/*-
* 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.
*/
#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("$FreeBSD$");
#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));
}
