From b4edee4292ab88c89a509de80bb1d1a3bf81940b Mon Sep 17 00:00:00 2001
From: William Dillon <wmdillon@me.com>
Date: Thu, 26 Feb 2026 16:28:19 -0500
Subject: [PATCH] fixing bugs - no longer panics when iteration < 0 or
 MaxIteration >= len(TheFibonacciSequence)-1

---
 cli/main.go                 |  8 ++++++++
 fibonacci/fibonacci.go      |  4 ++--
 fibonacci/fibonacci_test.go | 14 ++++++++++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/cli/main.go b/cli/main.go
index c59fa9a..3858bb6 100644
--- a/cli/main.go
+++ b/cli/main.go
@@ -71,6 +71,14 @@ func main() {
 			fmt.Fprintf(os.Stderr, "iteration %d would overflow int64 - using %d\n", iteration, maxIteration)
 			iteration = maxIteration
 		}
+	} else if iteration < 0 {
+		switch doPanic {
+		case true:
+			panic(fmt.Sprintf("error: input %d would cause index out of range exception\n", iteration))
+		default:
+			fmt.Fprintf(os.Stderr, "error: input %d would cause index out of range exception - using 0\n", iteration)
+			iteration = 0
+		}
 	}
 
 	backoff := &fibonacci.FibonacciBackoff{
diff --git a/fibonacci/fibonacci.go b/fibonacci/fibonacci.go
index e7179f0..d94c0fe 100644
--- a/fibonacci/fibonacci.go
+++ b/fibonacci/fibonacci.go
@@ -50,8 +50,8 @@ func (f *FibonacciBackoff) Next() time.Duration {
 	}
 
 	// increment f.Iteration if appropriate
-	maxIteration := int64(len(TheFibonacciSequence) + 1)
-	if f.MaxIteration > 0 {
+	maxIteration := int64(len(TheFibonacciSequence) - 1)
+	if f.MaxIteration > 0 && f.MaxIteration <= maxIteration {
 		maxIteration = f.MaxIteration
 	}
 	if f.foundMax == 0 {
diff --git a/fibonacci/fibonacci_test.go b/fibonacci/fibonacci_test.go
index 5d4ac3c..6b731f5 100644
--- a/fibonacci/fibonacci_test.go
+++ b/fibonacci/fibonacci_test.go
@@ -77,6 +77,20 @@ func TestFibonacciBackoffNextDoesNotOverflow(t *testing.T) {
 		}
 		previous = got
 	}
+	backoff.Reset()
+	backoff.PauseMultiplier = time.Nanosecond
+	for i := range len(TheFibonacciSequence) + 100 {
+		var want time.Duration
+		if i >= len(TheFibonacciSequence) {
+			want = time.Duration(TheFibonacciSequence[len(TheFibonacciSequence)-1])
+		} else {
+			want = time.Duration(TheFibonacciSequence[i])
+		}
+		got := backoff.Next()
+		if want != got {
+			t.Fatalf("error: wanted %v; got %v\n", want, got)
+		}
+	}
 }
 
 func TestFibonacciBackoffIterationLimit(t *testing.T) {