random.c revision 118731
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 * 3. All advertising materials mentioning features or use of this software 141573Srgrimes * must display the following acknowledgement: 151573Srgrimes * This product includes software developed by the University of 161573Srgrimes * California, Berkeley and its contributors. 171573Srgrimes * 4. Neither the name of the University nor the names of its contributors 181573Srgrimes * may be used to endorse or promote products derived from this software 191573Srgrimes * without specific prior written permission. 201573Srgrimes * 211573Srgrimes * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 221573Srgrimes * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 231573Srgrimes * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 241573Srgrimes * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 251573Srgrimes * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 261573Srgrimes * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 271573Srgrimes * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 281573Srgrimes * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 291573Srgrimes * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 301573Srgrimes * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 311573Srgrimes * SUCH DAMAGE. 321573Srgrimes */ 331573Srgrimes 341573Srgrimes#if defined(LIBC_SCCS) && !defined(lint) 3523662Speterstatic char sccsid[] = "@(#)random.c 8.2 (Berkeley) 5/19/95"; 361573Srgrimes#endif /* LIBC_SCCS and not lint */ 3792986Sobrien#include <sys/cdefs.h> 3892986Sobrien__FBSDID("$FreeBSD: head/lib/libc/stdlib/random.c 118731 2003-08-10 17:49:55Z ache $"); 391573Srgrimes 4071579Sdeischen#include "namespace.h" 4126624Sache#include <sys/time.h> /* for srandomdev() */ 4224151Sache#include <fcntl.h> /* for srandomdev() */ 431573Srgrimes#include <stdio.h> 441573Srgrimes#include <stdlib.h> 4524151Sache#include <unistd.h> /* for srandomdev() */ 4671579Sdeischen#include "un-namespace.h" 471573Srgrimes 481573Srgrimes/* 491573Srgrimes * random.c: 501573Srgrimes * 511573Srgrimes * An improved random number generation package. In addition to the standard 521573Srgrimes * rand()/srand() like interface, this package also has a special state info 531573Srgrimes * interface. The initstate() routine is called with a seed, an array of 541573Srgrimes * bytes, and a count of how many bytes are being passed in; this array is 551573Srgrimes * then initialized to contain information for random number generation with 561573Srgrimes * that much state information. Good sizes for the amount of state 571573Srgrimes * information are 32, 64, 128, and 256 bytes. The state can be switched by 581573Srgrimes * calling the setstate() routine with the same array as was initiallized 591573Srgrimes * with initstate(). By default, the package runs with 128 bytes of state 601573Srgrimes * information and generates far better random numbers than a linear 611573Srgrimes * congruential generator. If the amount of state information is less than 621573Srgrimes * 32 bytes, a simple linear congruential R.N.G. is used. 631573Srgrimes * 641573Srgrimes * Internally, the state information is treated as an array of longs; the 651573Srgrimes * zeroeth element of the array is the type of R.N.G. being used (small 661573Srgrimes * integer); the remainder of the array is the state information for the 671573Srgrimes * R.N.G. Thus, 32 bytes of state information will give 7 longs worth of 681573Srgrimes * state information, which will allow a degree seven polynomial. (Note: 691573Srgrimes * the zeroeth word of state information also has some other information 701573Srgrimes * stored in it -- see setstate() for details). 