2 * Ported from GNU libc to Windows by Ron Koenderink, 2007
5 /* Copyright (C) 1995 Free Software Foundation
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
12 The GNU C Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
17 You should have received a copy of the GNU Lesser General Public
18 License along with the GNU C Library; if not, write to the Free
19 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
23 * This is derived from the Berkeley source:
24 * @(#)random.c 5.5 (Berkeley) 7/6/88
25 * It was reworked for the GNU C Library by Roland McGrath.
26 * Rewritten to use reentrant functions by Ulrich Drepper, 1995.
30 Copyright (C) 1983 Regents of the University of California.
33 Redistribution and use in source and binary forms, with or without
34 modification, are permitted provided that the following conditions
37 1. Redistributions of source code must retain the above copyright
38 notice, this list of conditions and the following disclaimer.
39 2. Redistributions in binary form must reproduce the above copyright
40 notice, this list of conditions and the following disclaimer in the
41 documentation and/or other materials provided with the distribution.
42 4. Neither the name of the University nor the names of its contributors
43 may be used to endorse or promote products derived from this software
44 without specific prior written permission.
46 THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
47 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
48 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
49 ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
50 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
51 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
52 OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
53 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
54 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
55 OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
59 * Not available for empire use random.h
61 #include <bits/libc-lock.h>
70 /* An improved random number generation package. In addition to the standard
71 rand()/srand() like interface, this package also has a special state info
72 interface. The initstate() routine is called with a seed, an array of
73 bytes, and a count of how many bytes are being passed in; this array is
74 then initialized to contain information for random number generation with
75 that much state information. Good sizes for the amount of state
76 information are 32, 64, 128, and 256 bytes. The state can be switched by
77 calling the setstate() function with the same array as was initialized
78 with initstate(). By default, the package runs with 128 bytes of state
79 information and generates far better random numbers than a linear
80 congruential generator. If the amount of state information is less than
81 32 bytes, a simple linear congruential R.N.G. is used. Internally, the
82 state information is treated as an array of longs; the zeroth element of
83 the array is the type of R.N.G. being used (small integer); the remainder
84 of the array is the state information for the R.N.G. Thus, 32 bytes of
85 state information will give 7 longs worth of state information, which will
86 allow a degree seven polynomial. (Note: The zeroth word of state
87 information also has some other information stored in it; see setstate
88 for details). The random number generation technique is a linear feedback
89 shift register approach, employing trinomials (since there are fewer terms
90 to sum up that way). In this approach, the least significant bit of all
91 the numbers in the state table will act as a linear feedback shift register,
92 and will have period 2^deg - 1 (where deg is the degree of the polynomial
93 being used, assuming that the polynomial is irreducible and primitive).
94 The higher order bits will have longer periods, since their values are
95 also influenced by pseudo-random carries out of the lower bits. The
96 total period of the generator is approximately deg*(2**deg - 1); thus
97 doubling the amount of state information has a vast influence on the
98 period of the generator. Note: The deg*(2**deg - 1) is an approximation
99 only good for large deg, when the period of the shift register is the
100 dominant factor. With deg equal to seven, the period is actually much
101 longer than the 7*(2**7 - 1) predicted by this formula. */
105 /* For each of the currently supported random number generators, we have a
106 break value on the amount of state information (you need at least this many
107 bytes of state info to support this random number generator), a degree for
108 the polynomial (actually a trinomial) that the R.N.G. is based on, and
109 separation between the two lower order coefficients of the trinomial. */
111 /* Linear congruential. */
117 /* x**7 + x**3 + 1. */
129 /* x**31 + x**3 + 1. */
142 /* Array versions of the above information to make code run faster.
