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/* Hash table for checking keyword links. Implemented using double hashing.
Copyright (C) 1989-1998, 2000, 2002-2003 Free Software Foundation, Inc.
Written by Douglas C. Schmidt <schmidt@ics.uci.edu>
and Bruno Haible <bruno@clisp.org>.
This file is part of GNU GPERF.
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 3 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, see <https://www.gnu.org/licenses/>. */
/* Specification. */
#include "hash-table.h"
#include <stdio.h>
#include <string.h> /* declares memset(), strcmp() */
#include <hash.h>
#include "options.h"
/* We use a hash table with double hashing. This is the simplest kind of
hash table, given that we always only insert and never remove entries
from the hash table. */
/* To make double hashing efficient, there need to be enough spare entries. */
static const int size_factor = 10;
/* We make the size of the hash table a power of 2. This allows for two
optimizations: It eliminates the modulo instruction, and allows for an
easy secondary hashing function. */
/* Constructor. */
Hash_Table::Hash_Table (unsigned int size, bool ignore_length)
: _ignore_length (ignore_length),
_collisions (0)
{
/* There need to be enough spare entries. */
size = size * size_factor;
/* Find smallest power of 2 that is >= size. */
unsigned int shift = 0;
if ((size >> 16) > 0)
{
size = size >> 16;
shift += 16;
}
if ((size >> 8) > 0)
{
size = size >> 8;
shift += 8;
}
if ((size >> 4) > 0)
{
size = size >> 4;
shift += 4;
}
if ((size >> 2) > 0)
{
size = size >> 2;
shift += 2;
}
if ((size >> 1) > 0)
{
size = size >> 1;
shift += 1;
}
_log_size = shift;
_size = 1 << shift;
/* Allocate table. */
_table = new KeywordExt*[_size];
memset (_table, 0, _size * sizeof (*_table));
}
/* Destructor. */
Hash_Table::~Hash_Table ()
{
delete[] _table;
}
/* Print the table's contents. */
void
Hash_Table::dump () const
{
int field_width;
field_width = 0;
{
for (int i = _size - 1; i >= 0; i--)
if (_table[i])
if (field_width < _table[i]->_selchars_length)
field_width = _table[i]->_selchars_length;
}
fprintf (stderr,
"\ndumping the hash table\n"
"total available table slots = %d, total bytes = %d, total collisions = %d\n"
"location, %*s, keyword\n",
_size, _size * static_cast<unsigned int>(sizeof (*_table)),
_collisions, field_width, "keysig");
for (int i = _size - 1; i >= 0; i--)
if (_table[i])
{
fprintf (stderr, "%8d, ", i);
if (field_width > _table[i]->_selchars_length)
fprintf (stderr, "%*s", field_width - _table[i]->_selchars_length, "");
for (int j = 0; j < _table[i]->_selchars_length; j++)
putc (_table[i]->_selchars[j], stderr);
fprintf (stderr, ", %.*s\n",
_table[i]->_allchars_length, _table[i]->_allchars);
}
fprintf (stderr, "\nend dumping hash table\n\n");
}
/* Compares two items. */
inline bool
Hash_Table::equal (KeywordExt *item1, KeywordExt *item2) const
{
return item1->_selchars_length == item2->_selchars_length
&& memcmp (item1->_selchars, item2->_selchars,
item2->_selchars_length * sizeof (unsigned int))
== 0
&& (_ignore_length
|| item1->_allchars_length == item2->_allchars_length);
}
/* Attempts to insert ITEM in the table. If there is already an equal
entry in it, returns it. Otherwise inserts ITEM and returns NULL. */
KeywordExt *
Hash_Table::insert (KeywordExt *item)
{
unsigned hash_val =
hashpjw (reinterpret_cast<const unsigned char *>(item->_selchars),
item->_selchars_length * sizeof (unsigned int));
unsigned int probe = hash_val & (_size - 1);
unsigned int increment =
(((hash_val >> _log_size)
^ (_ignore_length ? 0 : item->_allchars_length))
<< 1) + 1;
/* Note that because _size is a power of 2 and increment is odd,
we have gcd(increment,_size) = 1, which guarantees that we'll find
an empty entry during the loop. */
while (_table[probe] != NULL)
{
if (equal (_table[probe], item))
return _table[probe];
_collisions++;
probe = (probe + increment) & (_size - 1);
}
_table[probe] = item;
return NULL;
}
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