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DEFINITIONS
This source file includes following definitions.
- alloc_array
- APR_DECLARE
- APR_DECLARE
- APR_DECLARE
- APR_DECLARE
- APR_DECLARE
- expand_array
- APR_DECLARE_NONSTD
- find_entry
- APR_DECLARE
- APR_DECLARE
- APR_DECLARE
- APR_DECLARE
- APR_DECLARE
- APR_DECLARE
- APR_DECLARE
/* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 "apr_private.h"
#include "apr_general.h"
#include "apr_pools.h"
#include "apr_hash.h"
#if APR_HAVE_STDLIB_H
#include <stdlib.h>
#endif
#if APR_HAVE_STRING_H
#include <string.h>
#endif
#if APR_POOL_DEBUG && APR_HAVE_STDIO_H
#include <stdio.h>
#endif
/*
* The internal form of a hash table.
*
* The table is an array indexed by the hash of the key; collisions
* are resolved by hanging a linked list of hash entries off each
* element of the array. Although this is a really simple design it
* isn't too bad given that pools have a low allocation overhead.
*/
typedef struct apr_hash_entry_t apr_hash_entry_t;
struct apr_hash_entry_t {
apr_hash_entry_t *next;
unsigned int hash;
const void *key;
apr_ssize_t klen;
const void *val;
};
/*
* Data structure for iterating through a hash table.
*
* We keep a pointer to the next hash entry here to allow the current
* hash entry to be freed or otherwise mangled between calls to
* apr_hash_next().
*/
struct apr_hash_index_t {
apr_hash_t *ht;
apr_hash_entry_t *this, *next;
unsigned int index;
};
/*
* The size of the array is always a power of two. We use the maximum
* index rather than the size so that we can use bitwise-AND for
* modular arithmetic.
* The count of hash entries may be greater depending on the chosen
* collision rate.
*/
struct apr_hash_t {
apr_pool_t *pool;
apr_hash_entry_t **array;
apr_hash_index_t iterator; /* For apr_hash_first(NULL, ...) */
unsigned int count, max;
apr_hashfunc_t hash_func;
apr_hash_entry_t *free; /* List of recycled entries */
};
#define INITIAL_MAX 15 /* tunable == 2^n - 1 */
/*
* Hash creation functions.
*/
static apr_hash_entry_t **alloc_array(apr_hash_t *ht, unsigned int max)
{
return apr_pcalloc(ht->pool, sizeof(*ht->array) * (max + 1));
}
APR_DECLARE(apr_hash_t *) apr_hash_make(apr_pool_t *pool)
{
apr_hash_t *ht;
ht = apr_palloc(pool, sizeof(apr_hash_t));
ht->pool = pool;
ht->free = NULL;
ht->count = 0;
ht->max = INITIAL_MAX;
ht->array = alloc_array(ht, ht->max);
ht->hash_func = apr_hashfunc_default;
return ht;
}
APR_DECLARE(apr_hash_t *) apr_hash_make_custom(apr_pool_t *pool,
apr_hashfunc_t hash_func)
{
apr_hash_t *ht = apr_hash_make(pool);
ht->hash_func = hash_func;
return ht;
}
/*
* Hash iteration functions.
*/
APR_DECLARE(apr_hash_index_t *) apr_hash_next(apr_hash_index_t *hi)
{
hi->this = hi->next;
while (!hi->this) {
if (hi->index > hi->ht->max)
return NULL;
hi->this = hi->ht->array[hi->index++];
}
hi->next = hi->this->next;
return hi;
}
APR_DECLARE(apr_hash_index_t *) apr_hash_first(apr_pool_t *p, apr_hash_t *ht)
{
apr_hash_index_t *hi;
if (p)
hi = apr_palloc(p, sizeof(*hi));
else
hi = &ht->iterator;
hi->ht = ht;
hi->index = 0;
hi->this = NULL;
hi->next = NULL;
return apr_hash_next(hi);
}
APR_DECLARE(void) apr_hash_this(apr_hash_index_t *hi,
const void **key,
apr_ssize_t *klen,
void **val)
{
if (key) *key = hi->this->key;
if (klen) *klen = hi->this->klen;
if (val) *val = (void *)hi->this->val;
}
/*
* Expanding a hash table
*/
static void expand_array(apr_hash_t *ht)
{
apr_hash_index_t *hi;
apr_hash_entry_t **new_array;
unsigned int new_max;
new_max = ht->max * 2 + 1;
new_array = alloc_array(ht, new_max);
for (hi = apr_hash_first(NULL, ht); hi; hi = apr_hash_next(hi)) {
unsigned int i = hi->this->hash & new_max;
hi->this->next = new_array[i];
new_array[i] = hi->this;
}
ht->array = new_array;
ht->max = new_max;
}
APR_DECLARE_NONSTD(unsigned int) apr_hashfunc_default(const char *char_key,
apr_ssize_t *klen)
{
unsigned int hash = 0;
const unsigned char *key = (const unsigned char *)char_key;
const unsigned char *p;
apr_ssize_t i;
/*
* This is the popular `times 33' hash algorithm which is used by
* perl and also appears in Berkeley DB. This is one of the best
* known hash functions for strings because it is both computed
* very fast and distributes very well.
