1181834Sroberto/* 2181834Sroberto * Copyright (c) 1983, 1993 3181834Sroberto * The Regents of the University of California. All rights reserved. 4181834Sroberto * 5181834Sroberto * Redistribution and use in source and binary forms, with or without 6181834Sroberto * modification, are permitted provided that the following conditions 7181834Sroberto * are met: 8181834Sroberto * 1. Redistributions of source code must retain the above copyright 9181834Sroberto * notice, this list of conditions and the following disclaimer. 10181834Sroberto * 2. Redistributions in binary form must reproduce the above copyright 11181834Sroberto * notice, this list of conditions and the following disclaimer in the 12181834Sroberto * documentation and/or other materials provided with the distribution. 13181834Sroberto * 3. All advertising materials mentioning features or use of this software 14181834Sroberto * must display the following acknowledgement: 15181834Sroberto * This product includes software developed by the University of 16181834Sroberto * California, Berkeley and its contributors. 17181834Sroberto * 4. Neither the name of the University nor the names of its contributors 18181834Sroberto * may be used to endorse or promote products derived from this software 19181834Sroberto * without specific prior written permission. 20181834Sroberto * 21181834Sroberto * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22181834Sroberto * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23181834Sroberto * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24181834Sroberto * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25181834Sroberto * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26181834Sroberto * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27181834Sroberto * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28181834Sroberto * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29181834Sroberto * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30181834Sroberto * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31181834Sroberto * SUCH DAMAGE. 32181834Sroberto * 33181834Sroberto * $FreeBSD: src/lib/libc/stdlib/random.c,v 1.4.2.2 1999/09/05 11:16:45 peter Exp $ 34181834Sroberto * 35181834Sroberto */ 36181834Sroberto 37181834Sroberto#if defined(LIBC_SCCS) && !defined(lint) 38181834Srobertostatic char sccsid[] = "@(#)random.c 8.2 (Berkeley) 5/19/95"; 39181834Sroberto#endif /* LIBC_SCCS and not lint */ 40181834Sroberto 41181834Sroberto#include "config.h" 42290000Sglebius#include <sys/types.h> 43181834Sroberto#ifdef HAVE_UNISTD_H 44181834Sroberto# include <unistd.h> 45181834Sroberto#endif 46181834Sroberto#include <stdio.h> 47181834Sroberto 48290000Sglebius#include <l_stdlib.h> 49181834Sroberto#include <ntp_random.h> 50181834Sroberto#include <ntp_unixtime.h> 51181834Sroberto 52181834Sroberto/* 53181834Sroberto * random.c: 54181834Sroberto * 55181834Sroberto * An improved random number generation package. In addition to the standard 56181834Sroberto * rand()/srand() like interface, this package also has a special state info 57181834Sroberto * interface. The initstate() routine is called with a seed, an array of 58181834Sroberto * bytes, and a count of how many bytes are being passed in; this array is 59181834Sroberto * then initialized to contain information for random number generation with 60181834Sroberto * that much state information. Good sizes for the amount of state 61181834Sroberto * information are 32, 64, 128, and 256 bytes. The state can be switched by 62181834Sroberto * calling the setstate() routine with the same array as was initiallized 63181834Sroberto * with initstate(). By default, the package runs with 128 bytes of state 64181834Sroberto * information and generates far better random numbers than a linear 65181834Sroberto * congruential generator. If the amount of state information is less than 66181834Sroberto * 32 bytes, a simple linear congruential R.N.G. is used. 67181834Sroberto * 68181834Sroberto * Internally, the state information is treated as an array of longs; the 69181834Sroberto * zeroeth element of the array is the type of R.N.G. being used (small 70181834Sroberto * integer); the remainder of the array is the state information for the 71181834Sroberto * R.N.G. Thus, 32 bytes of state information will give 7 longs worth of 72181834Sroberto * state information, which will allow a degree seven polynomial. (Note: 73181834Sroberto * the zeroeth word of state information also has some other information 74181834Sroberto * stored in it -- see setstate() for details). 