| /*␊ |
| * Copyright (c) 1983, 1993␊ |
| *␉The Regents of the University of California. All rights reserved.␊ |
| *␊ |
| * Redistribution and use in source and binary forms, with or without␊ |
| * modification, are permitted provided that the following conditions␊ |
| * are met:␊ |
| * 1. Redistributions of source code must retain the above copyright␊ |
| * notice, this list of conditions and the following disclaimer.␊ |
| * 2. Redistributions in binary form must reproduce the above copyright␊ |
| * notice, this list of conditions and the following disclaimer in the␊ |
| * documentation and/or other materials provided with the distribution.␊ |
| * 4. Neither the name of the University nor the names of its contributors␊ |
| * may be used to endorse or promote products derived from this software␊ |
| * without specific prior written permission.␊ |
| *␊ |
| * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND␊ |
| * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE␊ |
| * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE␊ |
| * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE␊ |
| * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL␊ |
| * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS␊ |
| * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)␊ |
| * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT␊ |
| * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY␊ |
| * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF␊ |
| * SUCH DAMAGE.␊ |
| */␊ |
| ␊ |
| #if defined(LIBC_SCCS) && !defined(lint)␊ |
| static char sccsid[] = "@(#)random.c␉8.2 (Berkeley) 5/19/95";␊ |
| #endif /* LIBC_SCCS and not lint */␊ |
| #include <sys/cdefs.h>␊ |
| __FBSDID("$FreeBSD: src/lib/libc/stdlib/random.c,v 1.25 2007/01/09 00:28:10 imp Exp $");␊ |
| ␊ |
| /*␊ |
| * We always compile with __DARWIN_UNIX03 set to one, relying on the fact that␊ |
| * (for non-LP64) sizeof(int) == sizeof(long) == sizeof(size_t), so that we␊ |
| * don't have to have two different versions of the prototypes. For LP64,␊ |
| * we only support the POSIX-compatible prototypes.␊ |
| */␊ |
| #undef ␉__DARWIN_UNIX03␊ |
| #define␉__DARWIN_UNIX03␉1␊ |
| #include "namespace.h"␊ |
| #include <sys/time.h> /* for srandomdev() */␊ |
| #include <fcntl.h> /* for srandomdev() */␊ |
| #include <stdint.h>␊ |
| #include <stdio.h>␊ |
| #include <stdlib.h>␊ |
| #include <unistd.h> /* for srandomdev() */␊ |
| #include "un-namespace.h"␊ |
| ␊ |
| /*␊ |
| * random.c:␊ |
| *␊ |
| * An improved random number generation package. In addition to the standard␊ |
| * rand()/srand() like interface, this package also has a special state info␊ |
| * interface. The initstate() routine is called with a seed, an array of␊ |
| * bytes, and a count of how many bytes are being passed in; this array is␊ |
| * then initialized to contain information for random number generation with␊ |
| * that much state information. Good sizes for the amount of state␊ |
| * information are 32, 64, 128, and 256 bytes. The state can be switched by␊ |
| * calling the setstate() routine with the same array as was initiallized␊ |
| * with initstate(). By default, the package runs with 128 bytes of state␊ |
| * information and generates far better random numbers than a linear␊ |
| * congruential generator. If the amount of state information is less than␊ |
