/* Copyright 2000-2004 The Apache Software Foundation
*
* 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.
* split from apache for general usage by Yankee
* use system malloc instead of apr_pool ,although it is not so effiecient but suitable for small
* scale usage.
*/
//#include "apr_private.h"
//#include "apr_general.h"
//#include "apr_pools.h"
#include "hash_modify.h"
//#if APR_HAVE_STDLIB_H
#include <stdlib.h>
//#endif
//#if APR_HAVE_STRING_H
#include <string.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;
};
#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 malloc(ht->pool, sizeof(*ht->array) * (max + 1));
}
apr_hash_t * apr_hash_make(void)
{
apr_hash_t *ht;
ht =malloc(pool, sizeof(apr_hash_t));
ht->pool = pool;
ht->count = 0;
ht->max = INITIAL_MAX;
ht->array = alloc_array(ht, ht->max);
return ht;
}
/*
* Hash iteration functions.
*/
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_hash_index_t * apr_hash_first(apr_pool_t *p, apr_hash_t *ht)
{
apr_hash_index_t *hi;
if (p)
hi = malloc(p, sizeof(*hi));
else
hi = &ht->iterator;
hi->ht = ht;
hi->index = 0;
hi->this = NULL;
hi->next = NULL;
return apr_hash_next(hi);
}
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;
}
/*
* 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;
const unsigned char *p;
unsigned int hash;
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>
*/
hash = 0;
if (klen == APR_HASH_KEY_STRING) {
for (p = key; *p; p++) {
hash = hash * 33 + *p;
}
klen = p - (const unsigned char *)key;
}
else {
for (p = key, i = klen; i; i--, p++) {
hash = hash * 33 + *p;
}
}
/* 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 */
he = malloc(ht->pool, sizeof(*he));
he->next = NULL;
he->hash = hash;
he->key = key;
he->klen = klen;
he->val = val;
*hep = he;