*
* The originator may be Dan Bernstein but the code in Berkeley DB
* cites Chris Torek as the source. The best citation I have found
* is "Chris Torek, Hash function for text in C, Usenet message
* <27038@mimsy.umd.edu> in comp.lang.c , October, 1990." in Rich
* Salz's USENIX 1992 paper about INN which can be found at
* <http://citeseer.nj.nec.com/salz92internetnews.html>.
*
* The magic of number 33, i.e. why it works better than many other
* constants, prime or not, has never been adequately explained by
* anyone. So I try an explanation: if one experimentally tests all
* multipliers between 1 and 256 (as I did while writing a low-level
* data structure library some time ago) one detects that even
* numbers are not useable at all. The remaining 128 odd numbers
* (except for the number 1) work more or less all equally well.
* They all distribute in an acceptable way and this way fill a hash
* table with an average percent of approx. 86%.
*
* If one compares the chi^2 values of the variants (see
* Bob Jenkins ``Hashing Frequently Asked Questions'' at
* http://burtleburtle.net/bob/hash/hashfaq.html for a description
* of chi^2), the number 33 not even has the best value. But the
* number 33 and a few other equally good numbers like 17, 31, 63,
* 127 and 129 have nevertheless a great advantage to the remaining
* numbers in the large set of possible multipliers: their multiply
* operation can be replaced by a faster operation based on just one
* shift plus either a single addition or subtraction operation. And
* because a hash function has to both distribute good _and_ has to
* be very fast to compute, those few numbers should be preferred.
*
* -- Ralf S. Engelschall <rse@engelschall.com>
*/
if (*klen == APR_HASH_KEY_STRING) {
for (p = key; *p; p++) {
hash = hash * 33 + *p;
}
*klen = p - key;
}
else {
for (p = key, i = *klen; i; i--, p++) {
hash = hash * 33 + *p;
}
}
return hash;
}
/*
* This is where we keep the details of the hash function and control
* the maximum collision rate.
*
* If val is non-NULL it creates and initializes a new hash entry if
* there isn't already one there; it returns an updatable pointer so
* that hash entries can be removed.
*/
static apr_hash_entry_t **find_entry(apr_hash_t *ht,
const void *key,
apr_ssize_t klen,
const void *val)
{
apr_hash_entry_t **hep, *he;
unsigned int hash;
hash = ht->hash_func(key, &klen);
/* scan linked list */
for (hep = &ht->array[hash & ht->max], he = *hep;
he; hep = &he->next, he = *hep) {
if (he->hash == hash
&& he->klen == klen
&& memcmp(he->key, key, klen) == 0)
break;
}
if (he || !val)
return hep;
/* add a new entry for non-NULL values */
if ((he = ht->free) != NULL)
ht->free = he->next;
else
he = apr_palloc(ht->pool, sizeof(*he));
he->next = NULL;
he->hash = hash;
he->key = key;
he->klen = klen;
he->val = val;
*hep = he;
ht->count++;
return hep;
}
APR_DECLARE(apr_hash_t *) apr_hash_copy(apr_pool_t *pool,
const apr_hash_t *orig)
{
apr_hash_t *ht;
apr_hash_entry_t *new_vals;
unsigned int i, j;
ht = apr_palloc(pool, sizeof(apr_hash_t) +
sizeof(*ht->array) * (orig->max + 1) +
sizeof(apr_hash_entry_t) * orig->count);
ht->pool = pool;
ht->free = NULL;
ht->count = orig->count;
ht->max = orig->max;
ht->hash_func = orig->hash_func;
ht->array = (apr_hash_entry_t **)((char *)ht + sizeof(apr_hash_t));
new_vals = (apr_hash_entry_t *)((char *)(ht) + sizeof(apr_hash_t) +
sizeof(*ht->array) * (orig->max + 1));
j = 0;
for (i = 0; i <= ht->max; i++) {
apr_hash_entry_t **new_entry = &(ht->array[i]);
apr_hash_entry_t *orig_entry = orig->array[i];
while (orig_entry) {
*new_entry = &new_vals[j++];
