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path: root/src/mesa/main/hash_table.c
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/*
 * Copyright © 2009,2012 Intel Corporation
 * Copyright © 1988-2004 Keith Packard and Bart Massey.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * Except as contained in this notice, the names of the authors
 * or their institutions shall not be used in advertising or
 * otherwise to promote the sale, use or other dealings in this
 * Software without prior written authorization from the
 * authors.
 *
 * Authors:
 *    Eric Anholt <eric@anholt.net>
 *    Keith Packard <keithp@keithp.com>
 */

/**
 * Implements an open-addressing, linear-reprobing hash table.
 *
 * For more information, see:
 *
 * http://cgit.freedesktop.org/~anholt/hash_table/tree/README
 */

#include <stdlib.h>
#include <string.h>

#include "main/hash_table.h"
#include "ralloc.h"

#define ARRAY_SIZE(array) (sizeof(array) / sizeof(array[0]))

static const uint32_t deleted_key_value;

/**
 * From Knuth -- a good choice for hash/rehash values is p, p-2 where
 * p and p-2 are both prime.  These tables are sized to have an extra 10%
 * free to avoid exponential performance degradation as the hash table fills
 */
static const struct {
   uint32_t max_entries, size, rehash;
} hash_sizes[] = {
   { 2,			5,		3	  },
   { 4,			7,		5	  },
   { 8,			13,		11	  },
   { 16,		19,		17	  },
   { 32,		43,		41        },
   { 64,		73,		71        },
   { 128,		151,		149       },
   { 256,		283,		281       },
   { 512,		571,		569       },
   { 1024,		1153,		1151      },
   { 2048,		2269,		2267      },
   { 4096,		4519,		4517      },
   { 8192,		9013,		9011      },
   { 16384,		18043,		18041     },
   { 32768,		36109,		36107     },
   { 65536,		72091,		72089     },
   { 131072,		144409,		144407    },
   { 262144,		288361,		288359    },
   { 524288,		576883,		576881    },
   { 1048576,		1153459,	1153457   },
   { 2097152,		2307163,	2307161   },
   { 4194304,		4613893,	4613891   },
   { 8388608,		9227641,	9227639   },
   { 16777216,		18455029,	18455027  },
   { 33554432,		36911011,	36911009  },
   { 67108864,		73819861,	73819859  },
   { 134217728,		147639589,	147639587 },
   { 268435456,		295279081,	295279079 },
   { 536870912,		590559793,	590559791 },
   { 1073741824,	1181116273,	1181116271},
   { 2147483648ul,	2362232233ul,	2362232231ul}
};

static int
entry_is_free(const struct hash_entry *entry)
{
   return entry->key == NULL;
}

static int
entry_is_deleted(const struct hash_table *ht, struct hash_entry *entry)
{
   return entry->key == ht->deleted_key;
}

static int
entry_is_present(const struct hash_table *ht, struct hash_entry *entry)
{
   return entry->key != NULL && entry->key != ht->deleted_key;
}

struct hash_table *
_mesa_hash_table_create(void *mem_ctx,
                        bool key_equals_function(const void *a,
                                                 const void *b))
{
   struct hash_table *ht;

   ht = ralloc(mem_ctx, struct hash_table);
   if (ht == NULL)
      return NULL;

   ht->mem_ctx = mem_ctx;
   ht->size_index = 0;
   ht->size = hash_sizes[ht->size_index].size;
   ht->rehash = hash_sizes[ht->size_index].rehash;
   ht->max_entries = hash_sizes[ht->size_index].max_entries;
   ht->key_equals_function = key_equals_function;
   ht->table = rzalloc_array(ht, struct hash_entry, ht->size);
   ht->entries = 0;
   ht->deleted_entries = 0;
   ht->deleted_key = &deleted_key_value;

   if (ht->table == NULL) {
      ralloc_free(ht);
      return NULL;
   }

   return ht;
}

/**
 * Frees the given hash table.
 *
 * If delete_function is passed, it gets called on each entry present before
 * freeing.
 */
void
_mesa_hash_table_destroy(struct hash_table *ht,
                         void (*delete_function)(struct hash_entry *entry))
{
   if (!ht)
      return;

   if (delete_function) {
      struct hash_entry *entry;

      hash_table_foreach(ht, entry) {
         delete_function(entry);
      }
   }
   ralloc_free(ht);
}

