random.c revision 1b126014efc04ffe7077a99fc30c310392e7c8c0
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License, Version 1.0 only
* (the "License"). You may not use this file except in compliance
* with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 1999 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
#pragma ident "%Z%%M% %I% %E% SMI"
#include <stdio.h>
#include <stdlib.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.
*/
/*
* 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 BREAK_1 32
#define DEG_1 7
#define SEP_1 3
#define BREAK_2 64
#define DEG_2 15
#define SEP_2 1
#define BREAK_3 128
#define DEG_3 31
#define SEP_3 3
#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.
*/
static struct _randomjunk {
/*
* 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).
*/
/*
* 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.
*/
long *state;
long *end_ptr;
/*
* 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.
*/
{ TYPE_3,
(long)0x9a319039, (long)0x32d9c024, (long)0x9b663182, (long)0x5da1f342,
(long)0xde3b81e0, (long)0xdf0a6fb5, (long)0xf103bc02, (long)0x48f340fb,
(long)0x7449e56b, (long)0xbeb1dbb0, (long)0xab5c5918, (long)0x946554fd,
(long)0x8c2e680f, (long)0xeb3d799f, (long)0xb11ee0b7, (long)0x2d436b86,
(long)0xda672e2a, (long)0x1588ca88, (long)0xe369735d, (long)0x904f35f7,
(long)0xd7158fd6, (long)0x6fa6f051, (long)0x616e6b96, (long)0xac94efdc,
(long)0x36413f93, (long)0xc622c298, (long)0xf5a42ab8, (long)0x8a88d77b,
(long)0xf5ad9d0e, (long)0x8999220b, (long)0x27fb47b9 },
};
long random(void);
static struct _randomjunk *
_randomjunk(void)
{
if (rp == 0) {
if (rp == 0)
return (0);
*rp = _randominit;
__randomjunk = rp;
}
return (rp);
}
/*
* 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
srandom(unsigned x)
{
int i;
if (rp == 0)
return;
} else {
}
random();
}
}
/*
* 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.
*
* Arguments:
* seed: seed for R. N. G.
* arg_state: pointer to state array
* n: # bytes of state info
*/
char *
{
char *ostate;
if (rp == 0)
return (0);
if (n < BREAK_0) {
"initstate: state array too small, ignored; minimum size is %d bytes\n",
BREAK_0);
return (0);
} else if (n < BREAK_1) {
} else if (n < BREAK_2) {
} else if (n < BREAK_3) {
} else if (n < BREAK_4) {
} else {
}
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.
*/
char *
{
long *new_state;
int type;
int rear;
char *ostate;
if (rp == 0)
return (0);
switch (type) {
case TYPE_0:
case TYPE_1:
case TYPE_2:
case TYPE_3:
case TYPE_4:
break;
default:
}
}
return (ostate);
}
/*
* 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 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
random(void)
{
long i;
if (rp == 0)
return (0);
} else {
}
return (i);
}