718870Srgrimes * 721573Srgrimes * The random number generation technique is a linear feedback shift register 731573Srgrimes * approach, employing trinomials (since there are fewer terms to sum up that 741573Srgrimes * way). In this approach, the least significant bit of all the numbers in 751573Srgrimes * the state table will act as a linear feedback shift register, and will 761573Srgrimes * have period 2^deg - 1 (where deg is the degree of the polynomial being 771573Srgrimes * used, assuming that the polynomial is irreducible and primitive). The 781573Srgrimes * higher order bits will have longer periods, since their values are also 791573Srgrimes * influenced by pseudo-random carries out of the lower bits. The total 801573Srgrimes * period of the generator is approximately deg*(2**deg - 1); thus doubling 811573Srgrimes * the amount of state information has a vast influence on the period of the 821573Srgrimes * generator. Note: the deg*(2**deg - 1) is an approximation only good for 8392889Sobrien * large deg, when the period of the shift is the dominant factor. 841573Srgrimes * With deg equal to seven, the period is actually much longer than the 851573Srgrimes * 7*(2**7 - 1) predicted by this formula. 8623662Speter * 8723662Speter * Modified 28 December 1994 by Jacob S. Rosenberg. 8823662Speter * The following changes have been made: 8923662Speter * All references to the type u_int have been changed to unsigned long. 9023662Speter * All references to type int have been changed to type long. Other 9123662Speter * cleanups have been made as well. A warning for both initstate and 9223662Speter * setstate has been inserted to the effect that on Sparc platforms 9323662Speter * the 'arg_state' variable must be forced to begin on word boundaries. 9423662Speter * This can be easily done by casting a long integer array to char *. 9523662Speter * The overall logic has been left STRICTLY alone. This software was 9623662Speter * tested on both a VAX and Sun SpacsStation with exactly the same 9723662Speter * results. The new version and the original give IDENTICAL results. 9823662Speter * The new version is somewhat faster than the original. As the 9923662Speter * documentation says: "By default, the package runs with 128 bytes of 10023662Speter * state information and generates far better random numbers than a linear 10123662Speter * congruential generator. If the amount of state information is less than 10223662Speter * 32 bytes, a simple linear congruential R.N.G. is used." For a buffer of 10323662Speter * 128 bytes, this new version runs about 19 percent faster and for a 16 10423662Speter * byte buffer it is about 5 percent faster. 1051573Srgrimes */ 1061573Srgrimes 1071573Srgrimes/* 1081573Srgrimes * For each of the currently supported random number generators, we have a 1091573Srgrimes * break value on the amount of state information (you need at least this 1101573Srgrimes * many bytes of state info to support this random number generator), a degree 1111573Srgrimes * for the polynomial (actually a trinomial) that the R.N.G. is based on, and 1121573Srgrimes * the separation between the two lower order coefficients of the trinomial. 1131573Srgrimes */ 1141573Srgrimes#define TYPE_0 0 /* linear congruential */ 1151573Srgrimes#define BREAK_0 8 1161573Srgrimes#define DEG_0 0 1171573Srgrimes#define SEP_0 0 1181573Srgrimes 1191573Srgrimes#define TYPE_1 1 /* x**7 + x**3 + 1 */ 1201573Srgrimes#define BREAK_1 32 1211573Srgrimes#define DEG_1 7 1221573Srgrimes#define SEP_1 3 1231573Srgrimes 1241573Srgrimes#define TYPE_2 2 /* x**15 + x + 1 */ 1251573Srgrimes#define BREAK_2 64 1261573Srgrimes#define DEG_2 15 1271573Srgrimes#define SEP_2 1 1281573Srgrimes 1291573Srgrimes#define TYPE_3 3 /* x**31 + x**3 + 1 */ 1301573Srgrimes#define BREAK_3 128 1311573Srgrimes#define DEG_3 31 1321573Srgrimes#define SEP_3 3 1331573Srgrimes 1341573Srgrimes#define TYPE_4 4 /* x**63 + x + 1 */ 1351573Srgrimes#define BREAK_4 256 1361573Srgrimes#define DEG_4 63 1371573Srgrimes#define SEP_4 1 1381573Srgrimes 1391573Srgrimes/* 1401573Srgrimes * Array versions of the above information to make code run faster -- 1411573Srgrimes * relies on fact that TYPE_i == i. 1421573Srgrimes */ 1431573Srgrimes#define MAX_TYPES 5 /* max number