random.c revision 92986
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 92986 2002-03-22 21:53:29Z obrien $"); 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 14523662Speterstatic long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }; 14623662Speterstatic long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }; 1471573Srgrimes 1481573Srgrimes/* 1491573Srgrimes * Initially, everything is set up as if from: 1501573Srgrimes * 15118832Sache * initstate(1, randtbl, 128); 1521573Srgrimes * 1531573Srgrimes * Note that this initialization takes advantage of the fact that srandom() 1541573Srgrimes * advances the front and rear pointers 10*rand_deg times, and hence the 1551573Srgrimes * rear pointer which starts at 0 will also end up at zero; thus the zeroeth 1561573Srgrimes * element of the state information, which contains info about the current 1571573Srgrimes * position of the rear pointer is just 1581573Srgrimes * 1591573Srgrimes * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3. 1601573Srgrimes */ 1611573Srgrimes 1621573Srgrimesstatic long randtbl[DEG_3 + 1] = { 1631573Srgrimes TYPE_3, 16418832Sache#ifdef USE_WEAK_SEEDING 16518832Sache/* Historic implementation compatibility */ 16618832Sache/* The random sequences do not vary much with the seed */ 1671573Srgrimes 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5, 1681573Srgrimes 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd, 1691573Srgrimes 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88, 1701573Srgrimes 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc, 1711573Srgrimes 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b, 1721573Srgrimes 0x27fb47b9, 17318832Sache#else /* !USE_WEAK_SEEDING */ 17418832Sache 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05, 17518832Sache 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454, 17618832Sache 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471, 17718832Sache 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1, 17818832Sache 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41, 17918832Sache 0xf3bec5da 18018832Sache#endif /* !USE_WEAK_SEEDING */ 1811573Srgrimes}; 1821573Srgrimes 1831573Srgrimes/* 1841573Srgrimes * fptr and rptr are two pointers into the state info, a front and a rear 1851573Srgrimes * pointer. These two pointers are always rand_sep places aparts, as they 1861573Srgrimes * cycle cyclically through the state information. (Yes, this does mean we 1871573Srgrimes * could get away with just one pointer, but the code for random() is more 1881573Srgrimes * efficient this way). The pointers are left positioned as they would be 1891573Srgrimes * from the call 1901573Srgrimes * 1911573Srgrimes * initstate(1, randtbl, 128); 1921573Srgrimes * 1931573Srgrimes * (The position of the rear pointer, rptr, is really 0 (as explained above 1941573Srgrimes * in the initialization of randtbl) because the state table pointer is set 1951573Srgrimes * to point to randtbl[1] (as explained below). 1961573Srgrimes */ 1971573Srgrimesstatic long *fptr = &randtbl[SEP_3 + 1]; 1981573Srgrimesstatic long *rptr = &randtbl[1]; 1991573Srgrimes 2001573Srgrimes/* 2011573Srgrimes * The following things are the pointer to the state information table, the 2021573Srgrimes * type of the current generator, the degree of the current polynomial being 2031573Srgrimes * used, and the separation between the two pointers. Note that for efficiency 2041573Srgrimes * of random(), we remember the first location of the state information, not 2051573Srgrimes * the zeroeth. Hence it is valid to access state[-1], which is used to 2061573Srgrimes * store the type of the R.N.G. Also, we remember the last location, since 2071573Srgrimes * this is more efficient than indexing every time to find the address of 2081573Srgrimes * the last element to see if the front and rear pointers have wrapped. 