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1 106 markom
/*
2
 * Copyright (c) 1983 Regents of the University of California.
3
 * All rights reserved.
4
 *
5
 * Redistribution and use in source and binary forms, with or without
6
 * modification, are permitted provided that the following conditions
7
 * are met:
8
 * 1. Redistributions of source code must retain the above copyright
9
 *    notice, this list of conditions and the following disclaimer.
10
 * 2. Redistributions in binary form must reproduce the above copyright
11
 *    notice, this list of conditions and the following disclaimer in the
12
 *    documentation and/or other materials provided with the distribution.
13
 * 3. [rescinded 22 July 1999]
14
 * 4. Neither the name of the University nor the names of its contributors
15
 *    may be used to endorse or promote products derived from this software
16
 *    without specific prior written permission.
17
 *
18
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
19
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
22
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28
 * SUCH DAMAGE.
29
 */
30
 
31
/*
32
 * This is derived from the Berkeley source:
33
 *      @(#)random.c    5.5 (Berkeley) 7/6/88
34
 * It was reworked for the GNU C Library by Roland McGrath.
35
 */
36
 
37
#include <errno.h>
38
 
39
#if 0
40
 
41
#include <ansidecl.h>
42
#include <limits.h>
43
#include <stddef.h>
44
#include <stdlib.h>
45
 
46
#else
47
 
48
#define ULONG_MAX  ((unsigned long)(~0L))     /* 0xFFFFFFFF for 32-bits */
49
#define LONG_MAX   ((long)(ULONG_MAX >> 1))   /* 0x7FFFFFFF for 32-bits*/
50
 
51
#ifdef __STDC__
52
#  define PTR void *
53
#  ifndef NULL
54
#    define NULL (void *) 0
55
#  endif
56
#else
57
#  define PTR char *
58
#  ifndef NULL
59
#    define NULL (void *) 0
60
#  endif
61
#endif
62
 
63
#endif
64
 
65
long int random ();
66
 
67
/* An improved random number generation package.  In addition to the standard
68
   rand()/srand() like interface, this package also has a special state info
69
   interface.  The initstate() routine is called with a seed, an array of
70
   bytes, and a count of how many bytes are being passed in; this array is
71
   then initialized to contain information for random number generation with
72
   that much state information.  Good sizes for the amount of state
73
   information are 32, 64, 128, and 256 bytes.  The state can be switched by
74
   calling the setstate() function with the same array as was initiallized
75
   with initstate().  By default, the package runs with 128 bytes of state
76
   information and generates far better random numbers than a linear
77
   congruential generator.  If the amount of state information is less than
78
   32 bytes, a simple linear congruential R.N.G. is used.  Internally, the
79
   state information is treated as an array of longs; the zeroeth element of
80
   the array is the type of R.N.G. being used (small integer); the remainder
81
   of the array is the state information for the R.N.G.  Thus, 32 bytes of
82
   state information will give 7 longs worth of state information, which will
83
   allow a degree seven polynomial.  (Note: The zeroeth word of state
84
   information also has some other information stored in it; see setstate
85
   for details).  The random number generation technique is a linear feedback
86
   shift register approach, employing trinomials (since there are fewer terms
87
   to sum up that way).  In this approach, the least significant bit of all
88
   the numbers in the state table will act as a linear feedback shift register,
89
   and will have period 2^deg - 1 (where deg is the degree of the polynomial
90
   being used, assuming that the polynomial is irreducible and primitive).
91
   The higher order bits will have longer periods, since their values are
92
   also influenced by pseudo-random carries out of the lower bits.  The
93
   total period of the generator is approximately deg*(2**deg - 1); thus
94
   doubling the amount of state information has a vast influence on the
95
   period of the generator.  Note: The deg*(2**deg - 1) is an approximation
96
   only good for large deg, when the period of the shift register is the
97
   dominant factor.  With deg equal to seven, the period is actually much
98
   longer than the 7*(2**7 - 1) predicted by this formula.  */
99
 
100
 
101
 
102
/* For each of the currently supported random number generators, we have a
103
   break value on the amount of state information (you need at least thi
104
   bytes of state info to support this random number generator), a degree for
105
   the polynomial (actually a trinomial) that the R.N.G. is based on, and
106
   separation between the two lower order coefficients of the trinomial.  */
107
 
108
/* Linear congruential.  */
109
#define TYPE_0          0
110
#define BREAK_0         8
111
#define DEG_0           0
112
#define SEP_0           0
113
 
114
/* x**7 + x**3 + 1.  */
115
#define TYPE_1          1
116
#define BREAK_1         32
117
#define DEG_1           7
118
#define SEP_1           3
119
 
