Return to random.c CVS log

Up to [Micropolis - Activity] / micropolis / src / sim

Annotation of micropolis/src/sim/random.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1983 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms, with or without
        !             6:  * modification, are permitted provided that the following conditions
        !             7:  * are met:
        !             8:  * 1. Redistributions of source code must retain the above copyright
        !             9:  *    notice, this list of conditions and the following disclaimer.
        !            10:  * 2. Redistributions in binary form must reproduce the above copyright
        !            11:  *    notice, this list of conditions and the following disclaimer in the
        !            12:  *    documentation and/or other materials provided with the distribution.
        !            13:  * 3. All advertising materials mentioning features or use of this software
        !            14:  *    must display the following acknowledgement:
        !            15:  *     This product includes software developed by the University of
        !            16:  *     California, Berkeley and its contributors.
        !            17:  * 4. Neither the name of the University nor the names of its contributors
        !            18:  *    may be used to endorse or promote products derived from this software
        !            19:  *    without specific prior written permission.
        !            20:  *
        !            21:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            22:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            23:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            24:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            25:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            26:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            27:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            28:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            29:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            30:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            31:  * SUCH DAMAGE.
        !            32:  */
        !            33: 
        !            34: #include "sim.h"
        !            35: 
        !            36: #include <stdio.h>
        !            37: #include <stdlib.h>
        !            38: 
        !            39: /*
        !            40:  * random.c:
        !            41:  *
        !            42:  * An improved random number generation package.  In addition to the standard
        !            43:  * rand()/srand() like interface, this package also has a special state info
        !            44:  * interface.  The initstate() routine is called with a seed, an array of
        !            45:  * bytes, and a count of how many bytes are being passed in; this array is
        !            46:  * then initialized to contain information for random number generation with
        !            47:  * that much state information.  Good sizes for the amount of state
        !            48:  * information are 32, 64, 128, and 256 bytes.  The state can be switched by
        !            49:  * calling the setstate() routine with the same array as was initiallized
        !            50:  * with initstate().  By default, the package runs with 128 bytes of state
        !            51:  * information and generates far better random numbers than a linear
        !            52:  * congruential generator.  If the amount of state information is less than
        !            53:  * 32 bytes, a simple linear congruential R.N.G. is used.
        !            54:  *
        !            55:  * Internally, the state information is treated as an array of longs; the
        !            56:  * zeroeth element of the array is the type of R.N.G. being used (small
        !            57:  * integer); the remainder of the array is the state information for the
        !            58:  * R.N.G.  Thus, 32 bytes of state information will give 7 longs worth of
        !            59:  * state information, which will allow a degree seven polynomial.  (Note:
        !            60:  * the zeroeth word of state information also has some other information
        !            61:  * stored in it -- see setstate() for details).
        !            62:  * 
        !            63:  * The random number generation technique is a linear feedback shift register
        !            64:  * approach, employing trinomials (since there are fewer terms to sum up that
        !            65:  * way).  In this approach, the least significant bit of all the numbers in
        !            66:  * the state table will act as a linear feedback shift register, and will
        !            67:  * have period 2^deg - 1 (where deg is the degree of the polynomial being
        !            68:  * used, assuming that the polynomial is irreducible and primitive).  The
        !            69:  * higher order bits will have longer periods, since their values are also
        !            70:  * influenced by pseudo-random carries out of the lower bits.  The total
        !            71:  * period of the generator is approximately deg*(2**deg - 1); thus doubling
        !            72:  * the amount of state information has a vast influence on the period of the
        !            73:  * generator.  Note: the deg*(2**deg - 1) is an approximation only good for
        !            74:  * large deg, when the period of the shift register is the dominant factor.
        !            75:  * With deg equal to seven, the period is actually much longer than the
        !            76:  * 7*(2**7 - 1) predicted by this formula.
        !            77:  */
        !            78: 
        !            79: /*
        !            80:  * For each of the currently supported random number generators, we have a
        !            81:  * break value on the amount of state information (you need at least this
        !            82:  * many bytes of state info to support this random number generator), a degree
        !            83:  * for the polynomial (actually a trinomial) that the R.N.G. is based on, and
        !            84:  * the separation between the two lower order coefficients of the trinomial.
