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380 lines
12 KiB
380 lines
12 KiB
/*
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* Copyright (c) 1983 Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms are permitted
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* provided that the above copyright notice and this paragraph are
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* duplicated in all such forms and that any documentation,
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* advertising materials, and other materials related to such
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* distribution and use acknowledge that the software was developed
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* by the University of California, Berkeley. The name of the
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* University may not be used to endorse or promote products derived
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* from this software without specific prior written permission.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
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* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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*/
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/*
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* Please note that as of July 22, 1999, the licensees and distributors
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* are no longer required to include the above mentioned acknowledgement
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* within advertising materials. For full details see
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* ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change
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*/
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/*
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* This is derived from the Berkeley source:
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* @(#)random.c 5.5 (Berkeley) 7/6/88
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* It was reworked for the GNU C Library by Roland McGrath.
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* Rewritten to be reentrant by Ulrich Drepper, 1995
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*/
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#include <limits.h>
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#include <stdlib.h>
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#include "vm_random.h"
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/* An improved random number generation package. In addition to the standard
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rand()/srand() like interface, this package also has a special state info
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interface. The initstate() routine is called with a seed, an array of
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bytes, and a count of how many bytes are being passed in; this array is
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then initialized to contain information for random number generation with
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that much state information. Good sizes for the amount of state
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information are 32, 64, 128, and 256 bytes. The state can be switched by
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calling the setstate() function with the same array as was initialized
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with initstate(). By default, the package runs with 128 bytes of state
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information and generates far better random numbers than a linear
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congruential generator. If the amount of state information is less than
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32 bytes, a simple linear congruential R.N.G. is used. Internally, the
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state information is treated as an array of longs; the zeroth element of
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the array is the type of R.N.G. being used (small integer); the remainder
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of the array is the state information for the R.N.G. Thus, 32 bytes of
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state information will give 7 longs worth of state information, which will
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allow a degree seven polynomial. (Note: The zeroth word of state
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information also has some other information stored in it; see setstate
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for details). The random number generation technique is a linear feedback
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shift register approach, employing trinomials (since there are fewer terms
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to sum up that way). In this approach, the least significant bit of all
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the numbers in the state table will act as a linear feedback shift register,
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and will have period 2^deg - 1 (where deg is the degree of the polynomial
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being used, assuming that the polynomial is irreducible and primitive).
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The higher order bits will have longer periods, since their values are
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also influenced by pseudo-random carries out of the lower bits. The
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total period of the generator is approximately deg*(2**deg - 1); thus
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doubling the amount of state information has a vast influence on the
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period of the generator. Note: The deg*(2**deg - 1) is an approximation
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only good for large deg, when the period of the shift register is the
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dominant factor. With deg equal to seven, the period is actually much
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longer than the 7*(2**7 - 1) predicted by this formula. */
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/* For each of the currently supported random number generators, we have a
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break value on the amount of state information (you need at least this many
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bytes of state info to support this random number generator), a degree for
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the polynomial (actually a trinomial) that the R.N.G. is based on, and
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separation between the two lower order coefficients of the trinomial. */
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/* Linear congruential. */
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#define TYPE_0 0
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#define BREAK_0 8
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#define DEG_0 0
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#define SEP_0 0
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/* x**7 + x**3 + 1. */
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#define TYPE_1 1
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#define BREAK_1 32
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#define DEG_1 7
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#define SEP_1 3
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/* x**15 + x + 1. */
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#define TYPE_2 2
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#define BREAK_2 64
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#define DEG_2 15
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#define SEP_2 1
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/* x**31 + x**3 + 1. */
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#define TYPE_3 3
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#define BREAK_3 128
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#define DEG_3 31
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#define SEP_3 3
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/* x**63 + x + 1. */
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#define TYPE_4 4
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#define BREAK_4 256
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#define DEG_4 63
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#define SEP_4 1
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/* Array versions of the above information to make code run faster.
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Relies on fact that TYPE_i == i. */
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#define MAX_TYPES 5 /* Max number of types above. */
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struct vm_random_poly_info
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{
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int seps[MAX_TYPES];
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int degrees[MAX_TYPES];
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};
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static struct vm_random_poly_info vm_random_poly_info =
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{
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{ SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
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{ DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
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};
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static int32_t vm_randtbl[DEG_3 + 1] =
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{
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TYPE_3,
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-1726662223, 379960547, 1735697613, 1040273694, 1313901226,
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1627687941, -179304937, -2073333483, 1780058412, -1989503057,
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-615974602, 344556628, 939512070, -1249116260, 1507946756,
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-812545463, 154635395, 1388815473, -1926676823, 525320961,
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-1009028674, 968117788, -123449607, 1284210865, 435012392,
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-2017506339, -911064859, -370259173, 1132637927, 1398500161,
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-205601318,
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};
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/* Initialize the random number generator based on the given seed. If the
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type is the trivial no-state-information type, just remember the seed.