| * 32 bytes, a simple linear congruential R.N.G. is used.␊ |
| *␊ |
| * Internally, the state information is treated as an array of uint32_t's; the␊ |
| * zeroeth element of the array is the type of R.N.G. being used (small␊ |
| * integer); the remainder of the array is the state information for the␊ |
| * R.N.G. Thus, 32 bytes of state information will give 7 ints worth of␊ |
| * state information, which will allow a degree seven polynomial. (Note:␊ |
| * the zeroeth word of state information also has some other information␊ |
| * stored in it -- see setstate() for details).␊ |
| *␊ |
| * The random number generation technique is a linear feedback shift register␊ |
| * approach, employing trinomials (since there are fewer terms to sum up that␊ |
| * way). In this approach, the least significant bit of all the numbers in␊ |
| * the state table will act as a linear feedback shift register, and will␊ |
| * have period 2^deg - 1 (where deg is the degree of the polynomial being␊ |
| * used, assuming that the polynomial is irreducible and primitive). The␊ |
| * higher order bits will have longer periods, since their values are also␊ |
| * influenced by pseudo-random carries out of the lower bits. The total␊ |
| * period of the generator is approximately deg*(2**deg - 1); thus doubling␊ |
| * the amount of state information has a vast influence on the period of the␊ |
| * generator. Note: the deg*(2**deg - 1) is an approximation only good for␊ |
| * large deg, when the period of the shift is the dominant factor.␊ |
| * With deg equal to seven, the period is actually much longer than the␊ |
| * 7*(2**7 - 1) predicted by this formula.␊ |
| *␊ |
| * Modified 28 December 1994 by Jacob S. Rosenberg.␊ |
| * The following changes have been made:␊ |
| * All references to the type u_int have been changed to unsigned long.␊ |
| * All references to type int have been changed to type long. Other␊ |
| * cleanups have been made as well. A warning for both initstate and␊ |
| * setstate has been inserted to the effect that on Sparc platforms␊ |
| * the 'arg_state' variable must be forced to begin on word boundaries.␊ |
| * This can be easily done by casting a long integer array to char *.␊ |
| * The overall logic has been left STRICTLY alone. This software was␊ |
| * tested on both a VAX and Sun SpacsStation with exactly the same␊ |
| * results. The new version and the original give IDENTICAL results.␊ |
| * The new version is somewhat faster than the original. As the␊ |
| * documentation says: "By default, the package runs with 128 bytes of␊ |
| * state information and generates far better random numbers than a linear␊ |
| * congruential generator. If the amount of state information is less than␊ |
| * 32 bytes, a simple linear congruential R.N.G. is used." For a buffer of␊ |
| * 128 bytes, this new version runs about 19 percent faster and for a 16␊ |
| * byte buffer it is about 5 percent faster.␊ |
| */␊ |
| ␊ |
| /*␊ |
| * For each of the currently supported random number generators, we have a␊ |
| * break value on the amount of state information (you need at least this␊ |
| * many bytes of state info to support this random number generator), a degree␊ |
| * for the polynomial (actually a trinomial) that the R.N.G. is based on, and␊ |
| * the separation between the two lower order coefficients of the trinomial.␊ |
| */␊ |
