wireshark/epan/wmem/wmem_map.c

/* wmem_map.c
 * Wireshark Memory Manager Hash Map
 * Copyright 2014, Evan Huus <eapache@gmail.com>
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <glib.h>

#include "wmem_core.h"
#include "wmem_map.h"

static guint32 x; /* Used for universal integer hashing (see the HASH macro) */

/* Used for the wmem_strong_hash() function */
static guint32 preseed;
static guint32 postseed;

void
wmem_init_hashing(void)
{
    x = g_random_int();

    preseed  = g_random_int();
    postseed = g_random_int();
}

typedef struct _wmem_map_item_t {
    const void *key;
    void *value;
    struct _wmem_map_item_t *next;
} wmem_map_item_t;

struct _wmem_map_t {
    guint count; /* number of items stored */

    /* The base-2 logarithm of the actual size of the table. We store this
     * value for efficiency in hashing, since finding the actual capacity
     * becomes just a left-shift (see the CAPACITY macro) whereas taking
     * logarithms is expensive. */
    guint capacity;

    wmem_map_item_t **table;

    GHashFunc  hash_func;
    GEqualFunc eql_func;

    wmem_allocator_t *allocator;
};

/* As per the comment on the 'capacity' member of the wmem_map_t struct, this is
 * the base-2 logarithm, meaning the actual default capacity is 2^5 = 32 */
#define WMEM_MAP_DEFAULT_CAPACITY 5

/* Macro for calculating the real capacity of the map by using a left-shift to
 * do the 2^x operation. */
#define CAPACITY(MAP) ((guint)(1 << (MAP)->capacity))

/* Efficient universal integer hashing:
 * https://en.wikipedia.org/wiki/Universal_hashing#Avoiding_modular_arithmetic
 */
#define HASH(MAP, KEY) \
    ((guint32)(((MAP)->hash_func(KEY) * x) >> (32 - (MAP)->capacity)))

wmem_map_t *
wmem_map_new(wmem_allocator_t *allocator,
        GHashFunc hash_func, GEqualFunc eql_func)
{
    wmem_map_t *map;

    map = wmem_new(allocator, wmem_map_t);

    map->count     = 0;
    map->capacity  = WMEM_MAP_DEFAULT_CAPACITY;
    map->table     = wmem_alloc0_array(allocator, wmem_map_item_t*, CAPACITY(map));
    map->hash_func = hash_func;
    map->eql_func  = eql_func;
    map->allocator = allocator;

    return map;
}

static inline void
wmem_map_grow(wmem_map_t *map)
{
    wmem_map_item_t **old_table, *cur, *nxt;
    guint             old_cap, i, slot;

    /* store the old table and capacity */
    old_table = map->table;
    old_cap   = CAPACITY(map);

    /* double the size (capacity is base-2 logarithm, so this just means
     * increment it) and allocate new table */
    map->capacity++;
    map->table = wmem_alloc0_array(map->allocator, wmem_map_item_t*, CAPACITY(map));

    /* copy all the elements over from the old table */
    for (i=0; i<old_cap; i++) {
        cur = old_table[i];
        while (cur) {
            nxt              = cur->next;
            slot             = HASH(map, cur->key);
            cur->next        = map->table[slot];
            map->table[slot] = cur;
            cur              = nxt;
        }
    }

    /* free the old table */
    wmem_free(map->allocator, old_table);
}

void *
wmem_map_insert(wmem_map_t *map, const void *key, void *value)
{
    wmem_map_item_t **item;
    void *old_val;

    /* get a pointer to the slot */
    item = &(map->table[HASH(map, key)]);

    /* check existing items in that slot */
    while (*item) {
        if (map->eql_func(key, (*item)->key)) {
            /* replace and return old value for this key */
            old_val = (*item)->value;
            (*item)->value = value;
            return old_val;
        }
        item = &((*item)->next);
    }

    /* insert new item */
    (*item) = wmem_new(map->allocator, wmem_map_item_t);

    (*item)->key   = key;
    (*item)->value = value;
    (*item)->next  = NULL;

    map->count++;

    /* increase size if we are over-full */
    if (map->count >= CAPACITY(map)) {
        wmem_map_grow(map);
    }

    /* no previous entry, return NULL */
    return NULL;
}

void *
wmem_map_lookup(wmem_map_t *map, const void *key)
{
    wmem_map_item_t *item;

    /* find correct slot */
    item = map->table[HASH(map, key)];

    /* scan list of items in this slot for the correct value */
    while (item) {
        if (map->eql_func(key, item->key)) {
            return item->value;
        }
        item = item->next;
    }

    return NULL;
}

void *
wmem_map_remove(wmem_map_t *map, const void *key)
{
    wmem_map_item_t **item, *tmp;
    void *value;

    /* get a pointer to the slot */
    item = &(map->table[HASH(map, key)]);

    /* check the items in that slot */
    while (*item) {
        if (map->eql_func(key, (*item)->key)) {
            /* found it */
            tmp     = (*item);
            value   = tmp->value;
            (*item) = tmp->next;
            wmem_free(map->allocator, tmp);
            map->count--;
            return value;
        }
        item = &((*item)->next);
    }

    /* didn't find it */
    return NULL;
}

/* Borrowed from Perl 5.18. This is based on Bob Jenkin's one-at-a-time
 * algorithm with some additional randomness seeded in. It is believed to be
 * generally secure against collision attacks. See
 * http://blog.booking.com/hardening-perls-hash-function.html
 */
guint32
wmem_strong_hash(const guint8 *buf, const size_t len)
{
    const guint8 * const end = (const guint8 *)buf + len;
    guint32 hash = preseed + (guint32)len;

    while (buf < end) {
        hash += (hash << 10);
        hash ^= (hash >> 6);
        hash += *buf++;
    }

    hash += (hash << 10);
    hash ^= (hash >> 6);
    hash += ((guint8*)&postseed)[0];

    hash += (hash << 10);
    hash ^= (hash >> 6);
    hash += ((guint8*)&postseed)[1];

    hash += (hash << 10);
    hash ^= (hash >> 6);
    hash += ((guint8*)&postseed)[2];

    hash += (hash << 10);
    hash ^= (hash >> 6);
    hash += ((guint8*)&postseed)[3];

    hash += (hash << 10);
    hash ^= (hash >> 6);

    hash += (hash << 3);
    hash ^= (hash >> 11);
    return (hash + (hash << 15));
}

guint
wmem_str_hash(gconstpointer key)
{
    return wmem_strong_hash((const guint8 *)key, strlen((const char *)key));
}

guint
wmem_int64_hash(gconstpointer key)
{
    return wmem_strong_hash((const guint8 *)key, sizeof(guint64));
}

guint
wmem_double_hash(gconstpointer key)
{
    return wmem_strong_hash((const guint8 *)key, sizeof(double));
}

/*
 * Editor modelines  -  http://www.wireshark.org/tools/modelines.html
 *
 * Local variables:
 * c-basic-offset: 4
 * tab-width: 8
 * indent-tabs-mode: nil
 * End:
 *
 * vi: set shiftwidth=4 tabstop=8 expandtab:
 * :indentSize=4:tabSize=8:noTabs=true:
 */