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glibc  2.9
random_r.c
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00001 /*
00002    Copyright (C) 1995, 2005 Free Software Foundation
00003 
00004    The GNU C Library is free software; you can redistribute it and/or
00005    modify it under the terms of the GNU Lesser General Public
00006    License as published by the Free Software Foundation; either
00007    version 2.1 of the License, or (at your option) any later version.
00008 
00009    The GNU C Library is distributed in the hope that it will be useful,
00010    but WITHOUT ANY WARRANTY; without even the implied warranty of
00011    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00012    Lesser General Public License for more details.
00013 
00014    You should have received a copy of the GNU Lesser General Public
00015    License along with the GNU C Library; if not, write to the Free
00016    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00017    02111-1307 USA.  */
00018 
00019 /*
00020    Copyright (C) 1983 Regents of the University of California.
00021    All rights reserved.
00022 
00023    Redistribution and use in source and binary forms, with or without
00024    modification, are permitted provided that the following conditions
00025    are met:
00026 
00027    1. Redistributions of source code must retain the above copyright
00028       notice, this list of conditions and the following disclaimer.
00029    2. Redistributions in binary form must reproduce the above copyright
00030       notice, this list of conditions and the following disclaimer in the
00031       documentation and/or other materials provided with the distribution.
00032    4. Neither the name of the University nor the names of its contributors
00033       may be used to endorse or promote products derived from this software
00034       without specific prior written permission.
00035 
00036    THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
00037    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
00038    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00039    ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
00040    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00041    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
00042    OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
00043    HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
00044    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
00045    OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
00046    SUCH DAMAGE.*/
00047 
00048 /*
00049  * This is derived from the Berkeley source:
00050  *     @(#)random.c  5.5 (Berkeley) 7/6/88
00051  * It was reworked for the GNU C Library by Roland McGrath.
00052  * Rewritten to be reentrant by Ulrich Drepper, 1995
00053  */
00054 
00055 #include <errno.h>
00056 #include <limits.h>
00057 #include <stddef.h>
00058 #include <stdlib.h>
00059 
00060 
00061 /* An improved random number generation package.  In addition to the standard
00062    rand()/srand() like interface, this package also has a special state info
00063    interface.  The initstate() routine is called with a seed, an array of
00064    bytes, and a count of how many bytes are being passed in; this array is
00065    then initialized to contain information for random number generation with
00066    that much state information.  Good sizes for the amount of state
00067    information are 32, 64, 128, and 256 bytes.  The state can be switched by
00068    calling the setstate() function with the same array as was initialized
00069    with initstate().  By default, the package runs with 128 bytes of state
00070    information and generates far better random numbers than a linear
00071    congruential generator.  If the amount of state information is less than
00072    32 bytes, a simple linear congruential R.N.G. is used.  Internally, the
00073    state information is treated as an array of longs; the zeroth element of
00074    the array is the type of R.N.G. being used (small integer); the remainder
00075    of the array is the state information for the R.N.G.  Thus, 32 bytes of
00076    state information will give 7 longs worth of state information, which will
00077    allow a degree seven polynomial.  (Note: The zeroth word of state
00078    information also has some other information stored in it; see setstate
00079    for details).  The random number generation technique is a linear feedback
00080    shift register approach, employing trinomials (since there are fewer terms
00081    to sum up that way).  In this approach, the least significant bit of all
00082    the numbers in the state table will act as a linear feedback shift register,
00083    and will have period 2^deg - 1 (where deg is the degree of the polynomial
00084    being used, assuming that the polynomial is irreducible and primitive).
00085    The higher order bits will have longer periods, since their values are
00086    also influenced by pseudo-random carries out of the lower bits.  The
00087    total period of the generator is approximately deg*(2**deg - 1); thus
00088    doubling the amount of state information has a vast influence on the
00089    period of the generator.  Note: The deg*(2**deg - 1) is an approximation
00090    only good for large deg, when the period of the shift register is the
00091    dominant factor.  With deg equal to seven, the period is actually much
00092    longer than the 7*(2**7 - 1) predicted by this formula.  */
00093 
00094 
00095 
00096 /* For each of the currently supported random number generators, we have a
00097    break value on the amount of state information (you need at least this many
00098    bytes of state info to support this random number generator), a degree for
00099    the polynomial (actually a trinomial) that the R.N.G. is based on, and
00100    separation between the two lower order coefficients of the trinomial.  */
00101 
00102 /* Linear congruential.  */
00103 #define       TYPE_0        0
00104 #define       BREAK_0              8
00105 #define       DEG_0         0
00106 #define       SEP_0         0
00107 
00108 /* x**7 + x**3 + 1.  */
00109 #define       TYPE_1        1
00110 #define       BREAK_1              32
00111 #define       DEG_1         7
00112 #define       SEP_1         3
00113 
00114 /* x**15 + x + 1.  */
00115 #define       TYPE_2        2
00116 #define       BREAK_2              64
00117 #define       DEG_2         15
00118 #define       SEP_2         1
00119 
00120 /* x**31 + x**3 + 1.  */
00121 #define       TYPE_3        3
00122 #define       BREAK_3              128
00123 #define       DEG_3         31
00124 #define       SEP_3         3
00125 
00126 /* x**63 + x + 1.  */
00127 #define       TYPE_4        4
00128 #define       BREAK_4              256
00129 #define       DEG_4         63
00130 #define       SEP_4         1
00131 
00132 
00133 /* Array versions of the above information to make code run faster.
