1 /*
2 * Copyright (c) 1983 Regents of the University of California.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms are permitted
6 * provided that the above copyright notice and this paragraph are
7 * duplicated in all such forms and that any documentation,
8 * advertising materials, and other materials related to such
9 * distribution and use acknowledge that the software was developed
10 * by the University of California, Berkeley. The name of the
11 * University may not be used to endorse or promote products derived
12 * from this software without specific prior written permission.
13 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
15 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
16 */
17
18 /* Several minor changes were made for the NetHack distribution to satisfy
19 * non-BSD compilers (by definition BSD compilers do not need to compile
20 * this file for NetHack). These changes consisted of:
21 * - changing the sccsid conditions to nested ifdefs from defined()s
22 * to accommodate stupid preprocessors
23 * - giving srandom() type void instead of allowing it to default to int
24 * - making the first return in initstate() return a value consistent
25 * with its type (instead of no value)
26 * - ANSI function prototyping in extern.h - therefore include hack.h
27 * instead of stdio.h and remove separate declaration of random() from
28 * the beginning of function srandom
29 * - moving sccsid after hack.h to allow precompiled headers, which
30 * means the defined()s would be ok again...
31 * - change fprintf(stderr, "x(%d)y\n", z) to impossible("x(%d)y", z)
32 * - remove useless variable `j' from srandom()
33 */
34
35 #include "hack.h"
36
37 #ifdef LIBC_SCCS
38 # ifndef lint
39 static char sccsid[] = "@(#)random.c 5.5 (Berkeley) 7/6/88";
40 # endif
41 #endif /* LIBC_SCCS and not lint */
42
43 /*
44 * random.c:
45 * An improved random number generation package. In addition to the standard
46 * rand()/srand() like interface, this package also has a special state info
47 * interface. The initstate() routine is called with a seed, an array of
48 * bytes, and a count of how many bytes are being passed in; this array is then
49 * initialized to contain information for random number generation with that
50 * much state information. Good sizes for the amount of state information are
51 * 32, 64, 128, and 256 bytes. The state can be switched by calling the
52 * setstate() routine with the same array as was initiallized with initstate().
53 * By default, the package runs with 128 bytes of state information and
54 * generates far better random numbers than a linear congruential generator.
55 * If the amount of state information is less than 32 bytes, a simple linear
56 * congruential R.N.G. is used.
57 * Internally, the state information is treated as an array of longs; the
58 * zeroeth element of the array is the type of R.N.G. being used (small
59 * integer); the remainder of the array is the state information for the
60 * R.N.G. Thus, 32 bytes of state information will give 7 longs worth of
61 * state information, which will allow a degree seven polynomial. (Note: the
62 * zeroeth word of state information also has some other information stored
63 * in it -- see setstate() for details).
64 * The random number generation technique is a linear feedback shift register
65 * approach, employing trinomials (since there are fewer terms to sum up that
66 * way). In this approach, the least significant bit of all the numbers in
67 * the state table will act as a linear feedback shift register, and will have
68 * period 2^deg - 1 (where deg is the degree of the polynomial being used,
69 * assuming that the polynomial is irreducible and primitive). The higher
70 * order bits will have longer periods, since their values are also influenced
71 * by pseudo-random carries out of the lower bits. The total period of the
72 * generator is approximately deg*(2**deg - 1); thus doubling the amount of
73 * state information has a vast influence on the period of the generator.
74 * Note: the deg*(2**deg - 1) is an approximation only good for large deg,
75 * when the period of the shift register is the dominant factor. With deg
76 * equal to seven, the period is actually much longer than the 7*(2**7 - 1)
77 * predicted by this formula.
78 */
79
80
81
82 /*
83 * For each of the currently supported random number generators, we have a
84 * break value on the amount of state information (you need at least this
85 * many bytes of state info to support this random number generator), a degree
86 * for the polynomial (actually a trinomial) that the R.N.G. is based on, and
87 * the separation between the two lower order coefficients of the trinomial.
88 */
89
90 #define TYPE_0 0 /* linear congruential */
91 #define BREAK_0 8
92 #define DEG_0 0
93 #define SEP_0 0
94
95 #define TYPE_1 1 /* x**7 + x**3 + 1 */
96 #define BREAK_1 32
97 #define DEG_1 7
98 #define SEP_1 3
99
100 #define TYPE_2 2 /* x**15 + x + 1 */
101 #define BREAK_2 64
102 #define DEG_2 15
103 #define SEP_2 1
104
105 #define TYPE_3 3 /* x**31 + x**3 + 1 */
106 #define BREAK_3 128
107 #define DEG_3 31
108 #define SEP_3 3
109
110 #define TYPE_4 4 /* x**63 + x + 1 */
111 #define BREAK_4 256
112 #define DEG_4 63
113 #define SEP_4 1
114
115
116 /*
117 * Array versions of the above information to make code run faster -- relies
118 * on fact that TYPE_i == i.
