random.c revision 75862
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 * 3350476Speter * $FreeBSD: head/lib/libc/stdlib/random.c 75862 2001-04-23 10:14:28Z ache $ 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 4171579Sdeischen#include "namespace.h" 4226624Sache#include <sys/time.h> /* for srandomdev() */ 4324151Sache#include <fcntl.h> /* for srandomdev() */ 441573Srgrimes#include <stdio.h> 451573Srgrimes#include <stdlib.h> 4624151Sache#include <unistd.h> /* for srandomdev() */ 4771579Sdeischen#include "un-namespace.h" 481573Srgrimes 491573Srgrimes/* 501573Srgrimes * random.c: 511573Srgrimes * 521573Srgrimes * An improved random number generation package. In addition to the standard 531573Srgrimes * rand()/srand() like interface, this package also has a special state info 541573Srgrimes * interface. The initstate() routine is called with a seed, an array of 551573Srgrimes * bytes, and a count of how many bytes are being passed in; this array is 561573Srgrimes * then initialized to contain information for random number generation with 571573Srgrimes * that much state information. Good sizes for the amount of state 581573Srgrimes * information are 32, 64, 128, and 256 bytes. The state can be switched by 591573Srgrimes * calling the setstate() routine with the same array as was initiallized 601573Srgrimes * with initstate(). By default, the package runs with 128 bytes of state 611573Srgrimes * information and generates far better random numbers than a linear 621573Srgrimes * congruential generator. If the amount of state information is less than 631573Srgrimes * 32 bytes, a simple linear congruential R.N.G. is used. 641573Srgrimes * 651573Srgrimes * Internally, the state information is treated as an array of longs; the 661573Srgrimes * zeroeth element of the array is the type of R.N.G. being used (small 671573Srgrimes * integer); the remainder of the array is the state information for the 681573Srgrimes * R.N.G. Thus, 32 bytes of state information will give 7 longs worth of 691573Srgrimes * state information, which will allow a degree seven polynomial. (Note: 701573Srgrimes * the zeroeth word of state information also has some other information 711573Srgrimes * stored in it -- see setstate() for details). 728870Srgrimes * 731573Srgrimes * The random number generation technique is a linear feedback shift register 741573Srgrimes * approach, employing trinomials (since there are fewer terms to sum up that 751573Srgrimes * way). In this approach, the least significant bit of all the numbers in 761573Srgrimes * the state table will act as a linear feedback shift register, and will 771573Srgrimes * have period 2^deg - 1 (where deg is the degree of the polynomial being 781573Srgrimes * used, assuming that the polynomial is irreducible and primitive). The 791573Srgrimes * higher order bits will have longer periods, since their values are also 801573Srgrimes * influenced by pseudo-random carries out of the lower bits. The total 811573Srgrimes * period of the generator is approximately deg*(2**deg - 1); thus doubling 821573Srgrimes * the amount of state information has a vast influence on the period of the 831573Srgrimes * generator. Note: the deg*(2**deg - 1) is an approximation only good for 841573Srgrimes * large deg, when the period of the shift register is the dominant factor. 851573Srgrimes * With deg equal to seven, the period is actually much longer than the 861573Srgrimes * 7*(2**7 - 1) predicted by this formula. 8723662Speter * 8823662Speter * Modified 28 December 1994 by Jacob S. Rosenberg. 