143 Relies on fact that TYPE_i == i. */
145 #define MAX_TYPES 5 /* Max number of types above. */
148 /* Initially, everything is set up as if from:
149 initstate(1, randtbl, 128);
150 Note that this initialization takes advantage of the fact that srandom
151 advances the front and rear pointers 10*rand_deg times, and hence the
152 rear pointer which starts at 0 will also end up at zero; thus the zeroth
153 element of the state information, which contains info about the current
154 position of the rear pointer is just
155 (MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3. */
157 static int32_t randtbl[DEG_3 + 1] =
161 -1726662223, 379960547, 1735697613, 1040273694, 1313901226,
162 1627687941, -179304937, -2073333483, 1780058412, -1989503057,
163 -615974602, 344556628, 939512070, -1249116260, 1507946756,
164 -812545463, 154635395, 1388815473, -1926676823, 525320961,
165 -1009028674, 968117788, -123449607, 1284210865, 435012392,
166 -2017506339, -911064859, -370259173, 1132637927, 1398500161,
171 static struct random_data unsafe_state =
173 /* FPTR and RPTR are two pointers into the state info, a front and a rear
174 pointer. These two pointers are always rand_sep places aparts, as they
175 cycle through the state information. (Yes, this does mean we could get
176 away with just one pointer, but the code for random is more efficient
177 this way). The pointers are left positioned as they would be from the call:
178 initstate(1, randtbl, 128);
179 (The position of the rear pointer, rptr, is really 0 (as explained above
180 in the initialization of randtbl) because the state table pointer is set
181 to point to randtbl[1] (as explained below).) */
183 /* .fptr =*/ &randtbl[SEP_3 + 1],
184 /* .rptr =*/ &randtbl[1],
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 zeroth. 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. */
195 /* .state =*/ &randtbl[1],
197 /* .rand_type =*/ TYPE_3,
198 /* .rand_deg =*/ DEG_3,
199 /* .rand_sep =*/ SEP_3,
201 /* .end_ptr =*/ &randtbl[sizeof (randtbl) / sizeof (randtbl[0])]
204 /* POSIX.1c requires that there is mutual exclusion for the `rand' and
205 `srand' functions to prevent concurrent calls from modifying common
207 __libc_lock_define_initialized (static1, lock)
209 /* Initialize the random number generator based on the given seed. If the
210 type is the trivial no-state-information type, just remember the seed.
211 Otherwise, initializes state[] based on the given "seed" via a linear
212 congruential generator. Then, the pointers are set to known locations
213 that are exactly rand_sep places apart. Lastly, it cycles the state
214 information a given number of times to get rid of any initial dependencies
215 introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
216 for default usage relies on values produced by this routine. */
221 __libc_lock_lock (lock);
222 (void) __srandom_r (x, &unsafe_state);
223 __libc_lock_unlock (lock);
226 weak_alias (__srandom, srandom)
227 weak_alias (__srandom, srand)
229 /* Initialize the state information in the given array of N bytes for
230 future random number generation. Based on the number of bytes we
231 are given, and the break values for the different R.N.G.'s, we choose
232 the best (largest) one we can and set things up for it. srandom is
233 then called to initialize the state information. Note that on return
234 from srandom, we set state[-1] to be the type multiplexed with the current
235 value of the rear pointer; this is so successive calls to initstate won't
236 lose this information and will be able to restart with setstate.
237 Note: The first thing we do is save the current state, if any, just like
238 setstate so that it doesn't matter when initstate is called.
239 Returns a pointer to the old state. */
241 __initstate (seed, arg_state, n)
248 __libc_lock_lock (lock);
250 ostate = &unsafe_state.state[-1];
252 __initstate_r (seed, arg_state, n, &unsafe_state);
254 __libc_lock_unlock (lock);
256 return (char *) ostate;
259 weak_alias (__initstate, initstate)
261 /* Restore the state from the given state array.
262 Note: It is important that we also remember the locations of the pointers
263 in the current state information, and restore the locations of the pointers
264 from the old state information. This is done by multiplexing the pointer
265 location into the zeroth word of the state information. Note that due
266 to the order in which things are done, it is OK to call setstate with the
267 same state as the current state
268 Returns a pointer to the old state information. */
270 __setstate (arg_state)
275 __libc_lock_lock (lock);
277 ostate = &unsafe_state.state[-1];
279 if (__setstate_r (arg_state, &unsafe_state) < 0)
282 __libc_lock_unlock (lock);
284 return (char *) ostate;
287 weak_alias (__setstate, setstate)
289 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
290 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
291 same in all the other cases due to all the global variables that have been
292 set up. The basic operation is to add the number at the rear pointer into
293 the one at the front pointer. Then both pointers are advanced to the next
294 location cyclically in the table. The value returned is the sum generated,
295 reduced to 31 bits by throwing away the "least random" low bit.
296 Note: The code takes advantage of the fact that both the front and
297 rear pointers can't wrap on the same call by not testing the rear
298 pointer if the front one has wrapped. Returns a 31-bit random number. */
305 __libc_lock_lock (lock);
307 (void) __random_r (&unsafe_state, &retval);
309 __libc_lock_unlock (lock);
314 weak_alias (__random, random)