4 * Copyright (c) 1997 Ben Harrison, and others
6 * This software may be copied and distributed for educational, research,
7 * and not for profit purposes provided that this copyright and statement
8 * are included in all such copies. Other copyrights may also apply.
12 /* Purpose: a simple random number generator -BEN- */
24 * Angband 2.7.9 introduced a new (optimized) random number generator,
25 * based loosely on the old "random.c" from Berkeley but with some major
26 * optimizations and algorithm changes. See below for more details.
28 * Code by myself (benh@phial.com) and Randy (randy@stat.tamu.edu).
30 * This code provides (1) a "decent" RNG, based on the "BSD-degree-63-RNG"
31 * used in Angband 2.7.8, but rather optimized, and (2) a "simple" RNG,
32 * based on the simple "LCRNG" currently used in Angband, but "corrected"
33 * to give slightly better values. Both of these are available in two
34 * flavors, first, the simple "mod" flavor, which is fast, but slightly
35 * biased at high values, and second, the simple "div" flavor, which is
36 * less fast (and potentially non-terminating) but which is not biased
37 * and is much less subject to low-bit-non-randomness problems.
39 * You can select your favorite flavor by proper definition of the
40 * "randint0()" macro in the "defines.h" file.
42 * Note that, in Angband 2.8.0, the "state" table will be saved in the
43 * savefile, so a special "initialization" phase will be necessary.
45 * Note the use of the "simple" RNG, first you activate it via
46 * "Rand_quick = TRUE" and "Rand_value = seed" and then it is used
47 * automatically used instead of the "complex" RNG, and when you are
48 * done, you de-activate it via "Rand_quick = FALSE" or choose a new
49 * seed via "Rand_value = seed".
52 * RNG algorithm was fully rewritten. Upper comment is OLD.
62 * Current "state" table for the RNG
63 * Only index 0 to 3 are used
65 u32b Rand_state[RAND_DEG] = {
74 * Initialize Xorshift Algorithm state
76 static void Rand_Xorshift_seed(u32b seed, u32b* state)
80 /* Initialize Xorshift Algorithm RNG */
81 for (i = 1; i <= 4; ++ i) {
82 seed = 1812433253UL * (seed ^ (seed >> 30)) + i;
90 static u32b Rand_Xorshift(u32b* state)
92 u32b t = state[0] ^ (state[0] << 11);
98 state[3] = (state[3] ^ (state[3] >> 19)) ^ (t ^ (t >> 8));
103 static const u32b Rand_Xorshift_max = 0xFFFFFFFF;
106 * Initialize the RNG using a new seed
108 void Rand_state_set(u32b seed)
110 Rand_Xorshift_seed(seed, Rand_state);
113 void Rand_state_init(void)
117 FILE *fp = fopen(RNG_DEVICE, "r");
120 fread(buf, sizeof(buf[0]), 4, fp);
121 } while ((buf[0] | buf[1] | buf[2] | buf[3]) == 0);
122 memcpy(Rand_state, buf, sizeof(buf));
125 #elif defined(WINDOWS)
127 HCRYPTPROV hProvider;
130 CryptAcquireContext(&hProvider, NULL, NULL, PROV_RSA_FULL, 0);
133 CryptGenRandom(hProvider, sizeof(buf[0]) * 4, (BYTE*)buf);
134 } while ((buf[0] | buf[1] | buf[2] | buf[3]) == 0);
136 CryptReleaseContext(hProvider, 0);
141 u32b seed = (time(NULL));
143 /* Mutate the seed on Unix machines */
144 seed = ((seed >> 3) * (getpid() << 1));
147 Rand_state_set(seed);
153 * Backup the RNG state
155 void Rand_state_backup(u32b* backup_state)
159 for (i = 0; i < 4; ++ i) {
160 backup_state[i] = Rand_state[i];
165 * Restore the RNG state
167 void Rand_state_restore(u32b* backup_state)
171 for (i = 0; i < 4; ++ i) {
172 Rand_state[i] = backup_state[i];
178 * Extract a "random" number from 0 to m-1, via "division"
180 static s32b Rand_div_impl(s32b m, u32b* state)
186 /* Hack -- simple case */
187 if (m <= 1) return (0);
189 scaling = Rand_Xorshift_max / m;
193 ret = Rand_Xorshift(state);
194 } while (ret >= past);
196 return ret / scaling;
199 s32b Rand_div(s32b m)
201 return Rand_div_impl(m, Rand_state);
208 * The number of entries in the "randnor_table"
210 #define RANDNOR_NUM 256
213 * The standard deviation of the "randnor_table"
215 #define RANDNOR_STD 64
218 * The normal distribution table for the "randnor()" function (below)
220 static s16b randnor_table[RANDNOR_NUM] =
222 206, 613, 1022, 1430, 1838, 2245, 2652, 3058,
223 3463, 3867, 4271, 4673, 5075, 5475, 5874, 6271,
224 6667, 7061, 7454, 7845, 8234, 8621, 9006, 9389,
225 9770, 10148, 10524, 10898, 11269, 11638, 12004, 12367,
