Ethiopian multiplication: Difference between revisions

=={{header|VBScript}}==

=====Implementation=====

Nowhere near as optimal a solution as the Ada. Yes, it could have made as optimal, but the long way seemed more interesting.

Demonstrates a List class. The .recall and .replace methods have bounds checking but the code does not test for the exception that would be raised. List class extends the storage allocated for the list when the occupation of the list goes beyond the original allocation.

<code>option explicit</code> makes sure that all variables are declared.

<lang vb>

option explicit

class List

private theList

private nOccupiable

private nTop

sub class_initialize

nTop = 0

nOccupiable = 100

redim theList( nOccupiable )

end sub

public sub store( x )

if nTop >= nOccupiable then

nOccupiable = nOccupiable + 100

redim preserve theList( nOccupiable )

end if

theList( nTop ) = x

nTop = nTop + 1

end sub

public function recall( n )

if n >= 0 and n <= nOccupiable then

recall = theList( n )

else

err.raise vbObjectError + 1000,,"Recall bounds error"

end if

end function

public sub replace( n, x )

if n >= 0 and n <= nOccupiable then

theList( n ) = x

else

err.raise vbObjectError + 1001,,"Replace bounds error"

end if

end sub

public property get listCount

listCount = nTop

end property

end class

function halve( n )

halve = int( n / 2 )

end function

function twice( n )

twice = int( n * 2 )

end function

function iseven( n )

iseven = ( ( n mod 2 ) = 0 )

end function

function multiply( n1, n2 )

dim LL

set LL = new List

dim RR

set RR = new List

LL.store n1

RR.store n2

do while n1 <> 1

n1 = halve( n1 )

LL.store n1

n2 = twice( n2 )

RR.store n2

loop

dim i

for i = 0 to LL.listCount

if iseven( LL.recall( i ) ) then

RR.replace i, 0

end if

next

dim total

total = 0

for i = 0 to RR.listCount

total = total + RR.recall( i )

next

multiply = total

end function

</lang>

=====Invocation=====

<lang vb>

wscript.echo multiply(17,34)

</lang>

=====Output=====

<lang vb>

578

</lang>