gnu / gcc / a6d3012b274f38b20e2a57162106f625746af6c6 / . / gcc / testsuite / objc.dg / gnu-encoding / generate-random.c

/* Copyright (C) 1995, 2004 Free Software Foundation | |

The GNU C Library is free software; you can redistribute it and/or | |

modify it under the terms of the GNU Lesser General Public | |

License as published by the Free Software Foundation; either | |

version 2.1 of the License, or (at your option) any later version. | |

The GNU C Library is distributed in the hope that it will be useful, | |

but WITHOUT ANY WARRANTY; without even the implied warranty of | |

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |

Lesser General Public License for more details. | |

You should have received a copy of the GNU Lesser General Public | |

License along with the GNU C Library; if not, write to the Free | |

Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA | |

02110-1301 USA. */ | |

/* | |

* 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. | |

*/ | |

/* | |

Copyright (C) 1983 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. | |

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.*/ | |

#include <limits.h> | |

#include <stdlib.h> | |

#include "generate-random.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 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 | |

/* 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. */ | |

/* 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 int 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 generate_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).) */ | |

&randtbl[SEP_3 + 1], /* fptr */ | |

&randtbl[1], /* rptr */ | |

/* 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. */ | |

&randtbl[1], /* state */ | |

TYPE_3, /* rand_type */ | |

DEG_3, /* rand_deg */ | |

SEP_3, /* rand_sep */ | |

&randtbl[sizeof (randtbl) / sizeof (randtbl[0])] /* end_ptr */ | |

}; | |

/* 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 | |

generate_srandom (unsigned int x) | |

{ | |

(void) generate_srandom_r (x, &unsafe_state); | |

} | |

/* 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 * | |

generate_initstate (unsigned int seed, char *arg_state, size_t n) | |

{ | |

int *ostate; | |

ostate = &unsafe_state.state[-1]; | |

generate_initstate_r (seed, arg_state, n, &unsafe_state); | |

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 * | |

generate_setstate (char *arg_state) | |

{ | |

int *ostate; | |

ostate = &unsafe_state.state[-1]; | |

if (generate_setstate_r (arg_state, &unsafe_state) < 0) | |

ostate = NULL; | |

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 | |

generate_random (void) | |

{ | |

int retval; | |

(void) generate_random_r (&unsafe_state, &retval); | |

return retval; | |

} |