119 */
120
121 #define MAX_TYPES 5 /* max number of types above */
122
123 static int degrees[ MAX_TYPES ] = { DEG_0, DEG_1, DEG_2,
124 DEG_3, DEG_4 };
125
126 static int seps[ MAX_TYPES ] = { SEP_0, SEP_1, SEP_2,
127 SEP_3, SEP_4 };
128
129
130
131 /*
132 * Initially, everything is set up as if from :
133 * initstate( 1, &randtbl, 128 );
134 * Note that this initialization takes advantage of the fact that srandom()
135 * advances the front and rear pointers 10*rand_deg times, and hence the
136 * rear pointer which starts at 0 will also end up at zero; thus the zeroeth
137 * element of the state information, which contains info about the current
138 * position of the rear pointer is just
139 * MAX_TYPES*(rptr - state) + TYPE_3 == TYPE_3.
140 */
141
142 static long randtbl[ DEG_3 + 1 ] = { TYPE_3,
143 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342,
144 0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb,
145 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
146 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86,
147 0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7,
148 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
149 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b,
150 0xf5ad9d0e, 0x8999220b, 0x27fb47b9 };
151
152 /*
153 * fptr and rptr are two pointers into the state info, a front and a rear
154 * pointer. These two pointers are always rand_sep places aparts, as they cycle
155 * cyclically through the state information. (Yes, this does mean we could get
156 * away with just one pointer, but the code for random() is more efficient this
157 * way). The pointers are left positioned as they would be from the call
158 * initstate( 1, randtbl, 128 )
159 * (The position of the rear pointer, rptr, is really 0 (as explained above
160 * in the initialization of randtbl) because the state table pointer is set
161 * to point to randtbl[1] (as explained below).
162 */
163
164 static long *fptr = &randtbl[ SEP_3 + 1 ];
165 static long *rptr = &randtbl[ 1 ];
166
167
168
169 /*
170 * The following things are the pointer to the state information table,
171 * the type of the current generator, the degree of the current polynomial
172 * being used, and the separation between the two pointers.
173 * Note that for efficiency of random(), we remember the first location of
174 * the state information, not the zeroeth. Hence it is valid to access
175 * state[-1], which is used to store the type of the R.N.G.
176 * Also, we remember the last location, since this is more efficient than
177 * indexing every time to find the address of the last element to see if
178 * the front and rear pointers have wrapped.
179 */
180
181 static long *state = &randtbl[ 1 ];
182
183 static int rand_type = TYPE_3;
184 static int rand_deg = DEG_3;
185 static int rand_sep = SEP_3;
186
187 static long *end_ptr = &randtbl[ DEG_3 + 1 ];
188
189
190
191 /*
192 * srandom:
193 * Initialize the random number generator based on the given seed. If the
194 * type is the trivial no-state-information type, just remember the seed.
195 * Otherwise, initializes state[] based on the given "seed" via a linear
196 * congruential generator. Then, the pointers are set to known locations
197 * that are exactly rand_sep places apart. Lastly, it cycles the state
198 * information a given number of times to get rid of any initial dependencies
199 * introduced by the L.C.R.N.G.
200 * Note that the initialization of randtbl[] for default usage relies on
201 * values produced by this routine.
202 */
203
204 void
srandom(x)205 srandom( x )
206
207 unsigned x;
208 {
209 register int i;
210
211 if( rand_type == TYPE_0 ) {
212 state[ 0 ] = x;
213 }
214 else {
215 state[ 0 ] = x;
216 for( i = 1; i < rand_deg; i++ ) {
217 state[i] = 1103515245*state[i - 1] + 12345;
218 }
219 fptr = &state[ rand_sep ];
220 rptr = &state[ 0 ];
221 for( i = 0; i < 10*rand_deg; i++ ) random();
222 }
223 }
224
225
226
227 /*
228 * initstate:
229 * Initialize the state information in the given array of n bytes for
230 * future random number generation. Based on the number of bytes we
231 * are given, and the break values for the different R.N.G.'s, we choose
232 * the best (largest) one we can and set things up for it. srandom() is
233 * then called to initialize the state information.
234 * Note that on return from srandom(), we set state[-1] to be the type
235 * multiplexed with the current value of the rear pointer; this is so
236 * successive calls to initstate() won't lose this information and will
237 * be able to restart with setstate().
238 * Note: the first thing we do is save the current state, if any, just like
239 * setstate() so that it doesn't matter when initstate is called.
240 * Returns a pointer to the old state.
