+/*****************************************************************************
+ * hashtables.c: Hash tables handling
+ *****************************************************************************
+ * Copyright (C) 2002-2004 the VideoLAN team
+ * $Id: variables.c 13991 2006-01-22 17:12:24Z zorglub $
+ *
+ * Authors: Samuel Hocevar <sam@zoy.org>
+ * Clément Stenac <zorglub@videolan.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., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+/*****************************************************************************
+ * Preamble
+ *****************************************************************************/
+#include <vlc/vlc.h>
+
+static uint64_t HashString ( const char *, int );
+static int FindSlot ( hashtable_entry_t *, int, uint64_t );
+static int LookupInner ( hashtable_entry_t *, int, uint64_t );
+
+
+
+void vlc_HashInsert( hashtable_entry_t **pp_array, int *pi_count, int i_id,
+ const char *psz_name, void *p_data )
+{
+ hashtable_entry_t *p_new;
+ int64_t i_hash = HashString( psz_name, i_id );
+ int i_new = FindSlot( *pp_array, *pi_count, i_hash );
+
+ *pp_array = realloc( *pp_array, ( *pi_count + 2) * sizeof( hashtable_entry_t ) );
+
+ memmove( *pp_array + i_new + 1 , *pp_array + i_new, ( *pi_count - i_new ) *
+ sizeof( hashtable_entry_t ) );
+ (*pi_count)++;
+
+ p_new = &((*pp_array)[i_new]);
+ p_new->i_hash = i_hash;
+ p_new->i_id = i_id;
+ p_new->psz_name = strdup( psz_name );
+ p_new->p_data = p_data;
+
+}
+
+void * vlc_HashRetrieve( hashtable_entry_t *p_array, int i_count, int i_id,
+ const char *psz_name )
+{
+ int i_new = vlc_HashLookup( p_array, i_count, i_id, psz_name );
+
+ if( i_new >= 0 && i_new < i_count )
+ {
+ return p_array[i_new].p_data;
+ }
+ return NULL;
+}
+
+/*****************************************************************************
+ * FindSlot: find an empty slot to insert a new variable
+ *****************************************************************************
+ * We use a recursive inner function indexed on the hash. This function does
+ * nothing in the rare cases where a collision may occur, see Lookup()
+ * to see how we handle them.
+ * XXX: does this really need to be written recursively?
+ *****************************************************************************/
+static int FindSlot( hashtable_entry_t *p_array, int i_count, uint64_t i_hash )
+{
+ int i_middle;
+
+
+ if( i_hash <= p_array[0].i_hash )
+ {
+ return 0;
+ }
+
+ if( i_hash >= p_array[i_count - 1].i_hash )
+ {
+ return i_count;
+ }
+
+ i_middle = i_count / 2;
+
+ /* We know that 0 < i_middle */
+ if( i_hash < p_array[i_middle].i_hash )
+ {
+ return FindSlot( p_array, i_middle, i_hash );
+ }
+
+ /* We know that i_middle + 1 < i_count */
+ if( i_hash > p_array[i_middle + 1].i_hash )
+ {
+ return i_middle + 1 + FindSlot( p_array + i_middle + 1,
+ i_count - i_middle - 1,
+ i_hash );
+ }
+
+ return i_middle + 1;
+}
+
+/*****************************************************************************
+ * Lookup: find an existing variable given its name and id
+ *****************************************************************************
+ * We use a recursive inner function indexed on the hash. Care is taken of
+ * possible hash collisions.
+ * XXX: does this really need to be written recursively?
+ *****************************************************************************/
+int vlc_HashLookup( hashtable_entry_t *p_array, int i_count,
+ int i_id, const char *psz_name )
+{
+ uint64_t i_hash;
+ int i, i_pos;
+
+ if( i_count == 0 )
+ {
+ return -1;
+ }
+
+ i_hash = HashString( psz_name, i_id );
+
+ i_pos = LookupInner( p_array, i_count, i_hash );
+
+ /* Hash not found */
+ if( i_hash != p_array[i_pos].i_hash )
+ {
+ return -1;
+ }
+
+ /* Hash found, entry found */
+ if( !strcmp( psz_name, p_array[i_pos].psz_name ) )
+ {
+ return i_pos;
+ }
+
+ /* Hash collision! This should be very rare, but we cannot guarantee
+ * it will never happen. Just do an exhaustive search amongst all
+ * entries with the same hash. */
+ for( i = i_pos - 1 ; i > 0 && i_hash == p_array[i].i_hash ; i-- )
+ {
+ if( !strcmp( psz_name, p_array[i].psz_name ) && p_array[i].i_id == i_id )
+ {
+ return i;
+ }
+ }
+
+ for( i = i_pos + 1 ; i < i_count && i_hash == p_array[i].i_hash ; i++ )
+ {
+ if( !strcmp( psz_name, p_array[i].psz_name ) && p_array[i].i_id == i_id )
+ {
+ return i;
+ }
+ }
+
+ /* Hash found, but entry not found */
+ return -1;
+}
+
+static int LookupInner( hashtable_entry_t *p_array, int i_count, uint64_t i_hash )
+{
+ int i_middle;
+
+ if( i_hash <= p_array[0].i_hash )
+ {
+ return 0;
+ }
+
+ if( i_hash >= p_array[i_count-1].i_hash )
+ {
+ return i_count - 1;
+ }
+
+ i_middle = i_count / 2;
+
+ /* We know that 0 < i_middle */
+ if( i_hash < p_array[i_middle].i_hash )
+ {
+ return LookupInner( p_array, i_middle, i_hash );
+ }
+
+ /* We know that i_middle + 1 < i_count */
+ if( i_hash > p_array[i_middle].i_hash )
+ {
+ return i_middle + LookupInner( p_array + i_middle,
+ i_count - i_middle,
+ i_hash );
+ }
+
+ return i_middle;
+}
+
+
+/*****************************************************************************
+ * HashString: our cool hash function
+ *****************************************************************************
+ * This function is not intended to be crypto-secure, we only want it to be
+ * fast and not suck too much. This one is pretty fast and did 0 collisions
+ * in wenglish's dictionary.
+ *****************************************************************************/
+static uint64_t HashString( const char *psz_string, int i_id )
+{
+ uint64_t i_hash = 0;
+
+ while( *psz_string )
+ {
+ i_hash += *psz_string++;
+ i_hash += i_hash << 10;
+ i_hash ^= i_hash >> 8;
+ }
+
+ i_hash += ( i_id << 32 );
+
+ return i_hash;
+}