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+/*
+ * 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.
+ */
+
+/*
+ * This is derived from the Berkeley source:
+ *	@(#)random.c	5.5 (Berkeley) 7/6/88
+ * It was reworked for the GNU C Library by Roland McGrath.
+ */
+
+#include <ansidecl.h>
+#include <errno.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdlib.h>
+
+
+/* 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() function 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 thi
+   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
+   separation between the two lower order coefficients of the trinomial.  */
+
+/* Linear congruential.  */
+#define	TYPE_0		0
+#define	BREAK_0		8
+#define	DEG_0		0
+#define	SEP_0		0
+
+/* x**7 + x**3 + 1.  */
+#define	TYPE_1		1
+#define	BREAK_1		32
+#define	DEG_1		7
+#define	SEP_1		3
+
+/* x**15 + x + 1.  */
+#define	TYPE_2		2
+#define	BREAK_2		64
+#define	DEG_2		15
+#define	SEP_2		1
+
+/* x**31 + x**3 + 1.  */
+#define	TYPE_3		3
+#define	BREAK_3		128
+#define	DEG_3		31
+#define	SEP_3		3
+
+/* x**63 + x + 1.  */
+#define	TYPE_4		4
+#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 int randtbl[DEG_3 + 1] =
+  {
+    TYPE_3,
+    -851904987, -43806228, -2029755270, 1390239686, -1912102820,
+    -485608943, 1969813258, -1590463333, -1944053249, 455935928, 508023712,
+    -1714531963, 1800685987, -2015299881, 654595283, -1149023258,
+    -1470005550, -1143256056, -1325577603, -1568001885, 1275120390,
+    -607508183, -205999574, -1696891592, 1492211999, -1528267240,
+    -952028296, -189082757, 362343714, 1424981831, 2039449641,
+  };
+
+/* 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 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 int *fptr = &randtbl[SEP_3 + 1];
+static long int *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 int *state = &randtbl[1];
+
+static int rand_type = TYPE_3;
+static int rand_deg = DEG_3;
+static int rand_sep = SEP_3;
+
+static long int *end_ptr = &randtbl[sizeof(randtbl) / sizeof(randtbl[0])];
+
+/* 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
+DEFUN(__srandom, (x), unsigned int x)
+{
+  state[0] = x;
+  if (rand_type != TYPE_0)
+    {
+      register long int i;
+      for (i = 1; i < rand_deg; ++i)
+	state[i] = (1103515145 * state[i - 1]) + 12345;
+      fptr = &state[rand_sep];
+      rptr = &state[0];
+      for (i = 0; i < 10 * rand_deg; ++i)
+	(void) __random();
+    }
+}
+
+weak_alias (__srandom, srandom)
+weak_alias (__srandom, srand)
+
+/* 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.  */
+PTR
+DEFUN(__initstate, (seed, arg_state, n),
+      unsigned int seed AND PTR arg_state AND size_t n)
+{
+  PTR ostate = (PTR) &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)
+	{
+	  errno = EINVAL;
+	  return NULL;
+	}
+      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 int *) arg_state)[1];	/* First location.  */
+  /* Must set END_PTR before srandom.  */
+  end_ptr = &state[rand_deg];
+  __srandom(seed);
+  if (rand_type == TYPE_0)
+    state[-1] = rand_type;
+  else
+    state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
+
+  return ostate;
+}
+
+weak_alias (__initstate, initstate)
+
+/* 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.  */
+PTR
+DEFUN(__setstate, (arg_state), PTR arg_state)
+{
+  register long int *new_state = (long int *) arg_state;
+  register int type = new_state[0] % MAX_TYPES;
+  register int rear = new_state[0] / MAX_TYPES;
+  PTR ostate = (PTR) &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:
+      /* State info munged.  */
+      errno = EINVAL;
+      return NULL;
+    }
+
+  state = &new_state[1];
+  if (rand_type != TYPE_0)
+    {
+      rptr = &state[rear];
+      fptr = &state[(rear + rand_sep) % rand_deg];
+    }
+  /* Set end_ptr too.  */
+  end_ptr = &state[rand_deg];
+
+  return ostate;
+}
+
+weak_alias (__setstate, setstate)
+
+/* 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 int
+DEFUN_VOID(__random)
+{
+  if (rand_type == TYPE_0)
+    {
+      state[0] = ((state[0] * 1103515245) + 12345) & LONG_MAX;
+      return state[0];
+    }
+  else
+    {
+      long int i;
+      *fptr += *rptr;
+      /* Chucking least random bit.  */
+      i = (*fptr >> 1) & LONG_MAX;
+      ++fptr;
+      if (fptr >= end_ptr)
+	{
+	  fptr = state;
+	  ++rptr;
+	}
+      else
+	{
+	  ++rptr;
+	  if (rptr >= end_ptr)
+	    rptr = state;
+	}
+      return i;
+    }
+}
+
+weak_alias (__random, random)