11573Srgrimes/* 21573Srgrimes * Copyright (c) 1983, 1993 31573Srgrimes * The Regents of the University of California. All rights reserved. 41573Srgrimes * 51573Srgrimes * Redistribution and use in source and binary forms, with or without 61573Srgrimes * modification, are permitted provided that the following conditions 71573Srgrimes * are met: 81573Srgrimes * 1. Redistributions of source code must retain the above copyright 91573Srgrimes * notice, this list of conditions and the following disclaimer. 101573Srgrimes * 2. Redistributions in binary form must reproduce the above copyright 111573Srgrimes * notice, this list of conditions and the following disclaimer in the 121573Srgrimes * documentation and/or other materials provided with the distribution. 131573Srgrimes * 4. Neither the name of the University nor the names of its contributors 141573Srgrimes * may be used to endorse or promote products derived from this software 151573Srgrimes * without specific prior written permission. 161573Srgrimes * 171573Srgrimes * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 181573Srgrimes * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 191573Srgrimes * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 201573Srgrimes * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 211573Srgrimes * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 221573Srgrimes * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 231573Srgrimes * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 241573Srgrimes * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 251573Srgrimes * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 261573Srgrimes * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 271573Srgrimes * SUCH DAMAGE. 281573Srgrimes */ 291573Srgrimes 301573Srgrimes#if defined(LIBC_SCCS) && !defined(lint) 3123662Speterstatic char sccsid[] = "@(#)random.c 8.2 (Berkeley) 5/19/95"; 321573Srgrimes#endif /* LIBC_SCCS and not lint */ 3392986Sobrien#include <sys/cdefs.h> 3492986Sobrien__FBSDID("$FreeBSD$"); 351573Srgrimes 3671579Sdeischen#include "namespace.h" 37251168Sdelphij#include <sys/param.h> 38251168Sdelphij#include <sys/sysctl.h> 39124738Sdas#include <stdint.h> 401573Srgrimes#include <stdio.h> 411573Srgrimes#include <stdlib.h> 4271579Sdeischen#include "un-namespace.h" 431573Srgrimes 441573Srgrimes/* 451573Srgrimes * random.c: 461573Srgrimes * 471573Srgrimes * An improved random number generation package. In addition to the standard 481573Srgrimes * rand()/srand() like interface, this package also has a special state info 491573Srgrimes * interface. The initstate() routine is called with a seed, an array of 501573Srgrimes * bytes, and a count of how many bytes are being passed in; this array is 511573Srgrimes * then initialized to contain information for random number generation with 521573Srgrimes * that much state information. Good sizes for the amount of state 531573Srgrimes * information are 32, 64, 128, and 256 bytes. The state can be switched by 541573Srgrimes * calling the setstate() routine with the same array as was initiallized 551573Srgrimes * with initstate(). By default, the package runs with 128 bytes of state 561573Srgrimes * information and generates far better random numbers than a linear 571573Srgrimes * congruential generator. If the amount of state information is less than 581573Srgrimes * 32 bytes, a simple linear congruential R.N.G. is used. 591573Srgrimes * 60124738Sdas * Internally, the state information is treated as an array of uint32_t's; the 611573Srgrimes * zeroeth element of the array is the type of R.N.G. being used (small 621573Srgrimes * integer); the remainder of the array is the state information for the 63124738Sdas * R.N.G. Thus, 32 bytes of state information will give 7 ints worth of 641573Srgrimes * state information, which will allow a degree seven polynomial. (Note: 651573Srgrimes * the zeroeth word of state information also has some other information 661573Srgrimes * stored in it -- see setstate() for details). 