8923662Speter * The following changes have been made: 9023662Speter * All references to the type u_int have been changed to unsigned long. 9123662Speter * All references to type int have been changed to type long. Other 9223662Speter * cleanups have been made as well. A warning for both initstate and 9323662Speter * setstate has been inserted to the effect that on Sparc platforms 9423662Speter * the 'arg_state' variable must be forced to begin on word boundaries. 9523662Speter * This can be easily done by casting a long integer array to char *. 9623662Speter * The overall logic has been left STRICTLY alone. This software was 9723662Speter * tested on both a VAX and Sun SpacsStation with exactly the same 9823662Speter * results. The new version and the original give IDENTICAL results. 9923662Speter * The new version is somewhat faster than the original. As the 10023662Speter * documentation says: "By default, the package runs with 128 bytes of 10123662Speter * state information and generates far better random numbers than a linear 10223662Speter * congruential generator. If the amount of state information is less than 10323662Speter * 32 bytes, a simple linear congruential R.N.G. is used." For a buffer of 10423662Speter * 128 bytes, this new version runs about 19 percent faster and for a 16 10523662Speter * byte buffer it is about 5 percent faster. 1061573Srgrimes */ 1071573Srgrimes 1081573Srgrimes/* 1091573Srgrimes * For each of the currently supported random number generators, we have a 1101573Srgrimes * break value on the amount of state information (you need at least this 1111573Srgrimes * many bytes of state info to support this random number generator), a degree 1121573Srgrimes * for the polynomial (actually a trinomial) that the R.N.G. is based on, and 1131573Srgrimes * the separation between the two lower order coefficients of the trinomial. 1141573Srgrimes */ 1151573Srgrimes#define TYPE_0 0 /* linear congruential */ 1161573Srgrimes#define BREAK_0 8 1171573Srgrimes#define DEG_0 0 1181573Srgrimes#define SEP_0 0 1191573Srgrimes 1201573Srgrimes#define TYPE_1 1 /* x**7 + x**3 + 1 */ 1211573Srgrimes#define BREAK_1 32 1221573Srgrimes#define DEG_1 7 1231573Srgrimes#define SEP_1 3 1241573Srgrimes 1251573Srgrimes#define TYPE_2 2 /* x**15 + x + 1 */ 1261573Srgrimes#define BREAK_2 64 1271573Srgrimes#define DEG_2 15 1281573Srgrimes#define SEP_2 1 1291573Srgrimes 1301573Srgrimes#define TYPE_3 3 /* x**31 + x**3 + 1 */ 1311573Srgrimes#define BREAK_3 128 1321573Srgrimes#define DEG_3 31 1331573Srgrimes#define SEP_3 3 1341573Srgrimes 1351573Srgrimes#define TYPE_4 4 /* x**63 + x + 1 */ 1361573Srgrimes#define BREAK_4 256 1371573Srgrimes#define DEG_4 63 1381573Srgrimes#define SEP_4 1 1391573Srgrimes 1401573Srgrimes/* 1411573Srgrimes * Array versions of the above information to make code run faster -- 1421573Srgrimes * relies on fact that TYPE_i == i. 1431573Srgrimes */ 1441573Srgrimes#define MAX_TYPES 5 /* max number of types above */ 1451573Srgrimes 14623662Speterstatic long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }; 14723662Speterstatic long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }; 1481573Srgrimes 1491573Srgrimes/* 1501573Srgrimes * Initially, everything is set up as if from: 1511573Srgrimes * 15218832Sache * initstate(1, randtbl, 128); 1531573Srgrimes * 1541573Srgrimes * Note that this initialization takes advantage of the fact that srandom() 1551573Srgrimes * advances the front and rear pointers 10*rand_deg times, and hence the 1561573Srgrimes * rear pointer which starts at 0 will also end up at zero; thus the zeroeth 1571573Srgrimes * element of the state information, which contains info about the current 1581573Srgrimes * position of the rear pointer is just 1591573Srgrimes * 1601573Srgrimes * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3. 