4.3BSD - /usr/src/games/fortune/rnd.c

   1: /*
   2:  * code for when the good (berkeley) random number generator is around
   3:  */
   4: 
   5: rnd(num)
   6: {
   7:     return (random() % num);
   8: }
   9: 
  10: srnd(num)
  11: {
  12:     srandom(num);
  13: }
  14: 
  15: #ifdef  NO_RANDOM
  16: 
  17: #ifndef lint
  18: static char sccsid[] = "@(#)random.c	4.2	(Berkeley)	83/01/02";
  19: #endif
  20: 
  21: #include    <stdio.h>
  22: 
  23: /*
  24:  * random.c:
  25:  * An improved random number generation package.  In addition to the standard
  26:  * rand()/srand() like interface, this package also has a special state info
  27:  * interface.  The initstate() routine is called with a seed, an array of
  28:  * bytes, and a count of how many bytes are being passed in; this array is then
  29:  * initialized to contain information for random number generation with that
  30:  * much state information.  Good sizes for the amount of state information are
  31:  * 32, 64, 128, and 256 bytes.  The state can be switched by calling the
  32:  * setstate() routine with the same array as was initiallized with initstate().
  33:  * By default, the package runs with 128 bytes of state information and
  34:  * generates far better random numbers than a linear congruential generator.
  35:  * If the amount of state information is less than 32 bytes, a simple linear
  36:  * congruential R.N.G. is used.
  37:  * Internally, the state information is treated as an array of longs; the
  38:  * zeroeth element of the array is the type of R.N.G. being used (small
  39:  * integer); the remainder of the array is the state information for the
  40:  * R.N.G.  Thus, 32 bytes of state information will give 7 longs worth of
  41:  * state information, which will allow a degree seven polynomial.  (Note: the
  42:  * zeroeth word of state information also has some other information stored
  43:  * in it -- see setstate() for details).
  44:  * The random number generation technique is a linear feedback shift register
  45:  * approach, employing trinomials (since there are fewer terms to sum up that
  46:  * way).  In this approach, the least significant bit of all the numbers in
  47:  * the state table will act as a linear feedback shift register, and will have
  48:  * period 2^deg - 1 (where deg is the degree of the polynomial being used,
  49:  * assuming that the polynomial is irreducible and primitive).  The higher
  50:  * order bits will have longer periods, since their values are also influenced
  51:  * by pseudo-random carries out of the lower bits.  The total period of the
  52:  * generator is approximately deg*(2**deg - 1); thus doubling the amount of
  53:  * state information has a vast influence on the period of the generator.
  54:  * Note: the deg*(2**deg - 1) is an approximation only good for large deg,
  55:  * when the period of the shift register is the dominant factor.  With deg
  56:  * equal to seven, the period is actually much longer than the 7*(2**7 - 1)
  57:  * predicted by this formula.
  58:  */
  59: 
  60: 
  61: 
  62: /*
  63:  * For each of the currently supported random number generators, we have a
  64:  * break value on the amount of state information (you need at least this
  65:  * many bytes of state info to support this random number generator), a degree
  66:  * for the polynomial (actually a trinomial) that the R.N.G. is based on, and
  67:  * the separation between the two lower order coefficients of the trinomial.
  68:  */
  69: 
  70: #define     TYPE_0      0       /* linear congruential */
  71: #define     BREAK_0     8
  72: #define     DEG_0       0
  73: #define     SEP_0       0
  74: 
  75: #define     TYPE_1      1       /* x**7 + x**3 + 1 */
  76: #define     BREAK_1     32
  77: #define     DEG_1       7
  78: #define     SEP_1       3
  79: 
  80: #define     TYPE_2      2       /* x**15 + x + 1 */
  81: #define     BREAK_2     64
  82: #define     DEG_2       15
  83: #define     SEP_2       1
  84: 
  85: #define     TYPE_3      3       /* x**31 + x**3 + 1 */
  86: #define     BREAK_3     128
  87: #define     DEG_3       31
  88: #define     SEP_3       3
  89: 
  90: #define     TYPE_4      4       /* x**63 + x + 1 */
  91: #define     BREAK_4     256
  92: #define     DEG_4       63
  93: #define     SEP_4       1
  94: 
  95: 
  96: /*
  97:  * Array versions of the above information to make code run faster -- relies
  98:  * on fact that TYPE_i == i.
  99:  */
 100: 
 101: #define     MAX_TYPES   5       /* max number of types above */
 102: 
 103: static  int     degrees[ MAX_TYPES ]    = { DEG_0, DEG_1, DEG_2,
 104:                                 DEG_3, DEG_4 };
 105: 
 106: static  int     seps[ MAX_TYPES ]   = { SEP_0, SEP_1, SEP_2,
 107:                                 SEP_3, SEP_4 };
 108: 
 109: 
 110: 
 111: /*
 112:  * Initially, everything is set up as if from :
 113:  *		initstate( 1, &randtbl, 128 );
 114:  * Note that this initialization takes advantage of the fact that srandom()
 115:  * advances the front and rear pointers 10*rand_deg times, and hence the
 116:  * rear pointer which starts at 0 will also end up at zero; thus the zeroeth
 117:  * element of the state information, which contains info about the current
 118:  * position of the rear pointer is just
 119:  *	MAX_TYPES*(rptr - state) + TYPE_3 == TYPE_3.