678870Srgrimes * 681573Srgrimes * The random number generation technique is a linear feedback shift register 691573Srgrimes * approach, employing trinomials (since there are fewer terms to sum up that 701573Srgrimes * way). In this approach, the least significant bit of all the numbers in 711573Srgrimes * the state table will act as a linear feedback shift register, and will 721573Srgrimes * have period 2^deg - 1 (where deg is the degree of the polynomial being 731573Srgrimes * used, assuming that the polynomial is irreducible and primitive). The 741573Srgrimes * higher order bits will have longer periods, since their values are also 751573Srgrimes * influenced by pseudo-random carries out of the lower bits. The total 761573Srgrimes * period of the generator is approximately deg*(2**deg - 1); thus doubling 771573Srgrimes * the amount of state information has a vast influence on the period of the 781573Srgrimes * generator. Note: the deg*(2**deg - 1) is an approximation only good for 7992889Sobrien * large deg, when the period of the shift is the dominant factor. 801573Srgrimes * With deg equal to seven, the period is actually much longer than the 811573Srgrimes * 7*(2**7 - 1) predicted by this formula. 8223662Speter * 8323662Speter * Modified 28 December 1994 by Jacob S. Rosenberg. 8423662Speter * The following changes have been made: 8523662Speter * All references to the type u_int have been changed to unsigned long. 8623662Speter * All references to type int have been changed to type long. Other 8723662Speter * cleanups have been made as well. A warning for both initstate and 8823662Speter * setstate has been inserted to the effect that on Sparc platforms 8923662Speter * the 'arg_state' variable must be forced to begin on word boundaries. 9023662Speter * This can be easily done by casting a long integer array to char *. 9123662Speter * The overall logic has been left STRICTLY alone. This software was 9223662Speter * tested on both a VAX and Sun SpacsStation with exactly the same 9323662Speter * results. The new version and the original give IDENTICAL results. 9423662Speter * The new version is somewhat faster than the original. As the 9523662Speter * documentation says: "By default, the package runs with 128 bytes of 9623662Speter * state information and generates far better random numbers than a linear 9723662Speter * congruential generator. If the amount of state information is less than 9823662Speter * 32 bytes, a simple linear congruential R.N.G. is used." For a buffer of 9923662Speter * 128 bytes, this new version runs about 19 percent faster and for a 16 10023662Speter * byte buffer it is about 5 percent faster. 1011573Srgrimes */ 1021573Srgrimes 1031573Srgrimes/* 1041573Srgrimes * For each of the currently supported random number generators, we have a 1051573Srgrimes * break value on the amount of state information (you need at least this 1061573Srgrimes * many bytes of state info to support this random number generator), a degree 1071573Srgrimes * for the polynomial (actually a trinomial) that the R.N.G. is based on, and 1081573Srgrimes * the separation between the two lower order coefficients of the trinomial. 1091573Srgrimes */ 1101573Srgrimes#define TYPE_0 0 /* linear congruential */ 1111573Srgrimes#define BREAK_0 8 1121573Srgrimes#define DEG_0 0 1131573Srgrimes#define SEP_0 0 1141573Srgrimes 1151573Srgrimes#define TYPE_1 1 /* x**7 + x**3 + 1 */ 1161573Srgrimes#define BREAK_1 32 1171573Srgrimes#define DEG_1 7 1181573Srgrimes#define SEP_1 3 1191573Srgrimes 1201573Srgrimes#define TYPE_2 2 /* x**15 + x + 1 */ 1211573Srgrimes#define BREAK_2 64 1221573Srgrimes#define DEG_2 15 1231573Srgrimes#define SEP_2 1 1241573Srgrimes 1251573Srgrimes#define TYPE_3 3 /* x**31 + x**3 + 1 */ 1261573Srgrimes#define BREAK_3 128 1271573Srgrimes#define DEG_3 31 1281573Srgrimes#define SEP_3 3 1291573Srgrimes 