Option Explicit
Dim CY As Boolean

Sub xror(ByRef v)
CY = v And 1
If v < 255 Then v = (v * 128) Mod 255
End Sub

Sub xrol(ByRef v)
CY = v And 128
If v < 255 Then v = (v * 2) Mod 255
End Sub

Sub xmsk(ByRef v, ByVal s)
v = s And 255
End Sub

Sub xand(ByRef v, ByVal s)
v = v And s
End Sub

Sub xmov(ByRef v, ByVal s)
v = s
End Sub

Sub xadd(ByRef v, ByVal s)
v = v + s
CY = v > 255
v = v And 255
End Sub

Sub xadc(ByRef v, ByVal s)
v = v + s - CY
CY = v > 255
v = v And 255
End Sub

Sub xsub(ByRef v, ByVal s)
v = v - s
CY = v And 256
v = v And 255
End Sub

Sub test(ByVal c, ByVal d)
Dim cd
'Debug.Print c, d
cd = c * d
Dim a, b, e, f
xror d
xmsk a, CY
xand a, c
xmov b, a
xrol c
xror d
xmsk e, CY
xand e, c
xmov f, e
xand e, 254
xadd a, e
xadc b, f
xrol c
xror d
xmsk e, CY
xand e, c
xmov f, e
xand e, 252
xadd a, e
xadc b, f
xrol c
xror d
xmsk e, CY
xand e, c
xmov f, e
xand e, 248
xadd a, e
xadc b, f
xrol c
xror d
xmsk e, CY
xand e, c
xmov f, e
xand e, 240
xadd a, e
xadc b, f
xrol c
xror d
xmsk e, CY
xand e, c
xmov f, e
xand e, 224
xadd a, e
xadc b, f
xrol c
xror d
xmsk e, CY
xand e, c
xmov f, e
xand e, 192
xadd a, e
xadc b, f
xrol c
xror d
xmsk e, CY
xand e, c
xmov f, e
xand e, 128
xadd a, e
xadc b, f
xsub b, a
'b = -b And 255
Debug.Assert b * 256 + a = cd
End Sub

Sub Main()
Dim i, j
For i = 0 To 255
    For j = 0 To 255
        test i, j
    Next
Next
End Sub