2 * Ported from GNU libc to Windows by Ron Koenderink, 2007
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53 * This is derived from the Berkeley source:
54 * @(#)random.c 5.5 (Berkeley) 7/6/88
55 * It was reworked for the GNU C Library by Roland McGrath.
56 * Rewritten to be reentrant by Ulrich Drepper, 1995
65 /* An improved random number generation package. In addition to the standard
66 rand()/srand() like interface, this package also has a special state info
67 interface. The initstate() routine is called with a seed, an array of
68 bytes, and a count of how many bytes are being passed in; this array is
69 then initialized to contain information for random number generation with
70 that much state information. Good sizes for the amount of state
71 information are 32, 64, 128, and 256 bytes. The state can be switched by
72 calling the setstate() function with the same array as was initialized
73 with initstate(). By default, the package runs with 128 bytes of state
74 information and generates far better random numbers than a linear
75 congruential generator. If the amount of state information is less than
76 32 bytes, a simple linear congruential R.N.G. is used. Internally, the
77 state information is treated as an array of longs; the zeroth element of
78 the array is the type of R.N.G. being used (small integer); the remainder
79 of the array is the state information for the R.N.G. Thus, 32 bytes of
80 state information will give 7 longs worth of state information, which will
81 allow a degree seven polynomial. (Note: The zeroth word of state
82 information also has some other information stored in it; see setstate
83 for details). The random number generation technique is a linear feedback
84 shift register approach, employing trinomials (since there are fewer terms
85 to sum up that way). In this approach, the least significant bit of all
86 the numbers in the state table will act as a linear feedback shift register,
87 and will have period 2^deg - 1 (where deg is the degree of the polynomial
88 being used, assuming that the polynomial is irreducible and primitive).
89 The higher order bits will have longer periods, since their values are
90 also influenced by pseudo-random carries out of the lower bits. The
91 total period of the generator is approximately deg*(2**deg - 1); thus
92 doubling the amount of state information has a vast influence on the
93 period of the generator. Note: The deg*(2**deg - 1) is an approximation
94 only good for large deg, when the period of the shift register is the
95 dominant factor. With deg equal to seven, the period is actually much
96 longer than the 7*(2**7 - 1) predicted by this formula. */
100 /* For each of the currently supported random number generators, we have a
101 break value on the amount of state information (you need at least this many
102 bytes of state info to support this random number generator), a degree for
103 the polynomial (actually a trinomial) that the R.N.G. is based on, and
104 separation between the two lower order coefficients of the trinomial. */
106 /* Linear congruential. */
112 /* x**7 + x**3 + 1. */
124 /* x**31 + x**3 + 1. */
137 /* Array versions of the above information to make code run faster.
138 Relies on fact that TYPE_i == i. */
140 #define MAX_TYPES 5 /* Max number of types above. */
142 struct random_poly_info
145 int degrees[MAX_TYPES];
148 static const struct random_poly_info random_poly_info =
150 { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
151 { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
157 /* Initialize the random number generator based on the given seed. If the
158 type is the trivial no-state-information type, just remember the seed.
159 Otherwise, initializes state[] based on the given "seed" via a linear
160 congruential generator. Then, the pointers are set to known locations
161 that are exactly rand_sep places apart. Lastly, it cycles the state
162 information a given number of times to get rid of any initial dependencies
163 introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
164 for default usage relies on values produced by this routine. */
166 __srandom_r (seed, buf)
168 struct random_data *buf;
179 type = buf->rand_type;
180 if ((unsigned int) type >= MAX_TYPES)
184 /* We must make sure the seed is not 0. Take arbitrarily 1 in this case. */
194 for (i = 1; i < kc; ++i)
197 state[i] = (16807 * state[i - 1]) % 2147483647;
198 but avoids overflowing 31 bits. */
199 long int hi = word / 127773;
200 long int lo = word % 127773;
201 word = 16807 * lo - 2836 * hi;
207 buf->fptr = &state[buf->rand_sep];
208 buf->rptr = &state[0];
213 (void) __random_r (buf, &discard);
223 weak_alias (__srandom_r, srandom_r)
225 /* Initialize the state information in the given array of N bytes for
226 future random number generation. Based on the number of bytes we
227 are given, and the break values for the different R.N.G.'s, we choose
228 the best (largest) one we can and set things up for it. srandom is
229 then called to initialize the state information. Note that on return
230 from srandom, we set state[-1] to be the type multiplexed with the current
231 value of the rear pointer; this is so successive calls to initstate won't
232 lose this information and will be able to restart with setstate.
