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| /* Copyright (C) 1995 DJ Delorie, see COPYING.DJ for details */ |
| /* This is file RANDOM.C */ |
| /* This file may have been modified by DJ Delorie (Jan 1995). If so, |
| ** these modifications are Coyright (C) 1993 DJ Delorie, 24 Kirsten Ave, |
| ** Rochester NH, 03867-2954, USA. |
| */ |
| |
| /* |
| * Copyright (c) 1983 Regents of the University of California. |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms are permitted |
| * provided that: (1) source distributions retain this entire copyright |
| * notice and comment, and (2) distributions including binaries display |
| * the following acknowledgement: ``This product includes software |
| * developed by the University of California, Berkeley and its contributors'' |
| * in the documentation or other materials provided with the distribution |
| * and in all advertising materials mentioning features or use of this |
| * software. 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 ``AS IS'' AND WITHOUT ANY EXPRESS OR |
| * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED |
| * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. |
| */ |
| |
| #include <stdlib.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 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 unsigned long randtbl[DEG_3 + 1] = { TYPE_3, |
| 0x9a319039U, 0x32d9c024U, 0x9b663182U, 0x5da1f342U, |
| 0xde3b81e0U, 0xdf0a6fb5U, 0xf103bc02U, 0x48f340fbU, |
| 0x7449e56bU, 0xbeb1dbb0U, 0xab5c5918U, 0x946554fdU, |
| 0x8c2e680fU, 0xeb3d799fU, 0xb11ee0b7U, 0x2d436b86U, |
| 0xda672e2aU, 0x1588ca88U, 0xe369735dU, 0x904f35f7U, |
| 0xd7158fd6U, 0x6fa6f051U, 0x616e6b96U, 0xac94efdcU, |
| 0x36413f93U, 0xc622c298U, 0xf5a42ab8U, 0x8a88d77bU, |
| 0xf5ad9d0eU, 0x8999220bU, 0x27fb47b9U }; |
| |
| /* |
| * 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. |
| */ |
| |
| int |
| srandom(int x) |
| { |
| 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++ ) |
| random(); |
| } |
| return 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 (unsigned seed, char *arg_state, int n) |
| { |
| 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_1) |
| { |
| if (n < BREAK_0) |
| return 0; |
| 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(char *arg_state) |
| { |
| long *new_state = (long *)arg_state; |
| int type = new_state[0]%MAX_TYPES; |
| 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; |
| } |
| 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 ther 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(void) |
| { |
| 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; |
| } |
| Property changes: |
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| Added: svn:executable |
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| \ No newline at end of property |
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