/*

 * CDDL HEADER START

 *

 * The contents of this file are subject to the terms of the

 * Common Development and Distribution License (the "License").

 * You may not use this file except in compliance with the License.

 *

 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE

 * or http://www.opensolaris.org/os/licensing.

 * See the License for the specific language governing permissions

 * and limitations under the License.

 *

 * When distributing Covered Code, include this CDDL HEADER in each

 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.

 * If applicable, add the following below this CDDL HEADER, with the

 * fields enclosed by brackets "[]" replaced with your own identifying

 * information: Portions Copyright [yyyy] [name of copyright owner]

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 */

/*

 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.

 * Use is subject to license terms.

 */

/*	Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T	*/

/*	  All Rights Reserved  	*/

/*

 * University Copyright- Copyright (c) 1982, 1986, 1988

 * The Regents of the University of California

 * All Rights Reserved

 *

 * University Acknowledgment- Portions of this document are derived from

 * software developed by the University of California, Berkeley, and its

 * contributors.

 */

#pragma ident	"%Z%%M%	%I%	%E% SMI"

#include "lint.h"

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/types.h>

#include <limits.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 ints; 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 register 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.

 */

/*

 * 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 */

static struct _randomjunk {

	unsigned int	degrees[MAX_TYPES];

	unsigned int	seps[MAX_TYPES];

	unsigned int	randtbl[ DEG_3 + 1 ];

/*

 * 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).

 */

	unsigned int	*fptr, *rptr;

/*

 * 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.

 */

	unsigned int	*state;

	unsigned int	rand_type, rand_deg, rand_sep;

	unsigned int	*end_ptr;

} *__randomjunk, *_randomjunk(void), _randominit = {

	/*

	 * 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.

	 */

	{ DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 },

	{ SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },

	{ TYPE_3,

	    0x9a319039U, 0x32d9c024U, 0x9b663182U, 0x5da1f342U,

	    0xde3b81e0U, 0xdf0a6fb5U, 0xf103bc02U, 0x48f340fbU,

	    0x7449e56bU, 0xbeb1dbb0U, 0xab5c5918U, 0x946554fdU,

	    0x8c2e680fU, 0xeb3d799fU, 0xb11ee0b7U, 0x2d436b86U,

	    0xda672e2aU, 0x1588ca88U, 0xe369735dU, 0x904f35f7U,

	    0xd7158fd6U, 0x6fa6f051U, 0x616e6b96U, 0xac94efdcU,

	    0x36413f93U, 0xc622c298U, 0xf5a42ab8U, 0x8a88d77bU,

			0xf5ad9d0eU, 0x8999220bU, 0x27fb47b9U },

	&_randominit.randtbl[ SEP_3 + 1 ],

	&_randominit.randtbl[ 1 ],

	&_randominit.randtbl[ 1 ],

	TYPE_3, DEG_3, SEP_3,

	&_randominit.randtbl[ DEG_3 + 1]

};

static struct _randomjunk *

_randomjunk(void)

{

	struct _randomjunk *rp = __randomjunk;

	if (rp == NULL) {

		rp = (struct _randomjunk *)malloc(sizeof (*rp));

		if (rp == NULL)

			return (NULL);

		(void) memcpy(rp, &_randominit, sizeof (*rp));

		__randomjunk = rp;

	}

	return (rp);

}

/*

 * 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.

 */

char  *

initstate(

	unsigned int seed,	/* seed for R. N. G. */

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

	size_t size)		/* # bytes of state info */

{

	unsigned int n;

	struct _randomjunk *rp = _randomjunk();

	char		*ostate;

	if (size > UINT_MAX)

		n = UINT_MAX;

	else

		n = (unsigned int)size;

	if (rp == NULL)

		return (NULL);

	ostate = (char *)(&rp->state[ -1 ]);

	if (rp->rand_type  ==  TYPE_0)  rp->state[ -1 ] = rp->rand_type;

	else  rp->state[ -1 ] =

	    (unsigned int)(MAX_TYPES*(rp->rptr - rp->state) + rp->rand_type);

	if (n  <  BREAK_1)  {

	    if (n  <  BREAK_0)  {

		return (NULL);

