limit max exponential to 30 and remove utils no longer needed

Author: Eskibear

src/refresh/RefreshTimer.ts

@@ -18,7 +18,7 @@
 
 const MinimumBackoffInMs = 30 * 1000; // 30s
 const MaximumBackoffInMs = 10 * 60 * 1000; // 10min
-const MaxSafeExponential = 53; // Used to avoid overflow, as Number.MAX_SAFE_INTEGER = 2^53 - 1.
+const MaxSafeExponential = 30; // Used to avoid overflow. bitwise operations in JavaScript are limited to 32 bits. It overflows at 2^31 - 1.
 const JitterRatio = 0.25;
 
 export class RefreshTimer {
@@ -41,13 +41,13 @@ export class RefreshTimer {
     }
 
     public backoff(): void {
-        this._backoffEnd = Date.now() + this._calculateBackoffTime();
         this._failedAttempts += 1;
+        this._backoffEnd = Date.now() + this._calculateBackoffTime();
     }
 
     public reset(): void {
-        this._backoffEnd = Date.now() + this._interval;
         this._failedAttempts = 0;
+        this._backoffEnd = Date.now() + this._interval;
     }
 
     private _calculateBackoffTime(): number {
@@ -66,9 +66,9 @@ export class RefreshTimer {
             maxBackoffMs = this._maxBackoff;
         }
 
-        // exponential: minBackoffMs * 2^failedAttempts
-        const exponential = Math.min(this._failedAttempts, MaxSafeExponential);
-        let calculatedBackoffMs = minBackoffMs * (efficientPowerOfTwo(exponential));
+        // exponential: minBackoffMs * 2^(failedAttempts-1)
+        const exponential = Math.min(this._failedAttempts - 1, MaxSafeExponential);
+        let calculatedBackoffMs = minBackoffMs * (1 << exponential);
         if (calculatedBackoffMs > maxBackoffMs) {
             calculatedBackoffMs = maxBackoffMs;
         }
@@ -80,24 +80,3 @@ export class RefreshTimer {
     }
 
 }
-
-/**
- * Efficient way to calculate 2^exponential.
- *
- * `Math.pow(base, exp)` is not used because it is less efficient and accurate by operating floating-point number.
- * `1 << exp` is not used because it returns wrong results when exp >= 31.
- */
-function efficientPowerOfTwo(positiveExponential: number) {
-    if (positiveExponential < 0) {
-        throw new Error("exponential must be a non-negative integer.");
-    } else if (positiveExponential > MaxSafeExponential) {
-        throw new Error(`exponential must be less than or equal to ${MaxSafeExponential}.`);
-    }
-
-    // bitwise operations in JavaScript are limited to 32 bits. It overflows at 2^31 - 1.
-    if (positiveExponential <= 30) {
-        return 1 << positiveExponential;
-    } else {
-        return (1 << 30) * (1 << (positiveExponential - 30));
-    }
-}