| #define␉TYPE_0␉␉0␉␉/* linear congruential */␊ |
| #define␉BREAK_0␉␉8␊ |
| #define␉DEG_0␉␉0␊ |
| #define␉SEP_0␉␉0␊ |
| ␊ |
| #define␉TYPE_1␉␉1␉␉/* x**7 + x**3 + 1 */␊ |
| #define␉BREAK_1␉␉32␊ |
| #define␉DEG_1␉␉7␊ |
| #define␉SEP_1␉␉3␊ |
| ␊ |
| #define␉TYPE_2␉␉2␉␉/* x**15 + x + 1 */␊ |
| #define␉BREAK_2␉␉64␊ |
| #define␉DEG_2␉␉15␊ |
| #define␉SEP_2␉␉1␊ |
| ␊ |
| #define␉TYPE_3␉␉3␉␉/* x**31 + x**3 + 1 */␊ |
| #define␉BREAK_3␉␉128␊ |
| #define␉DEG_3␉␉31␊ |
| #define␉SEP_3␉␉3␊ |
| ␊ |
| #define␉TYPE_4␉␉4␉␉/* x**63 + x + 1 */␊ |
| #define␉BREAK_4␉␉256␊ |
| #define␉DEG_4␉␉63␊ |
| #define␉SEP_4␉␉1␊ |
| ␊ |
| /*␊ |
| * Array versions of the above information to make code run faster --␊ |
| * relies on fact that TYPE_i == i.␊ |
| */␊ |
| #define␉MAX_TYPES␉5␉␉/* max number of types above */␊ |
| ␊ |
| #ifdef USE_WEAK_SEEDING␊ |
| #define NSHUFF 0␊ |
| #else /* !USE_WEAK_SEEDING */␊ |
| #define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */␊ |
| #endif /* !USE_WEAK_SEEDING */␊ |
| ␊ |
| static const int degrees[MAX_TYPES] =␉{ DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };␊ |
| static const int seps [MAX_TYPES] =␉{ SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };␊ |
| ␊ |
| /*␊ |
| * Initially, everything is set up as if from:␊ |
| *␊ |
| *␉initstate(1, randtbl, 128);␊ |
| *␊ |
| * Note that this initialization takes advantage of the fact that srandom()␊ |
| * advances the front and rear pointers 10*rand_deg times, and hence the␊ |
| * rear pointer which starts at 0 will also end up at zero; thus the zeroeth␊ |
| * element of the state information, which contains info about the current␊ |
| * position of the rear pointer is just␊ |
| *␊ |
| *␉MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3.␊ |
| */␊ |
| ␊ |
| static uint32_t randtbl[DEG_3 + 1] = {␊ |
| ␉TYPE_3,␊ |
| #ifdef USE_WEAK_SEEDING␊ |
| /* Historic implementation compatibility */␊ |
| /* The random sequences do not vary much with the seed */␊ |
| ␉0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5,␊ |
| ␉0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,␊ |
| ␉0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88,␊ |
| ␉0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,␊ |
| ␉0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b,␊ |
| ␉0x27fb47b9,␊ |
| #else /* !USE_WEAK_SEEDING */␊ |
| ␉0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05,␊ |
| ␉0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454,␊ |
| ␉0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471,␊ |
| ␉0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1,␊ |
| ␉0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41,␊ |
| ␉0xf3bec5da␊ |
| #endif /* !USE_WEAK_SEEDING */␊ |
| };␊ |
| ␊ |
| /*␊ |
| * fptr and rptr are two pointers into the state info, a front and a rear␊ |
| * pointer. These two pointers are always rand_sep places aparts, as they␊ |
| * cycle cyclically through the state information. (Yes, this does mean we␊ |
| * could get away with just one pointer, but the code for random() is more␊ |
| * efficient this way). The pointers are left positioned as they would be␊ |
| * from the call␊ |
| *␊ |
| *␉initstate(1, randtbl, 128);␊ |
| *␊ |
| * (The position of the rear pointer, rptr, is really 0 (as explained above␊ |
| * in the initialization of randtbl) because the state table pointer is set␊ |
| * to point to randtbl[1] (as explained below).␊ |
