fib.go

package main

import "fmt"
import "big"

func main() {
        fmt.Println(fib(50))
	fmt.Println(fibrec(big.NewInt(10)))
        fmt.Println(fibbig(big.NewInt(50)))
}

// The Good -- makes good use of parallel assignment
func magic(n int) uint64 {
	var a uint64 = 0
	var b uint64 = 1
	for i := 0; i < n; i++ {
		a, b = b, b + a
	}
	return b
}

// The Bad
func fibrec(n *big.Int) *big.Int {
	if n.Cmp(big.NewInt(0)) == 0 || n.Cmp(big.NewInt(1)) == 0 {
		return big.NewInt(1)
	} else {
		return big.NewInt(0).Add(
			fibrec(big.NewInt(0).Sub(n, big.NewInt(1))),
			fibrec(big.NewInt(0).Sub(n, big.NewInt(2))))
	}
	return big.NewInt(0)
}

// The Ugly
func fibbig(n *big.Int) *big.Int {
    a := big.NewInt(0)
    b := big.NewInt(1)
    c := big.NewInt(0)
    for i := big.NewInt(0); i.Cmp(n) == -1; i.Add(i, big.NewInt(1)) {
        c.Set(a)
        a.Set(b)
        b.Add(b, c)
    }
    return b;
}