fix: exponential backoff float64 overflow

backoff.go

@@ -1,6 +1,7 @@
 package repeat
 
 import (
+	"fmt"
 	"math/rand"
 	"time"
 )
@@ -128,16 +129,15 @@ func ExponentialBackoffAlgorithm(initialDelay time.Duration, maxDelay time.Durat
 
 	return func() time.Duration {
 		delay := nextDelay
-		nextDelay = nextDelay * multiplier
+		if nextDelay < limit {
+			nextDelay = nextDelay * multiplier
+		}
+		if nextDelay > limit {
+			nextDelay = limit
+		}
 
 		// Fix delay according to jitter.
-		delta := delay * jitter
-		delay = delay - delta + (2 * delta * rnd.Float64())
-
-		// Fix delay limits.
-		if delay > limit {
-			delay = limit
-		}
+		delay += delay * jitter * (2*rnd.Float64() - 1)
 
 		return time.Duration(delay)
 	}
@@ -207,6 +207,10 @@ func (s *ExponentialBackoffBuilder) WithMultiplier(m float64) *ExponentialBackof
 //
 // Default value is 0.
 func (s *ExponentialBackoffBuilder) WithJitter(j float64) *ExponentialBackoffBuilder {
+	if j < 0 || j > 1 {
+		panic(fmt.Sprintf(`repeat: jitter "%f" should in range [0..1]`, j))
+	}
+
 	s.Jitter = j
 	return s
 }

backoff_test.go

@@ -76,13 +76,12 @@ func TestExponentialBackoff(t *testing.T) {
 	ExponentialBackoff(354 * time.Millisecond).WithJitter(.9).WithMultiplier(1.12).WithMaxDelay(5 * time.Second).Set()(do)
 
 	initDelay := float64(354 * time.Millisecond)
-	for i := 0; i < 30; i++ {
-		c := math.Pow(1.12, float64(i))
-		fi := .9 * c
-		max := time.Duration((c + fi) * initDelay)
-		if max > 5*time.Second {
-			max = 5 * time.Second
+	for i := 0; i < 300; i++ {
+		c := math.Pow(1.12, float64(i)) * initDelay
+		if c > float64(5*time.Second) {
+			c = float64(5 * time.Second)
 		}
-		InRange(t, do.Backoff(), time.Duration((c-fi)*initDelay), max)
+		fi := .9 * c
+		InRange(t, do.Backoff(), time.Duration(c-fi), time.Duration(c+fi))
 	}
 }