wlgol/hashtable.c

// implementation of a hashtable

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "hashtable.h"



// entry in the hashtable
struct entry
{
	const char *key;
  void *value;
	struct entry *next;
};

struct htobj
{
	int size;
	struct entry **table;
};

struct item {
	struct entry *prev, *found;
	int index;
};

static unsigned int hash(const char *key)
{
	unsigned int hash = 0;

	while (*key)
	{
		hash = (hash << 5) - hash + *key++;
	}
	return hash;
}

hashtable hashtable_new(int size)
{
	// Allocate memory for the hashtable
	hashtable h = malloc(sizeof(struct htobj));

	// Set the size of the hashtable
	h->size = size;

	// Allocate memory for the entry pointers
	h->table = calloc(size, sizeof(struct entry *));

	// Return the newly created hashtable
	return h;
}


struct item hashtable_lookup_item(hashtable h, const char *key)
{
	struct item result = {
		.found = NULL,
		.index = -1,
	};

	int index = hash(key) % h->size;
	struct entry *e = h->table[index];
	struct entry *prev = NULL;

	while (e != NULL) {
		if (strcmp(e->key, key) == 0) {
			result.index = index;
			result.found = e;
			result.prev = prev;
			return result;
		}
		prev = e;
		e = e->next;
	}
	return result; // empty in this case
}

void *hashtable_set(hashtable h, const char *key, void *value)
{

	struct item item = hashtable_lookup_item(h, key);
	// not found - insert new
	if (item.found == NULL) {
		int index = hash(key) % h->size;

		// Create a new entry
		struct entry *e = malloc(sizeof(struct entry));
		e->key = strdup(key); // key is the copy
		e->value = value;
		e->next = NULL;

		// Insert the entry at the beginning of the linked list
		e->next = h->table[index];
		h->table[index] = e;
		return NULL;
	}
	// found replace the value
	void *old_value = item.found->value;
	item.found-> value = value;

	return old_value;
}

void *hashtable_lookup(hashtable h, const char *key)
{
	struct item item = hashtable_lookup_item(h, key);
	if (item.found != NULL) {
		return item.found->value;
	}
	return NULL;
}

void *hashtable_remove(hashtable h, const char *key)
{
	struct item item = hashtable_lookup_item(h, key);
	if (item.found == NULL) {
		return NULL;
	}
	// found, so detete it
  if (item.prev != NULL) {
  	item.prev->next = item.found->next;
  } else {
  	h->table[item.index] = item.found->next;
  }
  // free unused memory
  void *value = item.found->value; // remember value
  free((void*) item.found->key); // free key
  free((void*) item.found); // free entry

  return value;
}

void hashtable_destroy_bucket(hashtable h, int i)
{
	struct entry *e = h->table[i];
	while (e != NULL) {
		free((void*)e->key);
		e = e->next;
		free(e);
	}
}

void hashtable_destroy(hashtable h)
{
	if (h==NULL) return;
	for (int i = 0; i < h->size; i++) {
		hashtable_destroy_bucket(h, i);
	}
	free (h->table);
	free(h);
}

ht_iterator hashtable_iter(hashtable h)
{
	ht_iterator iter = {
		.h = h,
		.index = -1,
	  .entry = NULL,
	};

	return iter;
}

bool ht_iter_next(ht_iterator *iter)
{
	if (iter == NULL) {
		return false;
	}
	hashtable h = iter->h;

	while(true)	{
		if (iter->index >= h->size) {
			return false;
		}
		if (iter->entry == NULL) {
			iter->index++;
			iter->entry = h->table[iter->index];
		} else {
			iter->entry = iter->entry->next;
		}
		if (iter->entry != NULL) return true;
	}

}

const char *ht_iter_key(ht_iterator *iter)
{
	if (iter == NULL || iter->entry == NULL) return NULL;
	return iter->entry->key;
}

void *ht_iter_value(ht_iterator *iter)
{
	if (iter == NULL || iter->entry == NULL) return NULL;
	return iter->entry->value;
}