/** Sets the value of the key pointer used for deleted entries in the table.
 *
 * The assumption is that usually keys are actual pointers, so we use a
 * default value of a pointer to an arbitrary piece of storage in the library.
 * But in some cases a consumer wants to store some other sort of value in the
 * table, like a uint32_t, in which case that pointer may conflict with one of
 * their valid keys.  This lets that user select a safe value.
 *
 * This must be called before any keys are actually deleted from the table.
 */
void
_mesa_hash_table_set_deleted_key(struct hash_table *ht, const void *deleted_key)
{
   ht->deleted_key = deleted_key;
}

/**
 * Finds a hash table entry with the given key and hash of that key.
 *
 * Returns NULL if no entry is found.  Note that the data pointer may be
 * modified by the user.
 */
struct hash_entry *
_mesa_hash_table_search(struct hash_table *ht, uint32_t hash,
                        const void *key)
{
   uint32_t start_hash_address = hash % ht->size;
   uint32_t hash_address = start_hash_address;

   do {
      uint32_t double_hash;

      struct hash_entry *entry = ht->table + hash_address;

      if (entry_is_free(entry)) {
         return NULL;
      } else if (entry_is_present(ht, entry) && entry->hash == hash) {
         if (ht->key_equals_function(key, entry->key)) {
            return entry;
         }
      }

      double_hash = 1 + hash % ht->rehash;

      hash_address = (hash_address + double_hash) % ht->size;
   } while (hash_address != start_hash_address);

   return NULL;
}

static void
_mesa_hash_table_rehash(struct hash_table *ht, int new_size_index)
{
   struct hash_table old_ht;
   struct hash_entry *table, *entry;

   if (new_size_index >= ARRAY_SIZE(hash_sizes))
      return;

   table = rzalloc_array(ht, struct hash_entry,
                         hash_sizes[new_size_index].size);
   if (table == NULL)
      return;

   old_ht = *ht;

   ht->table = table;
   ht->size_index = new_size_index;
   ht->size = hash_sizes[ht->size_index].size;
   ht->rehash = hash_sizes[ht->size_index].rehash;
   ht->max_entries = hash_sizes[ht->size_index].max_entries;
   ht->entries = 0;
   ht->deleted_entries = 0;

   hash_table_foreach(&old_ht, entry) {
      _mesa_hash_table_insert(ht, entry->hash,
                              entry->key, entry->data);
   }

   ralloc_free(old_ht.table);
}

/**
 * Inserts the key with the given hash into the table.
 *
 * Note that insertion may rearrange the table on a resize or rehash,
 * so previously found hash_entries are no longer valid after this function.
 */
struct hash_entry *
_mesa_hash_table_insert(struct hash_table *ht, uint32_t hash,
                        const void *key, void *data)
{
   uint32_t start_hash_address, hash_address;

   if (ht->entries >= ht->max_entries) {
      _mesa_hash_table_rehash(ht, ht->size_index + 1);
   } else if (ht->deleted_entries + ht->entries >= ht->max_entries) {
      _mesa_hash_table_rehash(ht, ht->size_index);
   }

   start_hash_address = hash % ht->size;
   hash_address = start_hash_address;
   do {
      struct hash_entry *entry = ht->table + hash_address;
      uint32_t double_hash;

      if (!entry_is_present(ht, entry)) {
         if (entry_is_deleted(ht, entry))
            ht->deleted_entries--;
         entry->hash = hash;
         entry->key = key;
         entry->data = data;
         ht->entries++;
         return entry;
      }

