2 * Copyright (c) 1983 Regents of the University of California.
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.
19 * This is derived from the Berkeley source:
20 * @(#)random.c 5.5 (Berkeley) 7/6/88
21 * It was reworked for the GNU C Library by Roland McGrath.
22 * Rewritten to be reentrant by Ulrich Drepper, 1995
33 /* An improved random number generation package. In addition to the standard
34 rand()/srand() like interface, this package also has a special state info
35 interface. The initstate() routine is called with a seed, an array of
36 bytes, and a count of how many bytes are being passed in; this array is
37 then initialized to contain information for random number generation with
38 that much state information. Good sizes for the amount of state
39 information are 32, 64, 128, and 256 bytes. The state can be switched by
40 calling the setstate() function with the same array as was initialized
41 with initstate(). By default, the package runs with 128 bytes of state
42 information and generates far better random numbers than a linear
43 congruential generator. If the amount of state information is less than
44 32 bytes, a simple linear congruential R.N.G. is used. Internally, the
45 state information is treated as an array of longs; the zeroth element of
46 the array is the type of R.N.G. being used (small integer); the remainder
47 of the array is the state information for the R.N.G. Thus, 32 bytes of
48 state information will give 7 longs worth of state information, which will
49 allow a degree seven polynomial. (Note: The zeroth word of state
50 information also has some other information stored in it; see setstate
51 for details). The random number generation technique is a linear feedback
52 shift register approach, employing trinomials (since there are fewer terms
53 to sum up that way). In this approach, the least significant bit of all
54 the numbers in the state table will act as a linear feedback shift register,
55 and will have period 2^deg - 1 (where deg is the degree of the polynomial
56 being used, assuming that the polynomial is irreducible and primitive).
57 The higher order bits will have longer periods, since their values are
58 also influenced by pseudo-random carries out of the lower bits. The
59 total period of the generator is approximately deg*(2**deg - 1); thus
60 doubling the amount of state information has a vast influence on the
61 period of the generator. Note: The deg*(2**deg - 1) is an approximation
62 only good for large deg, when the period of the shift register is the
63 dominant factor. With deg equal to seven, the period is actually much
64 longer than the 7*(2**7 - 1) predicted by this formula. */
68 /* For each of the currently supported random number generators, we have a
69 break value on the amount of state information (you need at least this many
70 bytes of state info to support this random number generator), a degree for
71 the polynomial (actually a trinomial) that the R.N.G. is based on, and
72 separation between the two lower order coefficients of the trinomial. */
74 /* Linear congruential. */
80 /* x**7 + x**3 + 1. */
92 /* x**31 + x**3 + 1. */
105 /* Array versions of the above information to make code run faster.
106 Relies on fact that TYPE_i == i. */
108 #define MAX_TYPES 5 /* Max number of types above. */
110 struct random_poly_info
113 int degrees[MAX_TYPES];
116 static const struct random_poly_info random_poly_info =
118 { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
119 { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
125 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
126 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
127 same in all the other cases due to all the global variables that have been
128 set up. The basic operation is to add the number at the rear pointer into
129 the one at the front pointer. Then both pointers are advanced to the next
130 location cyclically in the table. The value returned is the sum generated,
131 reduced to 31 bits by throwing away the "least random" low bit.
132 Note: The code takes advantage of the fact that both the front and
133 rear pointers can't wrap on the same call by not testing the rear
134 pointer if the front one has wrapped. Returns a 31-bit random number. */
136 libc_hidden_proto(random_r)
137 int random_r(struct random_data *buf, int32_t *result)
141 if (buf == NULL || result == NULL)
146 if (buf->rand_type == TYPE_0)
148 int32_t val = state[0];
149 val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
155 int32_t *fptr = buf->fptr;
156 int32_t *rptr = buf->rptr;
157 int32_t *end_ptr = buf->end_ptr;
160 val = *fptr += *rptr;
161 /* Chucking least random bit. */
162 *result = (val >> 1) & 0x7fffffff;
181 __set_errno (EINVAL);
184 libc_hidden_def(random_r)
186 /* Initialize the random number generator based on the given seed. If the
187 type is the trivial no-state-information type, just remember the seed.
