2 * Copyright (c) 1983 Regents of the University of California.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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 [rescinded 22 July 1999]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.
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
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.
48 #define ULONG_MAX ((unsigned long)(~0L)) /* 0xFFFFFFFF for 32-bits */
49 #define LONG_MAX ((long)(ULONG_MAX >> 1)) /* 0x7FFFFFFF for 32-bits*/
54 # define NULL (void *) 0
59 # define NULL (void *) 0
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. */
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. */
108 /* Linear congruential. */
114 /* x**7 + x**3 + 1. */
126 /* x**31 + x**3 + 1. */
139 /* Array versions of the above information to make code run faster.
140 Relies on fact that TYPE_i == i. */
142 #define MAX_TYPES 5 /* Max number of types above. */
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
};
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. */
158 static long int randtbl
[DEG_3
+ 1] =
160 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342,
161 0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb,
162 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
163 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86,
164 0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7,
165 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
166 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b,
167 0xf5ad9d0e, 0x8999220b, 0x27fb47b9
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).) */
180 static long int *fptr
= &randtbl
[SEP_3
+ 1];
181 static long int *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 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. */
195 static long int *state
= &randtbl
[1];
197 static int rand_type
= TYPE_3
;
198 static int rand_deg
= DEG_3
;
199 static int rand_sep
= SEP_3
;
201 static long int *end_ptr
= &randtbl
[sizeof(randtbl
) / sizeof(randtbl
[0])];
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. */
216 if (rand_type
!= TYPE_0
)
219 for (i
= 1; i
< rand_deg
; ++i
)
220 state
[i
] = (1103515145 * state
[i
- 1]) + 12345;
221 fptr
= &state
[rand_sep
];
223 for (i
= 0; i
< 10 * rand_deg
; ++i
)
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. */
240 initstate (seed
, arg_state
, n
)
245 PTR ostate
= (PTR
) &state
[-1];
247 if (rand_type
== TYPE_0
)
248 state
[-1] = rand_type
;
250 state
[-1] = (MAX_TYPES
* (rptr
- state
)) + rand_type
;
262 else if (n
< BREAK_2
)
268 else if (n
< BREAK_3
)
274 else if (n
< BREAK_4
)
287 state
= &((long int *) arg_state
)[1]; /* First location. */
288 /* Must set END_PTR before srandom. */
289 end_ptr
= &state
[rand_deg
];
291 if (rand_type
== TYPE_0
)
292 state
[-1] = rand_type
;
294 state
[-1] = (MAX_TYPES
* (rptr
- state
)) + rand_type
;
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. */
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];
317 if (rand_type
== TYPE_0
)
318 state
[-1] = rand_type
;
320 state
[-1] = (MAX_TYPES
* (rptr
- state
)) + rand_type
;
330 rand_deg
= degrees
[type
];
331 rand_sep
= seps
[type
];
334 /* State info munged. */
339 state
= &new_state
[1];
340 if (rand_type
!= TYPE_0
)
343 fptr
= &state
[(rear
+ rand_sep
) % rand_deg
];
345 /* Set end_ptr too. */
346 end_ptr
= &state
[rand_deg
];
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. */
365 if (rand_type
== TYPE_0
)
367 state
[0] = ((state
[0] * 1103515245) + 12345) & LONG_MAX
;
374 /* Chucking least random bit. */
375 i
= (*fptr
>> 1) & LONG_MAX
;
This page took 0.037034 seconds and 4 git commands to generate.