/*

 * 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.

 * 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.

 *

 * $FreeBSD: src/lib/libc/stdlib/random.c,v 1.4.2.2 1999/09/05 11:16:45 peter Exp $

 *

 */

#if defined(LIBC_SCCS) && !defined(lint)

static char sccsid[] = "@(#)random.c  8.2 (Berkeley) 5/19/95";

#endif /* LIBC_SCCS and not lint */

#include "config.h"

#include <sys/types.h>

#ifdef HAVE_UNISTD_H

# include <unistd.h>

#endif

#include <stdio.h>

#include <l_stdlib.h>

#include <ntp_random.h>

#include <ntp_unixtime.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.

 *

 * 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

#define MAX_TYPES 5   /* max number of types above */

/*

 * 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 unsigned long 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 unsigned long *fptr = &randtbl[SEP_3 + 1];

static unsigned 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 unsigned long *state = &randtbl[1];

static long rand_type = TYPE_3;

static long rand_deg = DEG_3;

static long rand_sep = SEP_3;

static unsigned long *end_ptr = &randtbl[DEG_3 + 1];

static inline long good_rand (long);

static inline long

good_rand (

  register long 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.

 */

  register long hi, lo;

  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.

 */

void

ntp_srandom(

  unsigned long x

  )

{

  long i;

  if (rand_type == TYPE_0) {

    state[0] = x;

  } else {

    state[0] = x;

    for (i = 1; i < rand_deg; i++)

      state[i] = good_rand(state[i - 1]);

    fptr = &state[rand_sep];

    rptr = &state[0];

    for (i = 0; i < 10 * rand_deg; i++)

      x = ntp_random();

  }

  /* seed the likely faster (and poorer) rand() as well */

  srand((u_int)x);

}

/*

 * 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 urandom(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.

 */

#ifdef NEED_SRANDOMDEV

void

ntp_srandomdev( void )

{

  struct timeval tv;

  unsigned long junk; /* Purposely used uninitialized */

  GETTIMEOFDAY(&tv, NULL);

  ntp_srandom(getpid() ^ tv.tv_sec ^ tv.tv_usec ^ junk);

  return;

}

#endif

/*

 * ntp_initstate() and ntp_setstate() are unused in our codebase and

 * trigger warnings due to casting to a more-strictly-aligned pointer

 * on alignment-sensitive platforms.  #ifdef them away to save noise,

 * build time, and binary space, but retain the code in case we find a

 * use.

 */

#ifdef COMPILE_UNUSED_FUNCTIONS

/*

 * 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 long degrees[MAX_TYPES] =  { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };

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

/*

 * 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 a long

 * word boundary; otherwise a bus error will occur. Even so, lint will

 * complain about mis-alignment, but you should disregard these messages.

 */

char *

ntp_initstate(

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

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

  long n        /* # bytes of state info */

  )

{

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

  register long *long_arg_state = (long *) 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 = (unsigned long *) (long_arg_state + 1); /* first location */

  end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */

  ntp_srandom(seed);

  if (rand_type == TYPE_0)

    long_arg_state[0] = rand_type;

  else

    long_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 a long

 * word boundary; otherwise a bus error will occur. Even so, lint will

 * complain about mis-alignment, but you should disregard these messages.

 */

char *

ntp_setstate(

  char *arg_state     /* pointer to state array */

  )

{

  register unsigned long *new_state = (unsigned long *) arg_state;

  register long type = new_state[0] % MAX_TYPES;

  register long 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);

}

#endif  /* COMPILE_UNUSED_FUNCTIONS */

/*

 * 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.

 */

long

ntp_random( void )

{

  register long i;

  register unsigned long *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(i);

}