	    }

	    rp->rand_type = TYPE_0;

	    rp->rand_deg = DEG_0;

	    rp->rand_sep = SEP_0;

	} else  {

	    if (n  <  BREAK_2)  {

		rp->rand_type = TYPE_1;

		rp->rand_deg = DEG_1;

		rp->rand_sep = SEP_1;

	    } else  {

		if (n  <  BREAK_3)  {

		    rp->rand_type = TYPE_2;

		    rp->rand_deg = DEG_2;

		    rp->rand_sep = SEP_2;

		} else  {

		    if (n  <  BREAK_4)  {

			rp->rand_type = TYPE_3;

			rp->rand_deg = DEG_3;

			rp->rand_sep = SEP_3;

		    } else  {

			rp->rand_type = TYPE_4;

			rp->rand_deg = DEG_4;

			rp->rand_sep = SEP_4;

		    }

		}

	    }

	}

	/* first location */

	rp->state = &(((unsigned int *)(uintptr_t)arg_state)[1]);

	/* must set end_ptr before srandom */

	rp->end_ptr = &rp->state[rp->rand_deg];

	srandom(seed);

	if (rp->rand_type  ==  TYPE_0)  rp->state[ -1 ] = rp->rand_type;

	else

		rp->state[-1] = (unsigned int)(MAX_TYPES*

		    (rp->rptr - rp->state) + rp->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.

 */

char  *

setstate(const char *arg_state)

{

	struct _randomjunk *rp = _randomjunk();

	unsigned int	*new_state;

	unsigned int	type;

	unsigned int	rear;

	char		*ostate;

	if (rp == NULL)

		return (NULL);

	new_state = (unsigned int *)(uintptr_t)arg_state;

	type = new_state[0]%MAX_TYPES;

	rear = new_state[0]/MAX_TYPES;

	ostate = (char *)(&rp->state[ -1 ]);

	if (rp->rand_type  ==  TYPE_0) rp->state[ -1 ] = rp->rand_type;

	else

		rp->state[-1] = (unsigned int)(MAX_TYPES*

		    (rp->rptr - rp->state) + rp->rand_type);

	switch (type)  {

	    case  TYPE_0:

	    case  TYPE_1:

	    case  TYPE_2:

	    case  TYPE_3:

	    case  TYPE_4:

		rp->rand_type = type;

		rp->rand_deg = rp->degrees[ type ];

		rp->rand_sep = rp->seps[ type ];

		break;

	    default:

		return (NULL);

	}

	rp->state = &new_state[ 1 ];

	if (rp->rand_type  !=  TYPE_0)  {

	    rp->rptr = &rp->state[ rear ];

	    rp->fptr = &rp->state[ (rear + rp->rand_sep)%rp->rand_deg ];

	}

	rp->end_ptr = &rp->state[ rp->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 ther 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(void)

{

	struct _randomjunk *rp = _randomjunk();

	unsigned int	i;

	if (rp == NULL)

		return (0L);

	if (rp->rand_type  ==  TYPE_0)  {

	    i = rp->state[0] = (rp->state[0]*1103515245 + 12345)&0x7fffffff;

	} else  {

	    *rp->fptr += *rp->rptr;

	    i = (*rp->fptr >> 1)&0x7fffffff;	/* chucking least random bit */

	    if (++rp->fptr  >=  rp->end_ptr)  {

		rp->fptr = rp->state;

		++rp->rptr;

	    } else  {

		if (++rp->rptr  >=  rp->end_ptr)  rp->rptr = rp->state;

	    }

	}

	return ((long)i);

}

/*

 * 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(unsigned int x)

{

	struct _randomjunk *rp = _randomjunk();

	unsigned int	i;

	if (rp == NULL)

		return;

	if (rp->rand_type  ==  TYPE_0)  {

	    rp->state[ 0 ] = x;

	} else  {

	    rp->state[ 0 ] = x;

	    for (i = 1; i < rp->rand_deg; i++)  {

		rp->state[i] = 1103515245*rp->state[i - 1] + 12345;

	    }

	    rp->fptr = &rp->state[ rp->rand_sep ];

	    rp->rptr = &rp->state[ 0 ];

	    for (i = 0; i < 10*rp->rand_deg; i++)  (void)random();

	}

}