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[/] [openrisc/] [trunk/] [gnu-src/] [gcc-4.5.1/] [libiberty/] [random.c] - Blame information for rev 274

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1 274 jeremybenn
/*
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 [rescinded 22 July 1999]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
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 * It was reworked for the GNU C Library by Roland McGrath.
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 */
36
 
37
/*
38
 
39
@deftypefn Supplement {long int} random (void)
40
@deftypefnx Supplement void srandom (unsigned int @var{seed})
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@deftypefnx Supplement void* initstate (unsigned int @var{seed}, void *@var{arg_state}, unsigned long @var{n})
42
@deftypefnx Supplement void* setstate (void *@var{arg_state})
43
 
44
Random number functions.  @code{random} returns a random number in the
45
range 0 to @code{LONG_MAX}.  @code{srandom} initializes the random
46
number generator to some starting point determined by @var{seed}
47
(else, the values returned by @code{random} are always the same for each
48
run of the program).  @code{initstate} and @code{setstate} allow fine-grained
49
control over the state of the random number generator.
50
 
51
@end deftypefn
52
 
53
*/
54
 
55
#include <errno.h>
56
 
57
#if 0
58
 
59
#include <ansidecl.h>
60
#include <limits.h>
61
#include <stddef.h>
62
#include <stdlib.h>
63
 
64
#else
65
 
66
#define ULONG_MAX  ((unsigned long)(~0L))     /* 0xFFFFFFFF for 32-bits */
67
#define LONG_MAX   ((long)(ULONG_MAX >> 1))   /* 0x7FFFFFFF for 32-bits*/
68
 
69
#ifdef __STDC__
70
#  define PTR void *
71
#  ifndef NULL
72
#    define NULL (void *) 0
73
#  endif
74
#else
75
#  define PTR char *
76
#  ifndef NULL
77
#    define NULL (void *) 0
78
#  endif
79
#endif
80
 
81
#endif
82
 
83
long int random (void);
84
 
85
/* An improved random number generation package.  In addition to the standard
86
   rand()/srand() like interface, this package also has a special state info
87
   interface.  The initstate() routine is called with a seed, an array of
88
   bytes, and a count of how many bytes are being passed in; this array is
89
   then initialized to contain information for random number generation with
90
   that much state information.  Good sizes for the amount of state
91
   information are 32, 64, 128, and 256 bytes.  The state can be switched by
92
   calling the setstate() function with the same array as was initiallized
93
   with initstate().  By default, the package runs with 128 bytes of state
94
   information and generates far better random numbers than a linear
95
   congruential generator.  If the amount of state information is less than
96
   32 bytes, a simple linear congruential R.N.G. is used.  Internally, the
97
   state information is treated as an array of longs; the zeroeth element of
98
   the array is the type of R.N.G. being used (small integer); the remainder
99
   of the array is the state information for the R.N.G.  Thus, 32 bytes of
100
   state information will give 7 longs worth of state information, which will
101
   allow a degree seven polynomial.  (Note: The zeroeth word of state
102
   information also has some other information stored in it; see setstate
103
   for details).  The random number generation technique is a linear feedback
104
   shift register approach, employing trinomials (since there are fewer terms
105
   to sum up that way).  In this approach, the least significant bit of all
106
   the numbers in the state table will act as a linear feedback shift register,
107
   and will have period 2^deg - 1 (where deg is the degree of the polynomial
108
   being used, assuming that the polynomial is irreducible and primitive).
109
   The higher order bits will have longer periods, since their values are
110
   also influenced by pseudo-random carries out of the lower bits.  The
111
   total period of the generator is approximately deg*(2**deg - 1); thus
112
   doubling the amount of state information has a vast influence on the
113
   period of the generator.  Note: The deg*(2**deg - 1) is an approximation
114
   only good for large deg, when the period of the shift register is the
115
   dominant factor.  With deg equal to seven, the period is actually much
116
   longer than the 7*(2**7 - 1) predicted by this formula.  */
117
 
118
 
119
 
120
/* For each of the currently supported random number generators, we have a
121
   break value on the amount of state information (you need at least thi
122
   bytes of state info to support this random number generator), a degree for
123
   the polynomial (actually a trinomial) that the R.N.G. is based on, and
124
   separation between the two lower order coefficients of the trinomial.  */
125
 
126
/* Linear congruential.  */
127
#define TYPE_0          0
128
#define BREAK_0         8
129
#define DEG_0           0
130
#define SEP_0           0
131
 
132
/* x**7 + x**3 + 1.  */
133
#define TYPE_1          1
134
#define BREAK_1         32
135
#define DEG_1           7
136
#define SEP_1           3
137
 
