2 * Simple random number generator for testing.
3 * Copyright © 2022-2024 Nick Bowler
5 * This program is free software: you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation, either version 3 of the License, or
8 * (at your option) any later version.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program. If not, see <https://www.gnu.org/licenses/>.
18 * The RNG implementation is adapted from xoshiro256+ and splitmix64
19 * by David Blackman and Sebastiano Vigna, originally distributed under
20 * the Creative Commons Zero public domain dedication.
31 #if !TEST_RNG_NO_EXTERNAL_API
35 #define B64(x) ((x) & 0xffffffffffffffffull)
38 unsigned long long state[4];
41 /* Rotate val left by n bits. The behaviour is undefined if n is zero. */
42 static unsigned long long rot_left64(unsigned long long val, int n)
44 return B64( (val << n) | (val >> (64 - n)) );
47 static unsigned long long xoshiro256p(unsigned long long *s)
49 unsigned long long tmp, ret;
51 ret = B64(s[0] + s[3]);
52 tmp = B64(s[1] << 17);
59 s[3] = rot_left64(s[3], 45);
64 static unsigned long long splitmix64(unsigned long long *state)
68 z = B64(*state += 0x9e3779b97f4a7c15ull);
69 z = B64((z ^ (z >> 30)) * 0xbf58476d1ce4e5b9ull);
70 z = B64((z ^ (z >> 27)) * 0x94d049bb133111ebull);
75 #if !TEST_RNG_NO_EXTERNAL_API
76 struct test_rng *test_rng_alloc(const char *seed_str)
78 unsigned long long seed;
79 uintmax_t limit, seed_val;
82 limit = (uintmax_t)0xffffffff;
83 limit |= (limit << 16 << 16);
85 if (!test_strtoumax(&seed_val, seed_str, limit)) {
86 print_error("%s: invalid seed", seed_str);
91 rng = malloc_nofail(sizeof *rng);
92 rng->state[0] = splitmix64(&seed);
93 rng->state[1] = splitmix64(&seed);
94 rng->state[2] = splitmix64(&seed);
95 rng->state[3] = splitmix64(&seed);
100 void test_rng_free(struct test_rng *rng)
105 /* Calculate the least power of two greater than val, minus 1. */
106 static unsigned rng_mask(unsigned val)
113 if (UINT_MAX >= 65536)
119 unsigned test_rng_uniform_int(struct test_rng *rng, unsigned max)
121 unsigned mask = rng_mask(max-1);
122 unsigned long long val;
125 val = ( xoshiro256p(rng->state) >> 32 ) & mask;
126 } while (val >= max);