75181834Sroberto * 76181834Sroberto * The random number generation technique is a linear feedback shift register 77181834Sroberto * approach, employing trinomials (since there are fewer terms to sum up that 78181834Sroberto * way). In this approach, the least significant bit of all the numbers in 79181834Sroberto * the state table will act as a linear feedback shift register, and will 80181834Sroberto * have period 2^deg - 1 (where deg is the degree of the polynomial being 81181834Sroberto * used, assuming that the polynomial is irreducible and primitive). The 82181834Sroberto * higher order bits will have longer periods, since their values are also 83181834Sroberto * influenced by pseudo-random carries out of the lower bits. The total 84181834Sroberto * period of the generator is approximately deg*(2**deg - 1); thus doubling 85181834Sroberto * the amount of state information has a vast influence on the period of the 86181834Sroberto * generator. Note: the deg*(2**deg - 1) is an approximation only good for 87181834Sroberto * large deg, when the period of the shift register is the dominant factor. 88181834Sroberto * With deg equal to seven, the period is actually much longer than the 89181834Sroberto * 7*(2**7 - 1) predicted by this formula. 90181834Sroberto * 91181834Sroberto * Modified 28 December 1994 by Jacob S. Rosenberg. 92181834Sroberto * The following changes have been made: 93181834Sroberto * All references to the type u_int have been changed to unsigned long. 94181834Sroberto * All references to type int have been changed to type long. Other 95181834Sroberto * cleanups have been made as well. A warning for both initstate and 96181834Sroberto * setstate has been inserted to the effect that on Sparc platforms 97181834Sroberto * the 'arg_state' variable must be forced to begin on word boundaries. 98181834Sroberto * This can be easily done by casting a long integer array to char *. 99181834Sroberto * The overall logic has been left STRICTLY alone. This software was 100181834Sroberto * tested on both a VAX and Sun SpacsStation with exactly the same 101181834Sroberto * results. The new version and the original give IDENTICAL results. 102181834Sroberto * The new version is somewhat faster than the original. As the 103181834Sroberto * documentation says: "By default, the package runs with 128 bytes of 104181834Sroberto * state information and generates far better random numbers than a linear 105181834Sroberto * congruential generator. If the amount of state information is less than 106181834Sroberto * 32 bytes, a simple linear congruential R.N.G. is used." For a buffer of 107181834Sroberto * 128 bytes, this new version runs about 19 percent faster and for a 16 108181834Sroberto * byte buffer it is about 5 percent faster. 109181834Sroberto */ 110181834Sroberto 111181834Sroberto/* 112181834Sroberto * For each of the currently supported random number generators, we have a 113181834Sroberto * break value on the amount of state information (you need at least this 114181834Sroberto * many bytes of state info to support this random number generator), a degree 115181834Sroberto * for the polynomial (actually a trinomial) that the R.N.G. is based on, and 116181834Sroberto * the separation between the two lower order coefficients of the trinomial. 117181834Sroberto */ 118181834Sroberto#define TYPE_0 0 /* linear congruential */ 119181834Sroberto#define BREAK_0 8 120181834Sroberto#define DEG_0 0 121181834Sroberto#define SEP_0 0 122181834Sroberto 123181834Sroberto#define TYPE_1 1 /* x**7 + x**3 + 1 */ 124181834Sroberto#define BREAK_1 32 125181834Sroberto#define DEG_1 7 126181834Sroberto#define SEP_1 3 127181834Sroberto 128181834Sroberto#define TYPE_2 2 /* x**15 + x + 1 */ 129181834Sroberto#define BREAK_2 64 130181834Sroberto#define DEG_2 15 131181834Sroberto#define SEP_2 1 132181834Sroberto 133181834Sroberto#define TYPE_3 3 /* x**31 + x**3 + 1 */ 134181834Sroberto#define BREAK_3 128 135181834Sroberto#define DEG_3 31 136181834Sroberto#define SEP_3 3 137181834Sroberto 138181834Sroberto#define