188 Otherwise, initializes state[] based on the given "seed" via a linear
189 congruential generator. Then, the pointers are set to known locations
190 that are exactly rand_sep places apart. Lastly, it cycles the state
191 information a given number of times to get rid of any initial dependencies
192 introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
193 for default usage relies on values produced by this routine. */
194 libc_hidden_proto(srandom_r)
195 int srandom_r (unsigned int seed, struct random_data *buf)
206 type = buf->rand_type;
207 if ((unsigned int) type >= MAX_TYPES)
211 /* We must make sure the seed is not 0. Take arbitrarily 1 in this case. */
221 for (i = 1; i < kc; ++i)
224 state[i] = (16807 * state[i - 1]) % 2147483647;
225 but avoids overflowing 31 bits. */
226 long int hi = word / 127773;
227 long int lo = word % 127773;
228 word = 16807 * lo - 2836 * hi;
234 buf->fptr = &state[buf->rand_sep];
235 buf->rptr = &state[0];
240 (void) random_r (buf, &discard);
249 libc_hidden_def(srandom_r)
251 /* Initialize the state information in the given array of N bytes for
252 future random number generation. Based on the number of bytes we
253 are given, and the break values for the different R.N.G.'s, we choose
254 the best (largest) one we can and set things up for it. srandom is
255 then called to initialize the state information. Note that on return
256 from srandom, we set state[-1] to be the type multiplexed with the current
257 value of the rear pointer; this is so successive calls to initstate won't
258 lose this information and will be able to restart with setstate.
259 Note: The first thing we do is save the current state, if any, just like
260 setstate so that it doesn't matter when initstate is called.
261 Returns a pointer to the old state. */
262 libc_hidden_proto(initstate_r)
263 int initstate_r (unsigned int seed, char *arg_state, size_t n, struct random_data *buf)
274 type = n < BREAK_4 ? TYPE_3 : TYPE_4;
275 else if (n < BREAK_1)
279 __set_errno (EINVAL);
285 type = n < BREAK_2 ? TYPE_1 : TYPE_2;
287 degree = random_poly_info.degrees[type];
288 separation = random_poly_info.seps[type];
290 buf->rand_type = type;
291 buf->rand_sep = separation;
292 buf->rand_deg = degree;
293 state = &((int32_t *) arg_state)[1]; /* First location. */
294 /* Must set END_PTR before srandom. */
295 buf->end_ptr = &state[degree];
299 srandom_r (seed, buf);
303 state[-1] = (buf->rptr - state) * MAX_TYPES + type;
308 __set_errno (EINVAL);
311 libc_hidden_def(initstate_r)
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 zeroth 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 libc_hidden_proto(setstate_r)
322 int setstate_r (char *arg_state, struct random_data *buf)
324 int32_t *new_state = 1 + (int32_t *) arg_state;
331 if (arg_state == NULL || buf == NULL)
334 old_type = buf->rand_type;
335 old_state = buf->state;
336 if (old_type == TYPE_0)
337 old_state[-1] = TYPE_0;
339 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
341 type = new_state[-1] % MAX_TYPES;
342 if (type < TYPE_0 || type > TYPE_4)
345 buf->rand_deg = degree = random_poly_info.degrees[type];
346 buf->rand_sep = separation = random_poly_info.seps[type];
347 buf->rand_type = type;
351 int rear = new_state[-1] / MAX_TYPES;
352 buf->rptr = &new_state[rear];
353 buf->fptr = &new_state[(rear + separation) % degree];
355 buf->state = new_state;
356 /* Set end_ptr too. */
357 buf->end_ptr = &new_state[degree];
362 __set_errno (EINVAL);
365 libc_hidden_def(setstate_r)