2091573Srgrimes */ 2101573Srgrimesstatic long *state = &randtbl[1]; 21123662Speterstatic long rand_type = TYPE_3; 21223662Speterstatic long rand_deg = DEG_3; 21323662Speterstatic long rand_sep = SEP_3; 2141573Srgrimesstatic long *end_ptr = &randtbl[DEG_3 + 1]; 2151573Srgrimes 21692905Sobrienstatic inline long good_rand(long); 21718832Sache 21818832Sachestatic inline long good_rand (x) 21992889Sobrien long 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 */ 23792889Sobrien long hi, lo; 23818832Sache 23918832Sache hi = x / 127773; 24018832Sache lo = x % 127773; 24118832Sache x = 16807 * lo - 2836 * hi; 24218832Sache if (x <= 0) 24318832Sache x += 0x7fffffff; 24418832Sache return (x); 24518832Sache#endif /* !USE_WEAK_SEEDING */ 24618832Sache} 24718832Sache 24818832Sache/* 2491573Srgrimes * srandom: 2501573Srgrimes * 2511573Srgrimes * Initialize the random number generator based on the given seed. If the 2521573Srgrimes * type is the trivial no-state-information type, just remember the seed. 2531573Srgrimes * Otherwise, initializes state[] based on the given "seed" via a linear 2541573Srgrimes * congruential generator. Then, the pointers are set to known locations 2551573Srgrimes * that are exactly rand_sep places apart. Lastly, it cycles the state 2561573Srgrimes * information a given number of times to get rid of any initial dependencies 2571573Srgrimes * introduced by the L.C.R.N.G. Note that the initialization of randtbl[] 2581573Srgrimes * for default usage relies on values produced by this routine. 2591573Srgrimes */ 2601573Srgrimesvoid 2611573Srgrimessrandom(x) 26223662Speter unsigned long x; 2631573Srgrimes{ 26492889Sobrien long i; 2651573Srgrimes 2661573Srgrimes if (rand_type == TYPE_0) 2671573Srgrimes state[0] = x; 2681573Srgrimes else { 2691573Srgrimes state[0] = x; 2701573Srgrimes for (i = 1; i < rand_deg; i++) 27118832Sache state[i] = good_rand(state[i - 1]); 2721573Srgrimes fptr = &state[rand_sep]; 2731573Srgrimes rptr = &state[0]; 2741573Srgrimes for (i = 0; i < 10 * rand_deg; i++) 2751573Srgrimes (void)random(); 2761573Srgrimes } 2771573Srgrimes} 2781573Srgrimes 2791573Srgrimes/* 28024151Sache * srandomdev: 28124151Sache * 28224151Sache * Many programs choose the seed value in a totally predictable manner. 28324151Sache * This often causes problems. We seed the generator using the much more 28477851Sdd * secure random(4) interface. Note that this particular seeding 28524151Sache * procedure can generate states which are impossible to reproduce by 28624151Sache * calling srandom() with any value, since the succeeding terms in the 28724151Sache * state buffer are no longer derived from the LC algorithm applied to 28824151Sache * a fixed seed. 28924151Sache */ 29026624Sachevoid 29124151Sachesrandomdev() 29224151Sache{ 29326624Sache int fd, done; 29424151Sache size_t len; 29524151Sache 29624151Sache if (rand_type == TYPE_0) 29724151Sache len = sizeof state[0]; 29824151Sache else 29924151Sache len = rand_deg * sizeof state[0]; 30024151Sache 30126624Sache done = 0; 30285752Smarkm fd = _open("/dev/random", O_RDONLY, 0); 30326624Sache if (fd >= 0) { 30456698Sjasone if (_read(fd, (void *) state, len) == (ssize_t) len) 30526624Sache done = 1; 30656698Sjasone _close(fd); 30724151Sache } 30824151Sache 30926624Sache if (!done) { 31026624Sache struct timeval tv; 31126665Sache unsigned long junk; 31226624Sache 31326624Sache gettimeofday(&tv, NULL); 31475862Sache srandom((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk); 31526624Sache return; 31626624Sache } 31726624Sache 31824151Sache if (rand_type != TYPE_0) { 31924151Sache fptr = &state[rand_sep]; 32024151Sache rptr = &state[0]; 32124151Sache } 32224151Sache} 32324151Sache 32424151Sache/* 3251573Srgrimes * initstate: 3261573Srgrimes * 3271573Srgrimes * Initialize the state information in the given array of n bytes for future 3281573Srgrimes * random number generation. Based on the number of bytes we are given, and 3291573Srgrimes * the break values for the different R.N.G.'s, we choose the best (largest) 3301573Srgrimes * one we can and set things up for it. srandom() is then called to 3311573Srgrimes * initialize the state information. 