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46 #if defined(LIBC_SCCS) && !defined(lint)
47 static const char sccsid[] = "@(#)random.c 8.2 (Berkeley) 5/19/95";
48 #endif /* LIBC_SCCS and not lint */
50 #ifdef HAVE_CONFIG_H /* gawk addition */
63 #include "random.h" /* gawk addition */
65 #ifdef HAVE_SYS_TIME_H /* gawk addition */
70 #include <sys/cdefs.h>
71 __FBSDID("$FreeBSD: /repoman/r/ncvs/src/lib/libc/stdlib/random.c,v 1.24 2004/01/20 03:02:18 das Exp $");
73 #include "namespace.h"
74 #include <sys/time.h> /* for srandomdev() */
75 #include <fcntl.h> /* for srandomdev() */
79 #include <unistd.h> /* for srandomdev() */
80 #include "un-namespace.h"
86 * An improved random number generation package. In addition to the standard
87 * rand()/srand() like interface, this package also has a special state info
88 * interface. The initstate() routine is called with a seed, an array of
89 * bytes, and a count of how many bytes are being passed in; this array is
90 * then initialized to contain information for random number generation with
91 * that much state information. Good sizes for the amount of state
92 * information are 32, 64, 128, and 256 bytes. The state can be switched by
93 * calling the setstate() routine with the same array as was initiallized
94 * with initstate(). By default, the package runs with 128 bytes of state
95 * information and generates far better random numbers than a linear
96 * congruential generator. If the amount of state information is less than
97 * 32 bytes, a simple linear congruential R.N.G. is used.
99 * Internally, the state information is treated as an array of uint32_t's; the
100 * zeroeth element of the array is the type of R.N.G. being used (small
101 * integer); the remainder of the array is the state information for the
102 * R.N.G. Thus, 32 bytes of state information will give 7 ints worth of
103 * state information, which will allow a degree seven polynomial. (Note:
104 * the zeroeth word of state information also has some other information
105 * stored in it -- see setstate() for details).
107 * The random number generation technique is a linear feedback shift register
108 * approach, employing trinomials (since there are fewer terms to sum up that
109 * way). In this approach, the least significant bit of all the numbers in
110 * the state table will act as a linear feedback shift register, and will
111 * have period 2^deg - 1 (where deg is the degree of the polynomial being
112 * used, assuming that the polynomial is irreducible and primitive). The
113 * higher order bits will have longer periods, since their values are also
114 * influenced by pseudo-random carries out of the lower bits. The total
115 * period of the generator is approximately deg*(2**deg - 1); thus doubling
116 * the amount of state information has a vast influence on the period of the
117 * generator. Note: the deg*(2**deg - 1) is an approximation only good for
118 * large deg, when the period of the shift is the dominant factor.
119 * With deg equal to seven, the period is actually much longer than the
120 * 7*(2**7 - 1) predicted by this formula.
122 * Modified 28 December 1994 by Jacob S. Rosenberg.
123 * The following changes have been made:
124 * All references to the type u_int have been changed to unsigned long.
125 * All references to type int have been changed to type long. Other
126 * cleanups have been made as well. A warning for both initstate and
127 * setstate has been inserted to the effect that on Sparc platforms
128 * the 'arg_state' variable must be forced to begin on word boundaries.
129 * This can be easily done by casting a long integer array to char *.
130 * The overall logic has been left STRICTLY alone. This software was
131 * tested on both a VAX and Sun SpacsStation with exactly the same
132 * results. The new version and the original give IDENTICAL results.
133 * The new version is somewhat faster than the original. As the
134 * documentation says: "By default, the package runs with 128 bytes of
135 * state information and generates far better random numbers than a linear
136 * congruential generator. If the amount of state information is less than
137 * 32 bytes, a simple linear congruential R.N.G. is used." For a buffer of
138 * 128 bytes, this new version runs about 19 percent faster and for a 16
139 * byte buffer it is about 5 percent faster.
143 * For each of the currently supported random number generators, we have a
144 * break value on the amount of state information (you need at least this
145 * many bytes of state info to support this random number generator), a degree
146 * for the polynomial (actually a trinomial) that the R.N.G. is based on, and
147 * the separation between the two lower order coefficients of the trinomial.
149 #define TYPE_0 0 /* linear congruential */
154 #define TYPE_1 1 /* x**7 + x**3 + 1 */
159 #define TYPE_2 2 /* x**15 + x + 1 */
164 #define TYPE_3 3 /* x**31 + x**3 + 1 */
169 #define TYPE_4 4 /* x**63 + x + 1 */
175 * Array versions of the above information to make code run faster --
176 * relies on fact that TYPE_i == i.
