HashTable – a class module for storing (key,value) pairs

'----------------------------------------------' HASHTABLE class module'' This class implements a hashtable, a structure that offers many' of the features of a collectior or dictionary, and is often' even faster than the built-in collection.'' NOTE: must make Item the default member, using the Tools | Procedure ' Attributes dialog'' Usage:'   Dim ht As New HashTable'   ht.SetSize 10000           ' initial number of slots (the higher,'  the better)''   ' enforce case-insensitive key search'   ht.IgnoreCase = True'   ' add values'   ht.Add "key", value        ' add a value associated to a key'   ' count how many values are in the table'   Print ht.Count'   ' read/write a value'   Print ht("key")'   ht("key") = newValue''   ' remove a value'   ht.Remove "key"'   ' remove all values'   ht.RemoveAll'   ' check whether a value exists'   If ht.Exists("key") Then ...''   ' get the array of keys and values'   Dim keys() As String, values() As Variant'   keys() = ht.Keys'   values() = ht.Values''----------------------------------------------Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (dest As _    Any, source As Any, ByVal bytes As Long)' default valuesConst DEFAULT_HASHSIZE = 1024Const DEFAULT_LISTSIZE = 2048Const DEFAULT_CHUNKSIZE = 1024Option ExplicitPrivate Type SlotType    Key As String    Value As Variant    nextItem As Long      ' 0 if last itemEnd Type' for each hash code this array holds the first element' in slotTable() with the corresponding hash codeDim hashTbl() As Long' the array that holds the dataDim slotTable() As SlotType' pointer to first free slotDim FreeNdx As Long' size of hash tableDim m_HashSize As Long' size of slot tableDim m_ListSize As Long' chunk sizeDim m_ChunkSize As Long' items in the slot tableDim m_Count As Long' member variable for IgnoreCase propertyPrivate m_IgnoreCase As Boolean' True if keys are searched in case-unsensitive mode' this can be assigned to only when the hash table is emptyProperty Get IgnoreCase() As Boolean    IgnoreCase = m_IgnoreCaseEnd PropertyProperty Let IgnoreCase(ByVal newValue As Boolean)    If m_Count Then        Err.Raise 1001, , "The Hash Table isn't empty"    End If    m_IgnoreCase = newValueEnd Property' initialize the hash tableSub SetSize(ByVal HashSize As Long, Optional ByVal ListSize As Long, _    Optional ByVal ChunkSize As Long)    ' provide defaults    If ListSize <= 0 Then ListSize = m_ListSize    If ChunkSize <= 0 Then ChunkSize = m_ChunkSize    ' save size values    m_HashSize = HashSize    m_ListSize = ListSize    m_ChunkSize = ChunkSize    m_Count = 0    ' rebuild tables    FreeNdx = 0    ReDim hashTbl(0 To HashSize - 1) As Long    ReDim slotTable(0) As SlotType    ExpandSlotTable m_ListSizeEnd Sub' check whether an item is in the hash tableFunction Exists(Key As String) As Boolean    Exists = GetSlotIndex(Key) <> 0End Function' add a new element to the hash tableSub Add(Key As String, Value As Variant)    Dim ndx As Long, Create As Boolean        ' get the index to the slot where the value is    ' (allocate a new slot if necessary)    Create = True    ndx = GetSlotIndex(Key, Create)        If Create Then        ' the item was actually added        If IsObject(Value) Then            Set slotTable(ndx).Value = Value        Else            slotTable(ndx).Value = Value        End If    Else        ' raise error "This key is already associated with an item of this         ' collection"        Err.Raise 457    End IfEnd Sub' the value associated to a key' (empty if not found)Property Get Item(Key As String) As Variant    Dim ndx As Long    ' get the index to the slot where the value is    ndx = GetSlotIndex(Key)    If ndx = 0 Then        ' return Empty if not found    ElseIf IsObject(slotTable(ndx).Value) Then        Set Item = slotTable(ndx).Value    Else        Item = slotTable(ndx).Value    End IfEnd PropertyProperty Let Item(Key As String, Value As Variant)    Dim ndx As Long    ' get the index to the slot where the value is    ' (allocate a new slot if necessary)    ndx = GetSlotIndex(Key, True)    ' store the value    slotTable(ndx).Value = ValueEnd PropertyProperty Set Item(Key As String, Value As Object)    Dim ndx As Long    ' get the index to the slot where the value is    ' (allocate a new slot if necessary)    ndx = GetSlotIndex(Key, True)    ' store the value    Set slotTable(ndx).Value = ValueEnd Property' remove an item from the hash tableSub Remove(Key As String)    Dim ndx As Long, HCode As Long, LastNdx As Long    ndx = GetSlotIndex(Key, False, HCode, LastNdx)    ' raise error if no such element    If ndx = 0 Then Err.Raise 5        If LastNdx Then        ' this isn't the first item in the slotTable() array        slotTable(LastNdx).nextItem = slotTable(ndx).nextItem    ElseIf slotTable(ndx).nextItem Then        ' this is the first item in the slotTable() array        ' and is followed by one or more items        hashTbl(HCode) = slotTable(ndx).nextItem    Else        ' this is the only item in the slotTable() array        ' for this hash code        hashTbl(HCode) = 0    End If        ' put the element back in the free list    slotTable(ndx).nextItem = FreeNdx    FreeNdx = ndx    ' we have deleted an item    m_Count = m_Count - 1    End Sub' remove all items from the hash tableSub RemoveAll()    SetSize m_HashSize, m_ListSize, m_ChunkSizeEnd Sub' the number of items in the hash tableProperty Get Count() As Long    Count = m_CountEnd Property' the array of all keys' (VB5 users: convert return type to Variant)Property Get Keys() As Variant()    Dim i As Long, ndx As Long    Dim n As Long    ReDim res(0 To m_Count - 1) As Variant        For i = 0 To m_HashSize - 1        ' take the pointer from the hash table        ndx = hashTbl(i)        ' walk the slottable() array        Do While ndx            res(n) = slotTable(ndx).Key            n = n + 1            ndx = slotTable(ndx).nextItem        Loop    Next            ' assign to the result    Keys = res()End Property' the array of all values' (VB5 users: convert return type to Variant)Property Get Values() As Variant()    Dim i As Long, ndx As Long    Dim n As Long    ReDim res(0 To m_Count - 1) As Variant        For i = 0 To m_HashSize - 1        ' take the pointer from the hash table        ndx = hashTbl(i)        ' walk the slottable() array        Do While ndx            res(n) = slotTable(ndx).Value            n = n + 1            ndx = slotTable(ndx).nextItem        Loop    Next            ' assign to the result    Values = res()End Property'-----------------------------------------' Private procedures'-----------------------------------------Private Sub Class_Initialize()    ' initialize the tables at default size    SetSize DEFAULT_HASHSIZE, DEFAULT_LISTSIZE, DEFAULT_CHUNKSIZEEnd Sub' expand the slotTable() arrayPrivate Sub ExpandSlotTable(ByVal numEls As Long)    Dim newFreeNdx As Long, i As Long    newFreeNdx = UBound(slotTable) + 1        ReDim Preserve slotTable(0 To UBound(slotTable) + numEls) As SlotType    ' create the linked list of free items    For i = newFreeNdx To UBound(slotTable)        slotTable(i).nextItem = i + 1    Next    ' overwrite the last (wrong) value    slotTable(UBound(slotTable)).nextItem = FreeNdx    ' we now know where to pick the first free item    FreeNdx = newFreeNdxEnd Sub' return the hash code of a stringPrivate Function HashCode(Key As String) As Long    Dim lastEl As Long, i As Long        ' copy ansi codes into an array of long    lastEl = (Len(Key) - 1)  4    ReDim codes(lastEl) As Long    ' this also converts from Unicode to ANSI    CopyMemory codes(0), ByVal Key, Len(Key)        ' XOR the ANSI codes of all characters    For i = 0 To lastEl        HashCode = HashCode Xor codes(i)    Next    End Function' get the index where an item is stored or 0 if not found' if Create = True the item is created'' on exit Create=True only if a slot has been actually createdPrivate Function GetSlotIndex(ByVal Key As String, Optional Create As Boolean, _    Optional HCode As Long, Optional LastNdx As Long) As Long    Dim ndx As Long        ' raise error if invalid key    If Len(Key) = 0 Then Err.Raise 1001, , "Invalid key"        ' keep case-unsensitiveness into account    If m_IgnoreCase Then Key = UCase$(Key)    ' get the index in the hashTbl() array    HCode = HashCode(Key) Mod m_HashSize    ' get the pointer to the slotTable() array    ndx = hashTbl(HCode)        ' exit if there is no item with that hash code    Do While ndx        ' compare key with actual value        If slotTable(ndx).Key = Key Then Exit Do        ' remember last pointer        LastNdx = ndx        ' check the next item        ndx = slotTable(ndx).nextItem    Loop        ' create a new item if not there    If ndx = 0 And Create Then        ndx = GetFreeSlot()        PrepareSlot ndx, Key, HCode, LastNdx    Else        ' signal that no item has been created        Create = False    End If    ' this is the return value    GetSlotIndex = ndxEnd Function' return the first free slotPrivate Function GetFreeSlot() As Long    ' allocate new memory if necessary    If FreeNdx = 0 Then ExpandSlotTable m_ChunkSize    ' use the first slot    GetFreeSlot = FreeNdx    ' update the pointer to the first slot    FreeNdx = slotTable(GetFreeSlot).nextItem    ' signal this as the end of the linked list    slotTable(GetFreeSlot).nextItem = 0    ' we have one more item    m_Count = m_Count + 1End Function' assign a key and value to a given slotPrivate Sub PrepareSlot(ByVal Index As Long, ByVal Key As String, _    ByVal HCode As Long, ByVal LastNdx As Long)    ' assign the key    ' keep case-sensitiveness into account    If m_IgnoreCase Then Key = UCase$(Key)    slotTable(Index).Key = Key        If LastNdx Then        ' this is the successor of another slot        slotTable(LastNdx).nextItem = Index    Else        ' this is the first slot for a given hash code        hashTbl(HCode) = Index    End IfEnd Sub

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