(*new_entry)->hash = orig_entry->hash;
(*new_entry)->key = orig_entry->key;
(*new_entry)->klen = orig_entry->klen;
(*new_entry)->val = orig_entry->val;
new_entry = &((*new_entry)->next);
orig_entry = orig_entry->next;
}
*new_entry = NULL;
}
return ht;
}
APR_DECLARE(void *) apr_hash_get(apr_hash_t *ht,
const void *key,
apr_ssize_t klen)
{
apr_hash_entry_t *he;
he = *find_entry(ht, key, klen, NULL);
if (he)
return (void *)he->val;
else
return NULL;
}
APR_DECLARE(void) apr_hash_set(apr_hash_t *ht,
const void *key,
apr_ssize_t klen,
const void *val)
{
apr_hash_entry_t **hep;
hep = find_entry(ht, key, klen, val);
if (*hep) {
if (!val) {
/* delete entry */
apr_hash_entry_t *old = *hep;
*hep = (*hep)->next;
old->next = ht->free;
ht->free = old;
--ht->count;
}
else {
/* replace entry */
(*hep)->val = val;
/* check that the collision rate isn't too high */
if (ht->count > ht->max) {
expand_array(ht);
}
}
}
/* else key not present and val==NULL */
}
APR_DECLARE(unsigned int) apr_hash_count(apr_hash_t *ht)
{
return ht->count;
}
APR_DECLARE(void) apr_hash_clear(apr_hash_t *ht)
{
apr_hash_index_t *hi;
for (hi = apr_hash_first(NULL, ht); hi; hi = apr_hash_next(hi))
apr_hash_set(ht, hi->this->key, hi->this->klen, NULL);
}
APR_DECLARE(apr_hash_t*) apr_hash_overlay(apr_pool_t *p,
const apr_hash_t *overlay,
const apr_hash_t *base)
{
return apr_hash_merge(p, overlay, base, NULL, NULL);
}
APR_DECLARE(apr_hash_t *) apr_hash_merge(apr_pool_t *p,
const apr_hash_t *overlay,
const apr_hash_t *base,
void * (*merger)(apr_pool_t *p,
const void *key,
apr_ssize_t klen,
const void *h1_val,
const void *h2_val,
const void *data),
const void *data)
{
apr_hash_t *res;
apr_hash_entry_t *new_vals = NULL;
apr_hash_entry_t *iter;
apr_hash_entry_t *ent;
unsigned int i,j,k;
#if APR_POOL_DEBUG
/* we don't copy keys and values, so it's necessary that
* overlay->a.pool and base->a.pool have a life span at least
* as long as p
*/
if (!apr_pool_is_ancestor(overlay->pool, p)) {
fprintf(stderr,
"apr_hash_merge: overlay's pool is not an ancestor of p\n");
abort();
}
if (!apr_pool_is_ancestor(base->pool, p)) {
fprintf(stderr,
"apr_hash_merge: base's pool is not an ancestor of p\n");
abort();
}
#endif
res = apr_palloc(p, sizeof(apr_hash_t));
res->pool = p;
res->free = NULL;
res->hash_func = base->hash_func;
res->count = base->count;
res->max = (overlay->max > base->max) ? overlay->max : base->max;
if (base->count + overlay->count > res->max) {
res->max = res->max * 2 + 1;
}
res->array = alloc_array(res, res->max);
if (base->count + overlay->count) {
new_vals = apr_palloc(p, sizeof(apr_hash_entry_t) *
(base->count + overlay->count));
}
j = 0;
for (k = 0; k <= base->max; k++) {
for (iter = base->array[k]; iter; iter = iter->next) {
i = iter->hash & res->max;
new_vals[j].klen = iter->klen;
new_vals[j].key = iter->key;
new_vals[j].val = iter->val;
new_vals[j].hash = iter->hash;
new_vals[j].next = res->array[i];
res->array[i] = &new_vals[j];
j++;
}
}
for (k = 0; k <= overlay->max; k++) {
for (iter = overlay->array[k]; iter; iter = iter->next) {
i = iter->hash & res->max;
for (ent = res->array[i]; ent; ent = ent->next) {
if ((ent->klen == iter->klen) &&
(memcmp(ent->key, iter->key, iter->klen) == 0)) {
if (merger) {
ent->val = (*merger)(p, iter->key, iter->klen,
iter->val, ent->val, data);
}
else {
ent->val = iter->val;
}
break;
}
}
if (!ent) {
new_vals[j].klen = iter->klen;
new_vals[j].key = iter->key;
new_vals[j].val = iter->val;
new_vals[j].hash = iter->hash;
new_vals[j].next = res->array[i];
res->array[i] = &new_vals[j];
res->count++;
j++;
}
}
}
return res;
}
APR_POOL_IMPLEMENT_ACCESSOR(hash)