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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 2024-07-21 14:23:45 +0000