374 lines
12 KiB
C
374 lines
12 KiB
C
/*
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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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* 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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*/
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#include <errno.h>
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#if 0
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#include <ansidecl.h>
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#include <limits.h>
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#include <stddef.h>
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#include <stdlib.h>
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#else
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#define ULONG_MAX ((unsigned long)(~0L)) /* 0xFFFFFFFF for 32-bits */
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#define LONG_MAX ((long)(ULONG_MAX >> 1)) /* 0x7FFFFFFF for 32-bits*/
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#ifdef __STDC__
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# define PTR void *
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# define NULL (void *) 0
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#else
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# define PTR char *
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# define NULL 0
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#endif
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#endif
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long int random ();
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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 initiallized
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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 zeroeth 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 zeroeth 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 thi
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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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static int degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
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static int seps[MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
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/* Initially, everything is set up as if from:
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initstate(1, randtbl, 128);
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Note that this initialization takes advantage of the fact that srandom
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advances the front and rear pointers 10*rand_deg times, and hence the
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rear pointer which starts at 0 will also end up at zero; thus the zeroeth
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element of the state information, which contains info about the current
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position of the rear pointer is just
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(MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3. */
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static long int randtbl[DEG_3 + 1] =
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{ TYPE_3,
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0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342,
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0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb,
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0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
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0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86,
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0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7,
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0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
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0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b,
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0xf5ad9d0e, 0x8999220b, 0x27fb47b9
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};
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/* FPTR and RPTR are two pointers into the state info, a front and a rear
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pointer. These two pointers are always rand_sep places aparts, as they
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cycle through the state information. (Yes, this does mean we could get
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away with just one pointer, but the code for random is more efficient
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this way). The pointers are left positioned as they would be from the call:
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initstate(1, randtbl, 128);
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(The position of the rear pointer, rptr, is really 0 (as explained above
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in the initialization of randtbl) because the state table pointer is set
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to point to randtbl[1] (as explained below).) */
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static long int *fptr = &randtbl[SEP_3 + 1];
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static long int *rptr = &randtbl[1];
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/* The following things are the pointer to the state information table,
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the type of the current generator, the degree of the current polynomial
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being used, and the separation between the two pointers.
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Note that for efficiency of random, we remember the first location of
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the state information, not the zeroeth. Hence it is valid to access
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state[-1], which is used to store the type of the R.N.G.
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Also, we remember the last location, since this is more efficient than
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indexing every time to find the address of the last element to see if
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the front and rear pointers have wrapped. */
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static long int *state = &randtbl[1];
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static int rand_type = TYPE_3;
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static int rand_deg = DEG_3;
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static int rand_sep = SEP_3;
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static long int *end_ptr = &randtbl[sizeof(randtbl) / sizeof(randtbl[0])];
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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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void
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srandom (x)
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unsigned int x;
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{
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state[0] = x;
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if (rand_type != TYPE_0)
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{
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register long int i;
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for (i = 1; i < rand_deg; ++i)
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state[i] = (1103515145 * state[i - 1]) + 12345;
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fptr = &state[rand_sep];
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rptr = &state[0];
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for (i = 0; i < 10 * rand_deg; ++i)
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random();
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}
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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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PTR
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initstate (seed, arg_state, n)
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unsigned int seed;
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PTR arg_state;
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unsigned long n;
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{
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PTR ostate = (PTR) &state[-1];
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if (rand_type == TYPE_0)
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state[-1] = rand_type;
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else
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state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
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if (n < BREAK_1)
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{
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if (n < BREAK_0)
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{
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errno = EINVAL;
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return NULL;
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}
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rand_type = TYPE_0;
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rand_deg = DEG_0;
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rand_sep = SEP_0;
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}
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else if (n < BREAK_2)
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{
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rand_type = TYPE_1;
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rand_deg = DEG_1;
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rand_sep = SEP_1;
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}
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else if (n < BREAK_3)
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{
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rand_type = TYPE_2;
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rand_deg = DEG_2;
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rand_sep = SEP_2;
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}
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else if (n < BREAK_4)
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{
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rand_type = TYPE_3;
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rand_deg = DEG_3;
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rand_sep = SEP_3;
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}
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else
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{
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rand_type = TYPE_4;
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rand_deg = DEG_4;
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rand_sep = SEP_4;
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}
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state = &((long int *) arg_state)[1]; /* First location. */
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/* Must set END_PTR before srandom. */
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end_ptr = &state[rand_deg];
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srandom(seed);
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if (rand_type == TYPE_0)
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state[-1] = rand_type;
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else
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state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
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return ostate;
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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 zeroeth 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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PTR
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setstate (arg_state)
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PTR arg_state;
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{
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register long int *new_state = (long int *) arg_state;
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register int type = new_state[0] % MAX_TYPES;
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register int rear = new_state[0] / MAX_TYPES;
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PTR ostate = (PTR) &state[-1];
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if (rand_type == TYPE_0)
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state[-1] = rand_type;
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else
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state[-1] = (MAX_TYPES * (rptr - state)) + rand_type;
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switch (type)
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{
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case TYPE_0:
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case TYPE_1:
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case TYPE_2:
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case TYPE_3:
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case TYPE_4:
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rand_type = type;
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rand_deg = degrees[type];
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rand_sep = seps[type];
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break;
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default:
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/* State info munged. */
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errno = EINVAL;
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return NULL;
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}
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state = &new_state[1];
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if (rand_type != TYPE_0)
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{
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rptr = &state[rear];
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fptr = &state[(rear + rand_sep) % rand_deg];
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}
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/* Set end_ptr too. */
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end_ptr = &state[rand_deg];
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return ostate;
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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 ther 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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long int
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random ()
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{
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if (rand_type == TYPE_0)
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{
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state[0] = ((state[0] * 1103515245) + 12345) & LONG_MAX;
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return state[0];
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}
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else
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{
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long int i;
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*fptr += *rptr;
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/* Chucking least random bit. */
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i = (*fptr >> 1) & LONG_MAX;
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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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return i;
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}
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}
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