TYPE_4 4 /* x**63 + x + 1 */ 139181834Sroberto#define BREAK_4 256 140181834Sroberto#define DEG_4 63 141181834Sroberto#define SEP_4 1 142181834Sroberto 143181834Sroberto#define MAX_TYPES 5 /* max number of types above */ 144181834Sroberto 145181834Sroberto/* 146181834Sroberto * Initially, everything is set up as if from: 147181834Sroberto * 148181834Sroberto * initstate(1, randtbl, 128); 149181834Sroberto * 150181834Sroberto * Note that this initialization takes advantage of the fact that srandom() 151181834Sroberto * advances the front and rear pointers 10*rand_deg times, and hence the 152181834Sroberto * rear pointer which starts at 0 will also end up at zero; thus the zeroeth 153181834Sroberto * element of the state information, which contains info about the current 154181834Sroberto * position of the rear pointer is just 155181834Sroberto * 156181834Sroberto * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3. 157181834Sroberto */ 158181834Sroberto 159290000Sglebiusstatic unsigned long randtbl[DEG_3 + 1] = { 160181834Sroberto TYPE_3, 161181834Sroberto#ifdef USE_WEAK_SEEDING 162181834Sroberto/* Historic implementation compatibility */ 163181834Sroberto/* The random sequences do not vary much with the seed */ 164181834Sroberto 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5, 165181834Sroberto 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd, 166181834Sroberto 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88, 167181834Sroberto 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc, 168181834Sroberto 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b, 169181834Sroberto 0x27fb47b9, 170181834Sroberto#else /* !USE_WEAK_SEEDING */ 171181834Sroberto 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05, 172181834Sroberto 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454, 173181834Sroberto 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471, 174181834Sroberto 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1, 175181834Sroberto 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41, 176181834Sroberto 0xf3bec5da 177181834Sroberto#endif /* !USE_WEAK_SEEDING */ 178181834Sroberto}; 179181834Sroberto 180181834Sroberto/* 181181834Sroberto * fptr and rptr are two pointers into the state info, a front and a rear 182181834Sroberto * pointer. These two pointers are always rand_sep places aparts, as they 183181834Sroberto * cycle cyclically through the state information. (Yes, this does mean we 184181834Sroberto * could get away with just one pointer, but the code for random() is more 185181834Sroberto * efficient this way). The pointers are left positioned as they would be 186181834Sroberto * from the call 187181834Sroberto * 188181834Sroberto * initstate(1, randtbl, 128); 189181834Sroberto * 190181834Sroberto * (The position of the rear pointer, rptr, is really 0 (as explained above 191181834Sroberto * in the initialization of randtbl) because the state table pointer is set 192181834Sroberto * to point to randtbl[1] (as explained below). 193181834Sroberto */ 194290000Sglebiusstatic unsigned long *fptr = &randtbl[SEP_3 + 1]; 195290000Sglebiusstatic unsigned long *rptr = &randtbl[1]; 196181834Sroberto 197181834Sroberto/* 198181834Sroberto * The following things are the pointer to the state information table, the 199181834Sroberto * type of the current generator, the degree of the current polynomial being 200181834Sroberto * used, and the separation between the two pointers. Note that for efficiency 201181834Sroberto * of random(), we remember the first location of the state information, not 202181834Sroberto * the zeroeth. Hence it is valid to access state[-1], which is used to 203181834Sroberto * store the type of the R.N.G. Also, we remember the last location, since 204181834Sroberto * this is more efficient than indexing every time to find the address of 205181834Sroberto * the last element to see if the front and rear pointers have wrapped. 206181834Sroberto */ 207290000Sglebiusstatic unsigned long *state = &randtbl[1]; 208181834Srobertostatic long rand_type = TYPE_3; 209181834Srobertostatic long rand_deg = DEG_3; 210181834Srobertostatic long rand_sep = SEP_3; 211290000Sglebiusstatic unsigned long *end_ptr = &randtbl[DEG_3 + 1]; 212181834Sroberto 213290000Sglebiusstatic inline long good_rand (long); 214181834Sroberto 215181834Srobertostatic inline long 216181834Srobertogood_rand ( 217181834Sroberto register long x 218181834Sroberto ) 219181834Sroberto{ 220181834Sroberto#ifdef USE_WEAK_SEEDING 221181834Sroberto/* 222181834Sroberto * Historic implementation compatibility. 