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Diffstat (limited to 'libc/stdlib/random.c')
| -rw-r--r-- | libc/stdlib/random.c | 264 |
1 files changed, 241 insertions, 23 deletions
diff --git a/libc/stdlib/random.c b/libc/stdlib/random.c index cbd4206ae..bc20d1e1b 100644 --- a/libc/stdlib/random.c +++ b/libc/stdlib/random.c @@ -1,37 +1,255 @@ -#include <stdlib.h> +/* + * 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. + */ /* - * This generator is a combination of three linear congruential generators - * with periods or 2^15-405, 2^15-1041 and 2^15-1111. It has a period that - * is the product of these three numbers. + * 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 use reentrant functions by Ulrich Drepper, 1995. */ -static long int seed1 = 1; -static long int seed2 = 1; -static long int seed3 = 1; +#define _GNU_SOURCE +#include <features.h> +#include <limits.h> +#include <stddef.h> +#include <stdlib.h> +#ifdef __UCLIBC_HAS_THREADS__ +#include <pthread.h> +/* POSIX.1c requires that there is mutual exclusion for the `rand' and + `srand' functions to prevent concurrent calls from modifying common + data. */ +static pthread_mutex_t lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP; +#else +#define pthread_mutex_lock(x) +#define pthread_mutex_unlock(x) +#endif + +/* 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 -#define CRANK(a,b,c,m,s) \ - q = s/a; \ - s = b*(s-a*q) - c*q; \ - if(s<0) s+=m; +/* x**15 + x + 1. */ +#define TYPE_2 2 +#define BREAK_2 64 +#define DEG_2 15 +#define SEP_2 1 -long int random() +/* 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. */ + + +/* 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 zeroth + 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 int32_t randtbl[DEG_3 + 1] = { - register long int q; + TYPE_3, - CRANK(206, 157, 31, 32363, seed1); - CRANK(217, 146, 45, 31727, seed2); - CRANK(222, 142, 133, 31657, seed3); + -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, +}; - return seed1 ^ seed2 ^ seed3; + +static struct random_data unsafe_state = +{ + /* 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 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).) */ + + fptr : &randtbl[SEP_3 + 1], + 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 zeroth. 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. */ + + state : &randtbl[1], + + rand_type : TYPE_3, + rand_deg : DEG_3, + rand_sep : SEP_3, + + end_ptr : &randtbl[sizeof (randtbl) / sizeof (randtbl[0])] +}; + + +/* 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 int x) +{ + pthread_mutex_lock(&lock); + srandom_r (x, &unsafe_state); + pthread_mutex_unlock(&lock); +} +weak_alias (srandom, srand) + +/* 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. */ +char * initstate (unsigned int seed, char *arg_state, size_t n) +{ + int32_t *ostate; + + pthread_mutex_lock(&lock); + ostate = &unsafe_state.state[-1]; + initstate_r (seed, arg_state, n, &unsafe_state); + pthread_mutex_unlock(&lock); + return (char *) ostate; } -void srandom(unsigned int seed) +/* 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. */ +char * setstate (char *arg_state) { - seed &= RAND_MAX; - seed1 = seed % 32362 + 1; - seed2 = seed % 31726 + 1; - seed3 = seed % 31656 + 1; + int32_t *ostate; + + pthread_mutex_lock(&lock); + ostate = &unsafe_state.state[-1]; + if (setstate_r (arg_state, &unsafe_state) < 0) + ostate = NULL; + pthread_mutex_unlock(&lock); + return (char *) ostate; +} + +/* 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 int random () +{ + int32_t retval; + + pthread_mutex_lock(&lock); + random_r (&unsafe_state, &retval); + pthread_mutex_unlock(&lock); + return retval; } -weak_alias(srandom, srand); |