of types above */ 1441573Srgrimes 145118731Sache#ifdef USE_WEAK_SEEDING 146118731Sache#define NSHUFF 0 147118731Sache#else /* !USE_WEAK_SEEDING */ 148118731Sache#define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */ 149118731Sache#endif /* !USE_WEAK_SEEDING */ 150110321Sache 15123662Speterstatic long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }; 15223662Speterstatic long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }; 1531573Srgrimes 1541573Srgrimes/* 1551573Srgrimes * Initially, everything is set up as if from: 1561573Srgrimes * 15718832Sache * initstate(1, randtbl, 128); 1581573Srgrimes * 1591573Srgrimes * Note that this initialization takes advantage of the fact that srandom() 1601573Srgrimes * advances the front and rear pointers 10*rand_deg times, and hence the 1611573Srgrimes * rear pointer which starts at 0 will also end up at zero; thus the zeroeth 1621573Srgrimes * element of the state information, which contains info about the current 1631573Srgrimes * position of the rear pointer is just 1641573Srgrimes * 1651573Srgrimes * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3. 1661573Srgrimes */ 1671573Srgrimes 1681573Srgrimesstatic long randtbl[DEG_3 + 1] = { 1691573Srgrimes TYPE_3, 17018832Sache#ifdef USE_WEAK_SEEDING 17118832Sache/* Historic implementation compatibility */ 17218832Sache/* The random sequences do not vary much with the seed */ 1731573Srgrimes 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5, 1741573Srgrimes 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd, 1751573Srgrimes 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88, 1761573Srgrimes 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc, 1771573Srgrimes 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b, 1781573Srgrimes 0x27fb47b9, 17918832Sache#else /* !USE_WEAK_SEEDING */ 18018832Sache 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05, 18118832Sache 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454, 18218832Sache 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471, 18318832Sache 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1, 18418832Sache 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41, 18518832Sache 0xf3bec5da 18618832Sache#endif /* !USE_WEAK_SEEDING */ 1871573Srgrimes}; 1881573Srgrimes 1891573Srgrimes/* 1901573Srgrimes * fptr and rptr are two pointers into the state info, a front and a rear 1911573Srgrimes * pointer. These two pointers are always rand_sep places aparts, as they 1921573Srgrimes * cycle cyclically through the state information. (Yes, this does mean we 1931573Srgrimes * could get away with just one pointer, but the code for random() is more 1941573Srgrimes * efficient this way). The pointers are left positioned as they would be 1951573Srgrimes * from the call 1961573Srgrimes * 1971573Srgrimes * initstate(1, randtbl, 128); 1981573Srgrimes * 1991573Srgrimes * (The position of the rear pointer, rptr, is really 0 (as explained above 2001573Srgrimes * in the initialization of randtbl) because the state table pointer is set 2011573Srgrimes * to point to randtbl[1] (as explained below). 2021573Srgrimes */ 2031573Srgrimesstatic long *fptr = &randtbl[SEP_3 + 1]; 2041573Srgrimesstatic long *rptr = &randtbl[1]; 2051573Srgrimes 2061573Srgrimes/* 2071573Srgrimes * The following things are the pointer to the state information table, the 2081573Srgrimes * type of the current generator, the degree of the current polynomial being 2091573Srgrimes * used, and the separation between the two pointers. Note that for efficiency 2101573Srgrimes * of random(), we remember the first location of the state information, not 2111573Srgrimes * the zeroeth. Hence it is valid to access state[-1], which is used to 2121573Srgrimes * store the type of the R.N.G. Also, we remember the last location, since 2131573Srgrimes * this is more efficient than indexing every time to find the address of 2141573Srgrimes * the last element to see if the front and rear pointers have wrapped. 