libsmbns/common/smbns_hash.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved.
 */

/*
 * Generic hash table library. The hash table is an array of pointers
 * to items. Hash collisions are handled using linked lists from the
 * table entries. A handle is associated with each table, which is used
 * to maintain the hash table.
 *
 * +------+     +-------+    +----+    +----+
 * |handle|---> |index 0|--->|item|--->|item|--->
 * | ...  |     +-------+    +----+    +----+
 * | ...  |     |index 1|--->
 * +------+     +-------+    +----+    +----+    +----+
 *              |index 2|--->|item|--->|item|--->|item|--->
 *              +-------+    +----+    +----+    +----+
 *              | ...   |--->
 *              +-------+
 *              | ...   |--->
 *              +-------+
 *              |index n|--->
 *              +-------+
 *
 */

#include <stdlib.h>
#include <strings.h>
#include <smbns_hash.h>

static size_t ht_default_hash(HT_HANDLE *handle, const char *key);

/*
 * ht_is_power2
 *
 * Inline function to determine if a value is a power of two. This
 * function is used by the library to validate the table size when
 * a new table is created.
 *
 * Returns 1 if value given is power of two, otherwise returns 0.
 */
static size_t
ht_is_power2(size_t value)
{
    return (((value & (value - 1)) == 0)? 1 : 0);
}


/*
 * ht_create_table
 *
 * Create a hash table. The table size must be a positive integer and
 * must be a power of two. The key size must be a positive integer.
 * For null terminated keys, the key size does not need to include the
 * null terminating character. The type of key is indicated by the flags.
 *
 * The handle and the table are are malloc'd using a single call, to
 * avoid two allocations. The table is located immediately after the
 * handle.
 *
 * On success a pointer to an opaque handle is returned. Otherwise a
 * null pointer is returned.
 */
HT_HANDLE *
ht_create_table(size_t table_size, size_t key_size, size_t flags)
{
    HT_HANDLE *ht;
    size_t msize;
    size_t i;

    if ((table_size == 0) || (key_size == 0))
        return (NULL);

    if (ht_is_power2(table_size) == 0)
        return (NULL);

    msize = sizeof (HT_HANDLE) + (sizeof (HT_TABLE_ENTRY) * table_size);

    if ((ht = (HT_HANDLE *)malloc(msize)) == 0)
        return (NULL);

    /*LINTED E_BAD_PTR_CAST_ALIGN*/
    ht->ht_table = (HT_TABLE_ENTRY *)((char *)ht + sizeof (HT_HANDLE));
    ht->ht_table_size = table_size;
    ht->ht_table_mask = table_size - 1;
    ht->ht_key_size = key_size;
    ht->ht_total_items = 0;
    ht->ht_flags = flags;
    ht->ht_hash = ht_default_hash;
    ht->ht_callback = 0;
    ht->ht_sequence = random();
    ht->ht_cmp = ((flags & HTHF_FIXED_KEY) == 0)
        ? (HT_CMP)strncmp : (HT_CMP)memcmp;

    for (i = 0; i < table_size; i++)
        bzero(&ht->ht_table[i], sizeof (HT_TABLE_ENTRY));

    return (ht);
}


/*
 * ht_destroy_table
 *
 * Destroy a hash table. All entries in the table are removed, which
 * may invoke the callback if it's installed, and the memory is freed.
 */
void
ht_destroy_table(HT_HANDLE *handle)
{
    HT_ITEM *item;
    HT_ITERATOR iterator;

    if (handle == 0)
        return;

