correct decorrelated algorithm

Author: ph1ps

Sources/AsyncAlgorithms/Retry/Backoff.swift

@@ -17,11 +17,10 @@ public protocol BackoffStrategy<Duration> {
 }
 
 @available(iOS 16.0, macCatalyst 16.0, macOS 13.0, tvOS 16.0, visionOS 1.0, watchOS 9.0, *)
-@usableFromInline
-struct ConstantBackoffStrategy<Duration: DurationProtocol>: BackoffStrategy {
+@usableFromInline struct ConstantBackoffStrategy<Duration: DurationProtocol>: BackoffStrategy {
   @usableFromInline let constant: Duration
   @usableFromInline init(constant: Duration) {
-    precondition(constant >= .zero, "Constsnt must be greater than or equal to 0")
+    precondition(constant >= .zero, "Constant must be greater than or equal to 0")
     self.constant = constant
   }
   @inlinable func nextDuration() -> Duration {
@@ -30,8 +29,7 @@ struct ConstantBackoffStrategy<Duration: DurationProtocol>: BackoffStrategy {
 }
 
 @available(iOS 16.0, macCatalyst 16.0, macOS 13.0, tvOS 16.0, visionOS 1.0, watchOS 9.0, *)
-@usableFromInline
-struct LinearBackoffStrategy<Duration: DurationProtocol>: BackoffStrategy {
+@usableFromInline struct LinearBackoffStrategy<Duration: DurationProtocol>: BackoffStrategy {
   @usableFromInline var current: Duration
   @usableFromInline let increment: Duration
   @usableFromInline init(increment: Duration, initial: Duration) {
@@ -63,8 +61,7 @@ struct LinearBackoffStrategy<Duration: DurationProtocol>: BackoffStrategy {
 }
 
 @available(iOS 16.0, macCatalyst 16.0, macOS 13.0, tvOS 16.0, visionOS 1.0, watchOS 9.0, *)
-@usableFromInline
-struct MinimumBackoffStrategy<Base: BackoffStrategy>: BackoffStrategy {
+@usableFromInline struct MinimumBackoffStrategy<Base: BackoffStrategy>: BackoffStrategy {
   @usableFromInline var base: Base
   @usableFromInline let minimum: Base.Duration
   @usableFromInline init(base: Base, minimum: Base.Duration) {
@@ -77,8 +74,7 @@ struct MinimumBackoffStrategy<Base: BackoffStrategy>: BackoffStrategy {
 }
 
 @available(iOS 16.0, macCatalyst 16.0, macOS 13.0, tvOS 16.0, visionOS 1.0, watchOS 9.0, *)
-@usableFromInline
-struct MaximumBackoffStrategy<Base: BackoffStrategy>: BackoffStrategy {
+@usableFromInline struct MaximumBackoffStrategy<Base: BackoffStrategy>: BackoffStrategy {
   @usableFromInline var base: Base
   @usableFromInline let maximum: Base.Duration
   @usableFromInline init(base: Base, maximum: Base.Duration) {
@@ -91,22 +87,20 @@ struct MaximumBackoffStrategy<Base: BackoffStrategy>: BackoffStrategy {
 }
 
 @available(iOS 18.0, macCatalyst 18.0, macOS 15.0, tvOS 18.0, visionOS 2.0, watchOS 11.0, *)
-@usableFromInline
-struct FullJitterBackoffStrategy<Base: BackoffStrategy, RNG: RandomNumberGenerator>: BackoffStrategy where Base.Duration == Swift.Duration {
+@usableFromInline struct FullJitterBackoffStrategy<Base: BackoffStrategy, RNG: RandomNumberGenerator>: BackoffStrategy where Base.Duration == Swift.Duration {
   @usableFromInline var base: Base
   @usableFromInline var generator: RNG
   @usableFromInline init(base: Base, generator: RNG) {
     self.base = base
     self.generator = generator
   }
   @inlinable mutating func nextDuration() -> Base.Duration {
-    return .init(attoseconds: Int128.random(in: 0...base.nextDuration().attoseconds))
+    return .init(attoseconds: Int128.random(in: 0...base.nextDuration().attoseconds, using: &generator))
   }
 }
 
