169 Exploring the number of different ways a number can be expressed as a sum of powers of 2 -- v2.sf

#!/usr/bin/ruby

# Author: Trizen
# Date 18 March 2022
# https://github.com/trizen

# https://projecteuler.net/problem=169

# Runtime: 0.249s

func fusc(n) {

     var (a=1, b=0)

     if (n.is_even) {
        n.remove!(2)
     }

     for bit in (n.bits) {
        if (bit) {
            b += a
        }
        else {
            a += b
        }
     }

     return b
}

say fusc(10**25 + 1)