| */␊ |
| static uint32_t *fptr = &randtbl[SEP_3 + 1];␊ |
| static uint32_t *rptr = &randtbl[1];␊ |
| ␊ |
| /*␊ |
| * The following things are the pointer to the state information table, the␊ |
| * type of the current generator, the degree of the current polynomial being␊ |
| * used, and the separation between the two pointers. Note that for efficiency␊ |
| * of random(), we remember the first location of the state information, not␊ |
| * the zeroeth. Hence it is valid to access state[-1], which is used to␊ |
| * store the type of the R.N.G. Also, we remember the last location, since␊ |
| * this is more efficient than indexing every time to find the address of␊ |
| * the last element to see if the front and rear pointers have wrapped.␊ |
| */␊ |
| static uint32_t *state = &randtbl[1];␊ |
| static int rand_type = TYPE_3;␊ |
| static int rand_deg = DEG_3;␊ |
| static int rand_sep = SEP_3;␊ |
| static uint32_t *end_ptr = &randtbl[DEG_3 + 1];␊ |
| ␊ |
| static inline uint32_t good_rand(int32_t) __attribute__((always_inline));␊ |
| ␊ |
| static inline uint32_t good_rand (x)␊ |
| int32_t x;␊ |
| {␊ |
| #ifdef USE_WEAK_SEEDING␊ |
| /*␊ |
| * Historic implementation compatibility.␊ |
| * The random sequences do not vary much with the seed,␊ |
| * even with overflowing.␊ |
| */␊ |
| ␉return (1103515245 * x + 12345);␊ |
| #else /* !USE_WEAK_SEEDING */␊ |
| /*␊ |
| * Compute x = (7^5 * x) mod (2^31 - 1)␊ |
| * wihout overflowing 31 bits:␊ |
| * (2^31 - 1) = 127773 * (7^5) + 2836␊ |
| * From "Random number generators: good ones are hard to find",␊ |
| * Park and Miller, Communications of the ACM, vol. 31, no. 10,␊ |
| * October 1988, p. 1195.␊ |
| */␊ |
| ␉int32_t hi, lo;␊ |
| ␊ |
| ␉/* Can't be initialized with 0, so use another value. */␊ |
| ␉if (x == 0)␊ |
| ␉␉x = 123459876;␊ |
| ␉hi = x / 127773;␊ |
| ␉lo = x % 127773;␊ |
| ␉x = 16807 * lo - 2836 * hi;␊ |
| ␉if (x < 0)␊ |
| ␉␉x += 0x7fffffff;␊ |
| ␉return (x);␊ |
| #endif /* !USE_WEAK_SEEDING */␊ |
| }␊ |
| ␊ |
| /*␊ |
| * srandom:␊ |
| *␊ |
| * Initialize the random number generator based on the given seed. If the␊ |
| * type is the trivial no-state-information type, just remember the seed.␊ |
| * Otherwise, initializes state[] based on the given "seed" via a linear␊ |
| * congruential generator. Then, the pointers are set to known locations␊ |
| * that are exactly rand_sep places apart. Lastly, it cycles the state␊ |
| * information a given number of times to get rid of any initial dependencies␊ |
| * introduced by the L.C.R.N.G. Note that the initialization of randtbl[]␊ |
| * for default usage relies on values produced by this routine.␊ |
| */␊ |
| void␊ |
| srandom(x)␊ |
| unsigned x;␊ |
| {␊ |
| ␉int i, lim;␊ |
| ␊ |
| ␉state[0] = (uint32_t)x;␊ |
| ␉if (rand_type == TYPE_0)␊ |
| ␉␉lim = NSHUFF;␊ |
| ␉else {␊ |
| ␉␉for (i = 1; i < rand_deg; i++)␊ |
| ␉␉␉state[i] = good_rand(state[i - 1]);␊ |
| ␉␉fptr = &state[rand_sep];␊ |
| ␉␉rptr = &state[0];␊ |
| ␉␉lim = 10 * rand_deg;␊ |
| ␉}␊ |
| ␉for (i = 0; i < lim; i++)␊ |
| ␉␉(void)random();␊ |
| }␊ |
| ␊ |
| /*␊ |
| * srandomdev:␊ |
| *␊ |
| * Many programs choose the seed value in a totally predictable manner.␊ |
| * This often causes problems. We seed the generator using the much more␊ |
| * secure random(4) interface. Note that this particular seeding␊ |
| * procedure can generate states which are impossible to reproduce by␊ |
