Fibonacci calculator, ARGV[0] is the nth Fibonacci number.

fib.cr

require "./matrix.cr" # from https://github.com/Exilor/matrix.git the src.matrix.cr file -> https://github.com/Exilor/matrix/blob/master/src/matrix.cr
require "big_int"
require "benchmark"


def fib(n : BigInt)
  return 0 if n == 0
  return 1 if n <= 2

  number = Matrix.rows([[BigInt.new(1), BigInt.new(1)], [BigInt.new(1), BigInt.new(0)]])
  final  = Matrix.rows([[BigInt.new(1), BigInt.new(1)], [BigInt.new(1), BigInt.new(0)]])

  while n > 0
    final = final * number if n % 2 == 1
    number = number * number
    n /= BigInt.new(2)
  end
  return final[1, 1]
end

number = BigInt.new(0)
firstArg = BigInt.new(ARGV[0])
puts Benchmark.measure { number = fib(firstArg) }
puts "\n#{firstArg}th fibonacci number is:\n#{number}"