120
/* x**15 + x + 1.  */
121
#define TYPE_2          2
122
#define BREAK_2         64
123
#define DEG_2           15
124
#define SEP_2           1
125
 
126
/* x**31 + x**3 + 1.  */
127
#define TYPE_3          3
128
#define BREAK_3         128
129
#define DEG_3           31
130
#define SEP_3           3
131
 
132
/* x**63 + x + 1.  */
133
#define TYPE_4          4
134
#define BREAK_4         256
135
#define DEG_4           63
136
#define SEP_4           1
137
 
138
 
139
/* Array versions of the above information to make code run faster.
140
   Relies on fact that TYPE_i == i.  */
141
 
142
#define MAX_TYPES       5       /* Max number of types above.  */
143
 
144
static int degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
145
static int seps[MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
146
 
147
 
148
 
149
/* Initially, everything is set up as if from:
150
        initstate(1, randtbl, 128);
151
   Note that this initialization takes advantage of the fact that srandom
152
   advances the front and rear pointers 10*rand_deg times, and hence the
153
   rear pointer which starts at 0 will also end up at zero; thus the zeroeth
154
   element of the state information, which contains info about the current
155
   position of the rear pointer is just
156
        (MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3.  */
157
 
158
static long int randtbl[DEG_3 + 1] =
159
  { TYPE_3,
160
      0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342,
161
      0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb,
162
      0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
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      0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86,
164
      0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7,
165
      0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
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      0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b,
167
      0xf5ad9d0e, 0x8999220b, 0x27fb47b9
168
    };
169
 
170
/* FPTR and RPTR are two pointers into the state info, a front and a rear
171
   pointer.  These two pointers are always rand_sep places aparts, as they
172
   cycle through the state information.  (Yes, this does mean we could get
173
   away with just one pointer, but the code for random is more efficient
174
   this way).  The pointers are left positioned as they would be from the call:
175
        initstate(1, randtbl, 128);
176
   (The position of the rear pointer, rptr, is really 0 (as explained above
177
   in the initialization of randtbl) because the state table pointer is set
178
   to point to randtbl[1] (as explained below).)  */
179
 
180
static long int *fptr = &randtbl[SEP_3 + 1];
181
static long int *rptr = &randtbl[1];
182
 
183
 
184
 
185
/* The following things are the pointer to the state information table,
186
   the type of the current generator, the degree of the current polynomial
187
   being used, and the separation between the two pointers.
188
   Note that for efficiency of random, we remember the first location of
189
   the state information, not the zeroeth.  Hence it is valid to access
190
   state[-1], which is used to store the type of the R.N.G.
191
   Also, we remember the last location, since this is more efficient than
192
   indexing every time to find the address of the last element to see if
193
   the front and rear pointers have wrapped.  */
194
 
195
static long int *state = &randtbl[1];
196
 
197
static int rand_type = TYPE_3;
198
static int rand_deg = DEG_3;
199
static int rand_sep = SEP_3;
200
 
201
static long int *end_ptr = &randtbl[sizeof(randtbl) / sizeof(randtbl[0])];
202
 
203
/* Initialize the random number generator based on the given seed.  If the
204
   type is the trivial no-state-information type, just remember the seed.
205
   Otherwise, initializes state[] based on the given "seed" via a linear
206
   congruential generator.  Then, the pointers are set to known locations
207
   that are exactly rand_sep places apart.  Lastly, it cycles the state
208
   information a given number of times to get rid of any initial dependencies
209
   introduced by the L.C.R.N.G.  Note that the initialization of randtbl[]
210
   for default usage relies on values produced by this routine.  */
211
void
212
srandom (x)
213
  unsigned int x;
214
{
215
  state[0] = x;
216
  if (rand_type != TYPE_0)
217
    {
218
      register long int i;
219
      for (i = 1; i < rand_deg; ++i)
220
        state[i] = (1103515145 * state[i - 1]) + 12345;
221
      fptr = &state[rand_sep];
222
      rptr = &state[0];
223
      for (i = 0; i < 10 * rand_deg; ++i)
224
        random();
225
    }
226
}
227
 
228
/* Initialize the state information in the given array of N bytes for
229
   future random number generation.  Based on the number of bytes we
230
   are given, and the break values for the different R.N.G.'s, we choose
231
   the best (largest) one we can and set things up for it.  srandom is
232
   then called to initialize the state information.  Note that on return
233
   from srandom, we set state[-1] to be the type multiplexed with the current
234
   value of the rear pointer; this is so successive calls to initstate won't
235
   lose this information and will be able to restart with setstate.
236
   Note: The first thing we do is save the current state, if any, just like
237
   setstate so that it doesn't matter when initstate is called.
238
   Returns a pointer to the old state.  */
239
PTR
240
initstate (seed, arg_state, n)
241
  unsigned int seed;
242
  PTR arg_state;
243
  unsigned long n;
244
{
245
  PTR ostate = (PTR) &state[-1];
246
 
