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 #include <sys/file.h>
27 #include <unistd.h>
28 #else
29 #include <time.h>
30 #endif
31
32 #include "rand_xor.h"
33
34 /* Super fast random number generator.
35 *
36 * This rand_xorshift128plus function by Sebastiano Vigna belongs
37 * to the public domain.
38 */
39 uint64_t
40 rand_xorshift128plus(uint64_t *seed)
41 {
42 uint64_t *s = seed;
43
44 uint64_t s1 = s[0];
45 const uint64_t s0 = s[1];
46 s[0] = s0;
47 s1 ^= s1 << 23;
48 s[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5);
49
50 return s[1] + s0;
51 }
52
53 void
54 s_rand_xorshift128plus(uint64_t *seed, bool randomised_seed)
55 {
56 if (!randomised_seed)
57 goto fixed_seed;
58
59 #if defined(__linux__)
60 int fd = open("/dev/urandom", O_RDONLY);
61 if (fd < 0)
62 goto fixed_seed;
63
64 size_t seed_size = sizeof(uint64_t) * 2;
65 if (read(fd, seed, seed_size) != seed_size) {
66 close(fd);
67 goto fixed_seed;
68 }
69
70 close(fd);
71 return;
72
73 #else
74 seed[0] = 0x3bffb83978e24f88;
75 seed[1] = time(NULL);
76
77 return;
78 #endif
79
80 fixed_seed:
81
82 /* Fallback to a fixed seed */
83 seed[0] = 0x3bffb83978e24f88;
84 seed[1] = 0x9238d5d56c71cd35;
85 }