/* * random.c * * BSD random function to support the TclX random command on SysV based * systems. *----------------------------------------------------------------------------- * $Id: random.c,v 8.1 1997/04/17 04:58:30 markd Exp $ *----------------------------------------------------------------------------- */ /* * 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. All advertising materials mentioning features or use of this software * must display the following acknowledgement: * This product includes software developed by the University of * California, Berkeley and its contributors. * 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. */ /* * static char sccsid[] = "@(#)random.c 5.9 (Berkeley) 2/23/91"; */ #include <stdio.h> long random(); typedef unsigned int u_int; /* * 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 longs; 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 longs 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 long randtbl[DEG_3 + 1] = { TYPE_3, 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd, 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc, 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b, 0x27fb47b9, }; /* * 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 long *fptr = &randtbl[SEP_3 + 1]; static long *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 long *state = &randtbl[1]; static int rand_type = TYPE_3; static int rand_deg = DEG_3; static int rand_sep = SEP_3; static long *end_ptr = &randtbl[DEG_3 + 1]; /* * 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) u_int x; { register int i, j; if (rand_type == TYPE_0) state[0] = x; else { j = 1; state[0] = x; for (i = 1; i < rand_deg; i++) state[i] = 1103515245 * state[i - 1] + 12345; fptr = &state[rand_sep]; rptr = &state[0]; for (i = 0; i < 10 * rand_deg; i++) (void)random(); } } /* * 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 */ int n; /* # bytes of state info */ { register 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) { (void)fprintf(stderr, "random: not enough state (%d bytes); ignored.\n", n); return(0); } 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 = &(((long *)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) char *arg_state; { register long *new_state = (long *)arg_state; register int type = new_state[0] % MAX_TYPES; register int 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: (void)fprintf(stderr, "random: state info corrupted; not changed.\n"); } 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() { long 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(i); }

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