/*
 * 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. 
 */

/*
 * Some minor changes were made by me (C. Swiger): 
 *
 * removed SCCS gunk added external prototypes for both ANSI & non-ANSI
 * compilers removed unused variable "j" from srandom() re-indented and
 * respaced the code -- someone has one ugly coding style wrt whitespace
 * ;-).... 
 */

#include <stdio.h>

/* some prototypes - cba */
#ifndef NO_LINT_ARGS
#ifdef __STDC__
extern long random(void);
extern void srandom(unsigned int);
extern char *initstate(unsigned int, char *, int);
extern char *setstate(char *);
#else
extern long random();
extern int srandom();
extern char *initstate();
extern char *setstate();
#endif
#endif

/*
 * 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 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 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 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};



/*
 * 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 long         randtbl[DEG_3 + 1] = {TYPE_3,
			     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};

/*
 * 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 long        *fptr = &randtbl[SEP_3 + 1];
static long        *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 long        *state = &randtbl[1];

static int          rand_type = TYPE_3;
static int          rand_deg = DEG_3;
static int          rand_sep = SEP_3;

static long        *end_ptr = &randtbl[DEG_3 + 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. 
 */

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

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


/*
 * 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(seed, arg_state, n)
    unsigned            seed;	   /* seed for R. N. G. */
    char               *arg_state; /* pointer to state array */
    int                 n;	   /* # bytes of state info */
{
    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) {
	    fprintf(stderr,
		    "initstate: not enough state (%d bytes) with which to do jack; ignored.", n);
	    return (char *)0;
	}
	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 srandom */
    srandom(seed);
    if (rand_type == TYPE_0)
	state[-1] = rand_type;
    else
	state[-1] = 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. 
 */

char               *
setstate(arg_state)
    char               *arg_state;
{
    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:
	fprintf(stderr, "setstate: state info has been munged (%d); not changed.", type);
	break;
    }
    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 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()
{
    long                i;

    if (rand_type == TYPE_0) {
	i = state[0] = (state[0] * 1103515245 + 12345) & 0x7fffffff;
    } else {
	*fptr += *rptr;
	i = (*fptr >> 1) & 0x7fffffff;	/* chucking least random bit */
	if (++fptr >= end_ptr) {
	    fptr = state;
	    ++rptr;
	} else {
	    if (++rptr >= end_ptr)
		rptr = state;
	}
    }
    return (i);
}
