RosettaCodeData/Task/Fibonacci-sequence/Go/fibonacci-sequence-2.go

import (
   "math/big"
)

func fib(n uint64) *big.Int {
   if n < 2 {
      return big.NewInt(int64(n))
   }
   a, b := big.NewInt(0), big.NewInt(1)
   for n--; n > 0; n-- {
      a.Add(a, b)
      a, b = b, a
   }
   return b
}