/*

 * 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.

 * © Portions copyright (c) 2006 Nokia Corporation.  All rights reserved.

 */

#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 1.24 2004/01/20 03:02:18 das Exp $");

#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() */

/*

 * 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);

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.

 */

EXPORT_C

void

srandom(x)

	unsigned long 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();

}

#ifdef __SYMBIAN_COMPILE_UNUSED__

/*

 * 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 = 0;

		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];

	}

}

#endif

/*

 * 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.

 */

EXPORT_C

char *

initstate(seed, arg_state, n)

	unsigned long seed;		/* seed for R.N.G. */

	char *arg_state;		/* pointer to state array */

	long 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.

 */

EXPORT_C

char *

setstate(arg_state)

	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.

 */

EXPORT_C

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);

}