Initial Import

1 files changed, 462 insertions, 0 deletions

diff --git a/common/hash.c b/common/hash.c
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+/*
+ * 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"
+
+#ifdef HASH_TIMESTAMP
+#include <time.h>
+#endif
+
+#ifdef HASH_COPYKEYS
+  #define KEY_DATA(he) (void*)(((unsigned char*)(he)) + sizeof(*(he)))
+#else
+  #define KEY_DATA(he)  ((he)->key)
+#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 hash_entry_t hash_entry_t;
+
+struct hash_entry_t
+{
+  hash_entry_t* next;
+  unsigned int hash;
+#ifndef HASH_COPYKEYS
+  const void* key;
+  size_t klen;
+#endif
+  const void* val;
+#ifdef HASH_TIMESTAMP
+  time_t stamp;
+#endif
+};
+
+/*
+ * 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
+ * hash_next().
+ */
+struct hash_index_t
+{
+  hash_t* ht;
+  hash_entry_t* ths;
+  hash_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 hash_t
+{
+  hash_entry_t** array;
+  hash_index_t iterator;  /* For hash_first(...) */
+  unsigned int count;
+  unsigned int max;
+#ifdef HASH_COPYKEYS
+  unsigned int klen;
+#endif
+};
+
+#define INITIAL_MAX 15 /* tunable == 2^n - 1 */
+
+
+/*
+ * Hash creation functions.
+ */
+
+static hash_entry_t** alloc_array(hash_t* ht, unsigned int max)
+{
+  return malloc(sizeof(*(ht->array)) * (max + 1));
+}
+
+#ifdef HASH_COPYKEYS
+hash_t* hash_create(size_t klen)
+#else
+hash_t* hash_create()
+#endif
+{
+  hash_t* ht = malloc(sizeof(hash_t));
+  if(ht)
+  {
+    ht->count = 0;
+    ht->max = INITIAL_MAX;
+    ht->array = alloc_array(ht, ht->max);
+#ifdef HASH_COPYKEYS
+    ht->klen = klen;
+#endif
+
+    if(!ht->array)
+    {
+      free(ht);
+      return NULL;
+    }
+  }
+  return ht;
+}
+
+void hash_free(hash_t* ht)
+{
+  hash_index_t* hi;
+
+  for(hi = hash_first(ht); hi; hi = hash_next(hi))
+    free(hi->ths);
+
+  if(ht->array)
+    free(ht->array);
+
+  free(ht);
+}
+
+/*
+ * Hash iteration functions.
+ */
+
+hash_index_t* hash_next(hash_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;
+}
+
+hash_index_t* hash_first(hash_t* ht)
+{
+  hash_index_t* hi = &ht->iterator;
+
+  hi->ht = ht;
+  hi->index = 0;
+  hi->ths = NULL;
+  hi->next = NULL;
+  return hash_next(hi);
+}
+
+#ifdef HASH_COPYKEYS
+void* hash_this(hash_index_t* hi, const void** key)
+#else
+void* hash_this(hash_index_t* hi, const void** key, size_t* klen)
+#endif
+{
+  if(key)
+    *key = KEY_DATA(hi->ths);
+
+#ifndef HASH_COPYKEYS
+  if(klen)
+    *klen = hi->ths->klen;
+#endif
+
+  return (void*)hi->ths->val;
+}
+
+
+/*
+ * Expanding a hash table
+ */
+
+static int expand_array(hash_t* ht)
+{
+  hash_index_t* hi;
+  hash_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 = hash_first(ht); hi; hi = hash_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.