00134    Relies on fact that TYPE_i == i.  */
00135 
00136 #define       MAX_TYPES     5      /* Max number of types above.  */
00137 
00138 struct random_poly_info
00139 {
00140   int seps[MAX_TYPES];
00141   int degrees[MAX_TYPES];
00142 };
00143 
00144 static const struct random_poly_info random_poly_info =
00145 {
00146   { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
00147   { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
00148 };
00149 
00150 
00151 
00152 
00153 /* Initialize the random number generator based on the given seed.  If the
00154    type is the trivial no-state-information type, just remember the seed.
00155    Otherwise, initializes state[] based on the given "seed" via a linear
00156    congruential generator.  Then, the pointers are set to known locations
00157    that are exactly rand_sep places apart.  Lastly, it cycles the state
00158    information a given number of times to get rid of any initial dependencies
00159    introduced by the L.C.R.N.G.  Note that the initialization of randtbl[]
00160    for default usage relies on values produced by this routine.  */
00161 int
00162 __srandom_r (seed, buf)
00163      unsigned int seed;
00164      struct random_data *buf;
00165 {
00166   int type;
00167   int32_t *state;
00168   long int i;
00169   long int word;
00170   int32_t *dst;
00171   int kc;
00172 
00173   if (buf == NULL)
00174     goto fail;
00175   type = buf->rand_type;
00176   if ((unsigned int) type >= MAX_TYPES)
00177     goto fail;
00178 
00179   state = buf->state;
00180   /* We must make sure the seed is not 0.  Take arbitrarily 1 in this case.  */
00181   if (seed == 0)
00182     seed = 1;
00183   state[0] = seed;
00184   if (type == TYPE_0)
00185     goto done;
00186 
00187   dst = state;
00188   word = seed;
00189   kc = buf->rand_deg;
00190   for (i = 1; i < kc; ++i)
00191     {
00192       /* This does:
00193           state[i] = (16807 * state[i - 1]) % 2147483647;
00194         but avoids overflowing 31 bits.  */
00195       long int hi = word / 127773;
00196       long int lo = word % 127773;
00197       word = 16807 * lo - 2836 * hi;
00198       if (word < 0)
00199        word += 2147483647;
00200       *++dst = word;
00201     }
00202 
00203   buf->fptr = &state[buf->rand_sep];
00204   buf->rptr = &state[0];
00205   kc *= 10;
00206   while (--kc >= 0)
00207     {
00208       int32_t discard;
00209       (void) __random_r (buf, &discard);
00210     }
00211 
00212  done:
00213   return 0;
00214 
00215  fail:
00216   return -1;
00217 }
00218 
00219 weak_alias (__srandom_r, srandom_r)
00220 
00221 /* Initialize the state information in the given array of N bytes for
00222    future random number generation.  Based on the number of bytes we
00223    are given, and the break values for the different R.N.G.'s, we choose
00224    the best (largest) one we can and set things up for it.  srandom is
00225    then called to initialize the state information.  Note that on return
00226    from srandom, we set state[-1] to be the type multiplexed with the current
00227    value of the rear pointer; this is so successive calls to initstate won't
00228    lose this information and will be able to restart with setstate.
00229    Note: The first thing we do is save the current state, if any, just like
00230    setstate so that it doesn't matter when initstate is called.
