Annotation of embedaddon/ntp/libntp/ntp_random.c, revision 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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