/// <summary>
/// Try to store the entry into its Hash2 location. If that
/// fails then kick the entry in Hash2 to that entry's Hash2
/// location. Recurse until we either find an empty Hash2 slot
/// or try to kick an entry that is already in its Hash2
/// location into its Hash2 location (which would cause an
/// infinite loop).
/// </summary>
/// <param name="hashEntry">The hash entry to store.</param>
/// <returns>true if the hash entry was stored at its Hash2
/// location; false if storing the hash entry at its Hash2
/// location would cause an infinite loop.</returns>
private bool TryAssignAndKickOutIfNeeded(CuckooHashEntry hashEntry)
{
// Success is immediate if the Hash2 location is unused.
if (!this.hashTable.ContainsKey(hashEntry.Hash2))
{
this.NumValuesStoredAtSecondHash++;
this.hashTable[hashEntry.Hash2] = hashEntry;
return(true);
}
// Get the kicked out entry and fail if we have already seen
// that entry.
var kickedOutEntry = this.hashTable[hashEntry.Hash2];
if (kickedOutEntry.Seen)
{
return(false);
}
// Put the new word in the kicked out word's spot.
this.hashTable[hashEntry.Hash2] = hashEntry;
hashEntry.Seen = true;
this.NumValuesStoredAtFirstHash--;
this.NumValuesStoredAtSecondHash++;
// Try to store the kicked out entry in its Hash2 location,
// kicking out additional words as necessary.
kickedOutEntry.Seen = true;
return(this.TryAssignAndKickOutIfNeeded(kickedOutEntry));
}
/// <summary>
/// Try to add a value to the hash table. The hash functions
/// must be rebuilt if the add operation fails (and assuming
/// that you want to be able to add this value to the table).
/// The table must be cleared after rebuilding the hash
/// functions if the same CuckooHashTable object will be reused.
/// </summary>
/// <param name="value">The value to add to the hash
/// table.</param>
/// <returns>true if the value was added to the table; false if
/// trying to add the value caused an infinite loop.</returns>
public bool TryAddValue(TValue value)
{
// Wrap the value in a CuckooHashEntry.
var hashEntry = new CuckooHashEntry(this.chf1(value), this.chf2(value), value);
// Try to put the value in its first position.
if (!this.hashTable.ContainsKey(hashEntry.Hash1))
{
this.hashTable[hashEntry.Hash1] = hashEntry;
this.NumValuesStoredAtFirstHash++;
}
else
{
// We need to kick the entry in our Hash1 position into
// its Hash2 position. This could cause other entries
// to be kicked out of position, which could be an
// infinite loop. As such, we track the seen state of
// all of the entries and exit the loop if we try to
// kick out an object that has already been seen. The
// first step in this process is thus to clear the seen
// state for all of the entries.
foreach (var entry in this.hashTable.Values)
{
entry.Seen = false;
}
// Try to put the entry into its Hash2 location. If
// that fails then kick the entry in Hash2 to that
// entry's Hash2 location. Repeat until we either find
// an empty Hash2 slot or try to kick an entry that is
// already in its Hash2 location into its Hash2 location
// (which would cause an infinite loop).
if (!this.TryAssignAndKickOutIfNeeded(hashEntry))
{
return(false);
}
}
// We were successful in adding this entry to the hash table.
return(true);
}