| * calling srandom() with any value, since the succeeding terms in the␊ |
| * state buffer are no longer derived from the LC algorithm applied to␊ |
| * a fixed seed.␊ |
| */␊ |
| void␊ |
| srandomdev()␊ |
| {␊ |
| ␉int fd, done;␊ |
| ␉size_t len;␊ |
| ␊ |
| ␉if (rand_type == TYPE_0)␊ |
| ␉␉len = sizeof state[0];␊ |
| ␉else␊ |
| ␉␉len = rand_deg * sizeof state[0];␊ |
| ␊ |
| ␉done = 0;␊ |
| ␉fd = _open("/dev/random", O_RDONLY, 0);␊ |
| ␉if (fd >= 0) {␊ |
| ␉␉if (_read(fd, (void *) state, len) == (ssize_t) len)␊ |
| ␉␉␉done = 1;␊ |
| ␉␉_close(fd);␊ |
| ␉}␊ |
| ␊ |
| ␉if (!done) {␊ |
| ␉␉struct timeval tv;␊ |
| ␉␉unsigned long junk;␊ |
| ␊ |
| ␉␉gettimeofday(&tv, NULL);␊ |
| ␉␉srandom((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk);␊ |
| ␉␉return;␊ |
| ␉}␊ |
| ␊ |
| ␉if (rand_type != TYPE_0) {␊ |
| ␉␉fptr = &state[rand_sep];␊ |
| ␉␉rptr = &state[0];␊ |
| ␉}␊ |
| }␊ |
| ␊ |
| /*␊ |
| * initstate:␊ |
| *␊ |
| * Initialize the state information in the given array of n bytes for future␊ |
| * random number generation. Based on the number of bytes we are given, and␊ |
| * the break values for the different R.N.G.'s, we choose the best (largest)␊ |
| * one we can and set things up for it. srandom() is then called to␊ |
| * initialize the state information.␊ |
| *␊ |
| * Note that on return from srandom(), we set state[-1] to be the type␊ |
| * multiplexed with the current value of the rear pointer; this is so␊ |
| * successive calls to initstate() won't lose this information and will be␊ |
| * able to restart with setstate().␊ |
| *␊ |
| * Note: the first thing we do is save the current state, if any, just like␊ |
| * setstate() so that it doesn't matter when initstate is called.␊ |
| *␊ |
| * Returns a pointer to the old state.␊ |
| *␊ |
| * Note: The Sparc platform requires that arg_state begin on an int␊ |
| * word boundary; otherwise a bus error will occur. Even so, lint will␊ |
| * complain about mis-alignment, but you should disregard these messages.␊ |
| */␊ |
| char *␊ |
| initstate(seed, arg_state, n)␊ |
| unsigned seed;␉␉/* seed for R.N.G. */␊ |
| char *arg_state;␉␉/* pointer to state array */␊ |
| size_t n;␉␉␉␉/* # bytes of state info */␊ |
| {␊ |
| ␉char *ostate = (char *)(&state[-1]);␊ |
| ␉uint32_t *int_arg_state = (uint32_t *)arg_state;␊ |
| ␊ |
| ␉if (rand_type == TYPE_0)␊ |
| ␉␉state[-1] = rand_type;␊ |
| ␉else␊ |
| ␉␉state[-1] = MAX_TYPES * (rptr - state) + rand_type;␊ |
| ␉if (n < BREAK_0) {␊ |
| ␉␉(void)fprintf(stderr,␊ |
| "random: not enough state (%ld bytes); ignored.\n", n);␊ |
| ␉␉return(0);␊ |
| ␉}␊ |
| ␉if (n < BREAK_1) {␊ |
| ␉␉rand_type = TYPE_0;␊ |
| ␉␉rand_deg = DEG_0;␊ |
| ␉␉rand_sep = SEP_0;␊ |
| ␉} else if (n < BREAK_2) {␊ |
| ␉␉rand_type = TYPE_1;␊ |
| ␉␉rand_deg = DEG_1;␊ |
| ␉␉rand_sep = SEP_1;␊ |
| ␉} else if (n < BREAK_3) {␊ |
| ␉␉rand_type = TYPE_2;␊ |
| ␉␉rand_deg = DEG_2;␊ |
| ␉␉rand_sep = SEP_2;␊ |
| ␉} else if (n < BREAK_4) {␊ |
| ␉␉rand_type = TYPE_3;␊ |
| ␉␉rand_deg = DEG_3;␊ |
| ␉␉rand_sep = SEP_3;␊ |
| ␉} else {␊ |
| ␉␉rand_type = TYPE_4;␊ |
| ␉␉rand_deg = DEG_4;␊ |
| ␉␉rand_sep = SEP_4;␊ |
| ␉}␊ |
| ␉state = int_arg_state + 1; /* first location */␊ |
| ␉end_ptr = &state[rand_deg];␉/* must set end_ptr before srandom */␊ |
| ␉srandom(seed);␊ |
| ␉if (rand_type == TYPE_0)␊ |
| ␉␉int_arg_state[0] = rand_type;␊ |
| ␉else␊ |
