struct nlist *lookup(char *);
char *strdup(char *);

/* install:  put (name, defn) in hashtab */
struct nlist *install(char *name, char *defn)
{
    struct nlist *np;
    unsigned hashval;

    if ((np = lookup(name)) == NULL) {  /* not found */
        np = (struct nlist *) malloc(sizeof(*np));
        if (np == NULL || (np->name = strdup(name)) == NULL)
            return NULL;
        hashval = hash(name);
        np->next = hashtab[hashval];
        hashtab[hashval] = np;
    } else      /* already there */
        free((void *) np->defn);  /* free previous defn */
    if ((np->defn = strdup(defn)) == NULL)
        return NULL;
    return np;
}