      /* Implement replacement when another insert happens
       * with a matching key.  This is a relatively common
       * feature of hash tables, with the alternative
       * generally being "insert the new value as well, and
       * return it first when the key is searched for".
       *
       * Note that the hash table doesn't have a delete
       * callback.  If freeing of old data pointers is
       * required to avoid memory leaks, perform a search
       * before inserting.
       */
      if (entry->hash == hash &&
          ht->key_equals_function(key, entry->key)) {
         entry->key = key;
         entry->data = data;
         return entry;
      }


      double_hash = 1 + hash % ht->rehash;

      hash_address = (hash_address + double_hash) % ht->size;
   } while (hash_address != start_hash_address);

   /* We could hit here if a required resize failed. An unchecked-malloc
    * application could ignore this result.
    */
   return NULL;
}

/**
 * This function deletes the given hash table entry.
 *
 * Note that deletion doesn't otherwise modify the table, so an iteration over
 * the table deleting entries is safe.
 */
void
_mesa_hash_table_remove(struct hash_table *ht,
                        struct hash_entry *entry)
{
   if (!entry)
      return;

   entry->key = ht->deleted_key;
   ht->entries--;
   ht->deleted_entries++;
}

/**
 * This function is an iterator over the hash table.
 *
 * Pass in NULL for the first entry, as in the start of a for loop.  Note that
 * an iteration over the table is O(table_size) not O(entries).
 */
struct hash_entry *
_mesa_hash_table_next_entry(struct hash_table *ht,
                            struct hash_entry *entry)
{
   if (entry == NULL)
      entry = ht->table;
   else
      entry = entry + 1;

   for (; entry != ht->table + ht->size; entry++) {
      if (entry_is_present(ht, entry)) {
         return entry;
      }
   }

   return NULL;
}

/**
 * Returns a random entry from the hash table.
 *
 * This may be useful in implementing random replacement (as opposed
 * to just removing everything) in caches based on this hash table
 * implementation.  @predicate may be used to filter entries, or may
 * be set to NULL for no filtering.
 */
struct hash_entry *
_mesa_hash_table_random_entry(struct hash_table *ht,
                              bool (*predicate)(struct hash_entry *entry))
{
   struct hash_entry *entry;
   uint32_t i = rand() % ht->size;

   if (ht->entries == 0)
      return NULL;

   for (entry = ht->table + i; entry != ht->table + ht->size; entry++) {
      if (entry_is_present(ht, entry) &&
          (!predicate || predicate(entry))) {
         return entry;
      }
   }

   for (entry = ht->table; entry != ht->table + i; entry++) {
      if (entry_is_present(ht, entry) &&
          (!predicate || predicate(entry))) {
         return entry;
      }
   }

   return NULL;
}


/**
 * Quick FNV-1 hash implementation based on:
 * http://www.isthe.com/chongo/tech/comp/fnv/
 *
 * FNV-1 is not be the best hash out there -- Jenkins's lookup3 is supposed to
 * be quite good, and it probably beats FNV.  But FNV has the advantage that
 * it involves almost no code.  For an improvement on both, see Paul
 * Hsieh's http://www.azillionmonkeys.com/qed/hash.html
 */
uint32_t
_mesa_hash_data(const void *data, size_t size)
{
   uint32_t hash = 2166136261ul;
   const uint8_t *bytes = data;

   while (size-- != 0) {
      hash ^= *bytes;
      hash = hash * 0x01000193;
      bytes++;
   }

   return hash;
}

/** FNV-1 string hash implementation */
uint32_t
_mesa_hash_string(const char *key)
{
   uint32_t hash = 2166136261ul;

   while (*key != 0) {
      hash ^= *key;
      hash = hash * 0x01000193;
      key++;
   }

   return hash;
}

/**
 * String compare function for use as the comparison callback in
 * _mesa_hash_table_create().
 */
bool
_mesa_key_string_equal(const void *a, const void *b)
{
   return strcmp(a, b) == 0;
}

bool
_mesa_key_pointer_equal(const void *a, const void *b)
{
   return a == b;
}