Annotation of embedaddon/ntp/libntp/ntp_random.c, revision 1.1.1.1
1.1 misho 1: /*
2: * Copyright (c) 1983, 1993
3: * The Regents of the University of California. All rights reserved.
4: *
5: * Redistribution and use in source and binary forms, with or without
6: * modification, are permitted provided that the following conditions
7: * are met:
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. All advertising materials mentioning features or use of this software
14: * must display the following acknowledgement:
15: * This product includes software developed by the University of
16: * California, Berkeley and its contributors.
17: * 4. Neither the name of the University nor the names of its contributors
18: * may be used to endorse or promote products derived from this software
19: * without specific prior written permission.
20: *
21: * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24: * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31: * SUCH DAMAGE.
32: *
33: * $FreeBSD: src/lib/libc/stdlib/random.c,v 1.4.2.2 1999/09/05 11:16:45 peter Exp $
34: *
35: */
36:
37: #if defined(LIBC_SCCS) && !defined(lint)
38: static char sccsid[] = "@(#)random.c 8.2 (Berkeley) 5/19/95";
39: #endif /* LIBC_SCCS and not lint */
40:
41: #include "config.h"
42: #include <sys/types.h>
43: #ifdef HAVE_UNISTD_H
44: # include <unistd.h>
45: #endif
46: #include <stdio.h>
47:
48: #include <ntp_types.h>
49: #include <ntp_random.h>
50: #include <ntp_unixtime.h>
51:
52: /*
53: * random.c:
54: *
55: * An improved random number generation package. In addition to the standard
56: * rand()/srand() like interface, this package also has a special state info
57: * interface. The initstate() routine is called with a seed, an array of
58: * bytes, and a count of how many bytes are being passed in; this array is
59: * then initialized to contain information for random number generation with
60: * that much state information. Good sizes for the amount of state
61: * information are 32, 64, 128, and 256 bytes. The state can be switched by
62: * calling the setstate() routine with the same array as was initiallized
63: * with initstate(). By default, the package runs with 128 bytes of state
64: * information and generates far better random numbers than a linear
65: * congruential generator. If the amount of state information is less than
66: * 32 bytes, a simple linear congruential R.N.G. is used.
67: *
68: * Internally, the state information is treated as an array of longs; the
69: * zeroeth element of the array is the type of R.N.G. being used (small
70: * integer); the remainder of the array is the state information for the
71: * R.N.G. Thus, 32 bytes of state information will give 7 longs worth of
72: * state information, which will allow a degree seven polynomial. (Note:
73: * the zeroeth word of state information also has some other information
74: * stored in it -- see setstate() for details).
75: *
76: * The random number generation technique is a linear feedback shift register
77: * approach, employing trinomials (since there are fewer terms to sum up that
78: * way). In this approach, the least significant bit of all the numbers in
79: * the state table will act as a linear feedback shift register, and will
80: * have period 2^deg - 1 (where deg is the degree of the polynomial being
81: * used, assuming that the polynomial is irreducible and primitive). The
82: * higher order bits will have longer periods, since their values are also
83: * influenced by pseudo-random carries out of the lower bits. The total
84: * period of the generator is approximately deg*(2**deg - 1); thus doubling
85: * the amount of state information has a vast influence on the period of the
86: * generator. Note: the deg*(2**deg - 1) is an approximation only good for
87: * large deg, when the period of the shift register is the dominant factor.
88: * With deg equal to seven, the period is actually much longer than the
89: * 7*(2**7 - 1) predicted by this formula.
90: *
91: * Modified 28 December 1994 by Jacob S. Rosenberg.
92: * The following changes have been made:
93: * All references to the type u_int have been changed to unsigned long.
94: * All references to type int have been changed to type long. Other
95: * cleanups have been made as well. A warning for both initstate and
96: * setstate has been inserted to the effect that on Sparc platforms
97: * the 'arg_state' variable must be forced to begin on word boundaries.
98: * This can be easily done by casting a long integer array to char *.
99: * The overall logic has been left STRICTLY alone. This software was
100: * tested on both a VAX and Sun SpacsStation with exactly the same
101: * results. The new version and the original give IDENTICAL results.