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Otherwise, initializes state[] based on the given "seed" via a linear
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congruential generator. Then, the pointers are set to known locations
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that are exactly rand_sep places apart. Lastly, it cycles the state
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information a given number of times to get rid of any initial dependencies
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introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
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for default usage relies on values produced by this routine. */
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int vm_srandom (unsigned int seed,
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struct vm_random_data* buf)
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{
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int type;
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int32_t *state;
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long int i;
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long int word;
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int32_t *dst;
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int kc;
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if (buf == NULL)
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goto fail;
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type = buf->vm_rand_type;
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if ((unsigned int) type >= MAX_TYPES)
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goto fail;
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state = buf->state;
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/* We must make sure the seed is not 0. Take arbitrarily 1 in this case. */
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if (seed == 0)
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seed = 1;
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state[0] = seed;
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if (type == TYPE_0)
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goto done;
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dst = state;
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word = seed;
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kc = buf->vm_rand_deg;
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for (i = 1; i < kc; ++i)
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{
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/* This does:
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state[i] = (16807 * state[i - 1]) % 2147483647;
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but avoids overflowing 31 bits. */
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long int hi = word / 127773;
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long int lo = word % 127773;
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word = 16807 * lo - 2836 * hi;
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if (word < 0)
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word += 2147483647;
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*++dst = word;
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}
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buf->fptr = &state[buf->vm_rand_sep];
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buf->rptr = &state[0];
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kc *= 10;
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while (--kc >= 0)
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{
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vm_random (buf);
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}
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done:
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return 0;
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fail:
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return -1;
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}
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/* Initialize the state information in the given array of N bytes for
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future random number generation. Based on the number of bytes we
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are given, and the break values for the different R.N.G.'s, we choose
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the best (largest) one we can and set things up for it. srandom is
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then called to initialize the state information. Note that on return
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from srandom, we set state[-1] to be the type multiplexed with the current
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value of the rear pointer; this is so successive calls to initstate won't
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lose this information and will be able to restart with setstate.
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Note: The first thing we do is save the current state, if any, just like
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setstate so that it doesn't matter when initstate is called.
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Returns a pointer to the old state. */
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int vm_initstate (unsigned int seed,
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void* arg_state,
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size_t n,
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struct vm_random_data* buf)
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{
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int type;
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int degree;
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int separation;
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int32_t *state;
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if (buf == NULL)
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goto fail;
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if (n >= BREAK_3)
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type = n < BREAK_4 ? TYPE_3 : TYPE_4;
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else if (n < BREAK_1)
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{
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if (n < BREAK_0)
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{
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goto fail;
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}
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type = TYPE_0;
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}
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else
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type = n < BREAK_2 ? TYPE_1 : TYPE_2;
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degree = vm_random_poly_info.degrees[type];
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separation = vm_random_poly_info.seps[type];
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buf->vm_rand_type = type;
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buf->vm_rand_sep = separation;
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buf->vm_rand_deg = degree;
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state = &((int32_t *) arg_state)[1]; /* First location. */
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/* Must set END_PTR before srandom. */
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buf->end_ptr = &state[degree];
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buf->state = state;
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vm_srandom (seed, buf);
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state[-1] = TYPE_0;
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if (type != TYPE_0)
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state[-1] = (buf->rptr - state) * MAX_TYPES + type;
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return 0;
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fail:
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return -1;
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}
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/* Restore the state from the given state array.
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Note: It is important that we also remember the locations of the pointers
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in the current state information, and restore the locations of the pointers
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from the old state information. This is done by multiplexing the pointer
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location into the zeroth word of the state information. Note that due
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to the order in which things are done, it is OK to call setstate with the
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same state as the current state
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Returns a pointer to the old state information. */
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int vm_setstate (void* arg_state,
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struct vm_random_data* buf)
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{
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int32_t *new_state = (int32_t *) arg_state;
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int type;
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int old_type;
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int32_t *old_state;
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int degree;
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int separation;
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if (buf == NULL)
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goto fail;
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old_type = buf->vm_rand_type;
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old_state = buf->state;
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if (old_type == TYPE_0)
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old_state[-1] = TYPE_0;
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else
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old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
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type = new_state[0] % MAX_TYPES;
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if (type < TYPE_0 || type >= TYPE_4)
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goto fail;
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buf->vm_rand_deg = degree = vm_random_poly_info.degrees[type];
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buf->vm_rand_sep = separation = vm_random_poly_info.seps[type];
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buf->vm_rand_type = type;
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if (type != TYPE_0)
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{
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int rear = new_state[0] / MAX_TYPES;
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buf->rptr = &new_state[rear];
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buf->fptr = &new_state[(rear + separation) % degree];
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}
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buf->state = &new_state[1];
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/* Set end_ptr too. */
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buf->end_ptr = &new_state[degree];
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return 0;
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fail:
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return -1;
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}
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/* If we are using the trivial TYPE_0 R.N.G., just do the old linear
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congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
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same in all the other cases due to all the global variables that have been
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set up. The basic operation is to add the number at the rear pointer into
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the one at the front pointer. Then both pointers are advanced to the next
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location cyclically in the table. The value returned is the sum generated,
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reduced to 31 bits by throwing away the "least random" low bit.
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Note: The code takes advantage of the fact that both the front and
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rear pointers can't wrap on the same call by not testing the rear
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pointer if the front one has wrapped. Returns a 31-bit random number. */
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int32_t vm_random (struct vm_random_data* buf)
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{
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int32_t *state;
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int32_t result;
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if (buf == NULL)
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goto fail;
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state = buf->state;
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if (buf->vm_rand_type == TYPE_0)
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{
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int32_t val = state[0];
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val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
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state[0] = val;
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result = val;
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}
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else
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{
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int32_t *fptr = buf->fptr;
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int32_t *rptr = buf->rptr;
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int32_t *end_ptr = buf->end_ptr;
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int32_t val;
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val = *fptr += *rptr;
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/* Chucking least random bit. */
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result = (val >> 1) & 0x7fffffff;
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++fptr;
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if (fptr >= end_ptr)
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{
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fptr = state;
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++rptr;
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}
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else
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{
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++rptr;
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if (rptr >= end_ptr)
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rptr = state;
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}
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buf->fptr = fptr;
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buf->rptr = rptr;
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}
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return result;
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fail:
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return -1;
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}
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void vm_default_initstate( int seed,
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struct vm_random_data* buf ) {
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vm_initstate( seed,
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vm_randtbl,
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128,
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buf );
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}
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