#include <stdlib.h>
#include "hash.h"

#define HASHSIZE 101

static struct nlist *hashtab[HASHSIZE]; /* pointer table */

/* hash: form hash value from string */
unsigned hash(char *s) {
     unsigned hashval;

     for (hashval = 0; *s != '\0'; s++)
	  hashval = *s + 31 * hashval;
     return hashval % HASHSIZE;
}

/* lookup: look for s in hashtab */
struct nlist *lookup(char *s) {
     struct nlist *np;

     for (np = hashtab[hash(s)]; np != NULL; np = np->next)
	  if (strcmp(s, np->name) == 0)
	       return np;
     return NULL;
}

/* strdup: make a duplicate of s */
char *strdup(char *s) {
     char *p;

     p = (char *) malloc(strlen(s)+1);
     if (p != NULL)
	  strcpy(p, s);
     return p;
}

/* 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(struct nlist));
	  if (np == NULL || (np->name = strdup(name)) == NULL)
	       return NULL;
	  hashval = hash(name);
	  np->next = hashtab[hashval];
	  hashtab[hashval] = np;
     } else
	  free((void *) np->defn);
     if ((np->defn = strdup(defn)) == NULL)
	  return NULL;
     return np;
}

/* undef: remove name and its defn from hashtab */
int undef(char *name) {
     struct nlist *np, *fp;
     unsigned hashval;

     if ((np = lookup(name)) == NULL)
	  return -1;
     hashval = hash(name);
     fp = hashtab[hashval];
     if (fp == np) /* name to remove is at beginning of list */
	  hashtab[hashval] = fp->next;
     else {
	  while (fp->next != np)
	       fp = fp->next;
	  fp->next = np->next; /* skip out this mofo */
     }
     free((void *) np->name);
     free((void *) np->defn);
     free((void *) np);

     return 0;
}