2 * Copyright (c) 1983 Regents of the University of California.
5 * Redistribution and use in source and binary forms are permitted
6 * provided that: (1) source distributions retain this entire copyright
7 * notice and comment, and (2) distributions including binaries display
8 * the following acknowledgement: ``This product includes software
9 * developed by the University of California, Berkeley and its contributors''
10 * in the documentation or other materials provided with the distribution
11 * and in all advertising materials mentioning features or use of this
12 * software. Neither the name of the University nor the names of its
13 * contributors may be used to endorse or promote products derived
14 * from this software without specific prior written permission.
15 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
17 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
21 #include <proto/exec.h>
23 #include "__arosc_privdata.h"
25 #include <aros/symbolsets.h>
29 * An improved random number generation package. In addition to the standard
30 * rand()/srand() like interface, this package also has a special state info
31 * interface. The initstate() routine is called with a seed, an array of
32 * bytes, and a count of how many bytes are being passed in; this array is then
33 * initialized to contain information for random number generation with that
34 * much state information. Good sizes for the amount of state information are
35 * 32, 64, 128, and 256 bytes. The state can be switched by calling the
36 * setstate() routine with the same array as was initiallized with initstate().
37 * By default, the package runs with 128 bytes of state information and
38 * generates far better random numbers than a linear congruential generator.
39 * If the amount of state information is less than 32 bytes, a simple linear
40 * congruential R.N.G. is used.
41 * Internally, the state information is treated as an array of longs; the
42 * zeroeth element of the array is the type of R.N.G. being used (small
43 * integer); the remainder of the array is the state information for the
44 * R.N.G. Thus, 32 bytes of state information will give 7 longs worth of
45 * state information, which will allow a degree seven polynomial. (Note: the
46 * zeroeth word of state information also has some other information stored
47 * in it -- see setstate() for details).
48 * The random number generation technique is a linear feedback shift register
49 * approach, employing trinomials (since there are fewer terms to sum up that
50 * way). In this approach, the least significant bit of all the numbers in
51 * the state table will act as a linear feedback shift register, and will have
52 * period 2^deg - 1 (where deg is the degree of the polynomial being used,
53 * assuming that the polynomial is irreducible and primitive). The higher
54 * order bits will have longer periods, since their values are also influenced
55 * by pseudo-random carries out of the lower bits. The total period of the
56 * generator is approximately deg*(2**deg - 1); thus doubling the amount of
57 * state information has a vast influence on the period of the generator.
58 * Note: the deg*(2**deg - 1) is an approximation only good for large deg,
59 * when the period of the shift register is the dominant factor. With deg
60 * equal to seven, the period is actually much longer than the 7*(2**7 - 1)
61 * predicted by this formula.
65 * For each of the currently supported random number generators, we have a
66 * break value on the amount of state information (you need at least this
67 * many bytes of state info to support this random number generator), a degree
68 * for the polynomial (actually a trinomial) that the R.N.G. is based on, and
69 * the separation between the two lower order coefficients of the trinomial.
72 #define TYPE_0 0 /* linear congruential */
77 #define TYPE_1 1 /* x**7 + x**3 + 1 */
82 #define TYPE_2 2 /* x**15 + x + 1 */
87 #define TYPE_3 3 /* x**31 + x**3 + 1 */
92 #define TYPE_4 4 /* x**63 + x + 1 */
98 * Array versions of the above information to make code run faster -- relies
99 * on fact that TYPE_i == i.
102 #define MAX_TYPES 5 /* max number of types above */
104 static int const _degrees
[ MAX_TYPES
] = { DEG_0
, DEG_1
, DEG_2
,
107 static int const _seps
[ MAX_TYPES
] = { SEP_0
, SEP_1
, SEP_2
,
113 * Initially, everything is set up as if from :
114 * initstate( 1, &randtbl, 128 );
115 * Note that this initialization takes advantage of the fact that srandom()
116 * advances the front and rear pointers 10*rand_deg times, and hence the
117 * rear pointer which starts at 0 will also end up at zero; thus the zeroeth
118 * element of the state information, which contains info about the current
119 * position of the rear pointer is just
120 * MAX_TYPES*(rptr - state) + TYPE_3 == TYPE_3.
123 static long const _randtbl
[ DEG_3
+ 1 ] = { TYPE_3
,
124 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342,
125 0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb,
126 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
127 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86,
128 0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7,
129 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
130 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b,
131 0xf5ad9d0e, 0x8999220b, 0x27fb47b9 };
134 * fptr and rptr are two pointers into the state info, a front and a rear
135 * pointer. These two pointers are always rand_sep places aparts, as they cycle
136 * cyclically through the state information. (Yes, this does mean we could get
137 * away with just one pointer, but the code for random() is more efficient this
138 * way). The pointers are left positioned as they would be from the call
139 * initstate( 1, randtbl, 128 )
140 * (The position of the rear pointer, rptr, is really 0 (as explained above
141 * in the initialization of randtbl) because the state table pointer is set
142 * to point to randtbl[1] (as explained below).
