2 * Empire - A multi-player, client/server Internet based war game.
3 * Copyright (C) 1986-2013, 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, 2006-2012
42 #include "mt19937ar.h"
45 * Return non-zero with probability D.
50 return d > genrand_real2();
54 * Return non-zero with probability PCT%.
59 return roll(100) <= pct;
63 round_up_to_pow2(unsigned val)
76 * Return a random number in [0..N-1].
77 * N must be in [1..2^31-1].
82 unsigned pow2 = round_up_to_pow2(n);
86 r = genrand_int32() & (pow2 - 1);
92 * Return a random number in [1..N].
93 * N must be in [0..2^31-1].
102 * Round VAL to nearest integer (on the average).
103 * VAL's fractional part is chance to round up.
108 double flr = floor(val);
109 return (int)(flr + chance(val - flr));
113 * Seed the pseudo-random number generator with SEED.
114 * The sequence of pseudo-random numbers is repeatable by seeding it
115 * with the same value.
118 seed_prng(unsigned seed)
124 djb_hash(uint32_t hash, void *buf, size_t sz)
128 for (bp = buf; bp < (unsigned char *)buf + sz; bp++)
129 hash = hash * 33 ^ *bp;
135 * Pick a reasonably random seed for the pseudo-random number generator.
147 * Modern systems provide random number devices, but the details
148 * vary. On many systems, /dev/random blocks when the kernel
149 * entropy pool has been depleted, while /dev/urandom doesn't.
150 * The former should only be used for generating long-lived
151 * cryptographic keys. On other systems, both devices behave
152 * exactly the same, or only /dev/random exists.
154 * Try /dev/urandom first, and if it can't be opened, blindly try
157 fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK);
159 fd = open("/dev/random", O_RDONLY | O_NONBLOCK);
161 got_seed = read(fd, &seed, sizeof(seed)) == sizeof(seed);
166 /* Kernel didn't provide, fall back to hashing time and PID */
167 gettimeofday(&tv, NULL);
168 seed = djb_hash(5381, &tv, sizeof(tv));
170 seed = djb_hash(seed, &pid, sizeof(pid));