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Diffstat (limited to 'contrib/awk/random.c')
| -rw-r--r-- | contrib/awk/random.c | 379 |
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diff --git a/contrib/awk/random.c b/contrib/awk/random.c new file mode 100644 index 0000000..002b226 --- /dev/null +++ b/contrib/awk/random.c @@ -0,0 +1,379 @@ +/* + * Copyright (c) 1983 Regents of the University of California. + * All rights reserved. + * + * Redistribution and use in source and binary forms are permitted + * provided that the above copyright notice and this paragraph are + * duplicated in all such forms and that any documentation, + * advertising materials, and other materials related to such + * distribution and use acknowledge that the software was developed + * by the University of California, Berkeley. The name of the + * University may not 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 MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. + */ + +#if defined(LIBC_SCCS) && !defined(lint) +static char sccsid[] = "@(#)random.c 5.5 (Berkeley) 7/6/88"; +#endif /* LIBC_SCCS and not lint */ + +#include <stdio.h> +#include "random.h" /* GAWK ADDITION */ + +/* + * 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 +#ifdef _CRAY +#define DEG_3_P1 32 /* bug - do addition here */ +#define SEP_3_P1 4 /* *_3 + 1 = _3_P1 */ +#endif + +#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). + */ + +#ifdef _CRAY +static long *fptr = &randtbl[ SEP_3_P1 ]; +#else +static long *fptr = &randtbl[ SEP_3 + 1 ]; +#endif +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; + +#ifdef _CRAY +static long *end_ptr = &randtbl[ DEG_3_P1 ]; +#else +static long *end_ptr = &randtbl[ DEG_3 + 1 ]; +#endif + + + +/* + * 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 x; +{ + register int i, j; + long random(); + + 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(); + } +} + + + +/* + * 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 ) + + unsigned 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_1 ) { + if( n < BREAK_0 ) { + fprintf( stderr, "initstate: not enough state (%d bytes) with which to do jack; ignored.\n", n ); + 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( 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: + fprintf( stderr, "setstate: state info has been munged; 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 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() +{ + 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 ); +} |