00231    Returns a pointer to the old state.  */
00232 int
00233 __initstate_r (seed, arg_state, n, buf)
00234      unsigned int seed;
00235      char *arg_state;
00236      size_t n;
00237      struct random_data *buf;
00238 {
00239   if (buf == NULL)
00240     goto fail;
00241 
00242   int32_t *old_state = buf->state;
00243   if (old_state != NULL)
00244     {
00245       int old_type = buf->rand_type;
00246       if (old_type == TYPE_0)
00247        old_state[-1] = TYPE_0;
00248       else
00249        old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
00250     }
00251 
00252   int type;
00253   if (n >= BREAK_3)
00254     type = n < BREAK_4 ? TYPE_3 : TYPE_4;
00255   else if (n < BREAK_1)
00256     {
00257       if (n < BREAK_0)
00258        {
00259          __set_errno (EINVAL);
00260          goto fail;
00261        }
00262       type = TYPE_0;
00263     }
00264   else
00265     type = n < BREAK_2 ? TYPE_1 : TYPE_2;
00266 
00267   int degree = random_poly_info.degrees[type];
00268   int separation = random_poly_info.seps[type];
00269 
00270   buf->rand_type = type;
00271   buf->rand_sep = separation;
00272   buf->rand_deg = degree;
00273   int32_t *state = &((int32_t *) arg_state)[1];  /* First location.  */
00274   /* Must set END_PTR before srandom.  */
00275   buf->end_ptr = &state[degree];
00276 
00277   buf->state = state;
00278 
00279   __srandom_r (seed, buf);
00280 
00281   state[-1] = TYPE_0;
00282   if (type != TYPE_0)
00283     state[-1] = (buf->rptr - state) * MAX_TYPES + type;
00284 
00285   return 0;
00286 
00287  fail:
00288   __set_errno (EINVAL);
00289   return -1;
00290 }
00291 
00292 weak_alias (__initstate_r, initstate_r)
00293 
00294 /* Restore the state from the given state array.
00295    Note: It is important that we also remember the locations of the pointers
00296    in the current state information, and restore the locations of the pointers
00297    from the old state information.  This is done by multiplexing the pointer
00298    location into the zeroth word of the state information. Note that due
00299    to the order in which things are done, it is OK to call setstate with the
00300    same state as the current state
00301    Returns a pointer to the old state information.  */
00302 int
00303 __setstate_r (arg_state, buf)
00304      char *arg_state;
00305      struct random_data *buf;
00306 {
00307   int32_t *new_state = 1 + (int32_t *) arg_state;
00308   int type;
00309   int old_type;
00310   int32_t *old_state;
00311   int degree;
00312   int separation;
00313 
00314   if (arg_state == NULL || buf == NULL)
00315     goto fail;
00316 
00317   old_type = buf->rand_type;
00318   old_state = buf->state;
00319   if (old_type == TYPE_0)
00320     old_state[-1] = TYPE_0;
00321   else
00322     old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
00323 
00324   type = new_state[-1] % MAX_TYPES;
00325   if (type < TYPE_0 || type > TYPE_4)
00326     goto fail;
00327 
00328   buf->rand_deg = degree = random_poly_info.degrees[type];
00329   buf->rand_sep = separation = random_poly_info.seps[type];
00330   buf->rand_type = type;
00331 
00332   if (type != TYPE_0)
00333     {
00334       int rear = new_state[-1] / MAX_TYPES;
00335       buf->rptr = &new_state[rear];
00336       buf->fptr = &new_state[(rear + separation) % degree];
00337     }
00338   buf->state = new_state;
00339   /* Set end_ptr too.  */
00340   buf->end_ptr = &new_state[degree];
00341 
00342   return 0;
00343 
00344  fail:
00345   __set_errno (EINVAL);
00346   return -1;
00347 }
00348 
00349 weak_alias (__setstate_r, setstate_r)
00350 
00351 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
00352    congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
00353    same in all the other cases due to all the global variables that have been
00354    set up.  The basic operation is to add the number at the rear pointer into
00355    the one at the front pointer.  Then both pointers are advanced to the next
00356    location cyclically in the table.  The value returned is the sum generated,
00357    reduced to 31 bits by throwing away the "least random" low bit.
00358    Note: The code takes advantage of the fact that both the front and
00359    rear pointers can't wrap on the same call by not testing the rear
00360    pointer if the front one has wrapped.  Returns a 31-bit random number.  */
00361 
00362 int
00363 __random_r (buf, result)
00364      struct random_data *buf;
00365      int32_t *result;
00366 {
00367   int32_t *state;
00368 
00369   if (buf == NULL || result == NULL)
00370     goto fail;
00371 
00372   state = buf->state;
00373 
00374   if (buf->rand_type == TYPE_0)
00375     {
00376       int32_t val = state[0];
00377       val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
00378       state[0] = val;
00379       *result = val;
00380     }
00381   else
00382     {
00383       int32_t *fptr = buf->fptr;
00384       int32_t *rptr = buf->rptr;
00385       int32_t *end_ptr = buf->end_ptr;
00386       int32_t val;
00387 
00388       val = *fptr += *rptr;
00389       /* Chucking least random bit.  */
00390       *result = (val >> 1) & 0x7fffffff;
00391       ++fptr;
00392       if (fptr >= end_ptr)
00393        {
00394          fptr = state;
00395          ++rptr;
00396        }
00397       else
00398        {
00399          ++rptr;
00400          if (rptr >= end_ptr)
00401            rptr = state;
00402        }
00403       buf->fptr = fptr;
00404       buf->rptr = rptr;
00405     }
00406   return 0;
00407 
00408  fail:
00409   __set_errno (EINVAL);
00410   return -1;
00411 }
00412 
00413 weak_alias (__random_r, random_r)