| /* 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; |
| } |