 120:  */
 121: 
 122: static  long        randtbl[ DEG_3 + 1 ]    = { TYPE_3,
 123:                 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342,
 124:                 0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb,
 125:                 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
 126:                 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86,
 127:                 0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7,
 128:                 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
 129:                 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b,
 130:                     0xf5ad9d0e, 0x8999220b, 0x27fb47b9 };
 131: 
 132: /*
 133:  * fptr and rptr are two pointers into the state info, a front and a rear
 134:  * pointer.  These two pointers are always rand_sep places aparts, as they cycle
 135:  * cyclically through the state information.  (Yes, this does mean we could get
 136:  * away with just one pointer, but the code for random() is more efficient this
 137:  * way).  The pointers are left positioned as they would be from the call
 138:  *			initstate( 1, randtbl, 128 )
 139:  * (The position of the rear pointer, rptr, is really 0 (as explained above
 140:  * in the initialization of randtbl) because the state table pointer is set
 141:  * to point to randtbl[1] (as explained below).
 142:  */
 143: 
 144: static  long        *fptr           = &randtbl[ SEP_3 + 1 ];
 145: static  long        *rptr           = &randtbl[ 1 ];
 146: 
 147: 
 148: 
 149: /*
 150:  * The following things are the pointer to the state information table,
 151:  * the type of the current generator, the degree of the current polynomial
 152:  * being used, and the separation between the two pointers.
 153:  * Note that for efficiency of random(), we remember the first location of
 154:  * the state information, not the zeroeth.  Hence it is valid to access
 155:  * state[-1], which is used to store the type of the R.N.G.
 156:  * Also, we remember the last location, since this is more efficient than
 157:  * indexing every time to find the address of the last element to see if
 158:  * the front and rear pointers have wrapped.
 159:  */
 160: 
 161: static  long        *state          = &randtbl[ 1 ];
 162: 
 163: static  int     rand_type       = TYPE_3;
 164: static  int     rand_deg        = DEG_3;
 165: static  int     rand_sep        = SEP_3;
 166: 
 167: static  long        *end_ptr        = &randtbl[ DEG_3 + 1 ];
 168: 
 169: 
 170: 
 171: /*
 172:  * srandom:
 173:  * Initialize the random number generator based on the given seed.  If the
 174:  * type is the trivial no-state-information type, just remember the seed.
 175:  * Otherwise, initializes state[] based on the given "seed" via a linear
 176:  * congruential generator.  Then, the pointers are set to known locations
 177:  * that are exactly rand_sep places apart.  Lastly, it cycles the state
 178:  * information a given number of times to get rid of any initial dependencies
 179:  * introduced by the L.C.R.N.G.
 180:  * Note that the initialization of randtbl[] for default usage relies on
 181:  * values produced by this routine.
 182:  */
 183: 
 184: srandom( x )
 185: 
 186:     unsigned        x;
 187: {
 188:         register  int       i, j;
 189: 
 190:     if(  rand_type  ==  TYPE_0  )  {
 191:         state[ 0 ] = x;
 192:     }
 193:     else  {
 194:         j = 1;
 195:         state[ 0 ] = x;
 196:         for( i = 1; i < rand_deg; i++ )  {
 197:         state[i] = 1103515245*state[i - 1] + 12345;
 198:         }
 199:         fptr = &state[ rand_sep ];
 200:         rptr = &state[ 0 ];
 201:         for( i = 0; i < 10*rand_deg; i++ )  random();
 202:     }
 203: }
 204: 
 205: 
 206: 
 207: /*
 208:  * initstate:
 209:  * Initialize the state information in the given array of n bytes for
 210:  * future random number generation.  Based on the number of bytes we
 211:  * are given, and the break values for the different R.N.G.'s, we choose
 212:  * the best (largest) one we can and set things up for it.  srandom() is
 213:  * then called to initialize the state information.
 214:  * Note that on return from srandom(), we set state[-1] to be the type
 215:  * multiplexed with the current value of the rear pointer; this is so
 216:  * successive calls to initstate() won't lose this information and will
 217:  * be able to restart with setstate().
 218:  * Note: the first thing we do is save the current state, if any, just like
 219:  * setstate() so that it doesn't matter when initstate is called.
 220:  * Returns a pointer to the old state.