1611573Srgrimes */ 1621573Srgrimes 1631573Srgrimesstatic long randtbl[DEG_3 + 1] = { 1641573Srgrimes TYPE_3, 16518832Sache#ifdef USE_WEAK_SEEDING 16618832Sache/* Historic implementation compatibility */ 16718832Sache/* The random sequences do not vary much with the seed */ 1681573Srgrimes 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5, 1691573Srgrimes 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd, 1701573Srgrimes 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88, 1711573Srgrimes 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc, 1721573Srgrimes 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b, 1731573Srgrimes 0x27fb47b9, 17418832Sache#else /* !USE_WEAK_SEEDING */ 17518832Sache 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05, 17618832Sache 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454, 17718832Sache 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471, 17818832Sache 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1, 17918832Sache 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41, 18018832Sache 0xf3bec5da 18118832Sache#endif /* !USE_WEAK_SEEDING */ 1821573Srgrimes}; 1831573Srgrimes 1841573Srgrimes/* 1851573Srgrimes * fptr and rptr are two pointers into the state info, a front and a rear 1861573Srgrimes * pointer. These two pointers are always rand_sep places aparts, as they 1871573Srgrimes * cycle cyclically through the state information. (Yes, this does mean we 1881573Srgrimes * could get away with just one pointer, but the code for random() is more 1891573Srgrimes * efficient this way). The pointers are left positioned as they would be 1901573Srgrimes * from the call 1911573Srgrimes * 1921573Srgrimes * initstate(1, randtbl, 128); 1931573Srgrimes * 1941573Srgrimes * (The position of the rear pointer, rptr, is really 0 (as explained above 1951573Srgrimes * in the initialization of randtbl) because the state table pointer is set 1961573Srgrimes * to point to randtbl[1] (as explained below). 1971573Srgrimes */ 1981573Srgrimesstatic long *fptr = &randtbl[SEP_3 + 1]; 1991573Srgrimesstatic long *rptr = &randtbl[1]; 2001573Srgrimes 2011573Srgrimes/* 2021573Srgrimes * The following things are the pointer to the state information table, the 2031573Srgrimes * type of the current generator, the degree of the current polynomial being 2041573Srgrimes * used, and the separation between the two pointers. Note that for efficiency 2051573Srgrimes * of random(), we remember the first location of the state information, not 2061573Srgrimes * the zeroeth. Hence it is valid to access state[-1], which is used to 2071573Srgrimes * store the type of the R.N.G. Also, we remember the last location, since 2081573Srgrimes * this is more efficient than indexing every time to find the address of 2091573Srgrimes * the last element to see if the front and rear pointers have wrapped. 2101573Srgrimes */ 2111573Srgrimesstatic long *state = &randtbl[1]; 21223662Speterstatic long rand_type = TYPE_3; 21323662Speterstatic long rand_deg = DEG_3; 21423662Speterstatic long rand_sep = SEP_3; 2151573Srgrimesstatic long *end_ptr = &randtbl[DEG_3 + 1]; 2161573Srgrimes 21718832Sachestatic inline long good_rand __P((long)); 21818832Sache 21918832Sachestatic inline long good_rand (x) 22018832Sache register long x; 22118832Sache{ 22218832Sache#ifdef USE_WEAK_SEEDING 2231573Srgrimes/* 22418832Sache * Historic implementation compatibility. 22518832Sache * The random sequences do not vary much with the seed, 22618832Sache * even with overflowing. 