QuickSort

Sub QuickSort(arr As Variant, Optional numEls As Variant, _
    Optional descending As Boolean)

Dim value As Variant, temp As Variant
    Dim sp As Integer
    Dim leftStk(32) As Long, rightStk(32) As Long
    Dim leftNdx As Long, rightNdx As Long
    Dim i As Long, j As Long

' account for optional arguments
    If IsMissing(numEls) Then numEls = UBound(arr)
    ' init pointers
    leftNdx = LBound(arr)
    rightNdx = numEls
    ' init stack
    sp = 1
    leftStk(sp) = leftNdx
    rightStk(sp) = rightNdx

Do
        If rightNdx > leftNdx Then
            value = arr(rightNdx)
            i = leftNdx - 1
            j = rightNdx
            ' find the pivot item
            If descending Then
                Do
                    Do: i = i + 1: Loop Until arr(i) <= value
                    Do: j = j - 1: Loop Until j = leftNdx Or arr(j) >= value
                    temp = arr(i)
                    arr(i) = arr(j)
                    arr(j) = temp
                Loop Until j <= i
            Else
                Do
                    Do: i = i + 1: Loop Until arr(i) >= value
                    Do: j = j - 1: Loop Until j = leftNdx Or arr(j) <= value
                    temp = arr(i)
                    arr(i) = arr(j)
                    arr(j) = temp
                Loop Until j <= i
            End If
            ' swap found items
            temp = arr(j)
            arr(j) = arr(i)
            arr(i) = arr(rightNdx)
            arr(rightNdx) = temp
            ' push on the stack the pair of pointers that differ most
            sp = sp + 1
            If (i - leftNdx) > (rightNdx - i) Then
                leftStk(sp) = leftNdx
                rightStk(sp) = i - 1
                leftNdx = i + 1
            Else
                leftStk(sp) = i + 1
                rightStk(sp) = rightNdx
                rightNdx = i - 1
            End If
        Else
            ' pop a new pair of pointers off the stacks
            leftNdx = leftStk(sp)
            rightNdx = rightStk(sp)
            sp = sp - 1
            If sp = 0 Then Exit Do
        End If
    Loop
End Sub

Sub QuickSort(arr As Variant, Optional numEls As Variant, _
Optional descending As Boolean)

Dim value As Variant, temp As Variant
Dim sp As Integer
Dim leftStk(32) As Long, rightStk(32) As Long
Dim leftNdx As Long, rightNdx As Long
Dim i As Long, j As Long

' account for optional arguments

If IsMissing(numEls) Then numEls = UBound(arr)
' init pointers

leftNdx = LBound(arr)
rightNdx = numEls
' init stack

sp = 1
leftStk(sp) = leftNdx
rightStk(sp) = rightNdx

Do
If rightNdx > leftNdx Then
value = arr(rightNdx)
i = leftNdx - 1
j = rightNdx
' find the pivot item

If descending Then
Do
Do: i = i + 1: Loop Until arr(i) <= value
Do: j = j - 1: Loop Until j = leftNdx Or arr(j) >= value
temp = arr(i)
arr(i) = arr(j)
arr(j) = temp
Loop Until j <= i
Else
Do
Do: i = i + 1: Loop Until arr(i) >= value
Do: j = j - 1: Loop Until j = leftNdx Or arr(j) <= value
temp = arr(i)
arr(i) = arr(j)
arr(j) = temp
Loop Until j <= i
End If
' swap found items

temp = arr(j)
arr(j) = arr(i)
arr(i) = arr(rightNdx)
arr(rightNdx) = temp
' push on the stack the pair of pointers that differ most

sp = sp + 1
If (i - leftNdx) > (rightNdx - i) Then
leftStk(sp) = leftNdx
rightStk(sp) = i - 1
leftNdx = i + 1
Else
leftStk(sp) = i + 1
rightStk(sp) = rightNdx
rightNdx = i - 1
End If
Else
' pop a new pair of pointers off the stacks

leftNdx = leftStk(sp)
rightNdx = rightStk(sp)
sp = sp - 1
If sp = 0 Then Exit Do
End If
Loop
End Sub