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Diffstat (limited to 'lib/libc/stdlib/random.c')
| -rw-r--r-- | lib/libc/stdlib/random.c | 501 |
1 files changed, 501 insertions, 0 deletions
diff --git a/lib/libc/stdlib/random.c b/lib/libc/stdlib/random.c new file mode 100644 index 000000000000..6e9702229da8 --- /dev/null +++ b/lib/libc/stdlib/random.c @@ -0,0 +1,501 @@ +/*- + * SPDX-License-Identifier: BSD-3-Clause + * + * 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. + * 3. 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. + */ + +#include "namespace.h" +#include <sys/param.h> +#include <sys/sysctl.h> +#include <errno.h> +#include <stdint.h> +#include <stdlib.h> +#include "un-namespace.h" + +#include "random.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. + */ + +#define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */ + +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 }; +static const int breaks[MAX_TYPES] = { + BREAK_0, BREAK_1, BREAK_2, BREAK_3, BREAK_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 struct __random_state implicit = { + .rst_randtbl = { + TYPE_3, + 0x2cf41758, 0x27bb3711, 0x4916d4d1, 0x7b02f59f, 0x9b8e28eb, 0xc0e80269, + 0x696f5c16, 0x878f1ff5, 0x52d9c07f, 0x916a06cd, 0xb50b3a20, 0x2776970a, + 0xee4eb2a6, 0xe94640ec, 0xb1d65612, 0x9d1ed968, 0x1043f6b7, 0xa3432a76, + 0x17eacbb9, 0x3c09e2eb, 0x4f8c2b3, 0x708a1f57, 0xee341814, 0x95d0e4d2, + 0xb06f216c, 0x8bd2e72e, 0x8f7c38d7, 0xcfc6a8fc, 0x2a59495, 0xa20d2a69, + 0xe29d12d1 + }, + + /* + * 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). + */ + .rst_fptr = &implicit.rst_randtbl[SEP_3 + 1], + .rst_rptr = &implicit.rst_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. + */ + .rst_state = &implicit.rst_randtbl[1], + .rst_type = TYPE_3, + .rst_deg = DEG_3, + .rst_sep = SEP_3, + .rst_end_ptr = &implicit.rst_randtbl[DEG_3 + 1], +}; + +/* + * This is the same low quality PRNG used in rand(3) in FreeBSD 12 and prior. + * It may be sufficient for distributing bits and expanding a small seed + * integer into a larger state. + */ +static inline uint32_t +parkmiller32(uint32_t ctx) +{ +/* + * 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, x; + + /* Transform to [1, 0x7ffffffe] range. */ + x = (ctx % 0x7ffffffe) + 1; + hi = x / 127773; + lo = x % 127773; + x = 16807 * lo - 2836 * hi; + if (x < 0) + x += 0x7fffffff; + /* Transform to [0, 0x7ffffffd] range. */ + return (x - 1); +} + +/* + * 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_r(struct __random_state *estate, unsigned x) +{ + int i, lim; + + estate->rst_state[0] = (uint32_t)x; + if (estate->rst_type == TYPE_0) + lim = NSHUFF; + else { + for (i = 1; i < estate->rst_deg; i++) + estate->rst_state[i] = + parkmiller32(estate->rst_state[i - 1]); + estate->rst_fptr = &estate->rst_state[estate->rst_sep]; + estate->rst_rptr = &estate->rst_state[0]; + lim = 10 * estate->rst_deg; + } + for (i = 0; i < lim; i++) + (void)random_r(estate); +} + +void +srandom(unsigned x) +{ + srandom_r(&implicit, x); +} + +/* + * srandomdev: + * + * Many programs choose the seed value in a totally predictable manner. + * This often causes problems. We seed the generator using pseudo-random + * data from the kernel. + * + * 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_r(struct __random_state *estate) +{ + int mib[2]; + size_t expected, len; + + if (estate->rst_type == TYPE_0) + len = sizeof(estate->rst_state[0]); + else + len = estate->rst_deg * sizeof(estate->rst_state[0]); + expected = len; + + mib[0] = CTL_KERN; + mib[1] = KERN_ARND; + if (sysctl(mib, 2, estate->rst_state, &len, NULL, 0) == -1 || + len != expected) { + /* + * The sysctl cannot fail. If it does fail on some FreeBSD + * derivative or after some future change, just abort so that + * the problem will be found and fixed. abort is not normally + * suitable for a library but makes sense here. + */ + abort(); + } + + if (estate->rst_type != TYPE_0) { + estate->rst_fptr = &estate->rst_state[estate->rst_sep]; + estate->rst_rptr = &estate->rst_state[0]; + } +} + +void +srandomdev(void) +{ + srandomdev_r(&implicit); +} + +/* + * initstate_r: + * + * 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. + * + * Returns zero on success, or an