 221:  */
 222: 
 223: char  *
 224: initstate( seed, arg_state, n )
 225: 
 226:     unsigned        seed;           /* seed for R. N. G. */
 227:     char        *arg_state;     /* pointer to state array */
 228:     int         n;          /* # bytes of state info */
 229: {
 230:     register  char      *ostate     = (char *)( &state[ -1 ] );
 231: 
 232:     if(  rand_type  ==  TYPE_0  )  state[ -1 ] = rand_type;
 233:     else  state[ -1 ] = MAX_TYPES*(rptr - state) + rand_type;
 234:     if(  n  <  BREAK_1  )  {
 235:         if(  n  <  BREAK_0  )  {
 236:         fprintf( stderr, "initstate: not enough state (%d bytes) with which to do jack; ignored.\n" );
 237:         return;
 238:         }
 239:         rand_type = TYPE_0;
 240:         rand_deg = DEG_0;
 241:         rand_sep = SEP_0;
 242:     }
 243:     else  {
 244:         if(  n  <  BREAK_2  )  {
 245:         rand_type = TYPE_1;
 246:         rand_deg = DEG_1;
 247:         rand_sep = SEP_1;
 248:         }
 249:         else  {
 250:         if(  n  <  BREAK_3  )  {
 251:             rand_type = TYPE_2;
 252:             rand_deg = DEG_2;
 253:             rand_sep = SEP_2;
 254:         }
 255:         else  {
 256:             if(  n  <  BREAK_4  )  {
 257:             rand_type = TYPE_3;
 258:             rand_deg = DEG_3;
 259:             rand_sep = SEP_3;
 260:             }
 261:             else  {
 262:             rand_type = TYPE_4;
 263:             rand_deg = DEG_4;
 264:             rand_sep = SEP_4;
 265:             }
 266:         }
 267:         }
 268:     }
 269:     state = &(  ( (long *)arg_state )[1]  );    /* first location */
 270:     end_ptr = &state[ rand_deg ];   /* must set end_ptr before srandom */
 271:     srandom( seed );
 272:     if(  rand_type  ==  TYPE_0  )  state[ -1 ] = rand_type;
 273:     else  state[ -1 ] = MAX_TYPES*(rptr - state) + rand_type;
 274:     return( ostate );
 275: }
 276: 
 277: 
 278: 
 279: /*
 280:  * setstate:
 281:  * Restore the state from the given state array.
 282:  * Note: it is important that we also remember the locations of the pointers
 283:  * in the current state information, and restore the locations of the pointers
 284:  * from the old state information.  This is done by multiplexing the pointer
 285:  * location into the zeroeth word of the state information.
 286:  * Note that due to the order in which things are done, it is OK to call
 287:  * setstate() with the same state as the current state.
 288:  * Returns a pointer to the old state information.
 289:  */
 290: 
 291: char  *
 292: setstate( arg_state )
 293: 
 294:     char        *arg_state;
 295: {
 296:     register  long      *new_state  = (long *)arg_state;
 297:     register  int       type        = new_state[0]%MAX_TYPES;
 298:     register  int       rear        = new_state[0]/MAX_TYPES;
 299:     char            *ostate     = (char *)( &state[ -1 ] );
 300: 
 301:     if(  rand_type  ==  TYPE_0  )  state[ -1 ] = rand_type;
 302:     else  state[ -1 ] = MAX_TYPES*(rptr - state) + rand_type;
 303:     switch(  type  )  {
 304:         case  TYPE_0:
 305:         case  TYPE_1:
 306:         case  TYPE_2:
 307:         case  TYPE_3:
 308:         case  TYPE_4:
 309:         rand_type = type;
 310:         rand_deg = degrees[ type ];
 311:         rand_sep = seps[ type ];
 312:         break;
 313: 
 314:         default:
 315:         fprintf( stderr, "setstate: state info has been munged; not changed.\n" );
 316:     }
 317:     state = &new_state[ 1 ];
 318:     if(  rand_type  !=  TYPE_0  )  {
 319:         rptr = &state[ rear ];
 320:         fptr = &state[ (rear + rand_sep)%rand_deg ];
 321:     }
 322:     end_ptr = &state[ rand_deg ];       /* set end_ptr too */
 323:     return( ostate );
 324: }
 325: 
 326: 
 327: 
 328: /*
 329:  * random:
 330:  * If we are using the trivial TYPE_0 R.N.G., just do the old linear
 331:  * congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
 332:  * same in all ther other cases due to all the global variables that have been
 333:  * set up.  The basic operation is to add the number at the rear pointer into
 334:  * the one at the front pointer.  Then both pointers are advanced to the next
 335:  * location cyclically in the table.  The value returned is the sum generated,
 336:  * reduced to 31 bits by throwing away the "least random" low bit.
 337:  * Note: the code takes advantage of the fact that both the front and
 338:  * rear pointers can't wrap on the same call by not testing the rear
 339:  * pointer if the front one has wrapped.
 340:  * Returns a 31-bit random number.
 341:  */
 342: 
 343: long
 344: random()
 345: {
 346:     long        i;
 347: 
 348:     if(  rand_type  ==  TYPE_0  )  {
 349:         i = state[0] = ( state[0]*1103515245 + 12345 )&0x7fffffff;
 350:     }
 351:     else  {
 352:         *fptr += *rptr;
 353:         i = (*fptr >> 1)&0x7fffffff;    /* chucking least random bit */
 354:         if(  ++fptr  >=  end_ptr  )  {
 355:         fptr = state;
 356:         ++rptr;
 357:         }
 358:         else  {
 359:         if(  ++rptr  >=  end_ptr  )  rptr = state;
 360:         }
 361:     }
 362:     return( i );
 363: }
 364: 
 365: #endif	NO_RANDOM

Defined functions

Defined variables

Defined macros