project-euler/Sidef/025 1000-digit Fibonacci number -- v2.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Date: 05 November 2017
# https://github.com/trizen

# https://projecteuler.net/problem=25

# Runtime: 0.302s

func fib_len(n, base=10) {

    static S = (sqrt(1.25) + 0.5)
    static T = (1 - S)
    static W = (S - T)

    1 + ilog((S**n - T**n) / W, base)
}

say (^Inf -> first_by {|n| fib_len(n) == 1000 })