178 #define MAX_TYPES 5 /* max number of types above */
180 #ifdef USE_WEAK_SEEDING
182 #else /* !USE_WEAK_SEEDING */
183 #define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */
184 #endif /* !USE_WEAK_SEEDING */
186 static const int degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
187 static const int seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
190 * Initially, everything is set up as if from:
192 * initstate(1, randtbl, 128);
194 * Note that this initialization takes advantage of the fact that srandom()
195 * advances the front and rear pointers 10*rand_deg times, and hence the
196 * rear pointer which starts at 0 will also end up at zero; thus the zeroeth
197 * element of the state information, which contains info about the current
198 * position of the rear pointer is just
200 * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3.
203 static uint32_t randtbl[DEG_3 + 1] = {
205 #ifdef USE_WEAK_SEEDING
206 /* Historic implementation compatibility */
207 /* The random sequences do not vary much with the seed */
208 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5,
209 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
210 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88,
211 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
212 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b,
214 #else /* !USE_WEAK_SEEDING */
215 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05,
216 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454,
217 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471,
218 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1,
219 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41,
221 #endif /* !USE_WEAK_SEEDING */
225 * fptr and rptr are two pointers into the state info, a front and a rear
226 * pointer. These two pointers are always rand_sep places aparts, as they
227 * cycle cyclically through the state information. (Yes, this does mean we
228 * could get away with just one pointer, but the code for random() is more
229 * efficient this way). The pointers are left positioned as they would be
232 * initstate(1, randtbl, 128);
234 * (The position of the rear pointer, rptr, is really 0 (as explained above
235 * in the initialization of randtbl) because the state table pointer is set
236 * to point to randtbl[1] (as explained below).
238 static uint32_t *fptr = &randtbl[SEP_3 + 1];
239 static uint32_t *rptr = &randtbl[1];
242 * The following things are the pointer to the state information table, the
243 * type of the current generator, the degree of the current polynomial being
244 * used, and the separation between the two pointers. Note that for efficiency
245 * of random(), we remember the first location of the state information, not
246 * the zeroeth. Hence it is valid to access state[-1], which is used to
247 * store the type of the R.N.G. Also, we remember the last location, since
248 * this is more efficient than indexing every time to find the address of
249 * the last element to see if the front and rear pointers have wrapped.
251 static uint32_t *state = &randtbl[1];
252 static int rand_type = TYPE_3;
253 static int rand_deg = DEG_3;
254 static int rand_sep = SEP_3;
255 static uint32_t *end_ptr = &randtbl[DEG_3 + 1];
257 static inline uint32_t good_rand(int32_t);
259 static inline uint32_t good_rand (x)
262 #ifdef USE_WEAK_SEEDING
264 * Historic implementation compatibility.
265 * The random sequences do not vary much with the seed,
266 * even with overflowing.
268 return (1103515245 * x + 12345);
269 #else /* !USE_WEAK_SEEDING */
271 * Compute x = (7^5 * x) mod (2^31 - 1)
272 * wihout overflowing 31 bits:
273 * (2^31 - 1) = 127773 * (7^5) + 2836
274 * From "Random number generators: good ones are hard to find",
275 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
276 * October 1988, p. 1195.
280 /* Can't be initialized with 0, so use another value. */
285 x = 16807 * lo - 2836 * hi;
289 #endif /* !USE_WEAK_SEEDING */
295 * Initialize the random number generator based on the given seed. If the
296 * type is the trivial no-state-information type, just remember the seed.
297 * Otherwise, initializes state[] based on the given "seed" via a linear
298 * congruential generator. Then, the pointers are set to known locations
299 * that are exactly rand_sep places apart. Lastly, it cycles the state
300 * information a given number of times to get rid of any initial dependencies
301 * introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
302 * for default usage relies on values produced by this routine.
310 state[0] = (uint32_t)x;
311 if (rand_type == TYPE_0)
314 for (i = 1; i < rand_deg; i++)
315 state[i] = good_rand(state[i - 1]);
316 fptr = &state[rand_sep];
320 for (i = 0; i < lim; i++)
324 #if 0 /* gawk doesn't use this */
328 * Many programs choose the seed value in a totally predictable manner.
