Challenge for the day

[AD108]

Found this on the web. Wondered if anyone could (and wanted to) explain
line by line. Basically a very fast sorting method.

Sub QuickSort(List() As Integer)
' Sorts an array using Quick Sort algorithm
' Adapted from "Visual Basic Developers Guide"
' By D.F. Scott

Dim i As Integer, j As Integer, b As Integer
Dim l As Integer, t As Integer, r As Integer, d As Integer

Dim p(1 To 100) As Integer
Dim w(1 To 100) As Integer

k = 1
p(k) = LBound(List)
w(k) = UBound(List)
l = 1
d = 1
r = UBound(List)
Do
toploop:
If r - l < 9 Then GoTo bubsort
i = l
j = r
While j > i
comp = comp + 1
If List(i) > List(j) Then
swic = swic + 1
t = List(j)
oldx1 = List(j)
oldy1 = j
List(j) = List(i)
oldx2 = List(i)
oldy2 = i
newx1 = List(j)
newy1 = j
List(i) = t
newx2 = List(i)
newy2 = i
d = -d
End If
If d = -1 Then
j = j - 1
Else
i = i + 1
End If
Wend
j = j + 1
k = k + 1
If i - l < r - j Then
p(k) = j
w(k) = r
r = i
Else
p(k) = l
w(k) = i
l = j
End If
d = -d
GoTo toploop
bubsort:
If r - l > 0 Then
For i = l To r
b = i
For j = b + 1 To r
comp = comp + 1
If List(j) <= List(b) Then b = j
Next j
If i <> b Then
swic = swic + 1
t = List(b)
oldx1 = List(b)
oldy1 = b
List(b) = List(i)
oldx2 = List(i)
oldy2 = i
newx1 = List(b)
newy1 = b
List(i) = t
newx2 = List(i)
newy2 = i
End If
Next i
End If
l = p(k)
r = w(k)
k = k - 1
Loop Until k = 0
End Sub