247
  if (rand_type == TYPE_0)
248
    state[-1] = rand_type;
249
  else
250
    state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
251
  if (n < BREAK_1)
252
    {
253
      if (n < BREAK_0)
254
        {
255
          errno = EINVAL;
256
          return NULL;
257
        }
258
      rand_type = TYPE_0;
259
      rand_deg = DEG_0;
260
      rand_sep = SEP_0;
261
    }
262
  else if (n < BREAK_2)
263
    {
264
      rand_type = TYPE_1;
265
      rand_deg = DEG_1;
266
      rand_sep = SEP_1;
267
    }
268
  else if (n < BREAK_3)
269
    {
270
      rand_type = TYPE_2;
271
      rand_deg = DEG_2;
272
      rand_sep = SEP_2;
273
    }
274
  else if (n < BREAK_4)
275
    {
276
      rand_type = TYPE_3;
277
      rand_deg = DEG_3;
278
      rand_sep = SEP_3;
279
    }
280
  else
281
    {
282
      rand_type = TYPE_4;
283
      rand_deg = DEG_4;
284
      rand_sep = SEP_4;
285
    }
286
 
287
  state = &((long int *) arg_state)[1]; /* First location.  */
288
  /* Must set END_PTR before srandom.  */
289
  end_ptr = &state[rand_deg];
290
  srandom(seed);
291
  if (rand_type == TYPE_0)
292
    state[-1] = rand_type;
293
  else
294
    state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
295
 
296
  return ostate;
297
}
298
 
299
/* Restore the state from the given state array.
300
   Note: It is important that we also remember the locations of the pointers
301
   in the current state information, and restore the locations of the pointers
302
   from the old state information.  This is done by multiplexing the pointer
303
   location into the zeroeth word of the state information. Note that due
304
   to the order in which things are done, it is OK to call setstate with the
305
   same state as the current state
306
   Returns a pointer to the old state information.  */
307
 
308
PTR
309
setstate (arg_state)
310
  PTR arg_state;
311
{
312
  register long int *new_state = (long int *) arg_state;
313
  register int type = new_state[0] % MAX_TYPES;
314
  register int rear = new_state[0] / MAX_TYPES;
315
  PTR ostate = (PTR) &state[-1];
316
 
317
  if (rand_type == TYPE_0)
318
    state[-1] = rand_type;
319
  else
320
    state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
321
 
322
  switch (type)
323
    {
324
    case TYPE_0:
325
    case TYPE_1:
326
    case TYPE_2:
327
    case TYPE_3:
328
    case TYPE_4:
329
      rand_type = type;
330
      rand_deg = degrees[type];
331
      rand_sep = seps[type];
332
      break;
333
    default:
334
      /* State info munged.  */
335
      errno = EINVAL;
336
      return NULL;
337
    }
338
 
339
  state = &new_state[1];
340
  if (rand_type != TYPE_0)
341
    {
342
      rptr = &state[rear];
343
      fptr = &state[(rear + rand_sep) % rand_deg];
344
    }
345
  /* Set end_ptr too.  */
346
  end_ptr = &state[rand_deg];
347
 
348
  return ostate;
349
}
350
 
351
/* If we are using the trivial TYPE_0 R.N.G., just do the old linear
352
   congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
353
   same in all ther other cases due to all the global variables that have been
354
   set up.  The basic operation is to add the number at the rear pointer into
355
   the one at the front pointer.  Then both pointers are advanced to the next
356
   location cyclically in the table.  The value returned is the sum generated,
357
   reduced to 31 bits by throwing away the "least random" low bit.
358
   Note: The code takes advantage of the fact that both the front and
359
   rear pointers can't wrap on the same call by not testing the rear
360
   pointer if the front one has wrapped.  Returns a 31-bit random number.  */
361
 
362
long int
363
random ()
364
{
365
  if (rand_type == TYPE_0)
366
    {
367
      state[0] = ((state[0] * 1103515245) + 12345) & LONG_MAX;
368
      return state[0];
369
    }
370
  else
371
    {
372
      long int i;
373
      *fptr += *rptr;
374
      /* Chucking least random bit.  */
375
      i = (*fptr >> 1) & LONG_MAX;
376
      ++fptr;
377
      if (fptr >= end_ptr)
378
        {
379
          fptr = state;
380
          ++rptr;
381
        }
382
      else
383
        {
384
          ++rptr;
385
          if (rptr >= end_ptr)
386
            rptr = state;
387
        }
388
      return i;
389
    }
390
}

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