1 files changed, 430 insertions, 0 deletions

diff --git a/src/lib/libc/stdlib/random.c b/src/lib/libc/stdlib/random.c
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+/*
+ * 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.
+ * 3. 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.
+ */
+
+#if defined(LIBC_SCCS) && !defined(lint)
+static char *rcsid = "$OpenBSD: random.c,v 1.12 2003/06/02 20:18:38 millert Exp $";
+#endif /* LIBC_SCCS and not lint */
+
+#include <sys/param.h>
+#include <sys/sysctl.h>
+#include <sys/time.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+/*
+ * random.c:
+ *
+ * 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() routine 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 int32_t; 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 int32_ts 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 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
+ * the separation between the two lower order coefficients of the trinomial.
+ */
+#define TYPE_0          0               /* linear congruential */
+#define BREAK_0         8
+#define DEG_0           0
+#define SEP_0           0
+
+#define TYPE_1          1               /* x**7 + x**3 + 1 */
+#define BREAK_1         32
+#define DEG_1           7
+#define SEP_1           3
+
+#define TYPE_2          2               /* x**15 + x + 1 */
+#define BREAK_2         64
+#define DEG_2           15
+#define SEP_2           1
+
+#define TYPE_3          3               /* x**31 + x**3 + 1 */
+#define BREAK_3         128
+#define DEG_3           31
+#define SEP_3           3
+
+#define TYPE_4          4               /* x**63 + x + 1 */
+#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 int degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
+static int seps [MAX_TYPES] =   { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
+
+/*
+ * 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 zeroeth
+ * 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,
+        0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05, 
+        0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454, 
+        0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471, 
+        0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1, 
+        0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41, 
+        0xf3bec5da,
+};
+
+/*
+ * 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 cyclically 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).
+ */
+static int32_t *fptr = &randtbl[SEP_3 + 1];
+static int32_t *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 zeroeth.  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.
+ */
+static int32_t *state = &randtbl[1];
+static int32_t *end_ptr = &randtbl[DEG_3 + 1];
+static int rand_type = TYPE_3;
+static int rand_deg = DEG_3;
+static int rand_sep = SEP_3;
+
+/*
+ * srandom:
+ *
+ * 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(x)
+        unsigned int x;
+{
+        int i;
+        int32_t test;
+        div_t val;
+
+        if (rand_type == TYPE_0)
+                state[0] = x;
+        else {
+                state[0] = x;
+                for (i = 1; i < rand_deg; i++) {
+                        /*
+                         * Implement the following, without overflowing 31 bits:
+                         *
+                         *      state[i] = (16807 * state[i - 1]) % 2147483647;
+                         *
+                         *      2^31-1 (prime) = 2147483647 = 127773*16807+2836
+                         */
+                        val = div(state[i-1], 127773);
+                        test = 16807 * val.rem - 2836 * val.quot;
+                        state[i] = test + (test < 0 ? 2147483647 : 0);
+                }
+                fptr = &state[rand_sep];
+                rptr = &state[0];
+                for (i = 0; i < 10 * rand_deg; i++)
+                        (void)random();
+        }
+}
+
+/*
+ * srandomdev:
+ *
+ * Many programs choose the seed value in a totally predictable manner.
+ * This often causes problems.  We seed the generator using the much more
+ * secure arandom(4) interface.  Note that this particular seeding
+ * procedure can generate states which are impossible to reproduce by
+ * calling srandom() with any value, since the succeeding terms in the
+ * state buffer are no longer derived from the LC algorithm applied to
+ * a fixed seed.
+ */
+void
+srandomdev()
+{
+        int fd, i, mib[2], n;
+        size_t len;
+
+        if (rand_type == TYPE_0)
+                len = sizeof(state[0]);
+        else
+                len = rand_deg * sizeof(state[0]);
+
+        /*
+         * To get seed data, first try reading from /dev/arandom.
+         * If that fails, try the KERN_ARND sysctl() (one int at a time).
+         * As a last resort, call srandom().
