openflow/lib/hmap.c

/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
 * Junior University
 *
 * We are making the OpenFlow specification and associated documentation
 * (Software) available for public use and benefit with the expectation
 * that others will use, modify and enhance the Software and contribute
 * those enhancements back to the community. However, since we would
 * like to make the Software available for broadest use, with as few
 * restrictions as possible permission is hereby granted, free of
 * charge, to any person obtaining a copy of this Software to deal in
 * the Software under the copyrights without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * The name and trademarks of copyright holder(s) may NOT be used in
 * advertising or publicity pertaining to the Software or any
 * derivatives without specific, written prior permission.
 */

#include <config.h>
#include "hmap.h"
#include <assert.h>
#include <stdint.h>
#include "util.h"

/* Initializes 'hmap' as an empty hash table. */
void
hmap_init(struct hmap *hmap)
{
    hmap->buckets = &hmap->one;
    hmap->one = NULL;
    hmap->mask = 0;
    hmap->n = 0;
}

/* Frees memory reserved by 'hmap'.  It is the client's responsibility to free
 * the nodes themselves, if necessary. */
void
hmap_destroy(struct hmap *hmap)
{
    if (hmap && hmap->buckets != &hmap->one) {
        free(hmap->buckets);
    }
}

/* Exchanges hash maps 'a' and 'b'. */
void
hmap_swap(struct hmap *a, struct hmap *b)
{
    struct hmap tmp = *a;
    *a = *b;
    *b = tmp;
    if (a->buckets == &b->one) {
        a->buckets = &a->one;
    }
    if (b->buckets == &a->one) {
        b->buckets = &b->one;
    }
}

static void
resize(struct hmap *hmap, size_t new_mask)
{
    struct hmap tmp;
    size_t i;

    assert(!(new_mask & (new_mask + 1)));
    assert(new_mask != SIZE_MAX);

    hmap_init(&tmp);
    if (new_mask) {
        tmp.buckets = xmalloc(sizeof *tmp.buckets * (new_mask + 1));
        tmp.mask = new_mask;
        for (i = 0; i <= tmp.mask; i++) {
            tmp.buckets[i] = NULL;
        }
    }
    for (i = 0; i <= hmap->mask; i++) {
        struct hmap_node *node, *next;
        for (node = hmap->buckets[i]; node; node = next) {
            next = node->next;
            hmap_insert_fast(&tmp, node, node->hash);
        }
    }
    hmap_swap(hmap, &tmp);
    hmap_destroy(&tmp);
}

static size_t
calc_mask(size_t capacity)
{
    size_t mask = capacity / 2;
    mask |= mask >> 1;
    mask |= mask >> 2;
    mask |= mask >> 4;
    mask |= mask >> 8;
    mask |= mask >> 16;
#if SIZE_MAX > UINT32_MAX
    mask |= mask >> 32;
#endif

    /* If we need to dynamically allocate buckets we might as well allocate at
     * least 4 of them. */
    mask |= (mask & 1) << 1;

    return mask;
}

/* Expands 'hmap', if necessary, to optimize the performance of searches. */
void
hmap_expand(struct hmap *hmap)
{
    size_t new_mask = calc_mask(hmap->n);
    if (new_mask > hmap->mask) {
        resize(hmap, new_mask);
    }
}

/* Shrinks 'hmap', if necessary, to optimize the performance of iteration. */
void
hmap_shrink(struct hmap *hmap)
{
    size_t new_mask = calc_mask(hmap->n);
    if (new_mask < hmap->mask) {
        resize(hmap, new_mask);
    }
}

/* Expands 'hmap', if necessary, to optimize the performance of searches when
 * it has up to 'n' elements.  (But iteration will be slow in a hash map whose
 * allocated capacity is much higher than its current number of nodes.)  */
void
hmap_reserve(struct hmap *hmap, size_t n)
{
    size_t new_mask = calc_mask(n);
    if (new_mask > hmap->mask) {
        resize(hmap, new_mask);
    }
}