Merge pull request #301 from ktopley-apple/dispatch-time-overflows
Fix overflow traps in DispatchTime/DispatchWallTime/DispatchTimeInterval
diff --git a/src/swift/Time.swift b/src/swift/Time.swift
index 5522758..b6cd33c 100644
--- a/src/swift/Time.swift
+++ b/src/swift/Time.swift
@@ -123,6 +123,40 @@
}
}
+// Returns m1 * m2, clamped to the range [Int64.min, Int64.max].
+// Because of the way this function is used, we can always assume
+// that m2 > 0.
+private func clampedInt64Product(_ m1: Int64, _ m2: Int64) -> Int64 {
+ assert(m2 > 0, "multiplier must be positive")
+ let (result, overflow) = m1.multipliedReportingOverflow(by: m2)
+ if overflow {
+ return m1 > 0 ? Int64.max : Int64.min
+ }
+ return result
+}
+
+// Returns its argument clamped to the range [Int64.min, Int64.max].
+private func toInt64Clamped(_ value: Double) -> Int64 {
+ if value.isNaN { return Int64.max }
+ if value >= Double(Int64.max) { return Int64.max }
+ if value <= Double(Int64.min) { return Int64.min }
+ return Int64(value)
+}
+
+/// Represents a time interval that can be used as an offset from a `DispatchTime`
+/// or `DispatchWallTime`.
+///
+/// For example:
+/// let inOneSecond = DispatchTime.now() + DispatchTimeInterval.seconds(1)
+///
+/// If the requested time interval is larger then the internal representation
+/// permits, the result of adding it to a `DispatchTime` or `DispatchWallTime`
+/// is `DispatchTime.distantFuture` and `DispatchWallTime.distantFuture`
+/// respectively. Such time intervals compare as equal:
+///
+/// let t1 = DispatchTimeInterval.seconds(Int.max)
+/// let t2 = DispatchTimeInterval.milliseconds(Int.max)
+/// let result = t1 == t2 // true
public enum DispatchTimeInterval {
case seconds(Int)
case milliseconds(Int)
@@ -133,9 +167,9 @@
internal var rawValue: Int64 {
switch self {
- case .seconds(let s): return Int64(s) * Int64(NSEC_PER_SEC)
- case .milliseconds(let ms): return Int64(ms) * Int64(NSEC_PER_MSEC)
- case .microseconds(let us): return Int64(us) * Int64(NSEC_PER_USEC)
+ case .seconds(let s): return clampedInt64Product(Int64(s), Int64(NSEC_PER_SEC))
+ case .milliseconds(let ms): return clampedInt64Product(Int64(ms), Int64(NSEC_PER_MSEC))
+ case .microseconds(let us): return clampedInt64Product(Int64(us), Int64(NSEC_PER_USEC))
case .nanoseconds(let ns): return Int64(ns)
case .never: return Int64.max
}
@@ -162,16 +196,12 @@
}
public func +(time: DispatchTime, seconds: Double) -> DispatchTime {
- let interval = seconds * Double(NSEC_PER_SEC)
- let t = CDispatch.dispatch_time(time.rawValue,
- interval.isInfinite || interval.isNaN ? Int64.max : Int64(interval))
+ let t = CDispatch.dispatch_time(time.rawValue, toInt64Clamped(seconds * Double(NSEC_PER_SEC)));
return DispatchTime(rawValue: t)
}
public func -(time: DispatchTime, seconds: Double) -> DispatchTime {
- let interval = -seconds * Double(NSEC_PER_SEC)
- let t = CDispatch.dispatch_time(time.rawValue,
- interval.isInfinite || interval.isNaN ? Int64.min : Int64(interval))
+ let t = CDispatch.dispatch_time(time.rawValue, toInt64Clamped(-seconds * Double(NSEC_PER_SEC)));
return DispatchTime(rawValue: t)
}
@@ -186,15 +216,11 @@
}
public func +(time: DispatchWallTime, seconds: Double) -> DispatchWallTime {
- let interval = seconds * Double(NSEC_PER_SEC)
- let t = CDispatch.dispatch_time(time.rawValue,
- interval.isInfinite || interval.isNaN ? Int64.max : Int64(interval))
+ let t = CDispatch.dispatch_time(time.rawValue, toInt64Clamped(seconds * Double(NSEC_PER_SEC)));
return DispatchWallTime(rawValue: t)
}
public func -(time: DispatchWallTime, seconds: Double) -> DispatchWallTime {
- let interval = -seconds * Double(NSEC_PER_SEC)
- let t = CDispatch.dispatch_time(time.rawValue,
- interval.isInfinite || interval.isNaN ? Int64.min : Int64(interval))
+ let t = CDispatch.dispatch_time(time.rawValue, toInt64Clamped(-seconds * Double(NSEC_PER_SEC)));
return DispatchWallTime(rawValue: t)
}
