include/pub_tool_hashtable.h

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/*--- A hash table implementation.            pub_tool_hashtable.h ---*/
/*--------------------------------------------------------------------*/

/*
   This file is part of Valgrind, a dynamic binary instrumentation
   framework.

   Copyright (C) 2005-2017 Nicholas Nethercote
      njn@valgrind.org

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   This program 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
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307, USA.

   The GNU General Public License is contained in the file COPYING.
*/

#ifndef __PUB_TOOL_HASHTABLE_H
#define __PUB_TOOL_HASHTABLE_H

#include "pub_tool_basics.h"   // VG_ macro

/* Generic type for a separately-chained hash table.  Via a kind of dodgy
   C-as-C++ style inheritance, tools can extend the VgHashNode type, so long
   as the first two fields match the sizes of these two fields.  Requires
   a bit of casting by the tool. */

// Problems with this data structure:
// - Separate chaining gives bad cache behaviour.  Hash tables with linear
//   probing give better cache behaviour.

typedef
   struct _VgHashNode {
      struct _VgHashNode * next;
      UWord              key;
   }
   VgHashNode;

typedef struct _VgHashTable VgHashTable;

/* Make a new table.  Allocates the memory with VG_(calloc)(), so can
   be freed with VG_(free)().  The table starts small but will
   periodically be expanded.  This is transparent to the users of this
   module. The function never returns NULL. */
extern VgHashTable *VG_(HT_construct) ( const HChar* name );

/* Count the number of nodes in a table. */
extern UInt VG_(HT_count_nodes) ( const VgHashTable *table );

/* Add a node to the table.  Duplicate keys are permitted. */
extern void VG_(HT_add_node) ( VgHashTable *t, void* node );

/* Looks up a VgHashNode by key in the table.  
 * Returns NULL if not found.  If entries
 * with duplicate keys are present, the most recently-added of the dups will
 * be returned, but it's probably better to avoid dups altogether. */
extern void* VG_(HT_lookup) ( const VgHashTable *table, UWord key );

/* Removes a VgHashNode by key from the table.  Returns NULL if not found. */
extern void* VG_(HT_remove) ( VgHashTable *table, UWord key );

typedef Word  (*HT_Cmp_t) ( const void* node1, const void* node2 );

/* Same as VG_(HT_lookup) and VG_(HT_remove), but allowing a part of or
   the full element to be compared for equality, not only the key.
   The typical use for the below function is to store a hash value of the
   element in the key, and have the comparison function checking for equality
   of the full element data.
   Attention about the comparison function:
    * It must *not* compare the 'next' pointer.
    * when comparing the rest of the node, if the node data contains holes
      between components, either the node memory should be fully initialised
      (e.g. allocated using VG_(calloc)) or each component should be compared
       individually.
   Note that the cmp function is only called for elements that already
   have keys that are equal. So, it is not needed for cmp to check for
   key equality. */
extern void* VG_(HT_gen_lookup) ( const VgHashTable *table, const void* node,
                                  HT_Cmp_t cmp );
extern void* VG_(HT_gen_remove) ( VgHashTable *table, const void* node,
                                  HT_Cmp_t cmp );

/* Output detailed usage/collision statistics.
   cmp will be used to verify if 2 elements with the same key are equal.
   Use NULL cmp if the hash table elements are only to be compared by key. */
extern void VG_(HT_print_stats) ( const VgHashTable *table, HT_Cmp_t cmp );

/* Allocates a suitably-sized array, copies pointers to all the hashtable
   elements into it, then returns both the array and the size of it.  The
   array must be freed with VG_(free). If the hashtable is empty, the
   function returns NULL and assigns *nelems = 0. */
extern VgHashNode** VG_(HT_to_array) ( const VgHashTable *table,
                                       /*OUT*/ UInt* n_elems );

/* Reset the table's iterator to point to the first element. */
extern void VG_(HT_ResetIter) ( VgHashTable *table );

/* Return the element pointed to by the iterator and move on to the
   next one.  Returns NULL if the last one has been passed, or if
   HT_ResetIter() has not been called previously.  Asserts if the
   table has been modified (HT_add_node, HT_remove) since
   HT_ResetIter.  This guarantees that callers cannot screw up by
   modifying the table whilst iterating over it (and is necessary to
   make the implementation safe; specifically we must guarantee that
   the table will not get resized whilst iteration is happening.
   Since resizing only happens as a result of calling HT_add_node,
   disallowing HT_add_node during iteration should give the required
   assurance. */
extern void* VG_(HT_Next) ( VgHashTable *table );

/* Remove the element pointed to by the iterator and leave the iterator
   in a state where VG_(HT_Next) will return the element just after the removed
   node.
   This allows removing elements from the table whilst iterating over it.
   Note that removing an entry does not resize the hash table, making this
   safe. */
extern void VG_(HT_remove_at_Iter)( VgHashTable *table );

/* Destroy a table and deallocates the memory used by the nodes using
   freenode_fn.*/
extern void VG_(HT_destruct) ( VgHashTable *table, void(*freenode_fn)(void*) );


#endif   // __PUB_TOOL_HASHTABLE_H

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/*--- end                                                          ---*/
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