libstrophe-gh/src/hash.c

/* hash.c
** strophe XMPP client library -- hash table implementation
**
** Copyright (C) 2005-2009 Collecta, Inc.
**
**  This software is provided AS-IS with no warranty, either express
**  or implied.
**
**  This program is dual licensed under the MIT and GPLv3 licenses.
*/

/** @file
 *  Hash tables.
 */

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

#include "strophe.h"
#include "common.h"
#include "hash.h"

/* private types */
typedef struct _hashentry_t hashentry_t;

struct _hashentry_t {
    hashentry_t *next;
    char *key;
    void *value;
};

struct _hash_t {
    unsigned int ref;
    xmpp_ctx_t *ctx;
    hash_free_func free;
    int length;
    int num_keys;
    hashentry_t **entries;
};

struct _hash_iterator_t {
    unsigned int ref;
    hash_t *table;
    hashentry_t *entry;
    int index;
};

/** allocate and initialize a new hash table */
hash_t *hash_new(xmpp_ctx_t *ctx, int size, hash_free_func free_func)
{
    hash_t *result = NULL;

    result = xmpp_alloc(ctx, sizeof(hash_t));
    if (result != NULL) {
        result->entries = xmpp_alloc(ctx, size * sizeof(hashentry_t *));
        if (result->entries == NULL) {
            xmpp_free(ctx, result);
            return NULL;
        }
        memset(result->entries, 0, size * sizeof(hashentry_t *));
        result->length = size;

        result->ctx = ctx;
        result->free = free_func;
        result->num_keys = 0;
        /* give the caller a reference */
        result->ref = 1;
    }

    return result;
}

/** obtain a new reference to an existing hash table */
hash_t *hash_clone(hash_t *table)
{
    table->ref++;
    return table;
}

/** release a hash table that is no longer needed */
void hash_release(hash_t *table)
{
    xmpp_ctx_t *ctx = table->ctx;
    hashentry_t *entry, *next;
    int i;

    if (table->ref > 1)
        table->ref--;
    else {
        for (i = 0; i < table->length; i++) {
            entry = table->entries[i];
            while (entry != NULL) {
                next = entry->next;
                xmpp_free(ctx, entry->key);
                if (table->free)
                    table->free(ctx, entry->value);
                xmpp_free(ctx, entry);
                entry = next;
            }
        }
        xmpp_free(ctx, table->entries);
        xmpp_free(ctx, table);
    }
}

/** hash a key for our table lookup */
static int _hash_key(hash_t *table, const char *key)
{
    unsigned hash = 0;
    unsigned shift = 0;
    const unsigned char *c = (const unsigned char *)key;

    while (*c != 0) {
        /* assume 32 bit ints */
        hash ^= ((unsigned)*c++ << shift);
        shift += 8;
        if (shift > 24)
            shift = 0;
    }
    return hash % (unsigned)table->length;
}

hashentry_t *_hash_entry_find(hash_t *table, const char *key)
{
    hashentry_t *entry;
    int table_index = _hash_key(table, key);

    /* look up the hash entry */
    entry = table->entries[table_index];
    while (entry != NULL) {
        /* traverse the linked list looking for the key */
        if (!strcmp(key, entry->key)) {
            /* match */
            break;
        }
        entry = entry->next;
    }
    return entry;
}

/** add a key, value pair to a hash table.
 *  each key can appear only once; the value of any
 *  identical key will be replaced
 */
int hash_add(hash_t *table, const char *key, void *data)
{
    xmpp_ctx_t *ctx = table->ctx;
    hashentry_t *entry = NULL;
    int table_index = _hash_key(table, key);

    /* find and replace existing entry, if any */
    entry = _hash_entry_find(table, key);

    if (entry == NULL) {
        /* allocate and fill a new entry */
        entry = xmpp_alloc(ctx, sizeof(hashentry_t));
        if (!entry)
            return -1;
        entry->key = xmpp_strdup(ctx, key);
        if (!entry->key) {
            xmpp_free(ctx, entry);
            return -1;
        }
        /* insert ourselves in the linked list */
        entry->next = table->entries[table_index];
        table->entries[table_index] = entry;
        table->num_keys++;
    } else {
        if (table->free)
            table->free(ctx, entry->value);
    }

    entry->value = data;

    return 0;
}

/** look up a key in a hash table */
void *hash_get(hash_t *table, const char *key)
{
    hashentry_t *entry;

    entry = _hash_entry_find(table, key);
    return entry == NULL ? NULL : entry->value;
}

/** delete a key from a hash table */
int hash_drop(hash_t *table, const char *key)
{
    xmpp_ctx_t *ctx = table->ctx;
    hashentry_t *entry, *prev;
    int table_index = _hash_key(table, key);

    /* look up the hash entry */
    entry = table->entries[table_index];
    prev = NULL;
    while (entry != NULL) {
        /* traverse the linked list looking for the key */
        if (!strcmp(key, entry->key)) {
            /* match, remove the entry */
            xmpp_free(ctx, entry->key);
            if (table->free)
                table->free(ctx, entry->value);
            if (prev == NULL) {
                table->entries[table_index] = entry->next;
            } else {
                prev->next = entry->next;
            }
            xmpp_free(ctx, entry);
            table->num_keys--;
            return 0;
        }
        prev = entry;
        entry = entry->next;
    }
    /* no match */
    return -1;
}

int hash_num_keys(hash_t *table)
{
    return table->num_keys;
}

/** allocate and initialize a new iterator */
hash_iterator_t *hash_iter_new(hash_t *table)
{
    xmpp_ctx_t *ctx = table->ctx;
    hash_iterator_t *iter;

    iter = xmpp_alloc(ctx, sizeof(*iter));
    if (iter != NULL) {
        iter->ref = 1;
        iter->table = hash_clone(table);
        iter->entry = NULL;
        iter->index = -1;
    }

    return iter;
}

/** release an iterator that is no longer needed */
void hash_iter_release(hash_iterator_t *iter)
{
    xmpp_ctx_t *ctx = iter->table->ctx;

    iter->ref--;

    if (iter->ref == 0) { // ref is unsigned!!!
        hash_release(iter->table);
        xmpp_free(ctx, iter);
    }
}

/** return the next hash table key from the iterator.
    the returned key should not be freed */
const char *hash_iter_next(hash_iterator_t *iter)
{
    hash_t *table = iter->table;
    hashentry_t *entry = iter->entry;
    int i;

    /* advance until we find the next entry */
    if (entry != NULL)
        entry = entry->next;
    if (entry == NULL) {
        /* we're off the end of list, search for a new entry */
        i = iter->index + 1;
        while (i < iter->table->length) {
            entry = table->entries[i];
            if (entry != NULL) {
                iter->index = i;
                break;
            }
            i++;
        }
    }

    if (entry == NULL) {
        /* no more keys! */
        return NULL;
    }

    /* remember our current match */
    iter->entry = entry;
    return entry->key;
}