    /* To remove marked entries */
    (void) ht_clean_table(handle);
    while ((item = ht_findfirst(handle, &iterator)) != 0)
        (void) ht_remove_item(handle, item->hi_key);

    free(handle);
}


/*
 * ht_get_total_items
 *
 * Return the total number of items in the table. Returns -1 if the
 * handle is invalid.
 */
size_t
ht_get_total_items(HT_HANDLE *handle)
{
    if (handle == 0)
        return ((size_t)-1);

    return (handle->ht_total_items);
}


/*
 * ht_default_hash
 *
 * Default hash function to compute the table index (hash value) based
 * on the specified key. This will identify the location for the
 * corresponding item in the hash table. The handle and key pointers
 * should be validated before this function is called.
 *
 * Returns the table index location for the item.
 */
static size_t
ht_default_hash(HT_HANDLE *handle, const char *key)
{
    unsigned int hash_ndx = 0;
    size_t rval;

    if ((handle->ht_flags & HTHF_FIXED_KEY) == 0) {
        while (*key) {
            hash_ndx += *key;
            ++key;
        }
    } else {
        int key_len = handle->ht_key_size;

        while (key_len--) {
            hash_ndx += *key;
            ++key;
        }
    }

    rval = (hash_ndx * HASH_MESH_VALUE) & handle->ht_table_mask;
    return (rval);
}


/*
 * ht_set_cmpfn
 *
 * Replace the current compare function. As the this is function
 * for comparing items' key, it should not be called while there are
 * items in the table.
 */
void
ht_set_cmpfn(HT_HANDLE *handle, HT_CMP cmpfn)
{
    if (handle)
        handle->ht_cmp = cmpfn;
}

/*
 * ht_add_item
 *
 * Adds an item to a hash table. The hash table is identified by the
 * handle and the key is used to generate a hashed index. The data
 * item can be null; it is never dereferenced. We don't check for
 * duplicates. If duplicate keys are added to the table, the last
 * item added will be to the front of the duplicate list.
 *
 * The table sequence number may be modified here.
 *
 * If the item is successfully inserted, a pointer to the item object
 * is returned. Otherwise a null pointer is returned.
 */
HT_ITEM *
ht_add_item(HT_HANDLE *handle, const char *key, const void *data)
{
    size_t h_index, key_len;
    size_t msize;
    HT_ITEM *item;

    if (handle == 0 || key == 0)
        return (NULL);

    if (handle->ht_flags & HTHF_FIXED_KEY) {
        key_len = handle->ht_key_size;
    } else {
        key_len = strlen(key);

        if (key_len > handle->ht_key_size)
            return (NULL);

        /* Include the null terminator */
        ++key_len;
    }

    msize = key_len + sizeof (HT_ITEM);

    if ((item = malloc(msize)) == 0)
        return (NULL);

    item->hi_key = (char *)item + sizeof (HT_ITEM);
    (void) memcpy(item->hi_key, key, key_len);
    item->hi_data = (void *)data;
    item->hi_flags = 0;

    h_index = handle->ht_hash(handle, key);

    /*
     * Add to the front of the list.
     */
    item->hi_next = handle->ht_table[h_index].he_head;
    handle->ht_table[h_index].he_head = item;

    handle->ht_table[h_index].he_count++;
    handle->ht_total_items++;
    handle->ht_sequence++;

    return (item);
}


/*
 * ht_replace_item
 *
 * Replace an item in a hash table. The item associated with key is removed
 * using ht_remove_item and a new item is added using ht_add_item. We rely
 * on parameter validation in ht_remove_item and ht_add_item.
 *
 * The table sequence number may be modified here.
 */
HT_ITEM *
ht_replace_item(HT_HANDLE *handle, const char *key, const void *data)
{
    (void) ht_remove_item(handle, key);

    return (ht_add_item(handle, key, data));
}


/*
 * ht_remove_item
 *
 * Remove an item from a hash table. If there are duplicate keys, then the
 * first key found will be deleted. Note that the data pointer is never
 * dereferenced.  If a callback is installed, it will be invoked and the
 * return value will be null. Otherwise, the data pointer supplied by the
 * application will be returned. If there is an error, a null pointer will
 * be returned.
 *
 * The table sequence number may be modified here.
 */
void *
ht_remove_item(HT_HANDLE *handle, const char *key)
{
    size_t h_index;
    HT_ITEM *cur, *prev;
    int key_len;
    void *data = 0;

    if (handle == 0 || key == 0)
        return (NULL);

    if ((handle->ht_flags & HTHF_FIXED_KEY) == 0)
        key_len = strlen(key) + 1;
    else
        key_len = handle->ht_key_size;

    h_index = handle->ht_hash(handle, key);

    cur = handle->ht_table[h_index].he_head;
    prev = 0;

    while (cur) {
        if (!(cur->hi_flags & HTIF_MARKED_DELETED) &&
            (handle->ht_cmp(cur->hi_key, key, key_len) == 0)) {
            /* found key */
            if (prev == 0)
                handle->ht_table[h_index].he_head =
                    cur->hi_next;
            else
                prev->hi_next = cur->hi_next;

            if (handle->ht_callback)
                handle->ht_callback(cur);
            else
                data = cur->hi_data;