        !            85:  */
        !            86: #define        TYPE_0          0               /* linear congruential */
        !            87: #define        BREAK_0         8
        !            88: #define        DEG_0           0
        !            89: #define        SEP_0           0
        !            90: 
        !            91: #define        TYPE_1          1               /* x**7 + x**3 + 1 */
        !            92: #define        BREAK_1         32
        !            93: #define        DEG_1           7
        !            94: #define        SEP_1           3
        !            95: 
        !            96: #define        TYPE_2          2               /* x**15 + x + 1 */
        !            97: #define        BREAK_2         64
        !            98: #define        DEG_2           15
        !            99: #define        SEP_2           1
        !           100: 
        !           101: #define        TYPE_3          3               /* x**31 + x**3 + 1 */
        !           102: #define        BREAK_3         128
        !           103: #define        DEG_3           31
        !           104: #define        SEP_3           3
        !           105: 
        !           106: #define        TYPE_4          4               /* x**63 + x + 1 */
        !           107: #define        BREAK_4         256
        !           108: #define        DEG_4           63
        !           109: #define        SEP_4           1
        !           110: 
        !           111: /*
        !           112:  * Array versions of the above information to make code run faster --
        !           113:  * relies on fact that TYPE_i == i.
        !           114:  */
        !           115: #define        MAX_TYPES       5               /* max number of types above */
        !           116: 
        !           117: static int degrees[MAX_TYPES] =        { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
        !           118: static int seps [MAX_TYPES] =  { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
        !           119: 
        !           120: QUAD sim_random();
        !           121: void sim_srandom();
        !           122: char *sim_initstate();
        !           123: char *sim_setstate();
        !           124: 
        !           125: /*
        !           126:  * Initially, everything is set up as if from:
        !           127:  *
        !           128:  *     initstate(1, &randtbl, 128);
        !           129:  *
        !           130:  * Note that this initialization takes advantage of the fact that srandom()
        !           131:  * advances the front and rear pointers 10*rand_deg times, and hence the
        !           132:  * rear pointer which starts at 0 will also end up at zero; thus the zeroeth
        !           133:  * element of the state information, which contains info about the current
        !           134:  * position of the rear pointer is just
        !           135:  *
        !           136:  *     MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3.
        !           137:  */
        !           138: 
        !           139: static QUAD randtbl[DEG_3 + 1] = {
        !           140:        TYPE_3,
        !           141:        0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5,
        !           142:        0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
        !           143:        0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88,
        !           144:        0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
        !           145:        0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b,
        !           146:        0x27fb47b9,
        !           147: };
        !           148: 
        !           149: /*
        !           150:  * fptr and rptr are two pointers into the state info, a front and a rear
        !           151:  * pointer.  These two pointers are always rand_sep places aparts, as they
        !           152:  * cycle cyclically through the state information.  (Yes, this does mean we
        !           153:  * could get away with just one pointer, but the code for random() is more
        !           154:  * efficient this way).  The pointers are left positioned as they would be
        !           155:  * from the call
        !           156:  *
        !           157:  *     initstate(1, randtbl, 128);
        !           158:  *
        !           159:  * (The position of the rear pointer, rptr, is really 0 (as explained above
        !           160:  * in the initialization of randtbl) because the state table pointer is set
        !           161:  * to point to randtbl[1] (as explained below).
        !           162:  */
        !           163: static QUAD *fptr = &randtbl[SEP_3 + 1];
        !           164: static QUAD *rptr = &randtbl[1];
        !           165: 
        !           166: /*
        !           167:  * The following things are the pointer to the state information table, the
        !           168:  * type of the current generator, the degree of the current polynomial being
        !           169:  * used, and the separation between the two pointers.  Note that for efficiency
        !           170:  * of random(), we remember the first location of the state information, not
        !           171:  * the zeroeth.  Hence it is valid to access state[-1], which is used to
        !           172:  * store the type of the R.N.G.  Also, we remember the last location, since
        !           173:  * this is more efficient than indexing every time to find the address of
        !           174:  * the last element to see if the front and rear pointers have wrapped.