22718832Sache */ 22818832Sache return (1103515245 * x + 12345); 22918832Sache#else /* !USE_WEAK_SEEDING */ 23018832Sache/* 23118832Sache * Compute x = (7^5 * x) mod (2^31 - 1) 23218832Sache * wihout overflowing 31 bits: 23318832Sache * (2^31 - 1) = 127773 * (7^5) + 2836 23418832Sache * From "Random number generators: good ones are hard to find", 23518832Sache * Park and Miller, Communications of the ACM, vol. 31, no. 10, 23618832Sache * October 1988, p. 1195. 23718832Sache */ 23818832Sache register long hi, lo; 23918832Sache 24018832Sache hi = x / 127773; 24118832Sache lo = x % 127773; 24218832Sache x = 16807 * lo - 2836 * hi; 24318832Sache if (x <= 0) 24418832Sache x += 0x7fffffff; 24518832Sache return (x); 24618832Sache#endif /* !USE_WEAK_SEEDING */ 24718832Sache} 24818832Sache 24918832Sache/* 2501573Srgrimes * srandom: 2511573Srgrimes * 2521573Srgrimes * Initialize the random number generator based on the given seed. If the 2531573Srgrimes * type is the trivial no-state-information type, just remember the seed. 2541573Srgrimes * Otherwise, initializes state[] based on the given "seed" via a linear 2551573Srgrimes * congruential generator. Then, the pointers are set to known locations 2561573Srgrimes * that are exactly rand_sep places apart. Lastly, it cycles the state 2571573Srgrimes * information a given number of times to get rid of any initial dependencies 2581573Srgrimes * introduced by the L.C.R.N.G. Note that the initialization of randtbl[] 2591573Srgrimes * for default usage relies on values produced by this routine. 2601573Srgrimes */ 2611573Srgrimesvoid 2621573Srgrimessrandom(x) 26323662Speter unsigned long x; 2641573Srgrimes{ 26523662Speter register long i; 2661573Srgrimes 2671573Srgrimes if (rand_type == TYPE_0) 2681573Srgrimes state[0] = x; 2691573Srgrimes else { 2701573Srgrimes state[0] = x; 2711573Srgrimes for (i = 1; i < rand_deg; i++) 27218832Sache state[i] = good_rand(state[i - 1]); 2731573Srgrimes fptr = &state[rand_sep]; 2741573Srgrimes rptr = &state[0]; 2751573Srgrimes for (i = 0; i < 10 * rand_deg; i++) 2761573Srgrimes (void)random(); 2771573Srgrimes } 2781573Srgrimes} 2791573Srgrimes 2801573Srgrimes/* 28124151Sache * srandomdev: 28224151Sache * 28324151Sache * Many programs choose the seed value in a totally predictable manner. 28424151Sache * This often causes problems. We seed the generator using the much more 28524154Sache * secure urandom(4) interface. Note that this particular seeding 28624151Sache * procedure can generate states which are impossible to reproduce by 28724151Sache * calling srandom() with any value, since the succeeding terms in the 28824151Sache * state buffer are no longer derived from the LC algorithm applied to 28924151Sache * a fixed seed. 29024151Sache */ 29126624Sachevoid 29224151Sachesrandomdev() 29324151Sache{ 29426624Sache int fd, done; 29524151Sache size_t len; 29624151Sache 29724151Sache if (rand_type == TYPE_0) 29824151Sache len = sizeof state[0]; 29924151Sache else 30024151Sache len = rand_deg * sizeof state[0]; 30124151Sache 30226624Sache done = 0; 30356698Sjasone fd = _open("/dev/urandom", O_RDONLY, 0); 30426624Sache if (fd >= 0) { 30556698Sjasone if (_read(fd, (void *) state, len) == (ssize_t) len) 30626624Sache done = 1; 30756698Sjasone _close(fd); 30824151Sache } 30924151Sache 31026624Sache if (!done) { 31126624Sache struct timeval tv; 31226665Sache unsigned long junk; 31326624Sache 31426624Sache gettimeofday(&tv, NULL); 31575862Sache srandom((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk); 31626624Sache return; 31726624Sache } 31826624Sache 31924151Sache if (rand_type != TYPE_0) { 32024151Sache fptr = &state[rand_sep]; 32124151Sache rptr = &state[0]; 32224151Sache } 32324151Sache} 32424151Sache 32524151Sache/* 3261573Srgrimes * initstate: 3271573Srgrimes * 3281573Srgrimes * Initialize the state information in the given array of n bytes for future 3291573Srgrimes * random number generation. Based on the number of bytes we are given, and 3301573Srgrimes * the break values for the different R.N.G.'s, we choose the best (largest) 3311573Srgrimes * one we can and set things up for it. srandom() is then called to 3321573Srgrimes * initialize the state information. 