Problem Statement

Ethiopian multiplication is a method of multiplying integers using only addition, doubling, and halving.

Method:

For example:   17 × 34 Halving the first column: Doubling the second column: Strike-out rows whose first cell is even: Sum the remaining numbers in the right-hand column: So 17 multiplied by 34, by the Ethiopian method is 578.

The task is to define three named functions/methods/procedures/subroutines:

Use these functions to create a function that does Ethiopian multiplication.

Let's start with the solution:

MsgBox % Ethiopian(17, 34) "`n" Ethiopian2(17, 34)

; func definitions:
half( x ) {
	return x >> 1
}

double( x ) {
	return x << 1
}

isEven( x ) {
	return x & 1 == 0
}

Ethiopian( a, b ) {
	r := 0
	While (a >= 1) {
		if !isEven(a)
			r += b
		a := half(a)
		b := double(b)
	}
	return r
}

; or a recursive function:
Ethiopian2( a, b, r = 0 ) { ;omit r param on initial call
	return a==1 ? r+b : Ethiopian2( half(a), double(b), !isEven(a) ? r+b : r )
}