102: * The new version is somewhat faster than the original. As the
103: * documentation says: "By default, the package runs with 128 bytes of
104: * state information and generates far better random numbers than a linear
105: * congruential generator. If the amount of state information is less than
106: * 32 bytes, a simple linear congruential R.N.G. is used." For a buffer of
107: * 128 bytes, this new version runs about 19 percent faster and for a 16
108: * byte buffer it is about 5 percent faster.
109: */
110:
111: /*
112: * For each of the currently supported random number generators, we have a
113: * break value on the amount of state information (you need at least this
114: * many bytes of state info to support this random number generator), a degree
115: * for the polynomial (actually a trinomial) that the R.N.G. is based on, and
116: * the separation between the two lower order coefficients of the trinomial.
117: */
118: #define TYPE_0 0 /* linear congruential */
119: #define BREAK_0 8
120: #define DEG_0 0
121: #define SEP_0 0
122:
123: #define TYPE_1 1 /* x**7 + x**3 + 1 */
124: #define BREAK_1 32
125: #define DEG_1 7
126: #define SEP_1 3
127:
128: #define TYPE_2 2 /* x**15 + x + 1 */
129: #define BREAK_2 64
130: #define DEG_2 15
131: #define SEP_2 1
132:
133: #define TYPE_3 3 /* x**31 + x**3 + 1 */
134: #define BREAK_3 128
135: #define DEG_3 31
136: #define SEP_3 3
137:
138: #define TYPE_4 4 /* x**63 + x + 1 */
139: #define BREAK_4 256
140: #define DEG_4 63
141: #define SEP_4 1
142:
143: /*
144: * Array versions of the above information to make code run faster --
145: * relies on fact that TYPE_i == i.
146: */
147: #define MAX_TYPES 5 /* max number of types above */
148:
149: static long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
150: static long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
151:
152: /*
153: * Initially, everything is set up as if from:
154: *
155: * initstate(1, randtbl, 128);
156: *
157: * Note that this initialization takes advantage of the fact that srandom()
158: * advances the front and rear pointers 10*rand_deg times, and hence the
159: * rear pointer which starts at 0 will also end up at zero; thus the zeroeth
160: * element of the state information, which contains info about the current
161: * position of the rear pointer is just
162: *
163: * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3.
164: */
165:
166: static long randtbl[DEG_3 + 1] = {
167: TYPE_3,
168: #ifdef USE_WEAK_SEEDING
169: /* Historic implementation compatibility */
170: /* The random sequences do not vary much with the seed */
171: 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5,
172: 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
173: 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88,
174: 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
175: 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b,
176: 0x27fb47b9,
177: #else /* !USE_WEAK_SEEDING */
178: 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05,
179: 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454,
180: 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471,
181: 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1,
182: 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41,
183: 0xf3bec5da
184: #endif /* !USE_WEAK_SEEDING */
185: };
186:
187: /*
188: * fptr and rptr are two pointers into the state info, a front and a rear
189: * pointer. These two pointers are always rand_sep places aparts, as they
190: * cycle cyclically through the state information. (Yes, this does mean we
191: * could get away with just one pointer, but the code for random() is more
192: * efficient this way). The pointers are left positioned as they would be
193: * from the call
194: *
195: * initstate(1, randtbl, 128);
196: *
197: * (The position of the rear pointer, rptr, is really 0 (as explained above
198: * in the initialization of randtbl) because the state table pointer is set
199: * to point to randtbl[1] (as explained below).
200: */
201: static long *fptr = &randtbl[SEP_3 + 1];
202: static long *rptr = &randtbl[1];
203:
204: /*
205: * The following things are the pointer to the state information table, the
206: * type of the current generator, the degree of the current polynomial being
207: * used, and the separation between the two pointers. Note that for efficiency
208: * of random(), we remember the first location of the state information, not
209: * the zeroeth. Hence it is valid to access state[-1], which is used to
210: * store the type of the R.N.G. Also, we remember the last location, since
211: * this is more efficient than indexing every time to find the address of
212: * the last element to see if the front and rear pointers have wrapped.
213: */
214: static long *state = &randtbl[1];
215: static long rand_type = TYPE_3;
216: static long rand_deg = DEG_3;
217: static long rand_sep = SEP_3;
218: static long *end_ptr = &randtbl[DEG_3 + 1];
219:
220: static inline long good_rand (long);
221:
222: static inline long
223: good_rand (
224: register long x
225: )
226: {
227: #ifdef USE_WEAK_SEEDING
228: /*
229: * Historic implementation compatibility.