1301573Srgrimes#define TYPE_4 4 /* x**63 + x + 1 */ 1311573Srgrimes#define BREAK_4 256 1321573Srgrimes#define DEG_4 63 1331573Srgrimes#define SEP_4 1 1341573Srgrimes 1351573Srgrimes/* 1361573Srgrimes * Array versions of the above information to make code run faster -- 1371573Srgrimes * relies on fact that TYPE_i == i. 1381573Srgrimes */ 1391573Srgrimes#define MAX_TYPES 5 /* max number of types above */ 1401573Srgrimes 141118731Sache#ifdef USE_WEAK_SEEDING 142118731Sache#define NSHUFF 0 143118731Sache#else /* !USE_WEAK_SEEDING */ 144118731Sache#define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */ 145118731Sache#endif /* !USE_WEAK_SEEDING */ 146110321Sache 147124738Sdasstatic const int degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }; 148124738Sdasstatic const int seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }; 1491573Srgrimes 1501573Srgrimes/* 1511573Srgrimes * Initially, everything is set up as if from: 1521573Srgrimes * 15318832Sache * initstate(1, randtbl, 128); 1541573Srgrimes * 1551573Srgrimes * Note that this initialization takes advantage of the fact that srandom() 1561573Srgrimes * advances the front and rear pointers 10*rand_deg times, and hence the 1571573Srgrimes * rear pointer which starts at 0 will also end up at zero; thus the zeroeth 1581573Srgrimes * element of the state information, which contains info about the current 1591573Srgrimes * position of the rear pointer is just 1601573Srgrimes * 1611573Srgrimes * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3. 1621573Srgrimes */ 1631573Srgrimes 164124738Sdasstatic uint32_t randtbl[DEG_3 + 1] = { 1651573Srgrimes TYPE_3, 16618832Sache#ifdef USE_WEAK_SEEDING 16718832Sache/* Historic implementation compatibility */ 16818832Sache/* The random sequences do not vary much with the seed */ 1691573Srgrimes 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5, 1701573Srgrimes 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd, 1711573Srgrimes 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88, 1721573Srgrimes 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc, 1731573Srgrimes 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b, 1741573Srgrimes 0x27fb47b9, 17518832Sache#else /* !USE_WEAK_SEEDING */ 17618832Sache 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05, 17718832Sache 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454, 17818832Sache 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471, 17918832Sache 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1, 18018832Sache 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41, 18118832Sache 0xf3bec5da 18218832Sache#endif /* !USE_WEAK_SEEDING */ 1831573Srgrimes}; 1841573Srgrimes 1851573Srgrimes/* 1861573Srgrimes * fptr and rptr are two pointers into the state info, a front and a rear 1871573Srgrimes * pointer. These two pointers are always rand_sep places aparts, as they 1881573Srgrimes * cycle cyclically through the state information. (Yes, this does mean we 1891573Srgrimes * could get away with just one pointer, but the code for random() is more 1901573Srgrimes * efficient this way). The pointers are left positioned as they would be 1911573Srgrimes * from the call 1921573Srgrimes * 1931573Srgrimes * initstate(1, randtbl, 128); 1941573Srgrimes * 1951573Srgrimes * (The position of the rear pointer, rptr, is really 0 (as explained above 1961573Srgrimes * in the initialization of randtbl) because the state table pointer is set 1971573Srgrimes * to point to randtbl[1] (as explained below). 