+ */
+
+#ifdef HASH_COPYKEYS
+static hash_entry_t** find_entry(hash_t* ht, const void* key, const void* val)
+#else
+static hash_entry_t** find_entry(hash_t* ht, const void* key, size_t klen, const void* val)
+#endif
+{
+  hash_entry_t** hep;
+  hash_entry_t* he;
+  const unsigned char* p;
+  unsigned int hash;
+  size_t i;
+
+#ifdef HASH_COPYKEYS
+  size_t klen = ht->klen;
+#endif
+
+  /*
+   * 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;
+
+#ifndef HASH_COPYKEYS
+  if(klen == HASH_KEY_STRING)
+  {
+    for(p = key; *p; p++)
+      hash = hash * 33 + *p;
+
+    klen = p - (const unsigned char *)key;
+  }
+  else
+#endif
+  {
+    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 &&
+#ifndef HASH_COPYKEYS
+      he->klen == klen &&
+#endif
+      memcmp(KEY_DATA(he), key, klen) == 0)
+     break;
+  }
+
+  if(he || !val)
+    return hep;
+
+  /* add a new entry for non-NULL val */
+#ifdef HASH_COPYKEYS
+  he = malloc(sizeof(*he) + klen);
+#else
+  he = malloc(sizeof(*he));
+#endif
+
+  if(he)
+  {
+#ifdef HASH_COPYKEYS
+    /* Key data points past end of entry */
+    memcpy(KEY_DATA(he), key, klen);
+#else
+    /* Key points to external data */
+    he->key = key;
+    he->klen = klen;
+#endif
+
+    he->next = NULL;
+    he->hash = hash;
+    he->val  = val;
+
+#ifdef HASH_TIMESTAMP
+    he->stamp = 0;
+#endif
+
+    *hep = he;
+    ht->count++;
+  }
+
+  return hep;
+}
+
+#ifdef HASH_COPYKEYS
+void* hash_get(hash_t* ht, const void *key)
+{
+    hash_entry_t** he = find_entry(ht, key, NULL);
+#else
+void* hash_get(hash_t* ht, const void *key, size_t klen)
+{
+    hash_entry_t** he = find_entry(ht, key, klen, NULL);
+#endif
+
+    if(he && *he)
+      return (void*)((*he)->val);
+    else
+      return NULL;
+}
+
+#ifdef HASH_COPYKEYS
+int hash_set(hash_t* ht, const void* key, const void* val)
+{
+  hash_entry_t** hep = find_entry(ht, key, val);
+#else
+int hash_set(hash_t* ht, const void* key, size_t klen, const void* val)
+{
+  hash_entry_t** hep = find_entry(ht, key, klen, val);
+#endif
+
+  if(hep && *hep)
+  {
+    if(val)
+    {
+      /* replace entry */
+      (*hep)->val = val;
+
+#ifdef HASH_TIMESTAMP
+      /* Update or set the timestamp */
+      (*hep)->stamp = time(NULL);
+#endif
+
+      /* check that the collision rate isn't too high */
+      if(ht->count > ht->max)
+      {
+        if(!expand_array(ht))
+          return 0;
+      }
+
+      return 1;
+    }
+  }
+
+  return 0;
+}
+
+#ifdef HASH_COPYKEYS
+void hash_rem(hash_t* ht, const void* key)
+{
+  hash_entry_t** hep = find_entry(ht, key, NULL);
+#else
+void hash_rem(hash_t* ht, const void* key, size_t klen)
+{
+  hash_entry_t** hep = find_entry(ht, key, klen, NULL);
+#endif
+
+  if(hep && *hep)
+  {
+    hash_entry_t* old = *hep;
+    *hep = (*hep)->next;
+    --ht->count;
+    free(old);
+  }
+}
+
+unsigned int hash_count(hash_t* ht)
+{
+  return ht->count;
+}
+
+#ifdef HASH_TIMESTAMP
+int hash_purge(hash_t* ht, time_t stamp)
+{
+  hash_index_t* hi;
+  int r = 0;
+
+  for(hi = hash_first(ht); hi; hi = hash_next(hi))
+  {
+    if(hi->ths->stamp < stamp)
+    {
+      /* No need to check for errors as we're deleting */
+#ifdef HASH_COPYKEYS
+      hash_rem(ht, KEY_DATA(hi->ths));
+#else
+      hash_rem(ht, hi->ths->key, hi->ths->klen);
+#endif
+
+      r++;
+    }
+  }
+
+  return r;
+}
+
+#ifdef HASH_COPYKEYS
+void* hash_touch(hash_index_t* hi, const void** key);
+{
+  hash_entry_t** hep = find_entry(ht, key, NULL);
+#else
+void* hash_touch(hash_index_t* hi, const void** key, size_t* klen);
+{
+  hash_entry_t** hep = find_entry(ht, key, klen, NULL);
+#endif
+
+  if(he && *he)
+    ((*he)->stamp) = time(NULL);
+}
+
+#endif /* HASH_TIMESTAMP */