text: /* Copyright (C) 2004 Christopher Clark <firstname.lastname@cl.cam.ac.uk> */
  
  #include "hashtable.h"
  #include "hashtable_private.h"
  #include <stdlib.h>
  #include <stdio.h>
  #include <string.h>
  #include <math.h>
  
  /*
  Credit for primes table: Aaron Krowne
   http://br.endernet.org/~akrowne/
   http://planetmath.org/encyclopedia/GoodHashTablePrimes.html
  */
  static const unsigned int primes[] = {
  53, 97, 193, 389,
  769, 1543, 3079, 6151,
  12289, 24593, 49157, 98317,
  196613, 393241, 786433, 1572869,
  3145739, 6291469, 12582917, 25165843,
  50331653, 100663319, 201326611, 402653189,
  805306457, 1610612741
  };
  const unsigned int prime_table_length = sizeof(primes)/sizeof(primes[0]);
  const float max_load_factor = 0.65;
  
  /*****************************************************************************/
  struct hashtable *
  create_hashtable(unsigned int minsize,
                   unsigned int (*hashf) (void*),
                   int (*eqf) (void*,void*))
  {
      struct hashtable *h;
      unsigned int pindex, size = primes[0];
      /* Check requested hashtable isn't too large */
      if (minsize > (1u << 30)) return NULL;
      /* Enforce size as prime */
      for (pindex=0; pindex < prime_table_length; pindex++) {
          if (primes[pindex] > minsize) { size = primes[pindex]; break; }
      }
      h = (struct hashtable *)malloc(sizeof(struct hashtable));
      if (NULL == h) return NULL; /*oom*/
      h->table = (struct entry **)malloc(sizeof(struct entry*) * size);
      if (NULL == h->table) { free(h); return NULL; } /*oom*/
      memset(h->table, 0, size * sizeof(struct entry *));
      h->tablelength  = size;
      h->primeindex   = pindex;
      h->entrycount   = 0;
      h->hashfn       = hashf;
      h->eqfn         = eqf;
      h->loadlimit    = (unsigned int) ceil(size * max_load_factor);
      return h;
  }
  
  /*****************************************************************************/
  unsigned int
  hash(struct hashtable *h, void *k)
  {
      /* Aim to protect against poor hash functions by adding logic here
       * - logic taken from java 1.4 hashtable source */
      unsigned int i = h->hashfn(k);
      i += ~(i << 9);
      i ^=  ((i >> 14) | (i << 18)); /* >>> */
      i +=  (i << 4);
      i ^=  ((i >> 10) | (i << 22)); /* >>> */
      return i;
  }
  
  /*****************************************************************************/
  static int
  hashtable_expand(struct hashtable *h)
  {
      /* Double the size of the table to accomodate more entries */
      struct entry **newtable;
      struct entry *e;
      struct entry **pE;
      unsigned int newsize, i, index;
      /* Check we're not hitting max capacity */
      if (h->primeindex == (prime_table_length - 1)) return 0;
      newsize = primes[++(h->primeindex)];
  
      newtable = (struct entry **)malloc(sizeof(struct entry*) * newsize);
      if (NULL != newtable)
      {
          memset(newtable, 0, newsize * sizeof(struct entry *));
          /* This algorithm is not 'stable'. ie. it reverses the list
           * when it transfers entries between the tables */
          for (i = 0; i < h->tablelength; i++) {
              while (NULL != (e = h->table[i])) {
                  h->table[i] = e->next;
                  index = indexFor(newsize,e->h);
                  e->next = newtable[index];
                  newtable[index] = e;
              }
          }
          free(h->table);
          h->table = newtable;
      }
      /* Plan B: realloc instead */
      else 
      {
          newtable = (struct entry **)
                     realloc(h->table, newsize * sizeof(struct entry *));
          if (NULL == newtable) { (h->primeindex)--; return 0; }
          h->table = newtable;
          memset(newtable[h->tablelength], 0, newsize - h->tablelength);
          for (i = 0; i < h->tablelength; i++) {
              for (pE = &(newtable[i]), e = *pE; e != NULL; e = *pE) {
                  index = indexFor(newsize,e->h);
                  if (index == i)
                  {
                      pE = &(e->next);
                  }
                  else
                  {
                      *pE = e->next;
                      e->next = newtable[index];
                      newtable[index] = e;
                  }
              }
          }
      }
      h->tablelength = newsize;
      h->loadlimit   = (unsigned int) ceil(newsize * max_load_factor);
      return -1;
  }
  
