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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.
+ */
+
+/*
+ * Please note that as of July 22, 1999, the licensees and distributors
+ * are no longer required to include the above mentioned acknowledgement
+ * within advertising materials. For full details see
+ * ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change
+ */
+
+/*
+ * 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.
+ * Rewritten to be reentrant by Ulrich Drepper, 1995
+ */
+
+#include <limits.h>
+#include <stdlib.h>
+#include "vm_random.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 initialized
+ 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 zeroth 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 zeroth 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
+ 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. */
+
+struct vm_random_poly_info
+{
+ int seps[MAX_TYPES];
+ int degrees[MAX_TYPES];
+};
+
+static struct vm_random_poly_info vm_random_poly_info =
+{
+ { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
+ { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
+};
+
+static int32_t vm_randtbl[DEG_3 + 1] =
+ {
+ TYPE_3,
+
+ -1726662223, 379960547, 1735697613, 1040273694, 1313901226,
+ 1627687941, -179304937, -2073333483, 1780058412, -1989503057,
+ -615974602, 344556628, 939512070, -1249116260, 1507946756,
+ -812545463, 154635395, 1388815473, -1926676823, 525320961,
+ -1009028674, 968117788, -123449607, 1284210865, 435012392,
+ -2017506339, -911064859, -370259173, 1132637927, 1398500161,
+ -205601318,
+ };
+
+/* 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. */
+int vm_srandom (unsigned int seed,
+ struct vm_random_data* buf)
+{
+ int type;
+ int32_t *state;
+ long int i;
+ long int word;
+ int32_t *dst;
+ int kc;
+
+ if (buf == NULL)
+ goto fail;
+ type = buf->vm_rand_type;
+ if ((unsigned int) type >= MAX_TYPES)
+ goto fail;
+
+ state = buf->state;
+ /* We must make sure the seed is not 0. Take arbitrarily 1 in this case. */
+ if (seed == 0)
+ seed = 1;
+ state[0] = seed;
+ if (type == TYPE_0)
+ goto done;
+
+ dst = state;
+ word = seed;
+ kc = buf->vm_rand_deg;
+ for (i = 1; i < kc; ++i)
+ {
+ /* This does:
+ state[i] = (16807 * state[i - 1]) % 2147483647;
+ but avoids overflowing 31 bits. */
+ long int hi = word / 127773;
+ long int lo = word % 127773;
+ word = 16807 * lo - 2836 * hi;
+ if (word < 0)
+ word += 2147483647;
+ *++dst = word;
+ }
+
+ buf->fptr = &state[buf->vm_rand_sep];
+ buf->rptr = &state[0];
+ kc *= 10;
+ while (--kc >= 0)
+ {
+ vm_random (buf);
+ }
+
+ done:
+ return 0;
+
+ fail:
+ return -1;
+}
+
+/* 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. */
+int vm_initstate (unsigned int seed,
+ void* arg_state,
+ size_t n,
+ struct vm_random_data* buf)
+{
+ int type;
+ int degree;
+ int separation;
+ int32_t *state;
+
+ if (buf == NULL)
+ goto fail;
+
+ if (n >= BREAK_3)
+ type = n < BREAK_4 ? TYPE_3 : TYPE_4;
+ else if (n < BREAK_1)
+ {
+ if (n < BREAK_0)
+ {
+ goto fail;
+ }
+ type = TYPE_0;
+ }
+ else
+ type = n < BREAK_2 ? TYPE_1 : TYPE_2;
+
+ degree = vm_random_poly_info.degrees[type];
+ separation = vm_random_poly_info.seps[type];
+
+ buf->vm_rand_type = type;
+ buf->vm_rand_sep = separation;
+ buf->vm_rand_deg = degree;
+ state = &((int32_t *) arg_state)[1]; /* First location. */
+ /* Must set END_PTR before srandom. */
+ buf->end_ptr = &state[degree];
+
+ buf->state = state;
+
+ vm_srandom (seed, buf);
+
+ state[-1] = TYPE_0;
+ if (type != TYPE_0)
+ state[-1] = (buf->rptr - state) * MAX_TYPES + type;
+
+ return 0;
+
+ fail:
+ return -1;
+}
+
+/* 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 zeroth 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. */
+int vm_setstate (void* arg_state,
+ struct vm_random_data* buf)
+{
+ int32_t *new_state = (int32_t *) arg_state;
+ int type;
+ int old_type;
+ int32_t *old_state;
+ int degree;
+ int separation;
+
+ if (buf == NULL)
+ goto fail;
+
+ old_type = buf->vm_rand_type;
+ old_state = buf->state;
+ if (old_type == TYPE_0)
+ old_state[-1] = TYPE_0;
+ else
+ old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
+
+ type = new_state[0] % MAX_TYPES;
+ if (type < TYPE_0 || type >= TYPE_4)
+ goto fail;
+
+ buf->vm_rand_deg = degree = vm_random_poly_info.degrees[type];
+ buf->vm_rand_sep = separation = vm_random_poly_info.seps[type];
+ buf->vm_rand_type = type;
+
+ if (type != TYPE_0)
+ {
+ int rear = new_state[0] / MAX_TYPES;
+ buf->rptr = &new_state[rear];
+ buf->fptr = &new_state[(rear + separation) % degree];
+ }
+ buf->state = &new_state[1];
+ /* Set end_ptr too. */
+ buf->end_ptr = &new_state[degree];
+
+ return 0;
+
+ fail:
+ return -1;
+}
+
+/* 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. */
+
+int32_t vm_random (struct vm_random_data* buf)
+{
+ int32_t *state;
+ int32_t result;
+
+ if (buf == NULL)
+ goto fail;
+
+ state = buf->state;
+
+ if (buf->vm_rand_type == TYPE_0)
+ {
+ int32_t val = state[0];
+ val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
+ state[0] = val;
+ result = val;
+ }
+ else
+ {
+ int32_t *fptr = buf->fptr;
+ int32_t *rptr = buf->rptr;
+ int32_t *end_ptr = buf->end_ptr;
+ int32_t val;
+
+ val = *fptr += *rptr;
+ /* Chucking least random bit. */
+ result = (val >> 1) & 0x7fffffff;
+ ++fptr;
+ if (fptr >= end_ptr)
+ {
+ fptr = state;
+ ++rptr;
+ }
+ else
+ {
+ ++rptr;
+ if (rptr >= end_ptr)
+ rptr = state;
+ }
+ buf->fptr = fptr;
+ buf->rptr = rptr;
+ }
+ return result;
+
+ fail:
+ return -1;
+}
+
+void vm_default_initstate( int seed,
+ struct vm_random_data* buf ) {
+ vm_initstate( seed,
+ vm_randtbl,
+ 128,
+ buf );
+}
generated by cgit v1.2.1 (git 2.18.0) at 2024-11-18 07:35:59 +0000