147 * The following things are the pointer to the state information table,
148 * the type of the current generator, the degree of the current polynomial
149 * being used, and the separation between the two pointers.
150 * Note that for efficiency of random(), we remember the first location of
151 * the state information, not the zeroeth. Hence it is valid to access
152 * state[-1], which is used to store the type of the R.N.G.
153 * Also, we remember the last location, since this is more efficient than
154 * indexing every time to find the address of the last element to see if
155 * the front and rear pointers have wrapped.
158 struct random_state
{
159 int degrees
[ MAX_TYPES
];
160 int seps
[ MAX_TYPES
];
161 long randtbl
[ DEG_3
+ 1 ];
171 static void init_random_state(struct random_state
*rs
)
173 memcpy(rs
->degrees
, _degrees
, sizeof(_degrees
));
174 memcpy(rs
->seps
, _seps
, sizeof(_seps
));
175 memcpy(rs
->randtbl
, _randtbl
, sizeof(_randtbl
));
176 rs
->fptr
= &rs
->randtbl
[ SEP_3
+ 1 ];
177 rs
->rptr
= &rs
->randtbl
[ 1 ];
178 rs
->state
= &rs
->randtbl
[ 1 ];
179 rs
->rand_type
= TYPE_3
;
180 rs
->rand_deg
= DEG_3
;
181 rs
->rand_sep
= SEP_3
;
182 rs
->end_ptr
= &rs
->randtbl
[ DEG_3
+ 1 ];
186 static struct random_state
*get_random_state(void)
188 struct random_state
*rs
;
190 struct aroscbase
*base
= __GM_GetBase();
192 if (base
->acb_acud
.acud_random
)
193 return base
->acb_acud
.acud_random
;
195 if ((rs
= AllocMem(sizeof(*rs
), MEMF_ANY
))) {
196 init_random_state(rs
);
198 base
->acb_acud
.acud_random
= rs
;
205 static void free_random_state(struct aroscbase
*base
)
207 if (base
->acb_acud
.acud_random
) {
208 FreeMem(base
->acb_acud
.acud_random
, sizeof(struct random_state
));
209 base
->acb_acud
.acud_random
= NULL
;
213 ADD2CLOSELIB(free_random_state
, 0)
215 static struct random_state acud_random
;
217 static inline struct random_state
*get_random_state(void)
219 if (acud_random
.end_ptr
== NULL
)
220 init_random_state(&acud_random
);
230 * Initialize the random number generator based on the given seed. If the
231 * type is the trivial no-state-information type, just remember the seed.
232 * Otherwise, initializes state[] based on the given "seed" via a linear
233 * congruential generator. Then, the pointers are set to known locations
234 * that are exactly rand_sep places apart. Lastly, it cycles the state
235 * information a given number of times to get rid of any initial dependencies
236 * introduced by the L.C.R.N.G.
237 * Note that the initialization of randtbl[] for default usage relies on
238 * values produced by this routine.
245 void srandom(unsigned x
)
249 struct random_state
*rs
;
251 if (!(rs
= get_random_state()))
254 if( rs
->rand_type
== TYPE_0
) {
259 for( i
= 1; i
< rs
->rand_deg
; i
++ ) {
260 rs
->state
[i
] = 1103515245*rs
->state
[i
- 1] + 12345;
262 rs
->fptr
= &rs
->state
[ rs
->rand_sep
];
263 rs
->rptr
= &rs
->state
[ 0 ];
264 for( i
= 0; i
< 10*rs
->rand_deg
; i
++ ) random();
272 * Initialize the state information in the given array of n bytes for
273 * future random number generation. Based on the number of bytes we
274 * are given, and the break values for the different R.N.G.'s, we choose
275 * the best (largest) one we can and set things up for it. srandom() is
276 * then called to initialize the state information.
277 * Note that on return from srandom(), we set state[-1] to be the type
278 * multiplexed with the current value of the rear pointer; this is so
279 * successive calls to initstate() won't lose this information and will
280 * be able to restart with setstate().
281 * Note: the first thing we do is save the current state, if any, just like
282 * setstate() so that it doesn't matter when initstate is called.
283 * Returns a pointer to the old state.
