hash.c

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/* $Id: hash.c,v 1.4 1998/02/07 14:25:12 brianp Exp $ */
 
/*
 * Mesa 3-D graphics library
 * Version:  2.5
 * Copyright (C) 1995-1997  Brian Paul
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
 
/*
 * $Log: hash.c,v $
 * Revision 1.4  1998/02/07 14:25:12  brianp
 * fixed small Sun compiler warning (John Stone)
 *
 * Revision 1.3  1997/09/22 02:33:07  brianp
 * added HashRemove() and HashFirstEntry()
 *
 * Revision 1.2  1997/09/03 13:13:45  brianp
 * added a few pointer casts
 *
 * Revision 1.1  1997/08/22 01:15:10  brianp
 * Initial revision
 *
 */
 
 
#ifdef PC_HEADER
#include "all.h"
#else
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include "hash.h"
#endif
 
 
/*
 * Generic hash table.  Only dependency is the GLuint datatype.
 *
 * This is used to implement display list and texture object lookup.
 * NOTE: key=0 is illegal.
 */
 
 
#define TABLE_SIZE 1001
 
struct HashEntry {
   GLuint Key;
   void *Data;
   struct HashEntry *Next;
};
 
struct HashTable {
   struct HashEntry *Table[TABLE_SIZE];
   GLuint MaxKey;
};
 
 
 
/*
 * Return pointer to a new, empty hash table.
 */
struct HashTable *NewHashTable(void)
{
   return (struct HashTable *) calloc(sizeof (struct HashTable), 1);
}
 
 
 
/*
 * Delete a hash table.
 */
void DeleteHashTable(struct HashTable *table)
{
   GLuint i;
   assert(table);
   for (i=0;i<TABLE_SIZE;i++) {
      struct HashEntry *entry = table->Table[i];
      while (entry) {
     struct HashEntry *next = entry->Next;
     free(entry);
     entry = next;
      }
   }
   free(table);
}
 
 
 
/*
 * Lookup an entry in the hash table.
 * Input:  table - the hash table
 *         key - the key
 * Return:  user data pointer or NULL if key not in table
 */
void *HashLookup(const struct HashTable *table, GLuint key)
{
   GLuint pos;
   struct HashEntry *entry;
 
   assert(table);
   assert(key);
 
   pos = key % TABLE_SIZE;
   entry = table->Table[pos];
   while (entry) {
      if (entry->Key == key) {
     return entry->Data;
      }
      entry = entry->Next;
   }
   return NULL;
}
 
 
 
/*
 * Insert into the hash table.  If an entry with this key already exists
 * we'll replace the existing entry.
 * Input:  table - the hash table
 *         key - the key (not zero)
 *         data - pointer to user data
 */
void HashInsert(struct HashTable *table, GLuint key, void *data)
{
   /* search for existing entry with this key */
   GLuint pos;
   struct HashEntry *entry;
 
   assert(table);
   assert(key);
 
   if (key > table->MaxKey)
      table->MaxKey = key;
 
   pos = key % TABLE_SIZE;
   entry = table->Table[pos];
   while (entry) {
      if (entry->Key == key) {
         /* replace entry's data */
     entry->Data = data;
     return;
      }
      entry = entry->Next;
   }
 
   /* alloc and insert new table entry */
   entry = (struct HashEntry *) calloc(sizeof(struct HashEntry), 1);
   entry->Key = key;
   entry->Data = data;
   entry->Next = table->Table[pos];
   table->Table[pos] = entry;
}
 
 
 
/*
 * Remove an entry from the hash table.
 * Input:  table - the hash table
 *         key - key of entry to remove
 */
void HashRemove(struct HashTable *table, GLuint key)
{
   GLuint pos;
   struct HashEntry *entry, *prev;
 
   assert(table);
   assert(key);
 
   pos = key % TABLE_SIZE;
   prev = NULL;
   entry = table->Table[pos];
   while (entry) {
      if (entry->Key == key) {
         /* found it! */
         if (prev) {
            prev->Next = entry->Next;
         }
         else {
            table->Table[pos] = entry->Next;
         }
         free(entry);
     return;
      }
      prev = entry;
      entry = entry->Next;
   }
}
 
 
 
/*
 * Return the key of the "first" entry in the hash table.
 * By calling this function until zero is returned we can get
 * the keys of all entries in the table.
 */
GLuint HashFirstEntry(const struct HashTable *table)
{
   GLuint pos;
   assert(table);
   for (pos=0; pos < TABLE_SIZE; pos++) {
      if (table->Table[pos])
         return table->Table[pos]->Key;
   }
   return 0;
}
 
 
 
/*
 * Dump contents of hash table for debugging.
 */
void HashPrint(const struct HashTable *table)
{
   GLuint i;
   assert(table);
   for (i=0;i<TABLE_SIZE;i++) {
      struct HashEntry *entry = table->Table[i];
      while (entry) {
     printf("%u %p\n", entry->Key, entry->Data);
     entry = entry->Next;
      }
   }
}
 
 
 
/*
 * Find a block of 'numKeys' adjacent unused hash keys.
 * Input:  table - the hash table
 *         numKeys - number of keys needed
 * Return:  startint key of free block or 0 if failure
 */
GLuint HashFindFreeKeyBlock(const struct HashTable *table, GLuint numKeys)
{
   GLuint maxKey = ~((GLuint) 0);
   if (maxKey - numKeys > table->MaxKey) {
      /* the quick solution */
      return table->MaxKey + 1;
   }
   else {
      /* the slow solution */
      GLuint freeCount = 0;
      GLuint freeStart = 0;
      GLuint key;
      for (key=0; key!=maxKey; key++) {
     if (HashLookup(table, key)) {
        /* darn, this key is already in use */
        freeCount = 0;
        freeStart = key+1;
     }
     else {
        /* this key not in use, check if we've found enough */
        freeCount++;
        if (freeCount == numKeys) {
           return freeStart;
        }
     }
      }
      /* cannot allocate a block of numKeys consecutive keys */
      return 0;
   }
}
 
 
 
#ifdef HASH_TEST_HARNESS
int main(int argc, char *argv[])
{
   int a, b, c;
   struct HashTable *t;
 
   printf("&a = %p\n", &a);
   printf("&b = %p\n", &b);
 
   t = NewHashTable();
   HashInsert(t, 501, &a);
   HashInsert(t, 10, &c);
   HashInsert(t, 0xfffffff8, &b);
   HashPrint(t);
   printf("Find 501: %p\n", HashLookup(t,501));
   printf("Find 1313: %p\n", HashLookup(t,1313));
   printf("Find block of 100: %d\n", HashFindFreeKeyBlock(t, 100));
   DeleteHashTable(t);
 
   return 0;
}
#endif