1981573Srgrimes */ 199124738Sdasstatic uint32_t *fptr = &randtbl[SEP_3 + 1]; 200124738Sdasstatic uint32_t *rptr = &randtbl[1]; 2011573Srgrimes 2021573Srgrimes/* 2031573Srgrimes * The following things are the pointer to the state information table, the 2041573Srgrimes * type of the current generator, the degree of the current polynomial being 2051573Srgrimes * used, and the separation between the two pointers. Note that for efficiency 2061573Srgrimes * of random(), we remember the first location of the state information, not 2071573Srgrimes * the zeroeth. Hence it is valid to access state[-1], which is used to 2081573Srgrimes * store the type of the R.N.G. Also, we remember the last location, since 2091573Srgrimes * this is more efficient than indexing every time to find the address of 2101573Srgrimes * the last element to see if the front and rear pointers have wrapped. 2111573Srgrimes */ 212124738Sdasstatic uint32_t *state = &randtbl[1]; 213124738Sdasstatic int rand_type = TYPE_3; 214124738Sdasstatic int rand_deg = DEG_3; 215124738Sdasstatic int rand_sep = SEP_3; 216124738Sdasstatic uint32_t *end_ptr = &randtbl[DEG_3 + 1]; 2171573Srgrimes 218251165Sdelphijstatic inline uint32_t 219251165Sdelphijgood_rand(int32_t x) 22018832Sache{ 22118832Sache#ifdef USE_WEAK_SEEDING 2221573Srgrimes/* 22318832Sache * Historic implementation compatibility. 22418832Sache * The random sequences do not vary much with the seed, 22518832Sache * even with overflowing. 22618832Sache */ 22718832Sache return (1103515245 * x + 12345); 22818832Sache#else /* !USE_WEAK_SEEDING */ 22918832Sache/* 23018832Sache * Compute x = (7^5 * x) mod (2^31 - 1) 23118832Sache * wihout overflowing 31 bits: 23218832Sache * (2^31 - 1) = 127773 * (7^5) + 2836 23318832Sache * From "Random number generators: good ones are hard to find", 23418832Sache * Park and Miller, Communications of the ACM, vol. 31, no. 10, 23518832Sache * October 1988, p. 1195. 23618832Sache */ 237124738Sdas int32_t hi, lo; 23818832Sache 239110280Sache /* Can't be initialized with 0, so use another value. */ 240110280Sache if (x == 0) 241110280Sache x = 123459876; 24218832Sache hi = x / 127773; 24318832Sache lo = x % 127773; 24418832Sache x = 16807 * lo - 2836 * hi; 245110280Sache if (x < 0) 24618832Sache x += 0x7fffffff; 24718832Sache return (x); 24818832Sache#endif /* !USE_WEAK_SEEDING */ 24918832Sache} 25018832Sache 25118832Sache/* 2521573Srgrimes * srandom: 2531573Srgrimes * 2541573Srgrimes * Initialize the random number generator based on the given seed. If the 2551573Srgrimes * type is the trivial no-state-information type, just remember the seed. 2561573Srgrimes * Otherwise, initializes state[] based on the given "seed" via a linear 2571573Srgrimes * congruential generator. Then, the pointers are set to known locations 2581573Srgrimes * that are exactly rand_sep places apart. Lastly, it cycles the state 2591573Srgrimes * information a given number of times to get rid of any initial dependencies 2601573Srgrimes * introduced by the L.C.R.N.G. Note that the initialization of randtbl[] 2611573Srgrimes * for default usage relies on values produced by this routine. 2621573Srgrimes */ 2631573Srgrimesvoid 264251165Sdelphijsrandom(unsigned long x) 2651573Srgrimes{ 266124738Sdas int i, lim; 2671573Srgrimes 268124738Sdas state[0] = (uint32_t)x; 2691573Srgrimes if (rand_type == TYPE_0) 270110321Sache lim = NSHUFF; 2711573Srgrimes else { 2721573Srgrimes for (i = 1; i < rand_deg; i++) 27318832Sache state[i] = good_rand(state[i - 1]); 2741573Srgrimes fptr = &state[rand_sep]; 2751573Srgrimes rptr = &state[0]; 276110321Sache lim = 10 * rand_deg; 2771573Srgrimes } 278110321Sache for (i = 0; i < lim; i++) 279110321Sache (void)random(); 2801573Srgrimes} 2811573Srgrimes 2821573Srgrimes/* 28324151Sache * srandomdev: 28424151Sache * 28524151Sache * Many programs choose the seed value in a totally predictable manner. 286251168Sdelphij * This often causes problems. We seed the generator using pseudo-random 287251168Sdelphij * data from the kernel. 