random.c revision 24390
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. 3224390Sache * 3324390Sache * $Id$ 3424390Sache * 351573Srgrimes */ 361573Srgrimes 371573Srgrimes#if defined(LIBC_SCCS) && !defined(lint) 3823662Speterstatic char sccsid[] = "@(#)random.c 8.2 (Berkeley) 5/19/95"; 391573Srgrimes#endif /* LIBC_SCCS and not lint */ 401573Srgrimes 4124151Sache#include <fcntl.h> /* for srandomdev() */ 421573Srgrimes#include <stdio.h> 431573Srgrimes#include <stdlib.h> 4424151Sache#include <unistd.h> /* for srandomdev() */ 451573Srgrimes 461573Srgrimes/* 471573Srgrimes * random.c: 481573Srgrimes * 491573Srgrimes * An improved random number generation package. In addition to the standard 501573Srgrimes * rand()/srand() like interface, this package also has a special state info 511573Srgrimes * interface. The initstate() routine is called with a seed, an array of 521573Srgrimes * bytes, and a count of how many bytes are being passed in; this array is 531573Srgrimes * then initialized to contain information for random number generation with 541573Srgrimes * that much state information. Good sizes for the amount of state 551573Srgrimes * information are 32, 64, 128, and 256 bytes. The state can be switched by 561573Srgrimes * calling the setstate() routine with the same array as was initiallized 571573Srgrimes * with initstate(). By default, the package runs with 128 bytes of state 581573Srgrimes * information and generates far better random numbers than a linear 591573Srgrimes * congruential generator. If the amount of state information is less than 601573Srgrimes * 32 bytes, a simple linear congruential R.N.G. is used. 611573Srgrimes * 621573Srgrimes * Internally, the state information is treated as an array of longs; the 631573Srgrimes * zeroeth element of the array is the type of R.N.G. being used (small 641573Srgrimes * integer); the remainder of the array is the state information for the 651573Srgrimes * R.N.G. Thus, 32 bytes of state information will give 7 longs worth of 661573Srgrimes * state information, which will allow a degree seven polynomial. (Note: 671573Srgrimes * the zeroeth word of state information also has some other information 681573Srgrimes * stored in it -- see setstate() for details). 698870Srgrimes * 701573Srgrimes * The random number generation technique is a linear feedback shift register 711573Srgrimes * approach, employing trinomials (since there are fewer terms to sum up that 721573Srgrimes * way). In this approach, the least significant bit of all the numbers in 731573Srgrimes * the state table will act as a linear feedback shift register, and will 741573Srgrimes * have period 2^deg - 1 (where deg is the degree of the polynomial being 751573Srgrimes * used, assuming that the polynomial is irreducible and primitive). The 761573Srgrimes * higher order bits will have longer periods, since their values are also 771573Srgrimes * influenced by pseudo-random carries out of the lower bits. The total 781573Srgrimes * period of the generator is approximately deg*(2**deg - 1); thus doubling 791573Srgrimes * the amount of state information has a vast influence on the period of the 801573Srgrimes * generator. Note: the deg*(2**deg - 1) is an approximation only good for 811573Srgrimes * large deg, when the period of the shift register is the dominant factor. 821573Srgrimes * With deg equal to seven, the period is actually much longer than the 831573Srgrimes * 7*(2**7 - 1) predicted by this formula. 8423662Speter * 8523662Speter * Modified 28 December 1994 by Jacob S. Rosenberg. 8623662Speter * The following changes have been made: 8723662Speter * All references to the type u_int have been changed to unsigned long. 8823662Speter * All references to type int have been changed to type long. Other 8923662Speter * cleanups have been made as well. A warning for both initstate and 9023662Speter * setstate has been inserted to the effect that on Sparc platforms 9123662Speter * the 'arg_state' variable must be forced to begin on word boundaries. 9223662Speter * This can be easily done by casting a long integer array to char *. 