fibber

.go

package main

import (
	"math/big"
	"os"
	"strconv"
)

func Fib(n int) *big.Int {
	switch n {
	case 0:
		return big.NewInt(0)
	case 1:
		return big.NewInt(1)
	default:
		return calcFib(n)
	}
}

func calcFib(n int) *big.Int {
	zero := big.NewInt(0)
	prevHolder := big.NewInt(0)
	onePrev := big.NewInt(1)
	twoPrev := big.NewInt(0)
	accumulator := 3
	for accumulator <= n {
		prevHolder = prevHolder.Add(onePrev, zero)
		onePrev = onePrev.Add(onePrev, twoPrev)
		twoPrev = twoPrev.Add(prevHolder, zero)
		accumulator = accumulator + 1
	}
	return onePrev.Add(onePrev, twoPrev)
}

func main() {
	if len(os.Args) < 2 {
		println("fibber expects a positive integer as the second arg")
	}
	n, err := strconv.Atoi(os.Args[1])
	if err != nil || n < 0 {
		println("Invalid argument for fibber. Expected a positive integer as the second arg.")
		os.Exit(1)
	}
	println(Fib(n).String())
}