226 12727, 13085, 13440, 13792, 14140, 14486, 14828, 15168,
227 15504, 15836, 16166, 16492, 16814, 17133, 17449, 17761,
228 18069, 18374, 18675, 18972, 19266, 19556, 19842, 20124,
229 20403, 20678, 20949, 21216, 21479, 21738, 21994, 22245,
231 22493, 22737, 22977, 23213, 23446, 23674, 23899, 24120,
232 24336, 24550, 24759, 24965, 25166, 25365, 25559, 25750,
233 25937, 26120, 26300, 26476, 26649, 26818, 26983, 27146,
234 27304, 27460, 27612, 27760, 27906, 28048, 28187, 28323,
235 28455, 28585, 28711, 28835, 28955, 29073, 29188, 29299,
236 29409, 29515, 29619, 29720, 29818, 29914, 30007, 30098,
237 30186, 30272, 30356, 30437, 30516, 30593, 30668, 30740,
238 30810, 30879, 30945, 31010, 31072, 31133, 31192, 31249,
240 31304, 31358, 31410, 31460, 31509, 31556, 31601, 31646,
241 31688, 31730, 31770, 31808, 31846, 31882, 31917, 31950,
242 31983, 32014, 32044, 32074, 32102, 32129, 32155, 32180,
243 32205, 32228, 32251, 32273, 32294, 32314, 32333, 32352,
244 32370, 32387, 32404, 32420, 32435, 32450, 32464, 32477,
245 32490, 32503, 32515, 32526, 32537, 32548, 32558, 32568,
246 32577, 32586, 32595, 32603, 32611, 32618, 32625, 32632,
247 32639, 32645, 32651, 32657, 32662, 32667, 32672, 32677,
249 32682, 32686, 32690, 32694, 32698, 32702, 32705, 32708,
250 32711, 32714, 32717, 32720, 32722, 32725, 32727, 32729,
251 32731, 32733, 32735, 32737, 32739, 32740, 32742, 32743,
252 32745, 32746, 32747, 32748, 32749, 32750, 32751, 32752,
253 32753, 32754, 32755, 32756, 32757, 32757, 32758, 32758,
254 32759, 32760, 32760, 32761, 32761, 32761, 32762, 32762,
255 32763, 32763, 32763, 32764, 32764, 32764, 32764, 32765,
256 32765, 32765, 32765, 32766, 32766, 32766, 32766, 32767,
262 * Generate a random integer number of NORMAL distribution
264 * The table above is used to generate a pseudo-normal distribution,
265 * in a manner which is much faster than calling a transcendental
266 * function to calculate a true normal distribution.
268 * Basically, entry 64*N in the table above represents the number of
269 * times out of 32767 that a random variable with normal distribution
270 * will fall within N standard deviations of the mean. That is, about
271 * 68 percent of the time for N=1 and 95 percent of the time for N=2.
273 * The table above contains a "faked" final entry which allows us to
274 * pretend that all values in a normal distribution are strictly less
275 * than four standard deviations away from the mean. This results in
276 * "conservative" distribution of approximately 1/32768 values.
278 * Note that the binary search takes up to 16 quick iterations.
280 s16b randnor(int mean, int stand)
286 s16b high = RANDNOR_NUM;
289 if (stand < 1) return (mean);
291 /* Roll for probability */
292 tmp = (s16b)randint0(32768);
297 int mid = (low + high) >> 1;
299 /* Move right if forced */
300 if (randnor_table[mid] < tmp)
305 /* Move left otherwise */
312 /* Convert the index into an offset */
313 offset = (long)stand * (long)low / RANDNOR_STD;
315 /* One half should be negative */
316 if (randint0(100) < 50) return (mean - offset);
318 /* One half should be positive */
319 return (mean + offset);
325 * Generates damage for "2d6" style dice rolls
327 s16b damroll(int num, int sides)
330 for (i = 0; i < num; i++) sum += randint1(sides);
336 * Same as above, but always maximal
338 s16b maxroll(int num, int sides)
340 return (num * sides);
345 * Given a numerator and a denominator, supply a properly rounded result,
346 * using the RNG to smooth out remainders. -LM-
348 s32b div_round(s32b n, s32b d)
352 /* Refuse to divide by zero */
359 if ((ABS(n) % ABS(d)) > randint0(ABS(d)))
361 /* Increase the absolute value */
362 if (n * d > 0L) tmp += 1L;
374 * Extract a "random" number from 0 to m-1, using the RNG.
376 * This function should be used when generating random numbers in
377 * "external" program parts like the main-*.c files. It preserves
378 * the current RNG state to prevent influences on game-play.
380 * Could also use rand() from <stdlib.h> directly. XXX XXX XXX
382 s32b Rand_external(s32b m)
384 static bool initialized = FALSE;
385 static u32b Rand_state_external[4];
389 /* Initialize with new seed */
390 u32b seed = time(NULL);
391 Rand_Xorshift_seed(seed, Rand_state_external);
395 return Rand_div_impl(m, Rand_state_external);