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authorStef Walter <stef@memberwebs.com>2006-01-27 00:45:54 +0000
committerStef Walter <stef@memberwebs.com>2006-01-27 00:45:54 +0000
commit94dc650256935aa0c5cfff7675e535c54bb8c9b7 (patch)
tree429b6e7ab884bb6595dc574f1f433d2ba3f0560c /daemon/common/hash.c
parentd4835032aee718b51549938d10b5f8f20eb41c87 (diff)
Move rrdbot code into right project.
Diffstat (limited to 'daemon/common/hash.c')
-rw-r--r--daemon/common/hash.c380
1 files changed, 380 insertions, 0 deletions
diff --git a/daemon/common/hash.c b/daemon/common/hash.c
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+/*
+ * 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;
+}
+