            /*
             * Since the key and the item were allocated as
             * a single chunk, we only need one free here.
             */
            free(cur);

            handle->ht_table[h_index].he_count--;
            handle->ht_total_items--;
            handle->ht_sequence++;
            break;
        }

        prev = cur;
        cur = cur->hi_next;
    }

    return (data);
}

/*
 * ht_find_item
 *
 * Find an item in a hash table. If there are duplicate keys then the
 * first item found (which will be the last one added) will be returned.
 *
 * Returns a pointer to an item. Otherwise returns a null pointer to
 * indicate an error or that the key didn't match anything in the table.
 */
HT_ITEM *
ht_find_item(HT_HANDLE *handle, const char *key)
{
    size_t h_index;
    HT_ITEM *cur;
    int key_len;

    if (handle == 0 || key == 0)
        return (NULL);

    if ((handle->ht_flags & HTHF_FIXED_KEY) == 0)
        key_len = strlen(key) + 1;
    else
        key_len = handle->ht_key_size;

    h_index = handle->ht_hash(handle, key);
    cur = handle->ht_table[h_index].he_head;

    while (cur) {
        if (!(cur->hi_flags & HTIF_MARKED_DELETED) &&
            (handle->ht_cmp(cur->hi_key, key, key_len) == 0))
            return (cur);

        cur = cur->hi_next;
    }

    return (NULL);
}


/*
 * ht_register_callback
 *
 * Register an application callback function that can be used to process
 * an item when it is removed from the table, i.e. free any memory
 * allocated for that data item.
 *
 * The previous callback function pointer, which may be null, before
 * registering the new one. This provides the caller with the option to
 * restore a previous callback as required.
 */
HT_CALLBACK
ht_register_callback(HT_HANDLE *handle, HT_CALLBACK callback)
{
    HT_CALLBACK old_callback;

    if (handle == 0)
        return (NULL);

    old_callback = handle->ht_callback;
    handle->ht_callback = callback;

    return (old_callback);
}


/*
 * ht_clean_table
 *
 * This function removes all the items that are marked for deletion. Note
 * that this will invoke the callback, if one has been installed. If this
 * call is used, the callback mechanism is the only way for an application
 * to free the item data if it was dynamically allocated.
 *
 * The table sequence number may be modified here.
 *
 * Returns 0 if the handle is valid; otherwise returns -1.
 */
size_t
ht_clean_table(HT_HANDLE *handle)
{
    size_t i;
    HT_ITEM *cur, *prev;

    if (handle == 0)
        return ((size_t)-1);

    for (i = 0; i < handle->ht_table_size; i++) {
        cur = handle->ht_table[i].he_head;
        prev = 0;

        while (cur) {
            if (cur->hi_flags & HTIF_MARKED_DELETED) {
                /*
                 * We have a marked item: remove it.
                 */
                if (prev == 0)
                    handle->ht_table[i].he_head =
                        cur->hi_next;
                else
                    prev->hi_next = cur->hi_next;

                if (handle->ht_callback)
                    handle->ht_callback(cur);

                /*
                 * Since the key and the item were allocated as
                 * a single chunk, we only need one free here.
                 */
                free(cur);

                handle->ht_table[i].he_count--;
                handle->ht_sequence++;

                if (prev == 0)
                    cur = handle->ht_table[i].he_head;
                else
                    cur = prev->hi_next;
                continue;
            }

            prev = cur;
            cur = cur->hi_next;
        }
    }

    return (0);
}


/*
 * ht_mark_delete
 *
 * This function marks an item for deletion, which may be useful when
 * using findfirst/findnext to avoid modifying the table during the
 * table scan. Marked items can be removed later using ht_clean_table.
 */
void
ht_mark_delete(HT_HANDLE *handle, HT_ITEM *item)
{
    if (handle && item) {
        item->hi_flags |= HTIF_MARKED_DELETED;
        handle->ht_total_items--;
    }
}