223181834Sroberto * The random sequences do not vary much with the seed, 224181834Sroberto * even with overflowing. 225181834Sroberto */ 226181834Sroberto return (1103515245 * x + 12345); 227181834Sroberto#else /* !USE_WEAK_SEEDING */ 228181834Sroberto/* 229181834Sroberto * Compute x = (7^5 * x) mod (2^31 - 1) 230181834Sroberto * wihout overflowing 31 bits: 231181834Sroberto * (2^31 - 1) = 127773 * (7^5) + 2836 232181834Sroberto * From "Random number generators: good ones are hard to find", 233181834Sroberto * Park and Miller, Communications of the ACM, vol. 31, no. 10, 234181834Sroberto * October 1988, p. 1195. 235181834Sroberto */ 236181834Sroberto register long hi, lo; 237181834Sroberto 238181834Sroberto hi = x / 127773; 239181834Sroberto lo = x % 127773; 240181834Sroberto x = 16807 * lo - 2836 * hi; 241181834Sroberto if (x <= 0) 242181834Sroberto x += 0x7fffffff; 243181834Sroberto return (x); 244181834Sroberto#endif /* !USE_WEAK_SEEDING */ 245181834Sroberto} 246181834Sroberto 247181834Sroberto/* 248181834Sroberto * srandom: 249181834Sroberto * 250181834Sroberto * Initialize the random number generator based on the given seed. If the 251181834Sroberto * type is the trivial no-state-information type, just remember the seed. 252181834Sroberto * Otherwise, initializes state[] based on the given "seed" via a linear 253181834Sroberto * congruential generator. Then, the pointers are set to known locations 254181834Sroberto * that are exactly rand_sep places apart. Lastly, it cycles the state 255181834Sroberto * information a given number of times to get rid of any initial dependencies 256181834Sroberto * introduced by the L.C.R.N.G. Note that the initialization of randtbl[] 257181834Sroberto * for default usage relies on values produced by this routine. 258181834Sroberto */ 259181834Srobertovoid 260181834Srobertontp_srandom( 261181834Sroberto unsigned long x 262181834Sroberto ) 263181834Sroberto{ 264290000Sglebius long i; 265181834Sroberto 266290000Sglebius if (rand_type == TYPE_0) { 267181834Sroberto state[0] = x; 268290000Sglebius } else { 269181834Sroberto state[0] = x; 270181834Sroberto for (i = 1; i < rand_deg; i++) 271181834Sroberto state[i] = good_rand(state[i - 1]); 272181834Sroberto fptr = &state[rand_sep]; 273181834Sroberto rptr = &state[0]; 274181834Sroberto for (i = 0; i < 10 * rand_deg; i++) 275290000Sglebius x = ntp_random(); 276181834Sroberto } 277290000Sglebius 278290000Sglebius /* seed the likely faster (and poorer) rand() as well */ 279290000Sglebius srand((u_int)x); 280181834Sroberto} 281181834Sroberto 282181834Sroberto/* 283181834Sroberto * srandomdev: 284181834Sroberto * 285181834Sroberto * Many programs choose the seed value in a totally predictable manner. 286181834Sroberto * This often causes problems. We seed the generator using the much more 287181834Sroberto * secure urandom(4) interface. Note that this particular seeding 288181834Sroberto * procedure can generate states which are impossible to reproduce by 289181834Sroberto * calling srandom() with any value, since the succeeding terms in the 290181834Sroberto * state buffer are no longer derived from the LC algorithm applied to 291181834Sroberto * a fixed seed. 292181834Sroberto */ 293181834Sroberto#ifdef NEED_SRANDOMDEV 294181834Srobertovoid 295181834Srobertontp_srandomdev( void ) 296181834Sroberto{ 297181834Sroberto struct timeval tv; 298181834Sroberto unsigned long junk; /* Purposely used uninitialized */ 299181834Sroberto 300181834Sroberto GETTIMEOFDAY(&tv, NULL); 301181834Sroberto ntp_srandom(getpid() ^ tv.tv_sec ^ tv.tv_usec ^ junk); 302181834Sroberto return; 303181834Sroberto} 304181834Sroberto#endif 305181834Sroberto 306290000Sglebius 307181834Sroberto/* 308290000Sglebius * ntp_initstate() and ntp_setstate() are unused in our codebase and 309290000Sglebius * trigger warnings due to casting to a more-strictly-aligned pointer 310290000Sglebius * on alignment-sensitive platforms. #ifdef them away to save noise, 311290000Sglebius * build time, and binary space, but retain the code in