288251168Sdelphij * 289251168Sdelphij * Note that this particular seeding procedure can generate states 290251168Sdelphij * which are impossible to reproduce by calling srandom() with any 291251168Sdelphij * value, since the succeeding terms in the state buffer are no longer 292251168Sdelphij * derived from the LC algorithm applied to a fixed seed. 29324151Sache */ 29426624Sachevoid 295251165Sdelphijsrandomdev(void) 29624151Sache{ 297251168Sdelphij int mib[2]; 29824151Sache size_t len; 29924151Sache 30024151Sache if (rand_type == TYPE_0) 301251168Sdelphij len = sizeof(state[0]); 30224151Sache else 303251168Sdelphij len = rand_deg * sizeof(state[0]); 30424151Sache 305251168Sdelphij mib[0] = CTL_KERN; 306251168Sdelphij mib[1] = KERN_ARND; 307251168Sdelphij sysctl(mib, 2, state, &len, NULL, 0); 30824151Sache 30924151Sache if (rand_type != TYPE_0) { 31024151Sache fptr = &state[rand_sep]; 31124151Sache rptr = &state[0]; 31224151Sache } 31324151Sache} 31424151Sache 31524151Sache/* 3161573Srgrimes * initstate: 3171573Srgrimes * 3181573Srgrimes * Initialize the state information in the given array of n bytes for future 3191573Srgrimes * random number generation. Based on the number of bytes we are given, and 3201573Srgrimes * the break values for the different R.N.G.'s, we choose the best (largest) 3211573Srgrimes * one we can and set things up for it. srandom() is then called to 3221573Srgrimes * initialize the state information. 3238870Srgrimes * 3241573Srgrimes * Note that on return from srandom(), we set state[-1] to be the type 3251573Srgrimes * multiplexed with the current value of the rear pointer; this is so 3261573Srgrimes * successive calls to initstate() won't lose this information and will be 3271573Srgrimes * able to restart with setstate(). 3288870Srgrimes * 3291573Srgrimes * Note: the first thing we do is save the current state, if any, just like 3301573Srgrimes * setstate() so that it doesn't matter when initstate is called. 3311573Srgrimes * 3321573Srgrimes * Returns a pointer to the old state. 33323662Speter * 334124738Sdas * Note: The Sparc platform requires that arg_state begin on an int 33523662Speter * word boundary; otherwise a bus error will occur. Even so, lint will 33623662Speter * complain about mis-alignment, but you should disregard these messages. 3371573Srgrimes */ 3381573Srgrimeschar * 339251165Sdelphijinitstate(unsigned long seed, char *arg_state, long n) 3401573Srgrimes{ 34192889Sobrien char *ostate = (char *)(&state[-1]); 342124738Sdas uint32_t *int_arg_state = (uint32_t *)arg_state; 3431573Srgrimes 3441573Srgrimes if (rand_type == TYPE_0) 3451573Srgrimes state[-1] = rand_type; 3461573Srgrimes else 3471573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 3481573Srgrimes if (n < BREAK_0) { 3491573Srgrimes (void)fprintf(stderr, 35023662Speter "random: not enough state (%ld bytes); ignored.\n", n); 351251165Sdelphij return (0); 3521573Srgrimes } 3531573Srgrimes if (n < BREAK_1) { 3541573Srgrimes rand_type = TYPE_0; 3551573Srgrimes rand_deg = DEG_0; 3561573Srgrimes rand_sep = SEP_0; 3571573Srgrimes } else if (n < BREAK_2) { 3581573Srgrimes rand_type = TYPE_1; 3591573Srgrimes rand_deg = DEG_1; 3601573Srgrimes rand_sep = SEP_1; 3611573Srgrimes } else if (n < BREAK_3) { 3621573Srgrimes rand_type = TYPE_2; 3631573Srgrimes rand_deg = DEG_2; 3641573Srgrimes rand_sep = SEP_2; 3651573Srgrimes } else if (n < BREAK_4) { 3661573Srgrimes rand_type = TYPE_3; 3671573Srgrimes rand_deg = DEG_3; 3681573Srgrimes rand_sep = SEP_3; 3691573Srgrimes } else { 3701573Srgrimes rand_type = TYPE_4; 3711573Srgrimes rand_deg = DEG_4; 3721573Srgrimes rand_sep = SEP_4; 3731573Srgrimes } 374124738Sdas state = int_arg_state + 1; /* first location */ 3751573Srgrimes end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */ 3761573Srgrimes srandom(seed); 3771573Srgrimes if (rand_type == TYPE_0) 378124738Sdas int_arg_state[0] = rand_type; 3791573Srgrimes else 380124738Sdas int_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type; 381251165Sdelphij return (ostate); 3821573Srgrimes} 3831573Srgrimes 3841573Srgrimes/* 3851573Srgrimes * setstate: 3861573Srgrimes * 3871573Srgrimes * Restore the state from the given state array. 