233 Note: The first thing we do is save the current state, if any, just like
234 setstate so that it doesn't matter when initstate is called.
235 Returns a pointer to the old state. */
237 __initstate_r (seed, arg_state, n, buf)
241 struct random_data *buf;
252 old_state = buf->state;
253 if (old_state != NULL)
255 int old_type = buf->rand_type;
256 if (old_type == TYPE_0)
257 old_state[-1] = TYPE_0;
259 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
263 type = n < BREAK_4 ? TYPE_3 : TYPE_4;
264 else if (n < BREAK_1)
268 __set_errno (EINVAL);
274 type = n < BREAK_2 ? TYPE_1 : TYPE_2;
276 degree = random_poly_info.degrees[type];
277 separation = random_poly_info.seps[type];
279 buf->rand_type = type;
280 buf->rand_sep = separation;
281 buf->rand_deg = degree;
282 state = &((int32_t *) arg_state)[1]; /* First location. */
283 /* Must set END_PTR before srandom. */
284 buf->end_ptr = &state[degree];
288 __srandom_r (seed, buf);
292 state[-1] = (buf->rptr - state) * MAX_TYPES + type;
297 __set_errno (EINVAL);
301 weak_alias (__initstate_r, initstate_r)
303 /* Restore the state from the given state array.
304 Note: It is important that we also remember the locations of the pointers
305 in the current state information, and restore the locations of the pointers
306 from the old state information. This is done by multiplexing the pointer
307 location into the zeroth word of the state information. Note that due
308 to the order in which things are done, it is OK to call setstate with the
309 same state as the current state
310 Returns a pointer to the old state information. */
312 __setstate_r (arg_state, buf)
314 struct random_data *buf;
316 int32_t *new_state = 1 + (int32_t *) arg_state;
323 if (arg_state == NULL || buf == NULL)
326 old_type = buf->rand_type;
327 old_state = buf->state;
328 if (old_type == TYPE_0)
329 old_state[-1] = TYPE_0;
331 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
333 type = new_state[-1] % MAX_TYPES;
334 if (type < TYPE_0 || type > TYPE_4)
337 buf->rand_deg = degree = random_poly_info.degrees[type];
338 buf->rand_sep = separation = random_poly_info.seps[type];
339 buf->rand_type = type;
343 int rear = new_state[-1] / MAX_TYPES;
344 buf->rptr = &new_state[rear];
345 buf->fptr = &new_state[(rear + separation) % degree];
347 buf->state = new_state;
348 /* Set end_ptr too. */
349 buf->end_ptr = &new_state[degree];
354 __set_errno (EINVAL);
358 weak_alias (__setstate_r, setstate_r)
360 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
361 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
362 same in all the other cases due to all the global variables that have been
363 set up. The basic operation is to add the number at the rear pointer into
364 the one at the front pointer. Then both pointers are advanced to the next
365 location cyclically in the table. The value returned is the sum generated,
366 reduced to 31 bits by throwing away the "least random" low bit.
367 Note: The code takes advantage of the fact that both the front and
368 rear pointers can't wrap on the same call by not testing the rear
369 pointer if the front one has wrapped. Returns a 31-bit random number. */
372 __random_r (buf, result)
373 struct random_data *buf;
378 if (buf == NULL || result == NULL)
383 if (buf->rand_type == TYPE_0)
385 int32_t val = state[0];
386 val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
392 int32_t *fptr = buf->fptr;
393 int32_t *rptr = buf->rptr;
394 int32_t *end_ptr = buf->end_ptr;
397 val = *fptr += *rptr;
398 /* Chucking least random bit. */
399 *result = (val >> 1) & 0x7fffffff;
418 __set_errno (EINVAL);
422 weak_alias (__random_r, random_r)