241 */
242
243 char *
initstate(seed,arg_state,n)244 initstate( seed, arg_state, n )
245
246 unsigned seed; /* seed for R. N. G. */
247 char *arg_state; /* pointer to state array */
248 int n; /* # bytes of state info */
249 {
250 register char *ostate = (char *)( &state[ -1 ] );
251
252 if( rand_type == TYPE_0 ) state[ -1 ] = rand_type;
253 else state[ -1 ] = MAX_TYPES*(rptr - state) + rand_type;
254 if( n < BREAK_1 ) {
255 if( n < BREAK_0 ) {
256 impossible(
257 "initstate: not enough state (%d bytes) with which to do jack; ignored.", n);
258 return (char *)0;
259 }
260 rand_type = TYPE_0;
261 rand_deg = DEG_0;
262 rand_sep = SEP_0;
263 }
264 else {
265 if( n < BREAK_2 ) {
266 rand_type = TYPE_1;
267 rand_deg = DEG_1;
268 rand_sep = SEP_1;
269 }
270 else {
271 if( n < BREAK_3 ) {
272 rand_type = TYPE_2;
273 rand_deg = DEG_2;
274 rand_sep = SEP_2;
275 }
276 else {
277 if( n < BREAK_4 ) {
278 rand_type = TYPE_3;
279 rand_deg = DEG_3;
280 rand_sep = SEP_3;
281 }
282 else {
283 rand_type = TYPE_4;
284 rand_deg = DEG_4;
285 rand_sep = SEP_4;
286 }
287 }
288 }
289 }
290 state = &( ( (long *)arg_state )[1] ); /* first location */
291 end_ptr = &state[ rand_deg ]; /* must set end_ptr before srandom */
292 srandom( seed );
293 if( rand_type == TYPE_0 ) state[ -1 ] = rand_type;
294 else state[ -1 ] = MAX_TYPES*(rptr - state) + rand_type;
295 return( ostate );
296 }
297
298
299
300 /*
301 * setstate:
302 * Restore the state from the given state array.
303 * Note: it is important that we also remember the locations of the pointers
304 * in the current state information, and restore the locations of the pointers
305 * from the old state information. This is done by multiplexing the pointer
306 * location into the zeroeth word of the state information.
307 * Note that due to the order in which things are done, it is OK to call
308 * setstate() with the same state as the current state.
309 * Returns a pointer to the old state information.
310 */
311
312 char *
setstate(arg_state)313 setstate( arg_state )
314
315 char *arg_state;
316 {
317 register long *new_state = (long *)arg_state;
318 register int type = new_state[0]%MAX_TYPES;
319 register int rear = new_state[0]/MAX_TYPES;
320 char *ostate = (char *)( &state[ -1 ] );
321
322 if( rand_type == TYPE_0 ) state[ -1 ] = rand_type;
323 else state[ -1 ] = MAX_TYPES*(rptr - state) + rand_type;
324 switch( type ) {
325 case TYPE_0:
326 case TYPE_1:
327 case TYPE_2:
328 case TYPE_3:
329 case TYPE_4:
330 rand_type = type;
331 rand_deg = degrees[ type ];
332 rand_sep = seps[ type ];
333 break;
334
335 default:
336 impossible("setstate: state info has been munged (%d); not changed.", type);
337 break;
338 }
339 state = &new_state[ 1 ];
340 if( rand_type != TYPE_0 ) {
341 rptr = &state[ rear ];
342 fptr = &state[ (rear + rand_sep)%rand_deg ];
343 }
344 end_ptr = &state[ rand_deg ]; /* set end_ptr too */
345 return( ostate );
346 }
347
348
349
350 /*
351 * random:
352 * If we are using the trivial TYPE_0 R.N.G., just do the old linear
353 * congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
354 * same in all ther other cases due to all the global variables that have been
355 * set up. The basic operation is to add the number at the rear pointer into
356 * the one at the front pointer. Then both pointers are advanced to the next
357 * location cyclically in the table. The value returned is the sum generated,
358 * reduced to 31 bits by throwing away the "least random" low bit.
359 * Note: the code takes advantage of the fact that both the front and
360 * rear pointers can't wrap on the same call by not testing the rear
361 * pointer if the front one has wrapped.
362 * Returns a 31-bit random number.
363 */
364
365 long
random()366 random()
367 {
368 long i;
369
370 if( rand_type == TYPE_0 ) {
371 i = state[0] = ( state[0]*1103515245 + 12345 )&0x7fffffff;
372 }
373 else {
374 *fptr += *rptr;
375 i = (*fptr >> 1)&0x7fffffff; /* chucking least random bit */
376 if( ++fptr >= end_ptr ) {
377 fptr = state;
378 ++rptr;
379 }
380 else {
381 if( ++rptr >= end_ptr ) rptr = state;
382 }
383 }
384 return( i );
385 }
386
387