case we find a 312290000Sglebius * use. 313290000Sglebius */ 314290000Sglebius#ifdef COMPILE_UNUSED_FUNCTIONS 315290000Sglebius/* 316290000Sglebius * Array versions of the above information to make code run faster -- 317290000Sglebius * relies on fact that TYPE_i == i. 318290000Sglebius */ 319290000Sglebius#define MAX_TYPES 5 /* max number of types above */ 320290000Sglebius 321290000Sglebiusstatic long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }; 322290000Sglebiusstatic long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }; 323290000Sglebius 324290000Sglebius/* 325181834Sroberto * initstate: 326181834Sroberto * 327181834Sroberto * Initialize the state information in the given array of n bytes for future 328181834Sroberto * random number generation. Based on the number of bytes we are given, and 329181834Sroberto * the break values for the different R.N.G.'s, we choose the best (largest) 330181834Sroberto * one we can and set things up for it. srandom() is then called to 331181834Sroberto * initialize the state information. 332181834Sroberto * 333181834Sroberto * Note that on return from srandom(), we set state[-1] to be the type 334181834Sroberto * multiplexed with the current value of the rear pointer; this is so 335181834Sroberto * successive calls to initstate() won't lose this information and will be 336181834Sroberto * able to restart with setstate(). 337181834Sroberto * 338181834Sroberto * Note: the first thing we do is save the current state, if any, just like 339181834Sroberto * setstate() so that it doesn't matter when initstate is called. 340181834Sroberto * 341181834Sroberto * Returns a pointer to the old state. 342181834Sroberto * 343181834Sroberto * Note: The Sparc platform requires that arg_state begin on a long 344181834Sroberto * word boundary; otherwise a bus error will occur. Even so, lint will 345181834Sroberto * complain about mis-alignment, but you should disregard these messages. 346181834Sroberto */ 347181834Srobertochar * 348181834Srobertontp_initstate( 349181834Sroberto unsigned long seed, /* seed for R.N.G. */ 350181834Sroberto char *arg_state, /* pointer to state array */ 351181834Sroberto long n /* # bytes of state info */ 352181834Sroberto ) 353181834Sroberto{ 354181834Sroberto register char *ostate = (char *)(&state[-1]); 355181834Sroberto register long *long_arg_state = (long *) arg_state; 356181834Sroberto 357181834Sroberto if (rand_type == TYPE_0) 358181834Sroberto state[-1] = rand_type; 359181834Sroberto else 360181834Sroberto state[-1] = MAX_TYPES * (rptr - state) + rand_type; 361181834Sroberto if (n < BREAK_0) { 362181834Sroberto (void)fprintf(stderr, 363181834Sroberto "random: not enough state (%ld bytes); ignored.\n", n); 364181834Sroberto return(0); 365181834Sroberto } 366181834Sroberto if (n < BREAK_1) { 367181834Sroberto rand_type = TYPE_0; 368181834Sroberto rand_deg = DEG_0; 369181834Sroberto rand_sep = SEP_0; 370181834Sroberto } else if (n < BREAK_2) { 371181834Sroberto rand_type = TYPE_1; 372181834Sroberto rand_deg = DEG_1; 373181834Sroberto rand_sep = SEP_1; 374181834Sroberto } else if (n < BREAK_3) { 375181834Sroberto rand_type = TYPE_2; 376181834Sroberto rand_deg = DEG_2; 377181834Sroberto rand_sep = SEP_2; 378181834Sroberto } else if (n < BREAK_4) { 379181834Sroberto rand_type = TYPE_3; 380181834Sroberto rand_deg = DEG_3; 381181834Sroberto rand_sep = SEP_3; 382181834Sroberto } else { 383181834Sroberto rand_type = TYPE_4; 384181834Sroberto rand_deg = DEG_4; 385181834Sroberto rand_sep = SEP_4; 386181834Sroberto } 387290000Sglebius state = (unsigned long *) (long_arg_state + 1); /* first location */ 388181834Sroberto end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */ 389181834Sroberto ntp_srandom(seed); 390181834Sroberto if (rand_type == TYPE_0) 391181834Sroberto long_arg_state[0] = rand_type; 392181834Sroberto else 393181834Sroberto long_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type; 394181834Sroberto return(ostate); 395181834Sroberto} 396181834Sroberto 397181834Sroberto/* 398181834Sroberto * setstate: 399181834Sroberto * 400181834Sroberto * Restore the state from the given state array. 