/*
Example: 57 * 18
57 18
Halving the first column:
28 18
14
7
3
1
Doubling the second column:
28 36
14 72
7 144
3 288
1 576
Remove rows whose first cell is even:
18
28 36 x
14 72 x
7 144
3 288
1 576
Sum the remaining numbers in the right-hand column:
18
28 -
14 -
7 162
3 288
1 576
====
1026
*/
fn ethiopian_multiply(mut a: i32, mut b: i32) -> i32 {
let mut sum = 0;
while a > 0 {
if a % 2 == 1 { // keep only odd rows
sum += b;
println!("sum = {}", sum);
}
a /= 2; // halve left side
b *= 2; // double right side
println!("a = {} b = {}", a, b);
}
sum
}
fn main() {
let a = 57;
let b = 18;
println!("{}", ethiopian_multiply(a, b));
}
/*
run:
sum = 18
a = 28 b = 36
a = 14 b = 72
a = 7 b = 144
sum = 162
a = 3 b = 288
sum = 450
a = 1 b = 576
sum = 1026
a = 0 b = 1152
1026
*/