9323662Speter * The overall logic has been left STRICTLY alone. This software was 9423662Speter * tested on both a VAX and Sun SpacsStation with exactly the same 9523662Speter * results. The new version and the original give IDENTICAL results. 9623662Speter * The new version is somewhat faster than the original. As the 9723662Speter * documentation says: "By default, the package runs with 128 bytes of 9823662Speter * state information and generates far better random numbers than a linear 9923662Speter * congruential generator. If the amount of state information is less than 10023662Speter * 32 bytes, a simple linear congruential R.N.G. is used." For a buffer of 10123662Speter * 128 bytes, this new version runs about 19 percent faster and for a 16 10223662Speter * byte buffer it is about 5 percent faster. 1031573Srgrimes */ 1041573Srgrimes 1051573Srgrimes/* 1061573Srgrimes * For each of the currently supported random number generators, we have a 1071573Srgrimes * break value on the amount of state information (you need at least this 1081573Srgrimes * many bytes of state info to support this random number generator), a degree 1091573Srgrimes * for the polynomial (actually a trinomial) that the R.N.G. is based on, and 1101573Srgrimes * the separation between the two lower order coefficients of the trinomial. 1111573Srgrimes */ 1121573Srgrimes#define TYPE_0 0 /* linear congruential */ 1131573Srgrimes#define BREAK_0 8 1141573Srgrimes#define DEG_0 0 1151573Srgrimes#define SEP_0 0 1161573Srgrimes 1171573Srgrimes#define TYPE_1 1 /* x**7 + x**3 + 1 */ 1181573Srgrimes#define BREAK_1 32 1191573Srgrimes#define DEG_1 7 1201573Srgrimes#define SEP_1 3 1211573Srgrimes 1221573Srgrimes#define TYPE_2 2 /* x**15 + x + 1 */ 1231573Srgrimes#define BREAK_2 64 1241573Srgrimes#define DEG_2 15 1251573Srgrimes#define SEP_2 1 1261573Srgrimes 1271573Srgrimes#define TYPE_3 3 /* x**31 + x**3 + 1 */ 1281573Srgrimes#define BREAK_3 128 1291573Srgrimes#define DEG_3 31 1301573Srgrimes#define SEP_3 3 1311573Srgrimes 1321573Srgrimes#define TYPE_4 4 /* x**63 + x + 1 */ 1331573Srgrimes#define BREAK_4 256 1341573Srgrimes#define DEG_4 63 1351573Srgrimes#define SEP_4 1 1361573Srgrimes 1371573Srgrimes/* 1381573Srgrimes * Array versions of the above information to make code run faster -- 1391573Srgrimes * relies on fact that TYPE_i == i. 1401573Srgrimes */ 1411573Srgrimes#define MAX_TYPES 5 /* max number of types above */ 1421573Srgrimes 14323662Speterstatic long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }; 14423662Speterstatic long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }; 1451573Srgrimes 1461573Srgrimes/* 1471573Srgrimes * Initially, everything is set up as if from: 1481573Srgrimes * 14918832Sache * initstate(1, randtbl, 128); 1501573Srgrimes * 1511573Srgrimes * Note that this initialization takes advantage of the fact that srandom() 1521573Srgrimes * advances the front and rear pointers 10*rand_deg times, and hence the 1531573Srgrimes * rear pointer which starts at 0 will also end up at zero; thus the zeroeth 1541573Srgrimes * element of the state information, which contains info about the current 1551573Srgrimes * position of the rear pointer is just 1561573Srgrimes * 1571573Srgrimes * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3. 1581573Srgrimes */ 1591573Srgrimes 1601573Srgrimesstatic long randtbl[DEG_3 + 1] = { 1611573Srgrimes TYPE_3, 16218832Sache#ifdef USE_WEAK_SEEDING 16318832Sache/* Historic implementation compatibility */ 16418832Sache/* The random sequences do not vary much with the seed */ 1651573Srgrimes 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5, 1661573Srgrimes 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd, 1671573Srgrimes 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88, 1681573Srgrimes 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc, 1691573Srgrimes 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b, 1701573Srgrimes 0x27fb47b9, 17118832Sache#else /* !USE_WEAK_SEEDING */ 17218832Sache 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05, 17318832Sache 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454, 17418832Sache 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471, 