chore: import upstream snapshot with attribution

swift/StableDiffusion/pipeline/SampleTimer.swift

@@ -0,0 +1,78 @@
+// For licensing see accompanying LICENSE.md file.
+// Copyright (C) 2022 Apple Inc. All Rights Reserved.
+
+import Foundation
+
+/// A utility for timing events and tracking time statistics
+///
+/// Typical usage
+/// ```
+/// let timer: SampleTimer
+///
+/// for i in 0...<iterationCount {
+///     timer.start()
+///     doStuff()
+///     timer.stop()
+/// }
+///
+/// print(String(format: "mean: %.2f, var: %.2f",
+///              timer.mean, timer.variance))
+/// ```
+@available(iOS 16.2, macOS 13.1, *)
+public final class SampleTimer: Codable {
+    var startTime: CFAbsoluteTime?
+    var sum: Double = 0.0
+    var sumOfSquares: Double = 0.0
+    var count = 0
+    var samples: [Double] = []
+
+    public init() {}
+
+    /// Start a sample, noting the current time
+    public func start() {
+        startTime = CFAbsoluteTimeGetCurrent()
+    }
+
+    // Stop a sample and record the elapsed time
+    @discardableResult public func stop() -> Double {
+        guard let startTime = startTime else {
+            return 0
+        }
+
+        let elapsed = CFAbsoluteTimeGetCurrent() - startTime
+        sum += elapsed
+        sumOfSquares += elapsed * elapsed
+        count += 1
+        samples.append(elapsed)
+        return elapsed
+    }
+
+    /// Mean of all sampled times
+    public var mean: Double { sum / Double(count) }
+
+    /// Variance of all sampled times
+    public var variance: Double {
+        guard count > 1 else {
+            return 0.0
+        }
+        return sumOfSquares / Double(count - 1) - mean * mean
+    }
+
+    /// Standard deviation of all sampled times
+    public var stdev: Double { variance.squareRoot() }
+
+    /// Median of all sampled times
+    public var median: Double {
+        let sorted = samples.sorted()
+        let (q, r) = sorted.count.quotientAndRemainder(dividingBy: 2)
+        if r == 0 {
+            return (sorted[q] + sorted[q - 1]) / 2.0
+        } else {
+            return Double(sorted[q])
+        }
+    }
+
+    public var allSamples: [Double] {
+        samples
+    }
+}