diff options
Diffstat (limited to 'stdlib/random_r.c')
| -rw-r--r-- | stdlib/random_r.c | 337 |
1 files changed, 337 insertions, 0 deletions
diff --git a/stdlib/random_r.c b/stdlib/random_r.c new file mode 100644 index 0000000000..aa7a33fa6b --- /dev/null +++ b/stdlib/random_r.c @@ -0,0 +1,337 @@ +/* + * 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 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 be reentrent by Ulrich Drepper, 1995 + */ + +#include <errno.h> +#include <limits.h> +#include <stddef.h> +#include <stdlib.h> + + +/* 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 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 thi + 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 + +/* x**15 + x + 1. */ +#define TYPE_2 2 +#define BREAK_2 64 +#define DEG_2 15 +#define SEP_2 1 + +/* 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. */ + +static const int degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }; +static const int seps[MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }; + + + + +/* 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. */ +int +__srandom_r (x, buf) + unsigned int x; + struct random_data *buf; +{ + if (buf == NULL || buf->rand_type < TYPE_0 || buf->rand_type > TYPE_4) + return -1; + + buf->state[0] = x; + if (buf->rand_type != TYPE_0) + { + long int i; + for (i = 1; i < buf->rand_deg; ++i) + { + /* This does: + state[i] = (16807 * state[i - 1]) % 2147483647; + but avoids overflowing 31 bits. */ + long int hi = buf->state[i - 1] / 127773; + long int lo = buf->state[i - 1] % 127773; + long int test = 16807 * lo - 2836 * hi; + buf->state[i] = test + (test < 0 ? 2147483647 : 0); + } + buf->fptr = &buf->state[buf->rand_sep]; + buf->rptr = &buf->state[0]; + for (i = 0; i < 10 * buf->rand_deg; ++i) + { + long int discard; + (void) __random_r (buf, &discard); + } + } + + return 0; +} + +weak_alias (__srandom_r, srandom_r) +weak_alias (__srandom_r, srand_r) + +/* 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. */ +int +__initstate_r (seed, arg_state, n, buf) + unsigned int seed; + void *arg_state; + size_t n; + struct random_data *buf; +{ + if (buf == NULL) + return -1; + + if (buf->rand_type == TYPE_0) + buf->state[-1] = buf->rand_type; + else + buf->state[-1] = (MAX_TYPES * (buf->rptr - buf->state)) + buf->rand_type; + if (n < BREAK_1) + { + if (n < BREAK_0) + { + errno = EINVAL; + return -1; + } + buf->rand_type = TYPE_0; + buf->rand_deg = DEG_0; + buf->rand_sep = SEP_0; + } + else if (n < BREAK_2) + { + buf->rand_type = TYPE_1; + buf->rand_deg = DEG_1; + buf->rand_sep = SEP_1; + } + else if (n < BREAK_3) + { + buf->rand_type = TYPE_2; + buf->rand_deg = DEG_2; + buf->rand_sep = SEP_2; + } + else if (n < BREAK_4) + { + buf->rand_type = TYPE_3; + buf->rand_deg = DEG_3; + buf->rand_sep = SEP_3; + } + else + { + buf->rand_type = TYPE_4; + buf->rand_deg = DEG_4; + buf->rand_sep = SEP_4; + } + + buf->state = &((long int *) arg_state)[1]; /* First location. */ + /* Must set END_PTR before srandom. */ + buf->end_ptr = &buf->state[buf->rand_deg]; + + __srandom_r (seed, buf); + + if (buf->rand_type == TYPE_0) + buf->state[-1] = buf->rand_type; + else + buf->state[-1] = (MAX_TYPES * (buf->rptr - buf->state)) + buf->rand_type; + + return 0; +} + +weak_alias (__initstate_r, initstate_r) + +/* 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. */ +int +__setstate_r (arg_state, buf) + void *arg_state; + struct random_data *buf; +{ + long int *new_state = (long int *) arg_state; + int type = new_state[0] % MAX_TYPES; + int rear = new_state[0] / MAX_TYPES; + + if (buf == NULL) + return -1; + + if (buf->rand_type == TYPE_0) + buf->state[-1] = buf->rand_type; + else + buf->state[-1] = (MAX_TYPES * (buf->rptr - buf->state)) + buf->rand_type; + + switch (type) + { + case TYPE_0: + case TYPE_1: + case TYPE_2: + case TYPE_3: + case TYPE_4: + buf->rand_type = type; + buf->rand_deg = degrees[type]; + buf->rand_sep = seps[type]; + break; + default: + /* State info munged. */ + errno = EINVAL; + return -1; + } + + buf->state = &new_state[1]; + if (buf->rand_type != TYPE_0) + { + buf->rptr = &buf->state[rear]; + buf->fptr = &buf->state[(rear + buf->rand_sep) % buf->rand_deg]; + } + /* Set end_ptr too. */ + buf->end_ptr = &buf->state[buf->rand_deg]; + + return 0; +} + +weak_alias (__setstate_r, setstate_r) + +/* 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. */ + +int +__random_r (buf, result) + struct random_data *buf; + long int *result; +{ + if (buf == NULL || result == NULL) + return -1; + + if (buf->rand_type == TYPE_0) + { + buf->state[0] = ((buf->state[0] * 1103515245) + 12345) & LONG_MAX; + *result = buf->state[0]; + } + else + { + *buf->fptr += *buf->rptr; + /* Chucking least random bit. */ + *result = (*buf->fptr >> 1) & LONG_MAX; + ++buf->fptr; + if (buf->fptr >= buf->end_ptr) + { + buf->fptr = buf->state; + ++buf->rptr; + } + else + { + ++buf->rptr; + if (buf->rptr >= buf->end_ptr) + buf->rptr = buf->state; + } + } + return 0; +} + +weak_alias (__random_r, random_r) |