17518832Sache 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1, 17618832Sache 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41, 17718832Sache 0xf3bec5da 17818832Sache#endif /* !USE_WEAK_SEEDING */ 1791573Srgrimes}; 1801573Srgrimes 1811573Srgrimes/* 1821573Srgrimes * fptr and rptr are two pointers into the state info, a front and a rear 1831573Srgrimes * pointer. These two pointers are always rand_sep places aparts, as they 1841573Srgrimes * cycle cyclically through the state information. (Yes, this does mean we 1851573Srgrimes * could get away with just one pointer, but the code for random() is more 1861573Srgrimes * efficient this way). The pointers are left positioned as they would be 1871573Srgrimes * from the call 1881573Srgrimes * 1891573Srgrimes * initstate(1, randtbl, 128); 1901573Srgrimes * 1911573Srgrimes * (The position of the rear pointer, rptr, is really 0 (as explained above 1921573Srgrimes * in the initialization of randtbl) because the state table pointer is set 1931573Srgrimes * to point to randtbl[1] (as explained below). 1941573Srgrimes */ 1951573Srgrimesstatic long *fptr = &randtbl[SEP_3 + 1]; 1961573Srgrimesstatic long *rptr = &randtbl[1]; 1971573Srgrimes 1981573Srgrimes/* 1991573Srgrimes * The following things are the pointer to the state information table, the 2001573Srgrimes * type of the current generator, the degree of the current polynomial being 2011573Srgrimes * used, and the separation between the two pointers. Note that for efficiency 2021573Srgrimes * of random(), we remember the first location of the state information, not 2031573Srgrimes * the zeroeth. Hence it is valid to access state[-1], which is used to 2041573Srgrimes * store the type of the R.N.G. Also, we remember the last location, since 2051573Srgrimes * this is more efficient than indexing every time to find the address of 2061573Srgrimes * the last element to see if the front and rear pointers have wrapped. 2071573Srgrimes */ 2081573Srgrimesstatic long *state = &randtbl[1]; 20923662Speterstatic long rand_type = TYPE_3; 21023662Speterstatic long rand_deg = DEG_3; 21123662Speterstatic long rand_sep = SEP_3; 2121573Srgrimesstatic long *end_ptr = &randtbl[DEG_3 + 1]; 2131573Srgrimes 21418832Sachestatic inline long good_rand __P((long)); 21518832Sache 21618832Sachestatic inline long good_rand (x) 21718832Sache register long x; 21818832Sache{ 21918832Sache#ifdef USE_WEAK_SEEDING 2201573Srgrimes/* 22118832Sache * Historic implementation compatibility. 22218832Sache * The random sequences do not vary much with the seed, 22318832Sache * even with overflowing. 22418832Sache */ 22518832Sache return (1103515245 * x + 12345); 22618832Sache#else /* !USE_WEAK_SEEDING */ 22718832Sache/* 22818832Sache * Compute x = (7^5 * x) mod (2^31 - 1) 22918832Sache * wihout overflowing 31 bits: 23018832Sache * (2^31 - 1) = 127773 * (7^5) + 2836 23118832Sache * From "Random number generators: good ones are hard to find", 23218832Sache * Park and Miller, Communications of the ACM, vol. 31, no. 10, 23318832Sache * October 1988, p. 1195. 23418832Sache */ 23518832Sache register long hi, lo; 23618832Sache 23718832Sache hi = x / 127773; 23818832Sache lo = x % 127773; 23918832Sache x = 16807 * lo - 2836 * hi; 24018832Sache if (x <= 0) 24118832Sache x += 0x7fffffff; 24218832Sache return (x); 24318832Sache#endif /* !USE_WEAK_SEEDING */ 24418832Sache} 24518832Sache 24618832Sache/* 2471573Srgrimes * srandom: 2481573Srgrimes * 2491573Srgrimes * Initialize the random number generator based on the given seed. If the 2501573Srgrimes * type is the trivial no-state-information type, just remember the seed. 2511573Srgrimes * Otherwise, initializes state[] based on the given "seed" via a linear 2521573Srgrimes * congruential generator. Then, the pointers are set to known locations 2531573Srgrimes * that are exactly rand_sep places apart. Lastly, it cycles the state 2541573Srgrimes * information a given number of times to get rid of any initial dependencies 2551573Srgrimes * introduced by the L.C.R.N.G. Note that the initialization of randtbl[] 2561573Srgrimes * for default usage relies on values produced by this routine. 