+         */
+        if ((fd = open("/dev/arandom", O_RDONLY, 0)) != -1 &&
+            read(fd, (void *) state, len) == (ssize_t) len) {
+                close(fd);
+        } else {
+                if (fd != -1)
+                        close(fd);
+                mib[0] = CTL_KERN;
+                mib[1] = KERN_ARND;
+                n = len / sizeof(int);
+                len = sizeof(int);
+                for (i = 0; i < n; i++) {
+                        if (sysctl(mib, 2, (char *)((int *)state + i), &len,
+                            NULL, 0) == -1)
+                                break;
+                }
+                if (i != n) {
+                        struct timeval tv;
+                        u_int junk;
+
+                        /* XXX - this could be better */
+                        gettimeofday(&tv, NULL);
+                        srandom(getpid() ^ tv.tv_sec ^ tv.tv_usec ^ junk);
+                        return;
+                }
+        }
+
+        if (rand_type != TYPE_0) {
+                fptr = &state[rand_sep];
+                rptr = &state[0];
+        }
+}
+
+/*
+ * initstate:
+ *
+ * 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(seed, arg_state, n)
+        u_int seed;                     /* seed for R.N.G. */
+        char *arg_state;                /* pointer to state array */
+        size_t n;                       /* # bytes of state info */
+{
+        char *ostate = (char *)(&state[-1]);
+
+        if (rand_type == TYPE_0)
+                state[-1] = rand_type;
+        else
+                state[-1] = MAX_TYPES * (rptr - state) + rand_type;
+        if (n < BREAK_0)
+                return(NULL);
+        if (n < BREAK_1) {
+                rand_type = TYPE_0;
+                rand_deg = DEG_0;
+                rand_sep = SEP_0;
+        } else if (n < BREAK_2) {
+                rand_type = TYPE_1;
+                rand_deg = DEG_1;
+                rand_sep = SEP_1;
+        } else if (n < BREAK_3) {
+                rand_type = TYPE_2;
+                rand_deg = DEG_2;
+                rand_sep = SEP_2;
+        } else if (n < BREAK_4) {
+                rand_type = TYPE_3;
+                rand_deg = DEG_3;
+                rand_sep = SEP_3;
+        } else {
+                rand_type = TYPE_4;
+                rand_deg = DEG_4;
+                rand_sep = SEP_4;
+        }
+        state = &(((int32_t *)arg_state)[1]);   /* first location */
+        end_ptr = &state[rand_deg];     /* must set end_ptr before srandom */
+        srandom(seed);
+        if (rand_type == TYPE_0)
+                state[-1] = rand_type;
+        else
+                state[-1] = MAX_TYPES*(rptr - state) + rand_type;
+        return(ostate);
+}
+
+/*
+ * setstate:
+ *
+ * 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.
+ */
+char *
+setstate(arg_state)
+        const char *arg_state;
+{
+        int32_t *new_state = (int32_t *)arg_state;
+        int32_t type = new_state[0] % MAX_TYPES;
+        int32_t rear = new_state[0] / MAX_TYPES;
+        char *ostate = (char *)(&state[-1]);
+
+        if (rand_type == TYPE_0)
+                state[-1] = rand_type;
+        else
+                state[-1] = MAX_TYPES * (rptr - state) + rand_type;
+        switch(type) {
+        case TYPE_0:
+        case TYPE_1:
+        case TYPE_2:
+        case TYPE_3:
+        case TYPE_4:
+                rand_type = type;
+                rand_deg = degrees[type];
+                rand_sep = seps[type];
+                break;
+        default:
+                return(NULL);
+        }
+        state = &new_state[1];
+        if (rand_type != TYPE_0) {
+                rptr = &state[rear];
+                fptr = &state[(rear + rand_sep) % rand_deg];
+        }
+        end_ptr = &state[rand_deg];             /* set end_ptr too */
+        return(ostate);
+}
+
+/*
+ * random:
+ *
+ * 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
+random()
+{
+        int32_t i;
+
+        if (rand_type == TYPE_0)
+                i = state[0] = (state[0] * 1103515245 + 12345) & 0x7fffffff;
+        else {
+                *fptr += *rptr;
+                i = (*fptr >> 1) & 0x7fffffff;  /* chucking least random bit */
+                if (++fptr >= end_ptr) {
+                        fptr = state;
+                        ++rptr;
+                } else if (++rptr >= end_ptr)
+                        rptr = state;
+        }
+        return((long)i);
+}