138
/* x**15 + x + 1.  */
139
#define TYPE_2          2
140
#define BREAK_2         64
141
#define DEG_2           15
142
#define SEP_2           1
143
 
144
/* x**31 + x**3 + 1.  */
145
#define TYPE_3          3
146
#define BREAK_3         128
147
#define DEG_3           31
148
#define SEP_3           3
149
 
150
/* x**63 + x + 1.  */
151
#define TYPE_4          4
152
#define BREAK_4         256
153
#define DEG_4           63
154
#define SEP_4           1
155
 
156
 
157
/* Array versions of the above information to make code run faster.
158
   Relies on fact that TYPE_i == i.  */
159
 
160
#define MAX_TYPES       5       /* Max number of types above.  */
161
 
162
static int degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
163
static int seps[MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
164
 
165
 
166
 
167
/* Initially, everything is set up as if from:
168
        initstate(1, randtbl, 128);
169
   Note that this initialization takes advantage of the fact that srandom
170
   advances the front and rear pointers 10*rand_deg times, and hence the
171
   rear pointer which starts at 0 will also end up at zero; thus the zeroeth
172
   element of the state information, which contains info about the current
173
   position of the rear pointer is just
174
        (MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3.  */
175
 
176
static long int randtbl[DEG_3 + 1] =
177
  { TYPE_3,
178
      0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342,
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      0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb,
180
      0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
181
      0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86,
182
      0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7,
183
      0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
184
      0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b,
185
      0xf5ad9d0e, 0x8999220b, 0x27fb47b9
186
    };
187
 
188
/* FPTR and RPTR are two pointers into the state info, a front and a rear
189
   pointer.  These two pointers are always rand_sep places aparts, as they
190
   cycle through the state information.  (Yes, this does mean we could get
191
   away with just one pointer, but the code for random is more efficient
192
   this way).  The pointers are left positioned as they would be from the call:
193
        initstate(1, randtbl, 128);
194
   (The position of the rear pointer, rptr, is really 0 (as explained above
195
   in the initialization of randtbl) because the state table pointer is set
196
   to point to randtbl[1] (as explained below).)  */
197
 
198
static long int *fptr = &randtbl[SEP_3 + 1];
199
static long int *rptr = &randtbl[1];
200
 
201
 
202
 
203
/* The following things are the pointer to the state information table,
204
   the type of the current generator, the degree of the current polynomial
205
   being used, and the separation between the two pointers.
206
   Note that for efficiency of random, we remember the first location of
207
   the state information, not the zeroeth.  Hence it is valid to access
208
   state[-1], which is used to store the type of the R.N.G.
209
   Also, we remember the last location, since this is more efficient than
210
   indexing every time to find the address of the last element to see if
211
   the front and rear pointers have wrapped.  */
212
 
213
static long int *state = &randtbl[1];
214
 
215
static int rand_type = TYPE_3;
216
static int rand_deg = DEG_3;
217
static int rand_sep = SEP_3;
218
 
219
static long int *end_ptr = &randtbl[sizeof(randtbl) / sizeof(randtbl[0])];
220
 
221
/* Initialize the random number generator based on the given seed.  If the
222
   type is the trivial no-state-information type, just remember the seed.
223
   Otherwise, initializes state[] based on the given "seed" via a linear
224
   congruential generator.  Then, the pointers are set to known locations
225
   that are exactly rand_sep places apart.  Lastly, it cycles the state
226
   information a given number of times to get rid of any initial dependencies
227
   introduced by the L.C.R.N.G.  Note that the initialization of randtbl[]
228
   for default usage relies on values produced by this routine.  */
229
void
230
srandom (unsigned int x)
231
{
232
  state[0] = x;
233
  if (rand_type != TYPE_0)
234
    {
235
      register long int i;
236
      for (i = 1; i < rand_deg; ++i)
237
        state[i] = (1103515145 * state[i - 1]) + 12345;
238
      fptr = &state[rand_sep];
239
      rptr = &state[0];
240
      for (i = 0; i < 10 * rand_deg; ++i)
241
        random();
242
    }
243
}
244
 
245
/* Initialize the state information in the given array of N bytes for
246
   future random number generation.  Based on the number of bytes we
247
   are given, and the break values for the different R.N.G.'s, we choose
248
   the best (largest) one we can and set things up for it.  srandom is
249
   then called to initialize the state information.  Note that on return
250
   from srandom, we set state[-1] to be the type multiplexed with the current
251
   value of the rear pointer; this is so successive calls to initstate won't
252
   lose this information and will be able to restart with setstate.
253
   Note: The first thing we do is save the current state, if any, just like
254
   setstate so that it doesn't matter when initstate is called.
255
   Returns a pointer to the old state.  */
256
PTR
257
initstate (unsigned int seed, PTR arg_state, unsigned long n)
258
{
259
  PTR ostate = (PTR) &state[-1];
260
 