2571573Srgrimes */ 2581573Srgrimesvoid 2591573Srgrimessrandom(x) 26023662Speter unsigned long x; 2611573Srgrimes{ 26223662Speter register long i; 2631573Srgrimes 2641573Srgrimes if (rand_type == TYPE_0) 2651573Srgrimes state[0] = x; 2661573Srgrimes else { 2671573Srgrimes state[0] = x; 2681573Srgrimes for (i = 1; i < rand_deg; i++) 26918832Sache state[i] = good_rand(state[i - 1]); 2701573Srgrimes fptr = &state[rand_sep]; 2711573Srgrimes rptr = &state[0]; 2721573Srgrimes for (i = 0; i < 10 * rand_deg; i++) 2731573Srgrimes (void)random(); 2741573Srgrimes } 2751573Srgrimes} 2761573Srgrimes 2771573Srgrimes/* 27824151Sache * srandomdev: 27924151Sache * 28024151Sache * Many programs choose the seed value in a totally predictable manner. 28124151Sache * This often causes problems. We seed the generator using the much more 28224154Sache * secure urandom(4) interface. Note that this particular seeding 28324151Sache * procedure can generate states which are impossible to reproduce by 28424151Sache * calling srandom() with any value, since the succeeding terms in the 28524151Sache * state buffer are no longer derived from the LC algorithm applied to 28624151Sache * a fixed seed. 28724151Sache */ 28824151Sacheint 28924151Sachesrandomdev() 29024151Sache{ 29124151Sache int fd; 29224151Sache size_t len; 29324151Sache 29424151Sache if (rand_type == TYPE_0) 29524151Sache len = sizeof state[0]; 29624151Sache else 29724151Sache len = rand_deg * sizeof state[0]; 29824151Sache 29924151Sache fd = open("/dev/urandom", O_RDONLY, 0); 30024151Sache if (fd < 0) 30124151Sache return -1; 30224151Sache if (read(fd, (void *) state, len) < (ssize_t) len) { 30324151Sache close(fd); 30424151Sache return -1; 30524151Sache } 30624151Sache close(fd); 30724151Sache 30824151Sache if (rand_type != TYPE_0) { 30924151Sache fptr = &state[rand_sep]; 31024151Sache rptr = &state[0]; 31124151Sache } 31224151Sache return 0; 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 * 33423662Speter * Note: The Sparc platform requires that arg_state begin on a long 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 * 3391573Srgrimesinitstate(seed, arg_state, n) 34023662Speter unsigned long seed; /* seed for R.N.G. */ 3411573Srgrimes char *arg_state; /* pointer to state array */ 34223662Speter long n; /* # bytes of state info */ 3431573Srgrimes{ 3441573Srgrimes register char *ostate = (char *)(&state[-1]); 34523662Speter register long *long_arg_state = (long *) arg_state; 3461573Srgrimes 3471573Srgrimes if (rand_type == TYPE_0) 3481573Srgrimes state[-1] = rand_type; 3491573Srgrimes else 3501573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 3511573Srgrimes if (n < BREAK_0) { 3521573Srgrimes (void)fprintf(stderr, 35323662Speter "random: not enough state (%ld bytes); ignored.\n", n); 3541573Srgrimes return(0); 3551573Srgrimes } 3561573Srgrimes if (n < BREAK_1) { 3571573Srgrimes rand_type = TYPE_0; 3581573Srgrimes rand_deg = DEG_0; 3591573Srgrimes rand_sep = SEP_0; 3601573Srgrimes } else if (n < BREAK_2) { 3611573Srgrimes rand_type = TYPE_1; 3621573Srgrimes rand_deg = DEG_1; 3631573Srgrimes rand_sep = SEP_1; 3641573Srgrimes } else if (n < BREAK_3) { 3651573Srgrimes rand_type = TYPE_2; 3661573Srgrimes rand_deg = DEG_2; 3671573Srgrimes rand_sep = SEP_2; 3681573Srgrimes } else if (n < BREAK_4) { 3691573Srgrimes rand_type = TYPE_3; 3701573Srgrimes rand_deg = DEG_3; 3711573Srgrimes rand_sep = SEP_3; 3721573Srgrimes } else { 3731573Srgrimes rand_type = TYPE_4; 3741573Srgrimes rand_deg = DEG_4; 3751573Srgrimes rand_sep = SEP_4; 3761573Srgrimes } 37723662Speter state = (long *) (long_arg_state + 1); /* first location */ 3781573Srgrimes end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */ 3791573Srgrimes srandom(seed); 3801573Srgrimes if (rand_type == TYPE_0) 38123662Speter long_arg_state[0] = rand_type; 3821573Srgrimes else 38323662Speter long_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type; 3841573Srgrimes return(ostate); 3851573Srgrimes} 3861573Srgrimes 3871573Srgrimes/* 3881573Srgrimes * setstate: 3891573Srgrimes * 3901573Srgrimes * Restore the state from the given state array. 