/*
 * ht_clear_delete
 *
 * This function clear an item from marked for deletion list.
 */
void
ht_clear_delete(HT_HANDLE *handle, HT_ITEM *item)
{
    if (handle && item) {
        item->hi_flags &= ~HTIF_MARKED_DELETED;
        handle->ht_total_items++;
    }
}

/*
 * ht_bucket_search
 *
 * Returns first item which is not marked as deleted
 * in the specified bucket by 'head'
 */
static HT_ITEM *
ht_bucket_search(HT_ITEM *head)
{
    HT_ITEM *item = head;
    while ((item != 0) && (item->hi_flags & HTIF_MARKED_DELETED))
        item = item->hi_next;

    return (item);
}

/*
 * ht_findfirst
 *
 * This function is used to begin an iteration through the hash table.
 * The iterator is initialized and the first item in the table (as
 * determined by the hash algorithm) is returned. The current sequence
 * number is stored in the iterator to determine whether or not the
 * the table has changed between calls. If the table is empty, a null
 * pointer is returned.
 */
HT_ITEM *
ht_findfirst(HT_HANDLE *handle, HT_ITERATOR *iterator)
{
    HT_ITEM *item;
    size_t h_index;

    if (handle == 0 || iterator == 0 || handle->ht_total_items == 0)
        return (NULL);

    (void) memset(iterator, 0, sizeof (HT_ITERATOR));
    iterator->hti_handle = handle;
    iterator->hti_sequence = handle->ht_sequence;

    for (h_index = 0; h_index < handle->ht_table_size; ++h_index) {
        item = ht_bucket_search(handle->ht_table[h_index].he_head);
        if (item != 0) {
            iterator->hti_index = h_index;
            iterator->hti_item = item;
            return (item);
        }
    }

    return (NULL);
}

/*
 * ht_findnext
 *
 * Find the next item in the table for the given iterator. Iterators must
 * be initialized by ht_findfirst, which will also return the first item
 * in the table. If an item is available, a pointer to it is returned.
 * Otherwise a null pointer is returned. A null pointer may indicate:
 *
 *  - an invalid iterator (i.e. ht_findfirst has not been called)
 *  - the table has changed since the previous findfirst/findnext
 *  - the entire table has been traversed
 *
 * The caller can use ht_get_total_items to determine whether or not all
 * of the items in the table have been visited.
 */
HT_ITEM *
ht_findnext(HT_ITERATOR *iterator)
{
    HT_HANDLE *handle;
    HT_ITEM *item;
    size_t total;
    size_t index;

    if (iterator == 0 || iterator->hti_handle == 0 ||
        iterator->hti_sequence == 0) {
        /* Invalid iterator */
        return (NULL);
    }

    handle = iterator->hti_handle;

    if (iterator->hti_item == 0 ||
        iterator->hti_sequence != handle->ht_sequence) {
        /*
         * No more items or the table has changed
         * since the last call.
         */
        return (NULL);
    }

    /*
     * Check for another item in the current bucket.
     */
    item = ht_bucket_search(iterator->hti_item->hi_next);
    if (item != 0) {
        iterator->hti_item = item;
        return (item);
    }

    /*
     * Nothing else in the current bucket. Look for another
     * bucket with something in it and return the head item.
     */
    total = handle->ht_table_size;
    for (index = iterator->hti_index + 1; index < total; ++index) {
        item = ht_bucket_search(handle->ht_table[index].he_head);
        if (item != 0) {
            iterator->hti_index = index;
            iterator->hti_item = item;
            return (item);
        }
    }

    iterator->hti_index = 0;
    iterator->hti_item = 0;
    iterator->hti_sequence = 0;
    return (NULL);
}