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- /*
- * 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 use reentrant functions by Ulrich Drepper, 1995.
- */
- #include <features.h>
- #include <limits.h>
- #include <stddef.h>
- #include <stdlib.h>
- /* POSIX.1c requires that there is mutual exclusion for the `rand' and
- `srand' functions to prevent concurrent calls from modifying common
- data. */
- #include <bits/uClibc_mutex.h>
- __UCLIBC_MUTEX_STATIC(mylock, PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP);
- /* 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. */
- /* Keep constants in sync with random_r.c */
- /* 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
- #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] =
- {
- TYPE_3,
- -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,
- };
- 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)
- {
- __UCLIBC_MUTEX_LOCK(mylock);
- srandom_r (x, &unsafe_state);
- __UCLIBC_MUTEX_UNLOCK(mylock);
- }
- strong_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;
- __UCLIBC_MUTEX_LOCK(mylock);
- ostate = &unsafe_state.state[-1];
- initstate_r (seed, arg_state, n, &unsafe_state);
- __UCLIBC_MUTEX_UNLOCK(mylock);
- return (char *) ostate;
- }
- /* 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)
- {
- int32_t *ostate;
- __UCLIBC_MUTEX_LOCK(mylock);
- ostate = &unsafe_state.state[-1];
- if (setstate_r (arg_state, &unsafe_state) < 0)
- ostate = NULL;
- __UCLIBC_MUTEX_UNLOCK(mylock);
- 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 (void)
- {
- int32_t retval;
- __UCLIBC_MUTEX_LOCK(mylock);
- random_r (&unsafe_state, &retval);
- __UCLIBC_MUTEX_UNLOCK(mylock);
- return retval;
- }
- libc_hidden_def(random)
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