329 * This often causes problems. We seed the generator using the much more
330 * secure random(4) interface. Note that this particular seeding
331 * procedure can generate states which are impossible to reproduce by
332 * calling srandom() with any value, since the succeeding terms in the
333 * state buffer are no longer derived from the LC algorithm applied to
342 if (rand_type == TYPE_0)
343 len = sizeof state[0];
345 len = rand_deg * sizeof state[0];
348 fd = open("/dev/random", O_RDONLY, 0);
350 if (read(fd, (void *) state, len) == (ssize_t) len)
359 gettimeofday(&tv, NULL);
360 srandom((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk);
364 if (rand_type != TYPE_0) {
365 fptr = &state[rand_sep];
374 * Initialize the state information in the given array of n bytes for future
375 * random number generation. Based on the number of bytes we are given, and
376 * the break values for the different R.N.G.'s, we choose the best (largest)
377 * one we can and set things up for it. srandom() is then called to
378 * initialize the state information.
380 * Note that on return from srandom(), we set state[-1] to be the type
381 * multiplexed with the current value of the rear pointer; this is so
382 * successive calls to initstate() won't lose this information and will be
383 * able to restart with setstate().
385 * Note: the first thing we do is save the current state, if any, just like
386 * setstate() so that it doesn't matter when initstate is called.
388 * Returns a pointer to the old state.
390 * Note: The Sparc platform requires that arg_state begin on an int
391 * word boundary; otherwise a bus error will occur. Even so, lint will
392 * complain about mis-alignment, but you should disregard these messages.
395 initstate(seed, arg_state, n)
396 unsigned long seed; /* seed for R.N.G. */
397 char *arg_state; /* pointer to state array */
398 long n; /* # bytes of state info */
400 char *ostate = (char *)(&state[-1]);
401 uint32_t *int_arg_state = (uint32_t *)arg_state;
403 if (rand_type == TYPE_0)
404 state[-1] = rand_type;
406 state[-1] = MAX_TYPES * (rptr - state) + rand_type;
408 (void)fprintf(stderr,
409 "random: not enough state (%ld bytes); ignored.\n", n);
416 } else if (n < BREAK_2) {
420 } else if (n < BREAK_3) {
424 } else if (n < BREAK_4) {
433 state = int_arg_state + 1; /* first location */
434 end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */
436 if (rand_type == TYPE_0)
437 int_arg_state[0] = rand_type;
439 int_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type;
446 * Restore the state from the given state array.
448 * Note: it is important that we also remember the locations of the pointers
449 * in the current state information, and restore the locations of the pointers
450 * from the old state information. This is done by multiplexing the pointer
451 * location into the zeroeth word of the state information.
453 * Note that due to the order in which things are done, it is OK to call
454 * setstate() with the same state as the current state.
456 * Returns a pointer to the old state information.
458 * Note: The Sparc platform requires that arg_state begin on an int
459 * word boundary; otherwise a bus error will occur. Even so, lint will
460 * complain about mis-alignment, but you should disregard these messages.
464 char *arg_state; /* pointer to state array */
466 uint32_t *new_state = (uint32_t *)arg_state;
467 uint32_t type = new_state[0] % MAX_TYPES;
468 uint32_t rear = new_state[0] / MAX_TYPES;
469 char *ostate = (char *)(&state[-1]);
471 if (rand_type == TYPE_0)
472 state[-1] = rand_type;
474 state[-1] = MAX_TYPES * (rptr - state) + rand_type;
482 rand_deg = degrees[type];
483 rand_sep = seps[type];
486 (void)fprintf(stderr,
487 "random: state info corrupted; not changed.\n");
489 state = new_state + 1;
490 if (rand_type != TYPE_0) {
492 fptr = &state[(rear + rand_sep) % rand_deg];
494 end_ptr = &state[rand_deg]; /* set end_ptr too */
501 * If we are using the trivial TYPE_0 R.N.G., just do the old linear
502 * congruential bit. Otherwise, we do our fancy trinomial stuff, which is
503 * the same in all the other cases due to all the global variables that have
504 * been set up. The basic operation is to add the number at the rear pointer
505 * into the one at the front pointer. Then both pointers are advanced to
506 * the next location cyclically in the table. The value returned is the sum
507 * generated, reduced to 31 bits by throwing away the "least random" low bit.
509 * Note: the code takes advantage of the fact that both the front and
510 * rear pointers can't wrap on the same call by not testing the rear
511 * pointer if the front one has wrapped.
513 * Returns a 31-bit random number.
521 if (rand_type == TYPE_0) {
523 state[0] = i = (good_rand(i)) & 0x7fffffff;
526 * Use local variables rather than static variables for speed.
530 i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */
531 if (++f >= end_ptr) {
535 else if (++r >= end_ptr) {