261
  if (rand_type == TYPE_0)
262
    state[-1] = rand_type;
263
  else
264
    state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
265
  if (n < BREAK_1)
266
    {
267
      if (n < BREAK_0)
268
        {
269
          errno = EINVAL;
270
          return NULL;
271
        }
272
      rand_type = TYPE_0;
273
      rand_deg = DEG_0;
274
      rand_sep = SEP_0;
275
    }
276
  else if (n < BREAK_2)
277
    {
278
      rand_type = TYPE_1;
279
      rand_deg = DEG_1;
280
      rand_sep = SEP_1;
281
    }
282
  else if (n < BREAK_3)
283
    {
284
      rand_type = TYPE_2;
285
      rand_deg = DEG_2;
286
      rand_sep = SEP_2;
287
    }
288
  else if (n < BREAK_4)
289
    {
290
      rand_type = TYPE_3;
291
      rand_deg = DEG_3;
292
      rand_sep = SEP_3;
293
    }
294
  else
295
    {
296
      rand_type = TYPE_4;
297
      rand_deg = DEG_4;
298
      rand_sep = SEP_4;
299
    }
300
 
301
  state = &((long int *) arg_state)[1]; /* First location.  */
302
  /* Must set END_PTR before srandom.  */
303
  end_ptr = &state[rand_deg];
304
  srandom(seed);
305
  if (rand_type == TYPE_0)
306
    state[-1] = rand_type;
307
  else
308
    state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
309
 
310
  return ostate;
311
}
312
 
313
/* Restore the state from the given state array.
314
   Note: It is important that we also remember the locations of the pointers
315
   in the current state information, and restore the locations of the pointers
316
   from the old state information.  This is done by multiplexing the pointer
317
   location into the zeroeth word of the state information. Note that due
318
   to the order in which things are done, it is OK to call setstate with the
319
   same state as the current state
320
   Returns a pointer to the old state information.  */
321
 
322
PTR
323
setstate (PTR arg_state)
324
{
325
  register long int *new_state = (long int *) arg_state;
326
  register int type = new_state[0] % MAX_TYPES;
327
  register int rear = new_state[0] / MAX_TYPES;
328
  PTR ostate = (PTR) &state[-1];
329
 
330
  if (rand_type == TYPE_0)
331
    state[-1] = rand_type;
332
  else
333
    state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
334
 
335
  switch (type)
336
    {
337
    case TYPE_0:
338
    case TYPE_1:
339
    case TYPE_2:
340
    case TYPE_3:
341
    case TYPE_4:
342
      rand_type = type;
343
      rand_deg = degrees[type];
344
      rand_sep = seps[type];
345
      break;
346
    default:
347
      /* State info munged.  */
348
      errno = EINVAL;
349
      return NULL;
350
    }
351
 
352
  state = &new_state[1];
353
  if (rand_type != TYPE_0)
354
    {
355
      rptr = &state[rear];
356
      fptr = &state[(rear + rand_sep) % rand_deg];
357
    }
358
  /* Set end_ptr too.  */
359
  end_ptr = &state[rand_deg];
360
 
361
  return ostate;
362
}
363
 
364
/* If we are using the trivial TYPE_0 R.N.G., just do the old linear
365
   congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
366
   same in all ther other cases due to all the global variables that have been
367
   set up.  The basic operation is to add the number at the rear pointer into
368
   the one at the front pointer.  Then both pointers are advanced to the next
369
   location cyclically in the table.  The value returned is the sum generated,
370
   reduced to 31 bits by throwing away the "least random" low bit.
371
   Note: The code takes advantage of the fact that both the front and
372
   rear pointers can't wrap on the same call by not testing the rear
373
   pointer if the front one has wrapped.  Returns a 31-bit random number.  */
374
 
375
long int
376
random (void)
377
{
378
  if (rand_type == TYPE_0)
379
    {
380
      state[0] = ((state[0] * 1103515245) + 12345) & LONG_MAX;
381
      return state[0];
382
    }
383
  else
384
    {
385
      long int i;
386
      *fptr += *rptr;
387
      /* Chucking least random bit.  */
388
      i = (*fptr >> 1) & LONG_MAX;
389
      ++fptr;
390
      if (fptr >= end_ptr)
391
        {
392
          fptr = state;
393
          ++rptr;
394
        }
395
      else
396
        {
397
          ++rptr;
398
          if (rptr >= end_ptr)
399
            rptr = state;
400
        }
401
      return i;
402
    }
403
}

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