  /*****************************************************************************/
  unsigned int
  hashtable_count(struct hashtable *h)
  {
      return h->entrycount;
  }
  
  /*****************************************************************************/
  int
  hashtable_insert(struct hashtable *h, void *k, void *v)
  {
      /* This method allows duplicate keys - but they shouldn't be used */
      unsigned int index;
      struct entry *e;
      if (++(h->entrycount) > h->loadlimit)
      {
          /* Ignore the return value. If expand fails, we should
           * still try cramming just this value into the existing table
           * -- we may not have memory for a larger table, but one more
           * element may be ok. Next time we insert, we'll try expanding again.*/
          hashtable_expand(h);
      }
      e = (struct entry *)malloc(sizeof(struct entry));
      if (NULL == e) { --(h->entrycount); return 0; } /*oom*/
      e->h = hash(h,k);
      index = indexFor(h->tablelength,e->h);
      e->k = k;
      e->v = v;
      e->next = h->table[index];
      h->table[index] = e;
      return -1;
  }
  
  /*****************************************************************************/
  void * /* returns value associated with key */
  hashtable_search(struct hashtable *h, void *k)
  {
      struct entry *e;
      unsigned int hashvalue, index;
      hashvalue = hash(h,k);
      index = indexFor(h->tablelength,hashvalue);
      e = h->table[index];
      while (NULL != e)
      {
          /* Check hash value to short circuit heavier comparison */
          if ((hashvalue == e->h) && (h->eqfn(k, e->k))) return e->v;
          e = e->next;
      }
      return NULL;
  }
  
  /*****************************************************************************/
  void * /* returns value associated with key */
  hashtable_remove(struct hashtable *h, void *k)
  {
      /* TODO: consider compacting the table when the load factor drops enough,
       *       or provide a 'compact' method. */
  
      struct entry *e;
      struct entry **pE;
      void *v;
      unsigned int hashvalue, index;
  
      hashvalue = hash(h,k);
      index = indexFor(h->tablelength,hash(h,k));
      pE = &(h->table[index]);
      e = *pE;
      while (NULL != e)
      {
          /* Check hash value to short circuit heavier comparison */
          if ((hashvalue == e->h) && (h->eqfn(k, e->k)))
          {
              *pE = e->next;
              h->entrycount--;
              v = e->v;
              freekey(e->k);
              free(e);
              return v;
          }
          pE = &(e->next);
          e = e->next;
      }
      return NULL;
  }
  
  /*****************************************************************************/
  /* destroy */
  void
  hashtable_destroy(struct hashtable *h, int free_values)
  {
      unsigned int i;
      struct entry *e, *f;
      struct entry **table = h->table;
      if (free_values)
      {
          for (i = 0; i < h->tablelength; i++)
          {
              e = table[i];
              while (NULL != e)
              { f = e; e = e->next; freekey(f->k); free(f->v); free(f); }
          }
      }
      else
      {
          for (i = 0; i < h->tablelength; i++)
          {
              e = table[i];
              while (NULL != e)
              { f = e; e = e->next; freekey(f->k); free(f); }
          }
      }
      free(h->table);
      free(h);
  }
  
  /*
   * Copyright (c) 2002, Christopher Clark
   * 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.
   * 
   * * Neither the name of the original author; nor the names of any contributors
   * may 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.
  */
  