2151573Srgrimes */ 2161573Srgrimesstatic long *state = &randtbl[1]; 21723662Speterstatic long rand_type = TYPE_3; 21823662Speterstatic long rand_deg = DEG_3; 21923662Speterstatic long rand_sep = SEP_3; 2201573Srgrimesstatic long *end_ptr = &randtbl[DEG_3 + 1]; 2211573Srgrimes 22292905Sobrienstatic inline long good_rand(long); 22318832Sache 22418832Sachestatic inline long good_rand (x) 22592889Sobrien long x; 22618832Sache{ 22718832Sache#ifdef USE_WEAK_SEEDING 2281573Srgrimes/* 22918832Sache * Historic implementation compatibility. 23018832Sache * The random sequences do not vary much with the seed, 23118832Sache * even with overflowing. 23218832Sache */ 23318832Sache return (1103515245 * x + 12345); 23418832Sache#else /* !USE_WEAK_SEEDING */ 23518832Sache/* 23618832Sache * Compute x = (7^5 * x) mod (2^31 - 1) 23718832Sache * wihout overflowing 31 bits: 23818832Sache * (2^31 - 1) = 127773 * (7^5) + 2836 23918832Sache * From "Random number generators: good ones are hard to find", 24018832Sache * Park and Miller, Communications of the ACM, vol. 31, no. 10, 24118832Sache * October 1988, p. 1195. 24218832Sache */ 24392889Sobrien long hi, lo; 24418832Sache 245110280Sache /* Can't be initialized with 0, so use another value. */ 246110280Sache if (x == 0) 247110280Sache x = 123459876; 24818832Sache hi = x / 127773; 24918832Sache lo = x % 127773; 25018832Sache x = 16807 * lo - 2836 * hi; 251110280Sache if (x < 0) 25218832Sache x += 0x7fffffff; 25318832Sache return (x); 25418832Sache#endif /* !USE_WEAK_SEEDING */ 25518832Sache} 25618832Sache 25718832Sache/* 2581573Srgrimes * srandom: 2591573Srgrimes * 2601573Srgrimes * Initialize the random number generator based on the given seed. If the 2611573Srgrimes * type is the trivial no-state-information type, just remember the seed. 2621573Srgrimes * Otherwise, initializes state[] based on the given "seed" via a linear 2631573Srgrimes * congruential generator. Then, the pointers are set to known locations 2641573Srgrimes * that are exactly rand_sep places apart. Lastly, it cycles the state 2651573Srgrimes * information a given number of times to get rid of any initial dependencies 2661573Srgrimes * introduced by the L.C.R.N.G. Note that the initialization of randtbl[] 2671573Srgrimes * for default usage relies on values produced by this routine. 2681573Srgrimes */ 2691573Srgrimesvoid 2701573Srgrimessrandom(x) 27123662Speter unsigned long x; 2721573Srgrimes{ 273110321Sache long i, lim; 2741573Srgrimes 275110321Sache state[0] = x; 2761573Srgrimes if (rand_type == TYPE_0) 277110321Sache lim = NSHUFF; 2781573Srgrimes else { 2791573Srgrimes for (i = 1; i < rand_deg; i++) 28018832Sache state[i] = good_rand(state[i - 1]); 2811573Srgrimes fptr = &state[rand_sep]; 2821573Srgrimes rptr = &state[0]; 283110321Sache lim = 10 * rand_deg; 2841573Srgrimes } 285110321Sache for (i = 0; i < lim; i++) 286110321Sache (void)random(); 2871573Srgrimes} 2881573Srgrimes 2891573Srgrimes/* 29024151Sache * srandomdev: 29124151Sache * 29224151Sache * Many programs choose the seed value in a totally predictable manner. 29324151Sache * This often causes problems. We seed the generator using the much more 29477851Sdd * secure random(4) interface. Note that this particular seeding 29524151Sache * procedure can generate states which are impossible to reproduce by 29624151Sache * calling srandom() with any value, since the succeeding terms in the 29724151Sache * state buffer are no longer derived from the LC algorithm applied to 29824151Sache * a fixed seed. 29924151Sache */ 30026624Sachevoid 30124151Sachesrandomdev() 30224151Sache{ 30326624Sache int fd, done; 30424151Sache size_t len; 30524151Sache 30624151Sache if (rand_type == TYPE_0) 30724151Sache len = sizeof state[0]; 30824151Sache else 30924151Sache len = rand_deg * sizeof state[0]; 31024151Sache 31126624Sache done = 0; 31285752Smarkm fd = _open("/dev/random", O_RDONLY, 0); 31326624Sache if (fd >= 0) { 31456698Sjasone if (_read(fd, (void *) state, len) == (ssize_t) len) 