Am I doing execution timing measurement in Go in a useful way? - go

Question

My code:
// repeat fib(n) 10000 times
i := 10000
var total_time time.Duration
for i > 0 {
// do fib(n) -> f0
start := time.Now()
for n > 0 {
f0, f1, n = f1, f0.Add(f0, f1), n-1
}
total_time = total_time + time.Since(start)
i--
}
// and divide total execution time by 10000
var normalized_time = total_time / 10000
fmt.Println(normalized_time)
The execution times I'm seeing are so extremely short that I am suspicious that what I've done isn't useful. If it's wrong, what am I doing wrong and how can I make it right?

Answer 1

what am I doing wrong and how can I make it right?
Use the Go testing package for benchmarks. For example:
Write the Fibonacci number computation as a function in your code.
fibonacci.go:
package main
import "fmt"
// fibonacci returns the Fibonacci number for 0 <= n <= 92.
// OEIS: A000045: Fibonacci numbers:
// F(n) = F(n-1) + F(n-2) with F(0) = 0 and F(1) = 1.
func fibonacci(n int) int64 {
if n < 0 {
panic("n < 0")
}
f := int64(0)
a, b := int64(0), int64(1)
for i := 0; i <= n; i++ {
if a < 0 {
panic("overflow")
}
f, a, b = a, b, a+b
}
return f
}
func main() {
for _, n := range []int{0, 1, 2, 3, 90, 91, 92} {
fmt.Printf("%-2d %d\n", n, fibonacci(n))
}
}
Playground: https://play.golang.org/p/FFdG4RlNpUZ
Output:
$ go run fibonacci.go
0 0
1 1
2 1
3 2
90 2880067194370816120
91 4660046610375530309
92 7540113804746346429
$
Write and run some benchmarks using the Go testing package.
fibonacci_test.go:
package main
import "testing"
func BenchmarkFibonacciN0(b *testing.B) {
for i := 0; i < b.N; i++ {
fibonacci(0)
}
}
func BenchmarkFibonacciN92(b *testing.B) {
for i := 0; i < b.N; i++ {
fibonacci(92)
}
}
Output:
$ go test fibonacci.go fibonacci_test.go -bench=. -benchmem
goos: linux
goarch: amd64
BenchmarkFibonacciN0-4 367003574 3.25 ns/op 0 B/op 0 allocs/op
BenchmarkFibonacciN92-4 17369262 63.0 ns/op 0 B/op 0 allocs/op
$