287 initstate( seed
, arg_state
, n
)
289 unsigned seed
; /* seed for R. N. G. */
290 char *arg_state
; /* pointer to state array */
291 int n
; /* # bytes of state info */
293 struct random_state
*rs
;
294 register char *ostate
;
296 if (!(rs
= get_random_state()))
299 ostate
= (char *)( &rs
->state
[ -1 ] );
301 if( rs
->rand_type
== TYPE_0
) rs
->state
[ -1 ] = rs
->rand_type
;
302 else rs
->state
[ -1 ] = MAX_TYPES
*(rs
->rptr
- rs
->state
) + rs
->rand_type
;
307 rs
->rand_type
= TYPE_0
;
308 rs
->rand_deg
= DEG_0
;
309 rs
->rand_sep
= SEP_0
;
313 rs
->rand_type
= TYPE_1
;
314 rs
->rand_deg
= DEG_1
;
315 rs
->rand_sep
= SEP_1
;
319 rs
->rand_type
= TYPE_2
;
320 rs
->rand_deg
= DEG_2
;
321 rs
->rand_sep
= SEP_2
;
325 rs
->rand_type
= TYPE_3
;
326 rs
->rand_deg
= DEG_3
;
327 rs
->rand_sep
= SEP_3
;
330 rs
->rand_type
= TYPE_4
;
331 rs
->rand_deg
= DEG_4
;
332 rs
->rand_sep
= SEP_4
;
337 rs
->state
= &( ( (long *)arg_state
)[1] ); /* first location */
338 rs
->end_ptr
= &rs
->state
[ rs
->rand_deg
]; /* must set end_ptr before srandom */
340 if( rs
->rand_type
== TYPE_0
) rs
->state
[ -1 ] = rs
->rand_type
;
341 else rs
->state
[ -1 ] = MAX_TYPES
*(rs
->rptr
- rs
->state
) + rs
->rand_type
;
349 * Restore the state from the given state array.
350 * Note: it is important that we also remember the locations of the pointers
351 * in the current state information, and restore the locations of the pointers
352 * from the old state information. This is done by multiplexing the pointer
353 * location into the zeroeth word of the state information.
354 * Note that due to the order in which things are done, it is OK to call
355 * setstate() with the same state as the current state.
356 * Returns a pointer to the old state information.
359 char *setstate(char *arg_state
)
361 struct random_state
*rs
;
362 register long *new_state
;
367 if (!(rs
= get_random_state()) || arg_state
== NULL
)
370 new_state
= (long *)arg_state
;
371 type
= new_state
[0]%MAX_TYPES
;
372 rear
= new_state
[0]/MAX_TYPES
;
373 ostate
= (char *)(&rs
->state
[-1]);
376 if (rs
->rand_type
== TYPE_0
) rs
->state
[-1] = rs
->rand_type
;
377 else rs
->state
[ -1 ] = MAX_TYPES
*(rs
->rptr
- rs
->state
) + rs
->rand_type
;
386 rs
->rand_type
= type
;
387 rs
->rand_deg
= rs
->degrees
[type
];
388 rs
->rand_sep
= rs
->seps
[type
];
391 rs
->state
= &new_state
[1];
392 if (rs
->rand_type
!= TYPE_0
)
394 rs
->rptr
= &rs
->state
[rear
];
395 rs
->fptr
= &rs
->state
[(rear
+ rs
->rand_sep
)%rs
->rand_deg
];
397 rs
->end_ptr
= &rs
->state
[rs
->rand_deg
]; /* set end_ptr too */
406 * If we are using the trivial TYPE_0 R.N.G., just do the old linear
407 * congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
408 * same in all ther other cases due to all the global variables that have been
409 * set up. The basic operation is to add the number at the rear pointer into
410 * the one at the front pointer. Then both pointers are advanced to the next
411 * location cyclically in the table. The value returned is the sum generated,
412 * reduced to 31 bits by throwing away the "least random" low bit.
413 * Note: the code takes advantage of the fact that both the front and
414 * rear pointers can't wrap on the same call by not testing the rear
415 * pointer if the front one has wrapped.
416 * Returns a 31-bit random number.
422 struct random_state
*rs
;
425 if (!(rs
= get_random_state()))
428 if (rs
->rand_type
== TYPE_0
)
430 i
= rs
->state
[0] = (rs
->state
[0]*1103515245 + 12345)&0x7fffffff;
434 *rs
->fptr
+= *rs
->rptr
;
435 i
= (*rs
->fptr
>> 1)&0x7fffffff; /* chucking least random bit */
436 if (++rs
->fptr
>= rs
->end_ptr
)
438 rs
->fptr
= rs
->state
;
443 if (++rs
->rptr
>= rs
->end_ptr
) rs
->rptr
= rs
->state
;