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Diffstat (limited to 'src/common/hash.c')
| -rw-r--r-- | src/common/hash.c | 380 |
1 files changed, 0 insertions, 380 deletions
diff --git a/src/common/hash.c b/src/common/hash.c deleted file mode 100644 index 789e85c..0000000 --- a/src/common/hash.c +++ /dev/null @@ -1,380 +0,0 @@ -/* - * Copyright (c) 2004, Nate Nielsen - * All rights reserved. - * - * Redistribution and use in source and binary forms, with or without - * modification, are permitted provided that the following conditions - * are met: - * - * * Redistributions of source code must retain the above - * copyright notice, this list of conditions and the - * following disclaimer. - * * Redistributions in binary form must reproduce the - * above copyright notice, this list of conditions and - * the following disclaimer in the documentation and/or - * other materials provided with the distribution. - * * The names of contributors to this software may not be - * used to endorse or promote products derived from this - * software without specific prior written permission. - * - * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS - * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT - * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS - * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE - * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, - * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, - * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS - * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED - * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, - * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF - * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH - * DAMAGE. - */ - -/* - * Originally from apache 2.0 - * Modifications for general use by <nielsen@memberwebs.com> - */ - -/* 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. - */ - -#include <sys/types.h> -#include <stdlib.h> -#include "hash.h" - -#define KEY_DATA(he) ((he)->key) - -/* - * 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 hsh_entry_t hsh_entry_t; - -struct hsh_entry_t -{ - hsh_entry_t* next; - unsigned int hash; - const void* key; - size_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 - * hsh_next(). - */ -struct hsh_index_t -{ - hsh_t* ht; - hsh_entry_t* ths; - hsh_entry_t* 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 hsh_t -{ - hsh_entry_t** array; - hsh_index_t iterator; /* For hsh_first(...) */ - unsigned int count; - unsigned int max; -}; - - -#define INITIAL_MAX 15 /* tunable == 2^n - 1 */ -#define int_malloc malloc -#define int_calloc calloc -#define int_free free - -/* - * Hash creation functions. - */ - -static hsh_entry_t** alloc_array(hsh_t* ht, unsigned int max) -{ - return (hsh_entry_t**)int_calloc(sizeof(*(ht->array)), (max + 1)); -} - -hsh_t* hsh_create() -{ - hsh_t* ht = int_malloc(sizeof(hsh_t)); - if(ht) - { - ht->count = 0; - ht->max = INITIAL_MAX; - ht->array = alloc_array(ht, ht->max); - if(!ht->array) - { - int_free(ht); - return NULL; - } - } - return ht; -} - -void hsh_free(hsh_t* ht) -{ - hsh_index_t* hi; - - for(hi = hsh_first(ht); hi; hi = hsh_next(hi)) - int_free(hi->ths); - - if(ht->array) - int_free(ht->array); - - int_free(ht); -} - -/* - * Hash iteration functions. - */ - -hsh_index_t* hsh_next(hsh_index_t* hi) -{ - hi->ths = hi->next; - while(!hi->ths) - { - if(hi->index > hi->ht->max) - return NULL; - - hi->ths = hi->ht->array[hi->index++]; - } - hi->next = hi->ths->next; - return hi; -} - -hsh_index_t* hsh_first(hsh_t* ht) -{ - hsh_index_t* hi = &ht->iterator; - - hi->ht = ht; - hi->index = 0; - hi->ths = NULL; - hi->next = NULL; - return hsh_next(hi); -} - -void* hsh_this(hsh_index_t* hi, const void** key, size_t* klen) -{ - if(key) - *key = KEY_DATA(hi->ths); - if(klen) - *klen = hi->ths->klen; - return (void*)hi->ths->val; -} - - -/* - * Expanding a hash table - */ - -static int expand_array(hsh_t* ht) -{ - hsh_index_t* hi; - hsh_entry_t** new_array; - unsigned int new_max; - - new_max = ht->max * 2 + 1; - new_array = alloc_array(ht, new_max); - - if(!new_array) - return 0; - - for(hi = hsh_first(ht); hi; hi = hsh_next(hi)) - { - unsigned int i = hi->ths->hash & new_max; - hi->ths->next = new_array[i]; - new_array[i] = hi->ths; - } - - if(ht->array) - free(ht->array); - - ht->array = new_array; - ht->max = new_max; - return 1; -} - -/* - * 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 hsh_entry_t** find_entry(hsh_t* ht, const void* key, size_t klen, const void* val) -{ - hsh_entry_t** hep; - hsh_entry_t* he; - const unsigned char* p; - unsigned int hash; - size_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 == HSH_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(KEY_DATA(he), key, klen) == 0) - break; - } - - if(he || !val) - return hep; - - /* add a new entry for non-NULL val */ - he = int_malloc(sizeof(*he)); - - if(he) - { - /* Key points to external data */ - he->key = key; - he->klen = klen; - - he->next = NULL; - he->hash = hash; - he->val = val; - - *hep = he; - ht->count++; - } - - return hep; -} - -void* hsh_get(hsh_t* ht, const void *key, size_t klen) -{ - hsh_entry_t** he = find_entry(ht, key, klen, NULL); - - if(he && *he) - return (void*)((*he)->val); - else - return NULL; -} - -int hsh_set(hsh_t* ht, const void* key, size_t klen, void* val) -{ - hsh_entry_t** hep = find_entry(ht, key, klen, val); - - if(hep && *hep) - { - /* replace entry */ - (*hep)->val = val; - - /* check that the collision rate isn't too high */ - if(ht->count > ht->max) - { - if(!expand_array(ht)) - return 0; - } - - return 1; - } - - return 0; -} - -void* hsh_rem(hsh_t* ht, const void* key, size_t klen) -{ - hsh_entry_t** hep = find_entry(ht, key, klen, NULL); - void* val = NULL; - - if(hep && *hep) - { - hsh_entry_t* old = *hep; - *hep = (*hep)->next; - --ht->count; - val = (void*)old->val; - free(old); - } - - return val; -} - -unsigned int hsh_count(hsh_t* ht) -{ - return ht->count; -} - |