        !           175:  */
        !           176: static QUAD *state = &randtbl[1];
        !           177: static int rand_type = TYPE_3;
        !           178: static int rand_deg = DEG_3;
        !           179: static int rand_sep = SEP_3;
        !           180: static QUAD *end_ptr = &randtbl[DEG_3 + 1];
        !           181: 
        !           182: /*
        !           183:  * srandom:
        !           184:  *
        !           185:  * Initialize the random number generator based on the given seed.  If the
        !           186:  * type is the trivial no-state-information type, just remember the seed.
        !           187:  * Otherwise, initializes state[] based on the given "seed" via a linear
        !           188:  * congruential generator.  Then, the pointers are set to known locations
        !           189:  * that are exactly rand_sep places apart.  Lastly, it cycles the state
        !           190:  * information a given number of times to get rid of any initial dependencies
        !           191:  * introduced by the L.C.R.N.G.  Note that the initialization of randtbl[]
        !           192:  * for default usage relies on values produced by this routine.
        !           193:  */
        !           194: void
        !           195: sim_srandom(x)
        !           196:        unsigned int x;
        !           197: {
        !           198:        register int i, j;
        !           199: 
        !           200:        if (rand_type == TYPE_0)
        !           201:                state[0] = x;
        !           202:        else {
        !           203:                j = 1;
        !           204:                state[0] = x;
        !           205:                for (i = 1; i < rand_deg; i++)
        !           206:                        state[i] = 1103515245 * state[i - 1] + 12345;
        !           207:                fptr = &state[rand_sep];
        !           208:                rptr = &state[0];
        !           209:                for (i = 0; i < 10 * rand_deg; i++)
        !           210:                        (void)sim_random();
        !           211:        }
        !           212: }
        !           213: 
        !           214: /*
        !           215:  * initstate:
        !           216:  *
        !           217:  * Initialize the state information in the given array of n bytes for future
        !           218:  * random number generation.  Based on the number of bytes we are given, and
        !           219:  * the break values for the different R.N.G.'s, we choose the best (largest)
        !           220:  * one we can and set things up for it.  srandom() is then called to
        !           221:  * initialize the state information.
        !           222:  * 
        !           223:  * Note that on return from srandom(), we set state[-1] to be the type
        !           224:  * multiplexed with the current value of the rear pointer; this is so
        !           225:  * successive calls to initstate() won't lose this information and will be
        !           226:  * able to restart with setstate().
        !           227:  * 
        !           228:  * Note: the first thing we do is save the current state, if any, just like
        !           229:  * setstate() so that it doesn't matter when initstate is called.
        !           230:  *
        !           231:  * Returns a pointer to the old state.
        !           232:  */
        !           233: char *
        !           234: sim_initstate(seed, arg_state, n)
        !           235:        unsigned int seed;              /* seed for R.N.G. */
        !           236:        char *arg_state;                /* pointer to state array */
        !           237:        int n;                          /* # bytes of state info */
        !           238: {
        !           239:        register char *ostate = (char *)(&state[-1]);
        !           240: 
        !           241:        if (rand_type == TYPE_0)
        !           242:                state[-1] = rand_type;
        !           243:        else
        !           244:                state[-1] = MAX_TYPES * (rptr - state) + rand_type;
        !           245:        if (n < BREAK_0) {
        !           246:                (void)fprintf(stderr,
        !           247:                    "random: not enough state (%d bytes); ignored.\n", n);
        !           248:                return(0);
        !           249:        }
        !           250:        if (n < BREAK_1) {
        !           251:                rand_type = TYPE_0;
        !           252:                rand_deg = DEG_0;
        !           253:                rand_sep = SEP_0;
        !           254:        } else if (n < BREAK_2) {
        !           255:                rand_type = TYPE_1;
        !           256:                rand_deg = DEG_1;
        !           257:                rand_sep = SEP_1;
        !           258:        } else if (n < BREAK_3) {
        !           259:                rand_type = TYPE_2;
        !           260:                rand_deg = DEG_2;
        !           261:                rand_sep = SEP_2;
        !           262:        } else if (n < BREAK_4) {
        !           263:                rand_type = TYPE_3;
        !           264:                rand_deg = DEG_3;
        !           265:                rand_sep = SEP_3;
        !           266:        } else {
        !           267:                rand_type = TYPE_4;
        !           268:                rand_deg = DEG_4;
        !           269:                rand_sep = SEP_4;
        !           270:        }
        !           271:        state = &(((QUAD *)arg_state)[1]);      /* first location */
        !           272:        end_ptr = &state[rand_deg];     /* must set end_ptr before srandom */
        !           273:        sim_srandom(seed);
        !           274:        if (rand_type == TYPE_0)
        !           275:                state[-1] = rand_type;
        !           276:        else
        !           277:                state[-1] = MAX_TYPES*(rptr - state) + rand_type;
        !           278:        return(ostate);
        !           279: }
        !           280: 
        !           281: /*
        !           282:  * setstate:
        !           283:  *
        !           284:  * Restore the state from the given state array.
