fix #126: optimize fibonacci number algorithm

Makefile

@@ -9,24 +9,24 @@ generate:
 
 .PHONY: test
 test:                         #| Runs tests with race.
-	go test -race ./...
+	go test -race -timeout 1s ./...
 
 .PHONY: test-check
 test-check:                   #| Fast runs tests to check their compilation errors.
 	go test -run=^hack ./...
 
 .PHONY: test-with-coverage
 test-with-coverage:           #| Runs tests with coverage.
-	go test -cover ./...
+	go test -cover -timeout 1s  ./...
 
 .PHONY: test-with-coverage-formatted
 test-with-coverage-formatted: #| Runs tests with coverage and formats the result.
-	go test -cover ./... | column -t | sort -r
+	go test -cover -timeout 1s  ./... | column -t | sort -r
 
 .PHONY: test-with-coverage-profile
 test-with-coverage-profile:   #| Runs tests with coverage and collects the result.
-	go test -covermode count -coverprofile cover.out ./...
+	go test -covermode count -coverprofile cover.out -timeout 1s ./...
 
 .PHONY: test-example
 test-example:                 #| Runs example tests with coverage and collects the result.
-	go test -covermode count -coverprofile -run=Example -v example.out ./...
+	go test -covermode count -coverprofile -run=Example -timeout 1s -v example.out ./...

backoff/backoff.go

@@ -55,11 +55,12 @@ func Fibonacci(factor time.Duration) Algorithm {
 // fibonacciNumber calculates the Fibonacci sequence number for the given
 // sequence position.
 func fibonacciNumber(n uint) uint {
-	if 0 == n {
+	if n == 0 {
 		return 0
-	} else if 1 == n {
-		return 1
-	} else {
-		return fibonacciNumber(n-1) + fibonacciNumber(n-2)
 	}
+	var a, b uint = 0, 1
+	for i := uint(1); i < n; i++ {
+		a, b = b, a+b
+	}
+	return b
 }

backoff/backoff_test.go

@@ -84,4 +84,8 @@ func TestFibonacci(t *testing.T) {
 			t.Errorf("algorithm expected to return a %s duration, but received %s instead", expected, result)
 		}
 	}
+
+	t.Run("performance", func(t *testing.T) {
+		_ = Fibonacci(time.Millisecond)(50)
+	})
 }