2 * Empire - A multi-player, client/server Internet based war game.
3 * Copyright (C) 1986-2021, Dave Pare, Jeff Bailey, Thomas Ruschak,
4 * Ken Stevens, Steve McClure, Markus Armbruster
6 * Empire is free software: you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation, either version 3 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
21 * See files README, COPYING and CREDITS in the root of the source
22 * tree for related information and legal notices. It is expected
23 * that future projects/authors will amend these files as needed.
29 * Known contributors to this file:
30 * Markus Armbruster, 2006-2021
41 #include "mt19937ar.h"
44 * Return non-zero with probability @d.
49 return d > genrand_real2();
53 * Return non-zero with probability @pct%.
58 return roll(100) <= pct;
62 round_up_to_pow2(unsigned val)
75 * Return a random number in [0..@n-1].
76 * @n must be in [1..2^31-1].
81 unsigned pow2 = round_up_to_pow2(n);
85 r = genrand_int32() & (pow2 - 1);
91 * Return a random number in [1..@n].
92 * @n must be in [0..2^31-1].
101 * Round @val to nearest integer (on the average).
102 * @val's fractional part is chance to round up.
107 double flr = floor(val);
108 return (int)(flr + chance(val - flr));
112 * Seed the pseudo-random number generator with @seed.
113 * The sequence of pseudo-random numbers is repeatable by seeding it
114 * with the same value.
117 seed_prng(unsigned seed)
123 * Note: this is DJB's hash function when unsigned is 32 bits and hash
127 djb_hash(unsigned hash, void *buf, size_t sz)
131 for (bp = buf; bp < (unsigned char *)buf + sz; bp++)
132 hash = hash * 33 ^ *bp;
138 * Pick a reasonably random seed for the pseudo-random number generator.
151 * Modern systems provide random number devices, but the details
152 * vary. On many systems, /dev/random blocks when the kernel
153 * entropy pool has been depleted, while /dev/urandom doesn't.
154 * The former should only be used for generating long-lived
155 * cryptographic keys. On other systems, both devices behave
156 * exactly the same, or only /dev/random exists.
158 * Try /dev/urandom first, and if it can't be opened, blindly try
161 fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK);
163 fd = open("/dev/random", O_RDONLY | O_NONBLOCK);
165 got_seed = read(fd, &seed, sizeof(seed)) == sizeof(seed);
171 /* Kernel didn't provide, fall back to hashing time and PID */
172 gettimeofday(&tv, NULL);
173 seed = djb_hash(5381, &tv, sizeof(tv));
175 seed = djb_hash(seed, &pid, sizeof(pid));