230: * The random sequences do not vary much with the seed,
231: * even with overflowing.
232: */
233: return (1103515245 * x + 12345);
234: #else /* !USE_WEAK_SEEDING */
235: /*
236: * Compute x = (7^5 * x) mod (2^31 - 1)
237: * wihout overflowing 31 bits:
238: * (2^31 - 1) = 127773 * (7^5) + 2836
239: * From "Random number generators: good ones are hard to find",
240: * Park and Miller, Communications of the ACM, vol. 31, no. 10,
241: * October 1988, p. 1195.
242: */
243: register long hi, lo;
244:
245: hi = x / 127773;
246: lo = x % 127773;
247: x = 16807 * lo - 2836 * hi;
248: if (x <= 0)
249: x += 0x7fffffff;
250: return (x);
251: #endif /* !USE_WEAK_SEEDING */
252: }
253:
254: /*
255: * srandom:
256: *
257: * Initialize the random number generator based on the given seed. If the
258: * type is the trivial no-state-information type, just remember the seed.
259: * Otherwise, initializes state[] based on the given "seed" via a linear
260: * congruential generator. Then, the pointers are set to known locations
261: * that are exactly rand_sep places apart. Lastly, it cycles the state
262: * information a given number of times to get rid of any initial dependencies
263: * introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
264: * for default usage relies on values produced by this routine.
265: */
266: void
267: ntp_srandom(
268: unsigned long x
269: )
270: {
271: register long i;
272:
273: if (rand_type == TYPE_0)
274: state[0] = x;
275: else {
276: state[0] = x;
277: for (i = 1; i < rand_deg; i++)
278: state[i] = good_rand(state[i - 1]);
279: fptr = &state[rand_sep];
280: rptr = &state[0];
281: for (i = 0; i < 10 * rand_deg; i++)
282: (void)ntp_random();
283: }
284: }
285:
286: /*
287: * srandomdev:
288: *
289: * Many programs choose the seed value in a totally predictable manner.
290: * This often causes problems. We seed the generator using the much more
291: * secure urandom(4) interface. Note that this particular seeding
292: * procedure can generate states which are impossible to reproduce by
293: * calling srandom() with any value, since the succeeding terms in the
294: * state buffer are no longer derived from the LC algorithm applied to
295: * a fixed seed.
296: */
297: #ifdef NEED_SRANDOMDEV
298: void
299: ntp_srandomdev( void )
300: {
301: struct timeval tv;
302: unsigned long junk; /* Purposely used uninitialized */
303:
304: GETTIMEOFDAY(&tv, NULL);
305: ntp_srandom(getpid() ^ tv.tv_sec ^ tv.tv_usec ^ junk);
306: return;
307: }
308: #endif
309:
310: /*
311: * initstate:
312: *
313: * Initialize the state information in the given array of n bytes for future
314: * random number generation. Based on the number of bytes we are given, and
315: * the break values for the different R.N.G.'s, we choose the best (largest)
316: * one we can and set things up for it. srandom() is then called to
317: * initialize the state information.
318: *
319: * Note that on return from srandom(), we set state[-1] to be the type
320: * multiplexed with the current value of the rear pointer; this is so
321: * successive calls to initstate() won't lose this information and will be
322: * able to restart with setstate().
323: *
324: * Note: the first thing we do is save the current state, if any, just like
325: * setstate() so that it doesn't matter when initstate is called.
326: *
327: * Returns a pointer to the old state.
328: *
329: * Note: The Sparc platform requires that arg_state begin on a long
330: * word boundary; otherwise a bus error will occur. Even so, lint will
331: * complain about mis-alignment, but you should disregard these messages.
