🚀 go-pugleaf

In article <C1H7tG.7At.2@cs.cmu.edu> tgl+@cs.cmu.edu (Tom Lane) writes:
>What I need is a very very fast random number generator; it does NOT need to
>be cryptographically strong.


My favorite fast generator:

#define N_RANS  (65)
#define PRIMERADIX (1073741789)

long int  ran_arr[ N_RANS ] ;
int  ran_rdr = 0 ;


/* --------------------------------------------------------------------- */
/* raw_ran -- compute the next raw random number.			 */
/*	This routine uses only addition.				 */
/* --------------------------------------------------------------------- */

long int raw_ran()
{
    int  nrdr ;
    long int  v ;

    nrdr = ran_rdr + 1 ;
    if ( N_RANS <= nrdr ) nrdr = 0 ;
    v = ran_arr[ ran_rdr ] + ran_arr[ nrdr ] ;
    if ( v >= PRIMERADIX ) v -= PRIMERADIX ;	/* poor man's MOD function */
    ran_arr[ ran_rdr ] = v ;
    ran_rdr = nrdr ;
    return ( v ) ;
}   /* end of raw_ran */

/* --------------------------------------------------------------------- */
/* ran_radix --- return a random integer, radix r.			 */
/* --------------------------------------------------------------------- */

long int ran_radix( r )
long int r ;
{
    return ( raw_ran() % r ) ;
}   /* end of ran_radix */


You should fill the ran_arr with true random numbers, but I sometimes
use a typed string and then ask for (N_RANS)**2 raw_ran() values
before using a real one.

--Carl

-- 
-- <<Disclaimer: All opinions expressed are my own, of course.>>
-- Carl Ellison						cme@sw.stratus.com
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