usr/src/cmd/spell/spell.h

#include <stdio.h>
#include <ctype.h>

#ifndef unix
#define SHIFT   5
#define TABSIZE (int)(400000/(1<<SHIFT))
int     *tab;   /*honeywell loader deficiency*/
#else
#define Tolower(c)      (isupper(c)?tolower(c):c) /* ugh!!! */
#define SHIFT   4
#define TABSIZE 25000   /*(int)(400000/(1<<shift))--pdp11 compiler deficiency*/
short   tab[TABSIZE];
#endif
long    p[] = {
        399871,
        399887,
        399899,
        399911,
        399913,
        399937,
        399941,
        399953,
        399979,
        399983,
        399989,
};
#define NP      (sizeof(p)/sizeof(p[0]))
#define NW      30

/*
* Hash table for spelling checker has n bits.
* Each word w is hashed by k different (modular) hash functions, hi.
* The bits hi(w), i=1..k, are set for words in the dictionary.
* Assuming independence, the probability that no word of a d-word
* dictionary sets a particular bit is given by the Poisson formula
* P = exp(-y)*y**0/0!, where y=d*k/n.
* The probability that a random string is recognized as a word is then
* (1-P)**k.  For given n and d this is minimum when y=log(2), P=1/2,
* whence one finds, for example, that a 25000-word dictionary in a
* 400000-bit table works best with k=11.
*/

long    pow2[NP][NW];

prime(argc, argv) register char **argv;
{
        int i, j;
        long h;
        register long *lp;

#ifndef unix
        if ((tab = (int *)calloc(sizeof(*tab), TABSIZE)) == NULL)
                return(0);
#endif
        if (argc > 1) {
                FILE *f;
                if ((f = fopen(argv[1], "ri")) == NULL)
                        return(0);
                if (fread((char *)tab, sizeof(*tab), TABSIZE, f) != TABSIZE)
                        return(0);
                fclose(f);
        }
        for (i=0; i<NP; i++) {
                h = *(lp = pow2[i]) = 1<<14;
                for (j=1; j<NW; j++)
                        h = *++lp = (h<<7) % p[i];
        }
        return(1);
}

#define get(h)  (tab[h>>SHIFT]&(1<<((int)h&((1<<SHIFT)-1))))
#define set(h)  tab[h>>SHIFT] |= 1<<((int)h&((1<<SHIFT)-1))