        !           285:  *
        !           286:  * Note: it is important that we also remember the locations of the pointers
        !           287:  * in the current state information, and restore the locations of the pointers
        !           288:  * from the old state information.  This is done by multiplexing the pointer
        !           289:  * location into the zeroeth word of the state information.
        !           290:  *
        !           291:  * Note that due to the order in which things are done, it is OK to call
        !           292:  * setstate() with the same state as the current state.
        !           293:  *
        !           294:  * Returns a pointer to the old state information.
        !           295:  */
        !           296: char *
        !           297: sim_setstate(arg_state)
        !           298:        char *arg_state;
        !           299: {
        !           300:        register QUAD *new_state = (QUAD *)arg_state;
        !           301:        register int type = new_state[0] % MAX_TYPES;
        !           302:        register int rear = new_state[0] / MAX_TYPES;
        !           303:        char *ostate = (char *)(&state[-1]);
        !           304: 
        !           305:        if (rand_type == TYPE_0)
        !           306:                state[-1] = rand_type;
        !           307:        else
        !           308:                state[-1] = MAX_TYPES * (rptr - state) + rand_type;
        !           309:        switch(type) {
        !           310:        case TYPE_0:
        !           311:        case TYPE_1:
        !           312:        case TYPE_2:
        !           313:        case TYPE_3:
        !           314:        case TYPE_4:
        !           315:                rand_type = type;
        !           316:                rand_deg = degrees[type];
        !           317:                rand_sep = seps[type];
        !           318:                break;
        !           319:        default:
        !           320:                (void)fprintf(stderr,
        !           321:                    "random: state info corrupted; not changed.\n");
        !           322:        }
        !           323:        state = &new_state[1];
        !           324:        if (rand_type != TYPE_0) {
        !           325:                rptr = &state[rear];
        !           326:                fptr = &state[(rear + rand_sep) % rand_deg];
        !           327:        }
        !           328:        end_ptr = &state[rand_deg];             /* set end_ptr too */
        !           329:        return(ostate);
        !           330: }
        !           331: 
        !           332: /*
        !           333:  * random:
        !           334:  *
        !           335:  * If we are using the trivial TYPE_0 R.N.G., just do the old linear
        !           336:  * congruential bit.  Otherwise, we do our fancy trinomial stuff, which is
        !           337:  * the same in all the other cases due to all the global variables that have
        !           338:  * been set up.  The basic operation is to add the number at the rear pointer
        !           339:  * into the one at the front pointer.  Then both pointers are advanced to
        !           340:  * the next location cyclically in the table.  The value returned is the sum
        !           341:  * generated, reduced to 31 bits by throwing away the "least random" low bit.
        !           342:  *
        !           343:  * Note: the code takes advantage of the fact that both the front and
        !           344:  * rear pointers can't wrap on the same call by not testing the rear
        !           345:  * pointer if the front one has wrapped.
        !           346:  *
        !           347:  * Returns a 31-bit random number.
        !           348:  */
        !           349: QUAD
        !           350: sim_random()
        !           351: {
        !           352:        QUAD i;
        !           353: 
        !           354:        if (rand_type == TYPE_0)
        !           355:                i = state[0] = (state[0] * 1103515245 + 12345) & 0x7fffffff;
        !           356:        else {
        !           357:                *fptr += *rptr;
        !           358:                i = (*fptr >> 1) & 0x7fffffff;  /* chucking least random bit */
        !           359:                if (++fptr >= end_ptr) {
        !           360:                        fptr = state;
        !           361:                        ++rptr;
        !           362:                } else if (++rptr >= end_ptr)
        !           363:                        rptr = state;
        !           364:        }
        !           365:        return(i);
        !           366: }

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.