/* random.c - random number generation package *//* Copyright 1994 Wind River Systems, Inc. */#include "copyright_wrs.h"/* * Copyright (c) 1983 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. All advertising materials mentioning features or use of this software *    must display the following acknowledgement: *	This product includes software developed by the University of *	California, Berkeley and its contributors. * 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. *//*modification history--------------------01a,21dec94,dab  VxWorks port - first WRS version.	   +dzb  added: WRS copyright.*/#if defined(LIBC_SCCS) && !defined(lint)static char sccsid[] = "@(#)random.c	5.9 (Berkeley) 2/23/91";#endif /* LIBC_SCCS and not lint */#include "vxWorks.h"#include "stdio.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 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 *//* Forward declarations */long random();void srandom(u_int x);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. */voidsrandom(x)	u_int x;{	register int i, j;	if (rand_type == TYPE_0)		state[0] = x;	else {		j = 1;		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++)			(void)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)	u_int 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_0) {		(void)fprintf(stderr,		    "random: not enough state (%d 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 = &(((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:		(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. */longrandom(){	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);}