error number on failure. + * + * Note: There is no need for a setstate_r(); just use a new context. + */ +int +initstate_r(struct __random_state *estate, unsigned seed, uint32_t *arg_state, + size_t sz) +{ + if (sz < BREAK_0) + return (EINVAL); + + if (sz < BREAK_1) { + estate->rst_type = TYPE_0; + estate->rst_deg = DEG_0; + estate->rst_sep = SEP_0; + } else if (sz < BREAK_2) { + estate->rst_type = TYPE_1; + estate->rst_deg = DEG_1; + estate->rst_sep = SEP_1; + } else if (sz < BREAK_3) { + estate->rst_type = TYPE_2; + estate->rst_deg = DEG_2; + estate->rst_sep = SEP_2; + } else if (sz < BREAK_4) { + estate->rst_type = TYPE_3; + estate->rst_deg = DEG_3; + estate->rst_sep = SEP_3; + } else { + estate->rst_type = TYPE_4; + estate->rst_deg = DEG_4; + estate->rst_sep = SEP_4; + } + estate->rst_state = arg_state + 1; + estate->rst_end_ptr = &estate->rst_state[estate->rst_deg]; + srandom_r(estate, seed); + return (0); +} + +/* + * initstate: + * + * 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. + * + * Note that on return from initstate_r(), 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(). + * + * Returns a pointer to the old state. + * + * Despite the misleading "char *" type, arg_state must alias an array of + * 32-bit unsigned integer values. Naturally, such an array is 32-bit aligned. + * Usually objects are naturally aligned to at least 32-bits on all platforms, + * but if you treat the provided 'state' as char* you may inadvertently + * misalign it. Don't do that. + */ +char * +initstate(unsigned int seed, char *arg_state, size_t n) +{ + char *ostate = (char *)(&implicit.rst_state[-1]); + uint32_t *int_arg_state = (uint32_t *)arg_state; + int error; + + /* + * Persist rptr offset and rst_type in the first word of the prior + * state we are replacing. + */ + if (implicit.rst_type == TYPE_0) + implicit.rst_state[-1] = implicit.rst_type; + else + implicit.rst_state[-1] = MAX_TYPES * + (implicit.rst_rptr - implicit.rst_state) + + implicit.rst_type; + + error = initstate_r(&implicit, seed, int_arg_state, n); + if (error != 0) + return (NULL); + + /* + * Persist rptr offset and rst_type of the new state in its first word. + */ + if (implicit.rst_type == TYPE_0) + int_arg_state[0] = implicit.rst_type; + else + int_arg_state[0] = MAX_TYPES * + (implicit.rst_rptr - implicit.rst_state) + + implicit.rst_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(char *arg_state) +{ + 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 *)(&implicit.rst_state[-1]); + + if (type != TYPE_0 && rear >= degrees[type]) + return (NULL); + if (implicit.rst_type == TYPE_0) + implicit.rst_state[-1] = implicit.rst_type; + else + implicit.rst_state[-1] = MAX_TYPES * + (implicit.rst_rptr - implicit.rst_state) + + implicit.rst_type; + implicit.rst_type = type; + implicit.rst_deg = degrees[type]; + implicit.rst_sep = seps[type]; + implicit.rst_state = new_state + 1; + if (implicit.rst_type != TYPE_0) { + implicit.rst_rptr = &implicit.rst_state[rear]; + implicit.rst_fptr = &implicit.rst_state[ + (rear + implicit.rst_sep) % implicit.rst_deg]; + } + implicit.rst_end_ptr = &implicit.rst_state[implicit.rst_deg]; + 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_r(struct __random_state *estate) +{ + uint32_t i; + uint32_t *f, *r; + + if (estate->rst_type == TYPE_0) { + i = estate->rst_state[0]; + i = parkmiller32(i); + estate->rst_state[0] = i; + } else { + /* + * Use local variables rather than static variables for speed. + */ + f = estate->rst_fptr; + r = estate->rst_rptr; + *f += *r; + i = *f >> 1; /* chucking least random bit */ + if (++f >= estate->rst_end_ptr) { + f = estate->rst_state; + ++r; + } + else if (++r >= estate->rst_end_ptr) { + r = estate->rst_state; + } + + estate->rst_fptr = f; + estate->rst_rptr = r; + } + return ((long)i); +} + +long +random(void) +{ + return (random_r(&implicit)); +} + +struct __random_state * +allocatestate(unsigned type) +{ + size_t asize; + + /* No point using this interface to get the Park-Miller LCG. */ + if (type < TYPE_1) + abort(); + /* Clamp to widest supported variant. */ + if (type > (MAX_TYPES - 1)) + type = (MAX_TYPES - 1); + + asize = sizeof(struct __random_state) + (size_t)breaks[type]; + return (malloc(asize)); +} |