| ␉␉int_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type;␊ |
| ␉return(ostate);␊ |
| }␊ |
| ␊ |
| /*␊ |
| * setstate:␊ |
| *␊ |
| * Restore the state from the given state array.␊ |
| *␊ |
| * Note: it is important that we also remember the locations of the pointers␊ |
| * in the current state information, and restore the locations of the pointers␊ |
| * from the old state information. This is done by multiplexing the pointer␊ |
| * location into the zeroeth word of the state information.␊ |
| *␊ |
| * Note that due to the order in which things are done, it is OK to call␊ |
| * setstate() with the same state as the current state.␊ |
| *␊ |
| * Returns a pointer to the old state information.␊ |
| *␊ |
| * Note: The Sparc platform requires that arg_state begin on an int␊ |
| * word boundary; otherwise a bus error will occur. Even so, lint will␊ |
| * complain about mis-alignment, but you should disregard these messages.␊ |
| */␊ |
| char *␊ |
| setstate(arg_state)␊ |
| const char *arg_state;␉␉/* pointer to state array */␊ |
| {␊ |
| ␉uint32_t *new_state = (uint32_t *)arg_state;␊ |
| ␉uint32_t type = new_state[0] % MAX_TYPES;␊ |
| ␉uint32_t rear = new_state[0] / MAX_TYPES;␊ |
| ␉char *ostate = (char *)(&state[-1]);␊ |
| ␊ |
| ␉if (rand_type == TYPE_0)␊ |
| ␉␉state[-1] = rand_type;␊ |
| ␉else␊ |
| ␉␉state[-1] = MAX_TYPES * (rptr - state) + rand_type;␊ |
| ␉switch(type) {␊ |
| case TYPE_0:␊ |
| case TYPE_1:␊ |
| case TYPE_2:␊ |
| case TYPE_3:␊ |
| case TYPE_4:␊ |
| rand_type = type;␊ |
| rand_deg = degrees[type];␊ |
| rand_sep = seps[type];␊ |
| break;␊ |
| default:␊ |
| (void)fprintf(stderr,␊ |
| "random: state info corrupted; not changed.\n");␊ |
| ␉}␊ |
| ␉state = new_state + 1;␊ |
| ␉if (rand_type != TYPE_0) {␊ |
| ␉␉rptr = &state[rear];␊ |
| ␉␉fptr = &state[(rear + rand_sep) % rand_deg];␊ |
| ␉}␊ |
| ␉end_ptr = &state[rand_deg];␉␉/* set end_ptr too */␊ |
| ␉return(ostate);␊ |
| }␊ |
| ␊ |
| /*␊ |
| * random:␊ |
| *␊ |
| * If we are using the trivial TYPE_0 R.N.G., just do the old linear␊ |
| * congruential bit. Otherwise, we do our fancy trinomial stuff, which is␊ |
| * the same in all the other cases due to all the global variables that have␊ |
| * been set up. The basic operation is to add the number at the rear pointer␊ |
| * into the one at the front pointer. Then both pointers are advanced to␊ |
| * the next location cyclically in the table. The value returned is the sum␊ |
| * generated, reduced to 31 bits by throwing away the "least random" low bit.␊ |
| *␊ |
| * Note: the code takes advantage of the fact that both the front and␊ |
| * rear pointers can't wrap on the same call by not testing the rear␊ |
| * pointer if the front one has wrapped.␊ |
| *␊ |
| * Returns a 31-bit random number.␊ |
| */␊ |
| long␊ |
| random()␊ |
| {␊ |
| ␉uint32_t i;␊ |
| ␉uint32_t *f, *r;␊ |
| ␊ |
| ␉if (rand_type == TYPE_0) {␊ |
| ␉␉i = state[0];␊ |
| ␉␉state[0] = i = (good_rand(i)) & 0x7fffffff;␊ |
| ␉} else {␊ |
| ␉␉/*␊ |
| ␉␉ * Use local variables rather than static variables for speed.␊ |
| ␉␉ */␊ |
| ␉␉f = fptr; r = rptr;␊ |
| ␉␉*f += *r;␊ |
| ␉␉i = (*f >> 1) & 0x7fffffff;␉/* chucking least random bit */␊ |
| ␉␉if (++f >= end_ptr) {␊ |
| ␉␉␉f = state;␊ |
| ␉␉␉++r;␊ |
| ␉␉}␊ |
| ␉␉else if (++r >= end_ptr) {␊ |
| ␉␉␉r = state;␊ |
| ␉␉}␊ |
| ␊ |
| ␉␉fptr = f; rptr = r;␊ |
| ␉}␊ |
| ␉return((long)i);␊ |
| }␊ |