3338870Srgrimes * 3341573Srgrimes * Note that on return from srandom(), we set state[-1] to be the type 3351573Srgrimes * multiplexed with the current value of the rear pointer; this is so 3361573Srgrimes * successive calls to initstate() won't lose this information and will be 3371573Srgrimes * able to restart with setstate(). 3388870Srgrimes * 3391573Srgrimes * Note: the first thing we do is save the current state, if any, just like 3401573Srgrimes * setstate() so that it doesn't matter when initstate is called. 3411573Srgrimes * 3421573Srgrimes * Returns a pointer to the old state. 34323662Speter * 34423662Speter * Note: The Sparc platform requires that arg_state begin on a long 34523662Speter * word boundary; otherwise a bus error will occur. Even so, lint will 34623662Speter * complain about mis-alignment, but you should disregard these messages. 3471573Srgrimes */ 3481573Srgrimeschar * 3491573Srgrimesinitstate(seed, arg_state, n) 35023662Speter unsigned long seed; /* seed for R.N.G. */ 3511573Srgrimes char *arg_state; /* pointer to state array */ 35223662Speter long n; /* # bytes of state info */ 3531573Srgrimes{ 3541573Srgrimes register char *ostate = (char *)(&state[-1]); 35523662Speter register long *long_arg_state = (long *) arg_state; 3561573Srgrimes 3571573Srgrimes if (rand_type == TYPE_0) 3581573Srgrimes state[-1] = rand_type; 3591573Srgrimes else 3601573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 3611573Srgrimes if (n < BREAK_0) { 3621573Srgrimes (void)fprintf(stderr, 36323662Speter "random: not enough state (%ld bytes); ignored.\n", n); 3641573Srgrimes return(0); 3651573Srgrimes } 3661573Srgrimes if (n < BREAK_1) { 3671573Srgrimes rand_type = TYPE_0; 3681573Srgrimes rand_deg = DEG_0; 3691573Srgrimes rand_sep = SEP_0; 3701573Srgrimes } else if (n < BREAK_2) { 3711573Srgrimes rand_type = TYPE_1; 3721573Srgrimes rand_deg = DEG_1; 3731573Srgrimes rand_sep = SEP_1; 3741573Srgrimes } else if (n < BREAK_3) { 3751573Srgrimes rand_type = TYPE_2; 3761573Srgrimes rand_deg = DEG_2; 3771573Srgrimes rand_sep = SEP_2; 3781573Srgrimes } else if (n < BREAK_4) { 3791573Srgrimes rand_type = TYPE_3; 3801573Srgrimes rand_deg = DEG_3; 3811573Srgrimes rand_sep = SEP_3; 3821573Srgrimes } else { 3831573Srgrimes rand_type = TYPE_4; 3841573Srgrimes rand_deg = DEG_4; 3851573Srgrimes rand_sep = SEP_4; 3861573Srgrimes } 38723662Speter state = (long *) (long_arg_state + 1); /* first location */ 3881573Srgrimes end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */ 3891573Srgrimes srandom(seed); 3901573Srgrimes if (rand_type == TYPE_0) 39123662Speter long_arg_state[0] = rand_type; 3921573Srgrimes else 39323662Speter long_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type; 3941573Srgrimes return(ostate); 3951573Srgrimes} 3961573Srgrimes 3971573Srgrimes/* 3981573Srgrimes * setstate: 3991573Srgrimes * 4001573Srgrimes * Restore the state from the given state array. 4011573Srgrimes * 4021573Srgrimes * Note: it is important that we also remember the locations of the pointers 4031573Srgrimes * in the current state information, and restore the locations of the pointers 4041573Srgrimes * from the old state information. This is done by multiplexing the pointer 4051573Srgrimes * location into the zeroeth word of the state information. 