332: */
333: char *
334: ntp_initstate(
335: unsigned long seed, /* seed for R.N.G. */
336: char *arg_state, /* pointer to state array */
337: long n /* # bytes of state info */
338: )
339: {
340: register char *ostate = (char *)(&state[-1]);
341: register long *long_arg_state = (long *) arg_state;
342:
343: if (rand_type == TYPE_0)
344: state[-1] = rand_type;
345: else
346: state[-1] = MAX_TYPES * (rptr - state) + rand_type;
347: if (n < BREAK_0) {
348: (void)fprintf(stderr,
349: "random: not enough state (%ld bytes); ignored.\n", n);
350: return(0);
351: }
352: if (n < BREAK_1) {
353: rand_type = TYPE_0;
354: rand_deg = DEG_0;
355: rand_sep = SEP_0;
356: } else if (n < BREAK_2) {
357: rand_type = TYPE_1;
358: rand_deg = DEG_1;
359: rand_sep = SEP_1;
360: } else if (n < BREAK_3) {
361: rand_type = TYPE_2;
362: rand_deg = DEG_2;
363: rand_sep = SEP_2;
364: } else if (n < BREAK_4) {
365: rand_type = TYPE_3;
366: rand_deg = DEG_3;
367: rand_sep = SEP_3;
368: } else {
369: rand_type = TYPE_4;
370: rand_deg = DEG_4;
371: rand_sep = SEP_4;
372: }
373: state = (long *) (long_arg_state + 1); /* first location */
374: end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */
375: ntp_srandom(seed);
376: if (rand_type == TYPE_0)
377: long_arg_state[0] = rand_type;
378: else
379: long_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type;
380: return(ostate);
381: }
382:
383: /*
384: * setstate:
385: *
386: * Restore the state from the given state array.
387: *
388: * Note: it is important that we also remember the locations of the pointers
389: * in the current state information, and restore the locations of the pointers
390: * from the old state information. This is done by multiplexing the pointer
391: * location into the zeroeth word of the state information.
392: *
393: * Note that due to the order in which things are done, it is OK to call
394: * setstate() with the same state as the current state.
395: *
396: * Returns a pointer to the old state information.
397: *
398: * Note: The Sparc platform requires that arg_state begin on a long
399: * word boundary; otherwise a bus error will occur. Even so, lint will
400: * complain about mis-alignment, but you should disregard these messages.
401: */
402: char *
403: ntp_setstate(
404: char *arg_state /* pointer to state array */
405: )
406: {
407: register long *new_state = (long *) arg_state;
408: register long type = new_state[0] % MAX_TYPES;
409: register long rear = new_state[0] / MAX_TYPES;
410: char *ostate = (char *)(&state[-1]);
411:
412: if (rand_type == TYPE_0)
413: state[-1] = rand_type;
414: else
415: state[-1] = MAX_TYPES * (rptr - state) + rand_type;
416: switch(type) {
417: case TYPE_0:
418: case TYPE_1:
419: case TYPE_2:
420: case TYPE_3:
421: case TYPE_4:
422: rand_type = type;
423: rand_deg = degrees[type];
424: rand_sep = seps[type];
425: break;
426: default:
427: (void)fprintf(stderr,
428: "random: state info corrupted; not changed.\n");
429: }
430: state = (long *) (new_state + 1);
431: if (rand_type != TYPE_0) {
432: rptr = &state[rear];
433: fptr = &state[(rear + rand_sep) % rand_deg];
434: }
435: end_ptr = &state[rand_deg]; /* set end_ptr too */
436: return(ostate);
437: }
438:
439: /*
440: * random:
441: *
442: * If we are using the trivial TYPE_0 R.N.G., just do the old linear
443: * congruential bit. Otherwise, we do our fancy trinomial stuff, which is
444: * the same in all the other cases due to all the global variables that have
445: * been set up. The basic operation is to add the number at the rear pointer
446: * into the one at the front pointer. Then both pointers are advanced to
447: * the next location cyclically in the table. The value returned is the sum
448: * generated, reduced to 31 bits by throwing away the "least random" low bit.
449: *
450: * Note: the code takes advantage of the fact that both the front and
451: * rear pointers can't wrap on the same call by not testing the rear
452: * pointer if the front one has wrapped.
453: *
454: * Returns a 31-bit random number.
455: */
456: long
457: ntp_random( void )
458: {
459: register long i;
460: register long *f, *r;
461:
462: if (rand_type == TYPE_0) {
463: i = state[0];
464: state[0] = i = (good_rand(i)) & 0x7fffffff;
465: } else {
466: /*
467: * Use local variables rather than static variables for speed.
468: */
469: f = fptr; r = rptr;
470: *f += *r;
471: i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */
472: if (++f >= end_ptr) {
473: f = state;
474: ++r;
475: }
476: else if (++r >= end_ptr) {
477: r = state;
478: }
479:
480: fptr = f; rptr = r;
481: }
482: return(i);
483: }
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