31526624Sache done = 1; 31656698Sjasone _close(fd); 31724151Sache } 31824151Sache 31926624Sache if (!done) { 32026624Sache struct timeval tv; 32126665Sache unsigned long junk; 32226624Sache 32326624Sache gettimeofday(&tv, NULL); 32475862Sache srandom((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk); 32526624Sache return; 32626624Sache } 32726624Sache 32824151Sache if (rand_type != TYPE_0) { 32924151Sache fptr = &state[rand_sep]; 33024151Sache rptr = &state[0]; 33124151Sache } 33224151Sache} 33324151Sache 33424151Sache/* 3351573Srgrimes * initstate: 3361573Srgrimes * 3371573Srgrimes * Initialize the state information in the given array of n bytes for future 3381573Srgrimes * random number generation. Based on the number of bytes we are given, and 3391573Srgrimes * the break values for the different R.N.G.'s, we choose the best (largest) 3401573Srgrimes * one we can and set things up for it. srandom() is then called to 3411573Srgrimes * initialize the state information. 3428870Srgrimes * 3431573Srgrimes * Note that on return from srandom(), we set state[-1] to be the type 3441573Srgrimes * multiplexed with the current value of the rear pointer; this is so 3451573Srgrimes * successive calls to initstate() won't lose this information and will be 3461573Srgrimes * able to restart with setstate(). 3478870Srgrimes * 3481573Srgrimes * Note: the first thing we do is save the current state, if any, just like 3491573Srgrimes * setstate() so that it doesn't matter when initstate is called. 3501573Srgrimes * 3511573Srgrimes * Returns a pointer to the old state. 35223662Speter * 35323662Speter * Note: The Sparc platform requires that arg_state begin on a long 35423662Speter * word boundary; otherwise a bus error will occur. Even so, lint will 35523662Speter * complain about mis-alignment, but you should disregard these messages. 3561573Srgrimes */ 3571573Srgrimeschar * 3581573Srgrimesinitstate(seed, arg_state, n) 35923662Speter unsigned long seed; /* seed for R.N.G. */ 3601573Srgrimes char *arg_state; /* pointer to state array */ 36123662Speter long n; /* # bytes of state info */ 3621573Srgrimes{ 36392889Sobrien char *ostate = (char *)(&state[-1]); 36492889Sobrien long *long_arg_state = (long *) arg_state; 3651573Srgrimes 3661573Srgrimes if (rand_type == TYPE_0) 3671573Srgrimes state[-1] = rand_type; 3681573Srgrimes else 3691573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 3701573Srgrimes if (n < BREAK_0) { 3711573Srgrimes (void)fprintf(stderr, 37223662Speter "random: not enough state (%ld bytes); ignored.\n", n); 3731573Srgrimes return(0); 3741573Srgrimes } 3751573Srgrimes if (n < BREAK_1) { 3761573Srgrimes rand_type = TYPE_0; 3771573Srgrimes rand_deg = DEG_0; 3781573Srgrimes rand_sep = SEP_0; 3791573Srgrimes } else if (n < BREAK_2) { 3801573Srgrimes rand_type = TYPE_1; 3811573Srgrimes rand_deg = DEG_1; 3821573Srgrimes rand_sep = SEP_1; 3831573Srgrimes } else if (n < BREAK_3) { 3841573Srgrimes rand_type = TYPE_2; 3851573Srgrimes rand_deg = DEG_2; 3861573Srgrimes rand_sep = SEP_2; 3871573Srgrimes } else if (n < BREAK_4) { 3881573Srgrimes rand_type = TYPE_3; 3891573Srgrimes rand_deg = DEG_3; 3901573Srgrimes rand_sep = SEP_3; 3911573Srgrimes } else { 3921573Srgrimes rand_type = TYPE_4; 3931573Srgrimes rand_deg = DEG_4; 3941573Srgrimes rand_sep = SEP_4; 3951573Srgrimes } 39623662Speter state = (long *) (long_arg_state + 1); /* first location */ 3971573Srgrimes end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */ 3981573Srgrimes srandom(seed); 3991573Srgrimes if (rand_type == TYPE_0) 40023662Speter long_arg_state[0] = rand_type; 4011573Srgrimes else 40223662Speter long_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type; 4031573Srgrimes return(ostate); 4041573Srgrimes} 4051573Srgrimes 4061573Srgrimes/* 4071573Srgrimes * setstate: 4081573Srgrimes * 4091573Srgrimes * Restore the state from the given state array. 