3328870Srgrimes * 3331573Srgrimes * Note that on return from srandom(), we set state[-1] to be the type 3341573Srgrimes * multiplexed with the current value of the rear pointer; this is so 3351573Srgrimes * successive calls to initstate() won't lose this information and will be 3361573Srgrimes * able to restart with setstate(). 3378870Srgrimes * 3381573Srgrimes * Note: the first thing we do is save the current state, if any, just like 3391573Srgrimes * setstate() so that it doesn't matter when initstate is called. 3401573Srgrimes * 3411573Srgrimes * Returns a pointer to the old state. 34223662Speter * 34323662Speter * Note: The Sparc platform requires that arg_state begin on a long 34423662Speter * word boundary; otherwise a bus error will occur. Even so, lint will 34523662Speter * complain about mis-alignment, but you should disregard these messages. 3461573Srgrimes */ 3471573Srgrimeschar * 3481573Srgrimesinitstate(seed, arg_state, n) 34923662Speter unsigned long seed; /* seed for R.N.G. */ 3501573Srgrimes char *arg_state; /* pointer to state array */ 35123662Speter long n; /* # bytes of state info */ 3521573Srgrimes{ 35392889Sobrien char *ostate = (char *)(&state[-1]); 35492889Sobrien long *long_arg_state = (long *) arg_state; 3551573Srgrimes 3561573Srgrimes if (rand_type == TYPE_0) 3571573Srgrimes state[-1] = rand_type; 3581573Srgrimes else 3591573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 3601573Srgrimes if (n < BREAK_0) { 3611573Srgrimes (void)fprintf(stderr, 36223662Speter "random: not enough state (%ld bytes); ignored.\n", n); 3631573Srgrimes return(0); 3641573Srgrimes } 3651573Srgrimes if (n < BREAK_1) { 3661573Srgrimes rand_type = TYPE_0; 3671573Srgrimes rand_deg = DEG_0; 3681573Srgrimes rand_sep = SEP_0; 3691573Srgrimes } else if (n < BREAK_2) { 3701573Srgrimes rand_type = TYPE_1; 3711573Srgrimes rand_deg = DEG_1; 3721573Srgrimes rand_sep = SEP_1; 3731573Srgrimes } else if (n < BREAK_3) { 3741573Srgrimes rand_type = TYPE_2; 3751573Srgrimes rand_deg = DEG_2; 3761573Srgrimes rand_sep = SEP_2; 3771573Srgrimes } else if (n < BREAK_4) { 3781573Srgrimes rand_type = TYPE_3; 3791573Srgrimes rand_deg = DEG_3; 3801573Srgrimes rand_sep = SEP_3; 3811573Srgrimes } else { 3821573Srgrimes rand_type = TYPE_4; 3831573Srgrimes rand_deg = DEG_4; 3841573Srgrimes rand_sep = SEP_4; 3851573Srgrimes } 38623662Speter state = (long *) (long_arg_state + 1); /* first location */ 3871573Srgrimes end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */ 3881573Srgrimes srandom(seed); 3891573Srgrimes if (rand_type == TYPE_0) 39023662Speter long_arg_state[0] = rand_type; 3911573Srgrimes else 39223662Speter long_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type; 3931573Srgrimes return(ostate); 3941573Srgrimes} 3951573Srgrimes 3961573Srgrimes/* 3971573Srgrimes * setstate: 3981573Srgrimes * 3991573Srgrimes * Restore the state from the given state array. 4001573Srgrimes * 4011573Srgrimes * Note: it is important that we also remember the locations of the pointers 4021573Srgrimes * in the current state information, and restore the locations of the pointers 4031573Srgrimes * from the old state information. This is done by multiplexing the pointer 4041573Srgrimes * location into the zeroeth word of the state information. 