4061573Srgrimes * 4071573Srgrimes * Note that due to the order in which things are done, it is OK to call 4081573Srgrimes * setstate() with the same state as the current state. 4091573Srgrimes * 4101573Srgrimes * Returns a pointer to the old state information. 41123662Speter * 41223662Speter * Note: The Sparc platform requires that arg_state begin on a long 41323662Speter * word boundary; otherwise a bus error will occur. Even so, lint will 41423662Speter * complain about mis-alignment, but you should disregard these messages. 4151573Srgrimes */ 4161573Srgrimeschar * 4171573Srgrimessetstate(arg_state) 41823662Speter char *arg_state; /* pointer to state array */ 4191573Srgrimes{ 42023662Speter register long *new_state = (long *) arg_state; 42123662Speter register long type = new_state[0] % MAX_TYPES; 42223662Speter register long rear = new_state[0] / MAX_TYPES; 4231573Srgrimes char *ostate = (char *)(&state[-1]); 4241573Srgrimes 4251573Srgrimes if (rand_type == TYPE_0) 4261573Srgrimes state[-1] = rand_type; 4271573Srgrimes else 4281573Srgrimes state[-1] = MAX_TYPES * (rptr - state) + rand_type; 4291573Srgrimes switch(type) { 4301573Srgrimes case TYPE_0: 4311573Srgrimes case TYPE_1: 4321573Srgrimes case TYPE_2: 4331573Srgrimes case TYPE_3: 4341573Srgrimes case TYPE_4: 4351573Srgrimes rand_type = type; 4361573Srgrimes rand_deg = degrees[type]; 4371573Srgrimes rand_sep = seps[type]; 4381573Srgrimes break; 4391573Srgrimes default: 4401573Srgrimes (void)fprintf(stderr, 4411573Srgrimes "random: state info corrupted; not changed.\n"); 4421573Srgrimes } 44323662Speter state = (long *) (new_state + 1); 4441573Srgrimes if (rand_type != TYPE_0) { 4451573Srgrimes rptr = &state[rear]; 4461573Srgrimes fptr = &state[(rear + rand_sep) % rand_deg]; 4471573Srgrimes } 4481573Srgrimes end_ptr = &state[rand_deg]; /* set end_ptr too */ 4491573Srgrimes return(ostate); 4501573Srgrimes} 4511573Srgrimes 4521573Srgrimes/* 4531573Srgrimes * random: 4541573Srgrimes * 4551573Srgrimes * If we are using the trivial TYPE_0 R.N.G., just do the old linear 4561573Srgrimes * congruential bit. Otherwise, we do our fancy trinomial stuff, which is 4571573Srgrimes * the same in all the other cases due to all the global variables that have 4581573Srgrimes * been set up. The basic operation is to add the number at the rear pointer 4591573Srgrimes * into the one at the front pointer. Then both pointers are advanced to 4601573Srgrimes * the next location cyclically in the table. The value returned is the sum 4611573Srgrimes * generated, reduced to 31 bits by throwing away the "least random" low bit. 4621573Srgrimes * 4631573Srgrimes * Note: the code takes advantage of the fact that both the front and 4641573Srgrimes * rear pointers can't wrap on the same call by not testing the rear 4651573Srgrimes * pointer if the front one has wrapped. 4661573Srgrimes * 4671573Srgrimes * Returns a 31-bit random number. 4681573Srgrimes */ 4691573Srgrimeslong 4701573Srgrimesrandom() 4711573Srgrimes{ 47223662Speter register long i; 47323662Speter register long *f, *r; 4741573Srgrimes 47523662Speter if (rand_type == TYPE_0) { 47623662Speter i = state[0]; 47723662Speter state[0] = i = (good_rand(i)) & 0x7fffffff; 47823662Speter } else { 47923662Speter /* 48023662Speter * Use local variables rather than static variables for speed. 48123662Speter */ 48223662Speter f = fptr; r = rptr; 48323662Speter *f += *r; 48423662Speter i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */ 48523662Speter if (++f >= end_ptr) { 48623662Speter f = state; 48723662Speter ++r; 48823662Speter } 48923662Speter else if (++r >= end_ptr) { 49023662Speter r = state; 49123662Speter } 49223662Speter 49323662Speter fptr = f; rptr = r; 4941573Srgrimes } 4951573Srgrimes return(i); 4961573Srgrimes} 497