4101573Srgrimes * 4111573Srgrimes * Note: it is important that we also remember the locations of the pointers 4121573Srgrimes * in the current state information, and restore the locations of the pointers 4131573Srgrimes * from the old state information. This is done by multiplexing the pointer 4141573Srgrimes * location into the zeroeth word of the state information. 4151573Srgrimes * 4161573Srgrimes * Note that due to the order in which things are done, it is OK to call 4171573Srgrimes * setstate() with the same state as the current state. 4181573Srgrimes * 4191573Srgrimes * Returns a pointer to the old state information. 42023662Speter * 42123662Speter * Note: The Sparc platform requires that arg_state begin on a long 42223662Speter * word boundary; otherwise a bus error will occur. Even so, lint will 42323662Speter * complain about mis-alignment, but you should disregard these messages. 4241573Srgrimes */ 4251573Srgrimeschar * 4261573Srgrimessetstate(arg_state) 42723662Speter char *arg_state; /* pointer to state array */ 4281573Srgrimes{ 42992889Sobrien long *new_state = (long *) arg_state; 43092889Sobrien long type = new_state[0] % MAX_TYPES; 43192889Sobrien long rear = new_state[0] / MAX_TYPES; 4321573Srgrimes char *ostate = (char *)(&state[-1]); 4331573Srgrimes 4341573Srgrimes if (rand_type == TYPE_0) 4351573Srgrimes state[-1] = rand_type; 4361573Srgrimes else 4371573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 4381573Srgrimes switch(type) { 4391573Srgrimes case TYPE_0: 4401573Srgrimes case TYPE_1: 4411573Srgrimes case TYPE_2: 4421573Srgrimes case TYPE_3: 4431573Srgrimes case TYPE_4: 4441573Srgrimes rand_type = type; 4451573Srgrimes rand_deg = degrees[type]; 4461573Srgrimes rand_sep = seps[type]; 4471573Srgrimes break; 4481573Srgrimes default: 4491573Srgrimes (void)fprintf(stderr, 4501573Srgrimes "random: state info corrupted; not changed.\n"); 4511573Srgrimes } 45223662Speter state = (long *) (new_state + 1); 4531573Srgrimes if (rand_type != TYPE_0) { 4541573Srgrimes rptr = &state[rear]; 4551573Srgrimes fptr = &state[(rear + rand_sep) % rand_deg]; 4561573Srgrimes } 4571573Srgrimes end_ptr = &state[rand_deg]; /* set end_ptr too */ 4581573Srgrimes return(ostate); 4591573Srgrimes} 4601573Srgrimes 4611573Srgrimes/* 4621573Srgrimes * random: 4631573Srgrimes * 4641573Srgrimes * If we are using the trivial TYPE_0 R.N.G., just do the old linear 4651573Srgrimes * congruential bit. Otherwise, we do our fancy trinomial stuff, which is 4661573Srgrimes * the same in all the other cases due to all the global variables that have 4671573Srgrimes * been set up. The basic operation is to add the number at the rear pointer 4681573Srgrimes * into the one at the front pointer. Then both pointers are advanced to 4691573Srgrimes * the next location cyclically in the table. The value returned is the sum 4701573Srgrimes * generated, reduced to 31 bits by throwing away the "least random" low bit. 4711573Srgrimes * 4721573Srgrimes * Note: the code takes advantage of the fact that both the front and 4731573Srgrimes * rear pointers can't wrap on the same call by not testing the rear 4741573Srgrimes * pointer if the front one has wrapped. 4751573Srgrimes * 4761573Srgrimes * Returns a 31-bit random number. 4771573Srgrimes */ 4781573Srgrimeslong 4791573Srgrimesrandom() 4801573Srgrimes{ 48192889Sobrien long i; 48292889Sobrien long *f, *r; 4831573Srgrimes 48423662Speter if (rand_type == TYPE_0) { 48523662Speter i = state[0]; 48623662Speter state[0] = i = (good_rand(i)) & 0x7fffffff; 48723662Speter } else { 48823662Speter /* 48923662Speter * Use local variables rather than static variables for speed. 49023662Speter */ 49123662Speter f = fptr; r = rptr; 49223662Speter *f += *r; 49323662Speter i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */ 49423662Speter if (++f >= end_ptr) { 49523662Speter f = state; 49623662Speter ++r; 49723662Speter } 49823662Speter else if (++r >= end_ptr) { 49923662Speter r = state; 50023662Speter } 50123662Speter 50223662Speter fptr = f; rptr = r; 5031573Srgrimes } 5041573Srgrimes return(i); 5051573Srgrimes} 506