4051573Srgrimes * 4061573Srgrimes * Note that due to the order in which things are done, it is OK to call 4071573Srgrimes * setstate() with the same state as the current state. 4081573Srgrimes * 4091573Srgrimes * Returns a pointer to the old state information. 41023662Speter * 41123662Speter * Note: The Sparc platform requires that arg_state begin on a long 41223662Speter * word boundary; otherwise a bus error will occur. Even so, lint will 41323662Speter * complain about mis-alignment, but you should disregard these messages. 4141573Srgrimes */ 4151573Srgrimeschar * 4161573Srgrimessetstate(arg_state) 41723662Speter char *arg_state; /* pointer to state array */ 4181573Srgrimes{ 41992889Sobrien long *new_state = (long *) arg_state; 42092889Sobrien long type = new_state[0] % MAX_TYPES; 42192889Sobrien long rear = new_state[0] / MAX_TYPES; 4221573Srgrimes char *ostate = (char *)(&state[-1]); 4231573Srgrimes 4241573Srgrimes if (rand_type == TYPE_0) 4251573Srgrimes state[-1] = rand_type; 4261573Srgrimes else 4271573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 4281573Srgrimes switch(type) { 4291573Srgrimes case TYPE_0: 4301573Srgrimes case TYPE_1: 4311573Srgrimes case TYPE_2: 4321573Srgrimes case TYPE_3: 4331573Srgrimes case TYPE_4: 4341573Srgrimes rand_type = type; 4351573Srgrimes rand_deg = degrees[type]; 4361573Srgrimes rand_sep = seps[type]; 4371573Srgrimes break; 4381573Srgrimes default: 4391573Srgrimes (void)fprintf(stderr, 4401573Srgrimes "random: state info corrupted; not changed.\n"); 4411573Srgrimes } 44223662Speter state = (long *) (new_state + 1); 4431573Srgrimes if (rand_type != TYPE_0) { 4441573Srgrimes rptr = &state[rear]; 4451573Srgrimes fptr = &state[(rear + rand_sep) % rand_deg]; 4461573Srgrimes } 4471573Srgrimes end_ptr = &state[rand_deg]; /* set end_ptr too */ 4481573Srgrimes return(ostate); 4491573Srgrimes} 4501573Srgrimes 4511573Srgrimes/* 4521573Srgrimes * random: 4531573Srgrimes * 4541573Srgrimes * If we are using the trivial TYPE_0 R.N.G., just do the old linear 4551573Srgrimes * congruential bit. Otherwise, we do our fancy trinomial stuff, which is 4561573Srgrimes * the same in all the other cases due to all the global variables that have 4571573Srgrimes * been set up. The basic operation is to add the number at the rear pointer 4581573Srgrimes * into the one at the front pointer. Then both pointers are advanced to 4591573Srgrimes * the next location cyclically in the table. The value returned is the sum 4601573Srgrimes * generated, reduced to 31 bits by throwing away the "least random" low bit. 4611573Srgrimes * 4621573Srgrimes * Note: the code takes advantage of the fact that both the front and 4631573Srgrimes * rear pointers can't wrap on the same call by not testing the rear 4641573Srgrimes * pointer if the front one has wrapped. 4651573Srgrimes * 4661573Srgrimes * Returns a 31-bit random number. 4671573Srgrimes */ 4681573Srgrimeslong 4691573Srgrimesrandom() 4701573Srgrimes{ 47192889Sobrien long i; 47292889Sobrien long *f, *r; 4731573Srgrimes 47423662Speter if (rand_type == TYPE_0) { 47523662Speter i = state[0]; 47623662Speter state[0] = i = (good_rand(i)) & 0x7fffffff; 47723662Speter } else { 47823662Speter /* 47923662Speter * Use local variables rather than static variables for speed. 48023662Speter */ 48123662Speter f = fptr; r = rptr; 48223662Speter *f += *r; 48323662Speter i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */ 48423662Speter if (++f >= end_ptr) { 48523662Speter f = state; 48623662Speter ++r; 48723662Speter } 48823662Speter else if (++r >= end_ptr) { 48923662Speter r = state; 49023662Speter } 49123662Speter 49223662Speter fptr = f; rptr = r; 4931573Srgrimes } 4941573Srgrimes return(i); 4951573Srgrimes} 496