Fibonacci using Goroutines.

fibonacci.go

package main

import (
  "fmt"
)

var cache map[int64]int64 = make(map[int64]int64)

func fib_useCache() bool {
  return true
}
func fib_cache(n int64) (r int64, ok bool) {
  if fib_useCache() {
    r, ok = cache[n]
  } else {
    r, ok = 0, false
  }
  return
}
func fibonacci(n int64, c chan int64) {
  if n <= 2 {
    const result int64 = 1
    c <- result
  } else {
    v, exists := fib_cache(n)
    if !exists {
      nc := make(chan int64)
      var v1, v2 int64
      
      go fibonacci(n - 1, nc)
      if ( fib_useCache() ) {
        v1 = <- nc
      }
      go fibonacci(n - 2, nc)
      if ( !fib_useCache() ) {
        v1 = <- nc
      }
      v2 = <- nc
      
      v = v1 + v2
      cache[n] = v
    }
    
    c <- v
  }
}

func fib(n int64) (result int64) {
  result_c := make(chan int64)
  go fibonacci(n, result_c)
  
  result = <- result_c
  return
}

func main() {
  const n int64 = 20000000
  
  result := fib(n)
  output := fmt.Sprintf("Fibonacci(%d): %d", n, result)
  fmt.Println(output)
}