401181834Sroberto * 402181834Sroberto * Note: it is important that we also remember the locations of the pointers 403181834Sroberto * in the current state information, and restore the locations of the pointers 404181834Sroberto * from the old state information. This is done by multiplexing the pointer 405181834Sroberto * location into the zeroeth word of the state information. 406181834Sroberto * 407181834Sroberto * Note that due to the order in which things are done, it is OK to call 408181834Sroberto * setstate() with the same state as the current state. 409181834Sroberto * 410181834Sroberto * Returns a pointer to the old state information. 411181834Sroberto * 412181834Sroberto * Note: The Sparc platform requires that arg_state begin on a long 413181834Sroberto * word boundary; otherwise a bus error will occur. Even so, lint will 414181834Sroberto * complain about mis-alignment, but you should disregard these messages. 415181834Sroberto */ 416181834Srobertochar * 417181834Srobertontp_setstate( 418181834Sroberto char *arg_state /* pointer to state array */ 419181834Sroberto ) 420181834Sroberto{ 421290000Sglebius register unsigned long *new_state = (unsigned long *) arg_state; 422181834Sroberto register long type = new_state[0] % MAX_TYPES; 423181834Sroberto register long rear = new_state[0] / MAX_TYPES; 424181834Sroberto char *ostate = (char *)(&state[-1]); 425181834Sroberto 426181834Sroberto if (rand_type == TYPE_0) 427181834Sroberto state[-1] = rand_type; 428181834Sroberto else 429181834Sroberto state[-1] = MAX_TYPES * (rptr - state) + rand_type; 430181834Sroberto switch(type) { 431181834Sroberto case TYPE_0: 432181834Sroberto case TYPE_1: 433181834Sroberto case TYPE_2: 434181834Sroberto case TYPE_3: 435181834Sroberto case TYPE_4: 436181834Sroberto rand_type = type; 437181834Sroberto rand_deg = degrees[type]; 438181834Sroberto rand_sep = seps[type]; 439181834Sroberto break; 440181834Sroberto default: 441181834Sroberto (void)fprintf(stderr, 442181834Sroberto "random: state info corrupted; not changed.\n"); 443181834Sroberto } 444290000Sglebius state = (new_state + 1); 445181834Sroberto if (rand_type != TYPE_0) { 446181834Sroberto rptr = &state[rear]; 447181834Sroberto fptr = &state[(rear + rand_sep) % rand_deg]; 448181834Sroberto } 449181834Sroberto end_ptr = &state[rand_deg]; /* set end_ptr too */ 450181834Sroberto return(ostate); 451181834Sroberto} 452290000Sglebius#endif /* COMPILE_UNUSED_FUNCTIONS */ 453181834Sroberto 454290000Sglebius 455181834Sroberto/* 456181834Sroberto * random: 457181834Sroberto * 458181834Sroberto * If we are using the trivial TYPE_0 R.N.G., just do the old linear 459181834Sroberto * congruential bit. Otherwise, we do our fancy trinomial stuff, which is 460181834Sroberto * the same in all the other cases due to all the global variables that have 461181834Sroberto * been set up. The basic operation is to add the number at the rear pointer 462181834Sroberto * into the one at the front pointer. Then both pointers are advanced to 463181834Sroberto * the next location cyclically in the table. The value returned is the sum 464181834Sroberto * generated, reduced to 31 bits by throwing away the "least random" low bit. 465181834Sroberto * 466181834Sroberto * Note: the code takes advantage of the fact that both the front and 467181834Sroberto * rear pointers can't wrap on the same call by not testing the rear 468181834Sroberto * pointer if the front one has wrapped. 469181834Sroberto * 470181834Sroberto * Returns a 31-bit random number. 471181834Sroberto */ 472181834Srobertolong 473181834Srobertontp_random( void ) 474181834Sroberto{ 475181834Sroberto register long i; 476290000Sglebius register unsigned long *f, *r; 477181834Sroberto 478181834Sroberto if (rand_type == TYPE_0) { 479181834Sroberto i = state[0]; 480181834Sroberto state[0] = i = (good_rand(i)) & 0x7fffffff; 481181834Sroberto } else { 482181834Sroberto /* 483181834Sroberto * Use local variables rather than static variables for speed. 484181834Sroberto */ 485181834Sroberto f = fptr; r = rptr; 486181834Sroberto *f += *r; 487181834Sroberto i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */ 488181834Sroberto if (++f >= end_ptr) { 489181834Sroberto f = state; 490181834Sroberto ++r; 491181834Sroberto } 492181834Sroberto else if (++r >= end_ptr) { 493181834Sroberto r = state; 494181834Sroberto } 495181834Sroberto 496181834Sroberto fptr = f; rptr = r; 497181834Sroberto } 498181834Sroberto return(i); 499181834Sroberto} 500