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/* p 144 - 147 K&R */
/* C:\JPD\AStyle.exe --style=vtk --indent=spaces=2 --pad-oper --pad-comma --align-pointer=name --add-brackets --indent-switches --delete-empty-lines */
/* hash : form hash value from string s */
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#define HASHSIZE 201
static struct nlist *hashtab[HASHSIZE] ; /* pointer table */
struct nlist *lookup (char *s);
struct nlist *install (char *name, char *defn);
unsigned hash (char *s);
char *strduup(char *s);
int i = 0;
unsigned char stat[100];
struct nlist
{
struct nlist *next; /* next entry in chain */
char *name; /* defined name */
char *defn; /* replacement text */
};
/* make a duplicate of s */
char *strduup(char *s)
{
char *p;
p = (char *) malloc ((strlen(s)+1)); /* + 1 for '\0' */
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)
{
np = (struct nlist *) malloc(sizeof(*np)); /* not found */
if (np == NULL || (np->name = strduup(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 = strduup(defn)) == NULL)
return NULL;
printf("defn= %p name = %p", np->defn, np->name);
return np;
}
/* 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; /* found */
return NULL; /* not found */
}
int main(void)
{
char unhello [] = "Hello, world.";
int j;
install (unhello, (char *)hash ("Hello, world."));
hash ("hello, world.");
hash ("Helo, world.");
hash ("Hella, world.");
hash ("Hello, World.");
hash ("Hello, WOrld.");
hash ("Hello, worldd.");
hash ("Hello, wfrld.");
hash ("Hello, worf.");
hash ("Hlo, world.");
hash ("Hello, world.");
printf("\n\nstat = ");
for (j =0;j<i ;j++ )
{
printf("\t%d", stat[j]);
}
return 0;
}
unsigned hash (char *s)
{
unsigned hashval;
/* printf("\nhashval = %u\n", hashval); */
for (hashval = 0; *s != '\0' ; s++ )
{
hashval += *s + (31 * hashval);
printf("\n*s=%u + 31 * hashval = %u\t\t\t s = %s\n", *s, hashval, s );
}
stat[i] = (hashval % HASHSIZE);
i++;
printf("\n\n\t\ti = %d\t\t\tmodulo = %d\n", i, stat[i-1]);
return hashval % HASHSIZE;
}
int undef(char * name) {
struct nlist * np1, * np2;
if ((np1 = lookup(name)) == NULL) /* name not found */
return 1;
for ( np1 = np2 = hashtab[hash(name)]; np1 != NULL;
np2 = np1, np1 = np1->next ) {
if ( strcmp(name, np1->name) == 0 ) { /* name found */
/* Remove node from list */
if ( np1 == np2 )
hashtab[hash(name)] = np1->next;
else
np2->next = np1->next;
/* Free memory */
free(np1->name);
free(np1->defn);
free(np1);
return 0;
}
}
return 1; /* name not found */
} |