 @available(iOS 18.0, macCatalyst 18.0, macOS 15.0, tvOS 18.0, visionOS 2.0, watchOS 11.0, *)
-@usableFromInline
-struct EqualJitterBackoffStrategy<Base: BackoffStrategy, RNG: RandomNumberGenerator>: BackoffStrategy where Base.Duration == Swift.Duration {
+@usableFromInline struct EqualJitterBackoffStrategy<Base: BackoffStrategy, RNG: RandomNumberGenerator>: BackoffStrategy where Base.Duration == Swift.Duration {
   @usableFromInline var base: Base
   @usableFromInline var generator: RNG
   @usableFromInline init(base: Base, generator: RNG) {
@@ -120,23 +114,22 @@ struct EqualJitterBackoffStrategy<Base: BackoffStrategy, RNG: RandomNumberGenera
 }
 
 @available(iOS 18.0, macCatalyst 18.0, macOS 15.0, tvOS 18.0, visionOS 2.0, watchOS 11.0, *)
-@usableFromInline
-struct DecorrelatedJitterBackoffStrategy<Base: BackoffStrategy, RNG: RandomNumberGenerator>: BackoffStrategy where Base.Duration == Swift.Duration {
-  @usableFromInline var base: Base
+@usableFromInline struct DecorrelatedJitterBackoffStrategy<RNG: RandomNumberGenerator>: BackoffStrategy {
+  @usableFromInline let base: Duration
+  @usableFromInline let factor: Int
   @usableFromInline var generator: RNG
   @usableFromInline var current: Duration?
-  @usableFromInline let factor: Int
-  @usableFromInline init(base: Base, generator: RNG, factor: Int) {
+  @usableFromInline init(base: Duration, factor: Int, generator: RNG) {
     precondition(factor >= 1, "Factor must be greater than or equal to 1")
+    precondition(base >= .zero, "Base must be greater than or equal to 0")
     self.base = base
     self.generator = generator
     self.factor = factor
   }
-  @inlinable mutating func nextDuration() -> Base.Duration {
-    let base = base.nextDuration()
-    let current = current ?? base
-    let next = Duration(attoseconds: Int128.random(in: base.attoseconds...(current * factor).attoseconds, using: &generator))
-    self.current = next
+  @inlinable mutating func nextDuration() -> Duration {
+    let previous = current ?? base
+    let next = Duration(attoseconds: Int128.random(in: base.attoseconds...(previous * factor).attoseconds, using: &generator))
+    current = next
     return next
   }
 }
@@ -161,6 +154,9 @@ public enum Backoff {
   @inlinable public static func exponential(factor: Int, initial: Duration) -> some BackoffStrategy<Duration> {
     return ExponentialBackoffStrategy(factor: factor, initial: initial)
   }
+  @inlinable public static func decorrelatedJitter<RNG: RandomNumberGenerator>(factor: Int, base: Duration, using generator: RNG) -> some BackoffStrategy<Duration> {
+    return DecorrelatedJitterBackoffStrategy(base: base, factor: factor, generator: generator)
+  }
 }
 
 @available(iOS 16.0, macCatalyst 16.0, macOS 13.0, tvOS 16.0, visionOS 1.0, watchOS 9.0, *)
@@ -181,7 +177,4 @@ extension BackoffStrategy where Duration == Swift.Duration {
   @inlinable public func equalJitter<RNG: RandomNumberGenerator>(using generator: RNG = SystemRandomNumberGenerator()) -> some BackoffStrategy<Duration> {
     return EqualJitterBackoffStrategy(base: self, generator: generator)
   }
-  @inlinable public func decorrelatedJitter<RNG: RandomNumberGenerator>(factor: Int, using generator: RNG = SystemRandomNumberGenerator()) -> some BackoffStrategy<Duration> {
-    return DecorrelatedJitterBackoffStrategy(base: self, generator: generator, factor: factor)
-  }
 }