3881573Srgrimes * 3891573Srgrimes * Note: it is important that we also remember the locations of the pointers 3901573Srgrimes * in the current state information, and restore the locations of the pointers 3911573Srgrimes * from the old state information. This is done by multiplexing the pointer 3921573Srgrimes * location into the zeroeth word of the state information. 3931573Srgrimes * 3941573Srgrimes * Note that due to the order in which things are done, it is OK to call 3951573Srgrimes * setstate() with the same state as the current state. 3961573Srgrimes * 3971573Srgrimes * Returns a pointer to the old state information. 39823662Speter * 399124738Sdas * Note: The Sparc platform requires that arg_state begin on an int 40023662Speter * word boundary; otherwise a bus error will occur. Even so, lint will 40123662Speter * complain about mis-alignment, but you should disregard these messages. 4021573Srgrimes */ 4031573Srgrimeschar * 404251165Sdelphijsetstate(char *arg_state) 4051573Srgrimes{ 406124738Sdas uint32_t *new_state = (uint32_t *)arg_state; 407124738Sdas uint32_t type = new_state[0] % MAX_TYPES; 408124738Sdas uint32_t rear = new_state[0] / MAX_TYPES; 4091573Srgrimes char *ostate = (char *)(&state[-1]); 4101573Srgrimes 4111573Srgrimes if (rand_type == TYPE_0) 4121573Srgrimes state[-1] = rand_type; 4131573Srgrimes else 4141573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 4151573Srgrimes switch(type) { 4161573Srgrimes case TYPE_0: 4171573Srgrimes case TYPE_1: 4181573Srgrimes case TYPE_2: 4191573Srgrimes case TYPE_3: 4201573Srgrimes case TYPE_4: 4211573Srgrimes rand_type = type; 4221573Srgrimes rand_deg = degrees[type]; 4231573Srgrimes rand_sep = seps[type]; 4241573Srgrimes break; 4251573Srgrimes default: 4261573Srgrimes (void)fprintf(stderr, 4271573Srgrimes "random: state info corrupted; not changed.\n"); 4281573Srgrimes } 429124738Sdas state = new_state + 1; 4301573Srgrimes if (rand_type != TYPE_0) { 4311573Srgrimes rptr = &state[rear]; 4321573Srgrimes fptr = &state[(rear + rand_sep) % rand_deg]; 4331573Srgrimes } 4341573Srgrimes end_ptr = &state[rand_deg]; /* set end_ptr too */ 435251165Sdelphij return (ostate); 4361573Srgrimes} 4371573Srgrimes 4381573Srgrimes/* 4391573Srgrimes * random: 4401573Srgrimes * 4411573Srgrimes * If we are using the trivial TYPE_0 R.N.G., just do the old linear 4421573Srgrimes * congruential bit. Otherwise, we do our fancy trinomial stuff, which is 4431573Srgrimes * the same in all the other cases due to all the global variables that have 4441573Srgrimes * been set up. The basic operation is to add the number at the rear pointer 4451573Srgrimes * into the one at the front pointer. Then both pointers are advanced to 4461573Srgrimes * the next location cyclically in the table. The value returned is the sum 4471573Srgrimes * generated, reduced to 31 bits by throwing away the "least random" low bit. 4481573Srgrimes * 4491573Srgrimes * Note: the code takes advantage of the fact that both the front and 4501573Srgrimes * rear pointers can't wrap on the same call by not testing the rear 4511573Srgrimes * pointer if the front one has wrapped. 4521573Srgrimes * 4531573Srgrimes * Returns a 31-bit random number. 4541573Srgrimes */ 4551573Srgrimeslong 456251165Sdelphijrandom(void) 4571573Srgrimes{ 458124738Sdas uint32_t i; 459124738Sdas uint32_t *f, *r; 4601573Srgrimes 46123662Speter if (rand_type == TYPE_0) { 46223662Speter i = state[0]; 46323662Speter state[0] = i = (good_rand(i)) & 0x7fffffff; 46423662Speter } else { 46523662Speter /* 46623662Speter * Use local variables rather than static variables for speed. 46723662Speter */ 46823662Speter f = fptr; r = rptr; 46923662Speter *f += *r; 47023662Speter i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */ 47123662Speter if (++f >= end_ptr) { 47223662Speter f = state; 47323662Speter ++r; 47423662Speter } 47523662Speter else if (++r >= end_ptr) { 47623662Speter r = state; 47723662Speter } 47823662Speter 47923662Speter fptr = f; rptr = r; 4801573Srgrimes } 481251165Sdelphij return ((long)i); 4821573Srgrimes} 483