/*
 * Copyright (c) 1983 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */
#ifndef lint
static char sccsid[] =
"@(#)randm.c	5.5 (Berkeley) 7/6/88; 1.1 (BeEF) 1/5/95";
#endif /* !defined(lint) */
#include <stdio.h>
/*
 * randm.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 ini_st(.) 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
 * set_st(.) routine with the same array as was initialized with ini_st(.).
 * 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 longs; 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 longs 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 set_st(.) 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

/*
 * Initially, everything is set up as if from:
 *		ini_st(1, &randtbl, 128);
 * Note that this initialization takes advantage of the fact that srandm(.)
 * 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 unsigned long randtbl[DEG_3 + 1] = {
	(unsigned long) TYPE_3,
#ifdef __STDC__
	0x9a319039UL, 0x32d9c024UL, 0x9b663182UL, 0x5da1f342UL,
	0xde3b81e0UL, 0xdf0a6fb5UL, 0xf103bc02UL, 0x48f340fbUL,
	0x7449e56bUL, 0xbeb1dbb0UL, 0xab5c5918UL, 0x946554fdUL,
	0x8c2e680fUL, 0xeb3d799fUL, 0xb11ee0b7UL, 0x2d436b86UL,
	0xda672e2aUL, 0x1588ca88UL, 0xe369735dUL, 0x904f35f7UL,
	0xd7158fd6UL, 0x6fa6f051UL, 0x616e6b96UL, 0xac94efdcUL,
	0x36413f93UL, 0xc622c298UL, 0xf5a42ab8UL, 0x8a88d77bUL,
	0xf5ad9d0eUL, 0x8999220bUL, 0x27fb47b9UL
#else
	0x9a319039L, 0x32d9c024L, 0x9b663182L, 0x5da1f342L,
	0xde3b81e0L, 0xdf0a6fb5L, 0xf103bc02L, 0x48f340fbL,
	0x7449e56bL, 0xbeb1dbb0L, 0xab5c5918L, 0x946554fdL,
	0x8c2e680fL, 0xeb3d799fL, 0xb11ee0b7L, 0x2d436b86L,
	0xda672e2aL, 0x1588ca88L, 0xe369735dL, 0x904f35f7L,
	0xd7158fd6L, 0x6fa6f051L, 0x616e6b96L, 0xac94efdcL,
	0x36413f93L, 0xc622c298L, 0xf5a42ab8L, 0x8a88d77bL,
	0xf5ad9d0eL, 0x8999220bL, 0x27fb47b9L
#endif
};

/*
 * 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 randm(.) is more efficient this
 * way).  The pointers are left positioned as they would be from the call
 *			ini_st(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 long *fptr = (long *) &randtbl[SEP_3 + 1];
static long *rptr = (long *) &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 randm(.), 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 long *state = (long *) &randtbl[1];
static int rand_type = TYPE_3;
static int rand_deg = DEG_3;
static int rand_sep = SEP_3;
static long *end_ptr = (long *) &randtbl[DEG_3 + 1];

/*
 * randm:
 * 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
#ifdef __STDC__
randm(void)
#else
randm( )
#endif
{
	long i;

	if (rand_type == TYPE_0)
		i = state[0] = (state[0] * 1103515245L + 12345L) & 0x7fffffffL;
	else {
		*fptr += *rptr;
		i = (*fptr >> 1) & 0x7fffffffL;	/* chucking least random bit */
		if (++fptr >= end_ptr) {
			fptr = state;
			++rptr;
		}
		else if (++rptr >= end_ptr)
			rptr = state;
	}
	return i;
}

/*
 * srandm:
 * 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
#ifdef __STDC__
srandm(unsigned x)
#else
srandm(x)
unsigned x;
#endif
{
    	register int i;

	if (rand_type == TYPE_0)
		state[0] = x;
	else {
		state[0] = x;
		for(i = 1; i < rand_deg; i++)
			state[i] = 1103515245L * state[i - 1] + 12345L;
		fptr = &state[rand_sep];
		rptr = &state[0];
		for(i = 0; i < 10 * rand_deg; i++)
			(void) randm( );
	}
}

#if 0
/*
 * 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 int degrees[MAX_TYPES] = {
	DEG_0, DEG_1, DEG_2, DEG_3, DEG_4
};

static int seps[MAX_TYPES] = {
	SEP_0, SEP_1, SEP_2, SEP_3, SEP_4
};

/*
 * ini_st:
 * 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.  srandm(.) is
 * then called to initialize the state information.
 * Note that on return from srandm(.), we set state[-1] to be the type
 * multiplexed with the current value of the rear pointer; this is so
 * successive calls to ini_st(.) won't lose this information and will
 * be able to restart with set_st(.).
 * Note: the first thing we do is save the current state, if any, just like
 * set_st(.) so that it doesn't matter when ini_st is called.
 * Returns a pointer to the old state.
 */
char *
#ifdef __STDC__
ini_st(unsigned seed, char *arg_state, int n)
#else
ini_st(seed, arg_state, n)
unsigned seed;			/* seed for R. N. G. */
char *arg_state;		/* pointer to state array */
int n;				/* # bytes of state info */
#endif
{
	register char *ostate = (char *) (&state[-1]);

	if (rand_type == TYPE_0)
		state[-1] = rand_type;
	else
		state[-1] = MAX_TYPES * (rptr - state) + rand_type;
	if (n < BREAK_1) {
		if (n < BREAK_0) {
#define	MSG "%s: not enough state (%d bytes) with which to do jack; ignored.\n"
			(void) printf(MSG, "ini_st", n);
#undef	MSG
			return ostate;
		}
		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 = &(((long *) arg_state)[1]);	/* first location */
	end_ptr = &state[rand_deg];	/* must set end_ptr before srandm */
	srandm(seed);
	if (rand_type == TYPE_0)
		state[-1] = rand_type;
	else
		state[-1] = MAX_TYPES * (rptr - state) + rand_type;
	return ostate;
}

/*
 * set_st:
 * 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
 * set_st(.) with the same state as the current state.
 * Returns a pointer to the old state information.
 */
char *
#ifdef __STDC__
set_st(char *arg_state)
#else
set_st(arg_state)
char *arg_state;
#endif
{
	register long *new_state = (long *) arg_state;
	register int type = new_state[0] % MAX_TYPES;
	register int 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) printf(
			"set_st: state info has been munged; 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;
}
#endif	/* 0 */
