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Diffstat (limited to 'lib/libc/stdlib/random.c')
| -rw-r--r-- | lib/libc/stdlib/random.c | 400 |
1 files changed, 400 insertions, 0 deletions
diff --git a/lib/libc/stdlib/random.c b/lib/libc/stdlib/random.c new file mode 100644 index 000000000000..7c76158d9b97 --- /dev/null +++ b/lib/libc/stdlib/random.c @@ -0,0 +1,400 @@ +/* + * Copyright (c) 1983, 1993 + * The Regents of the University of California. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the University of + * California, Berkeley and its contributors. + * 4. Neither the name of the University nor the names of its contributors + * may be used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +#if defined(LIBC_SCCS) && !defined(lint) +static char sccsid[] = "@(#)random.c 8.2 (Berkeley) 5/19/95"; +#endif /* LIBC_SCCS and not lint */ + +#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. + * + * Modified 28 December 1994 by Jacob S. Rosenberg. + * The following changes have been made: + * All references to the type u_int have been changed to unsigned long. + * All references to type int have been changed to type long. Other + * cleanups have been made as well. A warning for both initstate and + * setstate has been inserted to the effect that on Sparc platforms + * the 'arg_state' variable must be forced to begin on word boundaries. + * This can be easily done by casting a long integer array to char *. + * The overall logic has been left STRICTLY alone. This software was + * tested on both a VAX and Sun SpacsStation with exactly the same + * results. The new version and the original give IDENTICAL results. + * The new version is somewhat faster than the original. As the + * documentation says: "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." For a buffer of + * 128 bytes, this new version runs about 19 percent faster and for a 16 + * byte buffer it is about 5 percent faster. + */ + +/* + * 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 TYPE_1 1 /* x**7 + x**3 + 1 */ +#define BREAK_1 32 +#define DEG_1 7 +#define SEP_1 3 + +#define TYPE_2 2 /* x**15 + x + 1 */ +#define BREAK_2 64 +#define DEG_2 15 +#define SEP_2 1 + +#define TYPE_3 3 /* x**31 + x**3 + 1 */ +#define BREAK_3 128 +#define DEG_3 31 +#define SEP_3 3 + +#define TYPE_4 4 /* x**63 + x + 1 */ +#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 */ + +static long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }; +static long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }; + +/* + * 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. + */ + +static long randtbl[DEG_3 + 1] = { + TYPE_3, + 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5, + 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd, + 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88, + 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc, + 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b, + 0x27fb47b9, +}; + +/* + * 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). + */ +static long *fptr = &randtbl[SEP_3 + 1]; +static long *rptr = &randtbl[1]; + +/* + * 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. + */ +static long *state = &randtbl[1]; +static long rand_type = TYPE_3; +static long rand_deg = DEG_3; +static long rand_sep = SEP_3; +static long *end_ptr = &randtbl[DEG_3 + 1]; + +/* + * 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(x) + unsigned long x; +{ + register long i; + + if (rand_type == TYPE_0) + state[0] = x; + else { + state[0] = x; + for (i = 1; i < rand_deg; i++) + state[i] = 1103515245 * state[i - 1] + 12345; + fptr = &state[rand_sep]; + rptr = &state[0]; + for (i = 0; i < 10 * rand_deg; i++) + (void)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. + * + * Note: The Sparc platform requires that arg_state begin on a long + * word boundary; otherwise a bus error will occur. Even so, lint will + * complain about mis-alignment, but you should disregard these messages. + */ +char * +initstate(seed, arg_state, n) + unsigned long seed; /* seed for R.N.G. */ + char *arg_state; /* pointer to state array */ + long n; /* # bytes of state info */ +{ + register char *ostate = (char *)(&state[-1]); + register long *long_arg_state = (long *) arg_state; + + if (rand_type == TYPE_0) + state[-1] = rand_type; + else + state[-1] = MAX_TYPES * (rptr - state) + rand_type; + if (n < BREAK_0) { + (void)fprintf(stderr, + "random: not enough state (%ld bytes); ignored.\n", n); + return(0); + } + if (n < BREAK_1) { + rand_type = TYPE_0; + rand_deg = DEG_0; + rand_sep = SEP_0; + } else if (n < BREAK_2) { + rand_type = TYPE_1; + rand_deg = DEG_1; + rand_sep = SEP_1; + } else if (n < BREAK_3) { + rand_type = TYPE_2; + rand_deg = DEG_2; + rand_sep = SEP_2; + } else if (n < BREAK_4) { + rand_type = TYPE_3; + rand_deg = DEG_3; + rand_sep = SEP_3; + } else { + rand_type = TYPE_4; + rand_deg = DEG_4; + rand_sep = SEP_4; + } + state = (long *) (long_arg_state + 1); /* first location */ + end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */ + srandom(seed); + if (rand_type == TYPE_0) + long_arg_state[0] = rand_type; + else + long_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type; + 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. + * + * Note: The Sparc platform requires that arg_state begin on a long + * word boundary; otherwise a bus error will occur. Even so, lint will + * complain about mis-alignment, but you should disregard these messages. + */ +char * +setstate(arg_state) + char *arg_state; /* pointer to state array */ +{ + register long *new_state = (long *) arg_state; + register long type = new_state[0] % MAX_TYPES; + register long rear = new_state[0] / MAX_TYPES; + char *ostate = (char *)(&state[-1]); + + if (rand_type == TYPE_0) + state[-1] = rand_type; + else + state[-1] = MAX_TYPES * (rptr - state) + rand_type; + switch(type) { + case TYPE_0: + case TYPE_1: + case TYPE_2: + case TYPE_3: + case TYPE_4: + rand_type = type; + rand_deg = degrees[type]; + rand_sep = seps[type]; + break; + default: + (void)fprintf(stderr, + "random: state info corrupted; not changed.\n"); + } + state = (long *) (new_state + 1); + if (rand_type != TYPE_0) { + rptr = &state[rear]; + fptr = &state[(rear + rand_sep) % rand_deg]; + } + end_ptr = &state[rand_deg]; /* set end_ptr too */ + 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 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. + */ +long +random() +{ + register long i; + register long *f, *r; + + if (rand_type == TYPE_0) { + i = state[0]; + state[0] = i = (i * 1103515245 + 12345) & 0x7fffffff; + } else { + /* + * Use local variables rather than static variables for speed. + */ + f = fptr; r = rptr; + *f += *r; + i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */ + if (++f >= end_ptr) { + f = state; + ++r; + } + else if (++r >= end_ptr) { + r = state; + } + + fptr = f; rptr = r; + } + return(i); +} |