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/*
* Copyright (c) 2008, 2009, 2010 Nicira Networks.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <config.h>
#include "hmap.h"
#include <assert.h>
#include <stdint.h>
#include <string.h>
#include "coverage.h"
#include "random.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);
}
}
/* Removes all node from 'hmap', leaving it ready to accept more nodes. Does
* not free memory allocated for 'hmap'.
*
* This function is appropriate when 'hmap' will soon have about as many
* elements as it before. If 'hmap' will likely have fewer elements than
* before, use hmap_destroy() followed by hmap_clear() to save memory and
* iteration time. */
void
hmap_clear(struct hmap *hmap)
{
if (hmap->n > 0) {
hmap->n = 0;
memset(hmap->buckets, 0, (hmap->mask + 1) * sizeof *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;
hmap_moved(a);
hmap_moved(b);
}
/* Adjusts 'hmap' to compensate for having moved position in memory (e.g. due
* to realloc()). */
void
hmap_moved(struct hmap *hmap)
{
if (!hmap->mask) {
hmap->buckets = &hmap->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;
int count = 0;
for (node = hmap->buckets[i]; node; node = next) {
next = node->next;
hmap_insert_fast(&tmp, node, node->hash);
count++;
}
if (count > 5) {
COVERAGE_INC(hmap_pathological);
}
}
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) {
COVERAGE_INC(hmap_expand);
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) {
COVERAGE_INC(hmap_shrink);
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) {
COVERAGE_INC(hmap_reserve);
resize(hmap, new_mask);
}
}
/* Adjusts 'hmap' to compensate for 'old_node' having moved position in memory
* to 'node' (e.g. due to realloc()). */
void
hmap_node_moved(struct hmap *hmap,
struct hmap_node *old_node, struct hmap_node *node)
{
struct hmap_node **bucket = &hmap->buckets[node->hash & hmap->mask];
while (*bucket != old_node) {
bucket = &(*bucket)->next;
}
*bucket = node;
}
/* Chooses and returns a randomly selected node from 'hmap', which must not be
* empty.
*
* I wouldn't depend on this algorithm to be fair, since I haven't analyzed it.
* But it does at least ensure that any node in 'hmap' can be chosen. */
struct hmap_node *
hmap_random_node(const struct hmap *hmap)
{
struct hmap_node *bucket, *node;
size_t n, i;
/* Choose a random non-empty bucket. */
for (i = random_uint32(); ; i++) {
bucket = hmap->buckets[i & hmap->mask];
if (bucket) {
break;
}
}
/* Count nodes in bucket. */
n = 0;
for (node = bucket; node; node = node->next) {
n++;
}
/* Choose random node from bucket. */
i = random_range(n);
for (node = bucket; i-- > 0; node = node->next) {
continue;
}
return node;
}
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