3911573Srgrimes * 3921573Srgrimes * Note: it is important that we also remember the locations of the pointers 3931573Srgrimes * in the current state information, and restore the locations of the pointers 3941573Srgrimes * from the old state information. This is done by multiplexing the pointer 3951573Srgrimes * location into the zeroeth word of the state information. 3961573Srgrimes * 3971573Srgrimes * Note that due to the order in which things are done, it is OK to call 3981573Srgrimes * setstate() with the same state as the current state. 3991573Srgrimes * 4001573Srgrimes * Returns a pointer to the old state information. 40123662Speter * 40223662Speter * Note: The Sparc platform requires that arg_state begin on a long 40323662Speter * word boundary; otherwise a bus error will occur. Even so, lint will 40423662Speter * complain about mis-alignment, but you should disregard these messages. 4051573Srgrimes */ 4061573Srgrimeschar * 4071573Srgrimessetstate(arg_state) 40823662Speter char *arg_state; /* pointer to state array */ 4091573Srgrimes{ 41023662Speter register long *new_state = (long *) arg_state; 41123662Speter register long type = new_state[0] % MAX_TYPES; 41223662Speter register long rear = new_state[0] / MAX_TYPES; 4131573Srgrimes char *ostate = (char *)(&state[-1]); 4141573Srgrimes 4151573Srgrimes if (rand_type == TYPE_0) 4161573Srgrimes state[-1] = rand_type; 4171573Srgrimes else 4181573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 4191573Srgrimes switch(type) { 4201573Srgrimes case TYPE_0: 4211573Srgrimes case TYPE_1: 4221573Srgrimes case TYPE_2: 4231573Srgrimes case TYPE_3: 4241573Srgrimes case TYPE_4: 4251573Srgrimes rand_type = type; 4261573Srgrimes rand_deg = degrees[type]; 4271573Srgrimes rand_sep = seps[type]; 4281573Srgrimes break; 4291573Srgrimes default: 4301573Srgrimes (void)fprintf(stderr, 4311573Srgrimes "random: state info corrupted; not changed.\n"); 4321573Srgrimes } 43323662Speter state = (long *) (new_state + 1); 4341573Srgrimes if (rand_type != TYPE_0) { 4351573Srgrimes rptr = &state[rear]; 4361573Srgrimes fptr = &state[(rear + rand_sep) % rand_deg]; 4371573Srgrimes } 4381573Srgrimes end_ptr = &state[rand_deg]; /* set end_ptr too */ 4391573Srgrimes return(ostate); 4401573Srgrimes} 4411573Srgrimes 4421573Srgrimes/* 4431573Srgrimes * random: 4441573Srgrimes * 4451573Srgrimes * If we are using the trivial TYPE_0 R.N.G., just do the old linear 4461573Srgrimes * congruential bit. Otherwise, we do our fancy trinomial stuff, which is 4471573Srgrimes * the same in all the other cases due to all the global variables that have 4481573Srgrimes * been set up. The basic operation is to add the number at the rear pointer 4491573Srgrimes * into the one at the front pointer. Then both pointers are advanced to 4501573Srgrimes * the next location cyclically in the table. The value returned is the sum 4511573Srgrimes * generated, reduced to 31 bits by throwing away the "least random" low bit. 4521573Srgrimes * 4531573Srgrimes * Note: the code takes advantage of the fact that both the front and 4541573Srgrimes * rear pointers can't wrap on the same call by not testing the rear 4551573Srgrimes * pointer if the front one has wrapped. 4561573Srgrimes * 4571573Srgrimes * Returns a 31-bit random number. 4581573Srgrimes */ 4591573Srgrimeslong 4601573Srgrimesrandom() 4611573Srgrimes{ 46223662Speter register long i; 46323662Speter register long *f, *r; 4641573Srgrimes 46523662Speter if (rand_type == TYPE_0) { 46623662Speter i = state[0]; 46723662Speter state[0] = i = (good_rand(i)) & 0x7fffffff; 46823662Speter } else { 46923662Speter /* 47023662Speter * Use local variables rather than static variables for speed. 47123662Speter */ 47223662Speter f = fptr; r = rptr; 47323662Speter *f += *r; 47423662Speter i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */ 47523662Speter if (++f >= end_ptr) { 47623662Speter f = state; 47723662Speter ++r; 47823662Speter } 47923662Speter else if (++r >= end_ptr) { 48023662Speter r = state; 48123662Speter } 48223662Speter 48323662Speter fptr = f; rptr = r; 4841573Srgrimes } 4851573Srgrimes return(i); 4861573Srgrimes} 487