Update Stopwatch to log fractional milliseconds.

core-util/src/main/java/org/signal/core/util/DoubleExtensions.kt

@@ -5,9 +5,6 @@
 
 package org.signal.core.util
 
-import kotlin.math.pow
-import kotlin.math.round
-
 /**
  * Rounds a number to the specified number of places. e.g.
  *
@@ -15,6 +12,5 @@ import kotlin.math.round
  * 1.123456f.roundedString(5) = 1.12346
  */
 fun Double.roundedString(places: Int): String {
-  val powerMultiplier = 10f.pow(places)
-  return (round(this * powerMultiplier) / powerMultiplier).toString()
+  return String.format("%.${places}f", this)
 }

core-util/src/main/java/org/signal/core/util/FloatExtensions.kt

@@ -5,9 +5,6 @@
 
 package org.signal.core.util
 
-import kotlin.math.pow
-import kotlin.math.round
-
 /**
  * Rounds a number to the specified number of places. e.g.
  *
@@ -15,6 +12,5 @@ import kotlin.math.round
  * 1.123456f.roundedString(5) = 1.12346
  */
 fun Float.roundedString(places: Int): String {
-  val powerMultiplier = 10f.pow(places)
-  return (round(this * powerMultiplier) / powerMultiplier).toString()
+  return String.format("%.${places}f", this)
 }

core-util/src/main/java/org/signal/core/util/Stopwatch.java

@@ -1,63 +0,0 @@
-package org.signal.core.util;
-
-import androidx.annotation.NonNull;
-
-import org.signal.core.util.logging.Log;
-
-import java.util.LinkedList;
-import java.util.List;
-
-public class Stopwatch {
-
-  private final long        startTime;
-  private final String      title;
-  private final List<Split> splits;
-
-  public Stopwatch(@NonNull String title) {
-    this.startTime = System.currentTimeMillis();
-    this.title     = title;
-    this.splits    = new LinkedList<>();
-  }
-
-  public void split(@NonNull String label) {
-    splits.add(new Split(System.currentTimeMillis(), label));
-  }
-
-  public void stop(@NonNull String tag) {
-    Log.d(tag, stopAndGetLogString(tag));
-  }
-
-  public String stopAndGetLogString(String tag) {
-    StringBuilder out = new StringBuilder();
-    out.append("[").append(title).append("] ");
-
-    if (splits.size() > 0) {
-      out.append(splits.get(0).label).append(": ");
-      out.append(splits.get(0).time - startTime);
-      out.append("  ");
-    }
-
-    if (splits.size() > 1) {
-      for (int i = 1; i < splits.size(); i++) {
-        out.append(splits.get(i).label).append(": ");
-        out.append(splits.get(i).time - splits.get(i - 1).time);
-        out.append("  ");
-      }
-
-      out.append("total: ").append(splits.get(splits.size() - 1).time - startTime);
-    }
-
-    return out.toString();
-  }
-
-
-  private static class Split {
-    final long   time;
-    final String label;
-
-    Split(long time, String label) {
-      this.time  = time;
-      this.label = label;
-    }
-  }
-}

core-util/src/main/java/org/signal/core/util/Stopwatch.kt

@@ -0,0 +1,74 @@
+package org.signal.core.util
+
+import org.signal.core.util.logging.Log
+import kotlin.time.Duration.Companion.nanoseconds
+import kotlin.time.DurationUnit
+
+/**
+ * Simple utility to easily track the time a multi-step operation takes via splits.
+ *
+ * e.g.
+ *
+ * ```kotlin
+ * val stopwatch = Stopwatch("my-event")
+ * stopwatch.split("split-1")
+ * stopwatch.split("split-2")
+ * stopwatch.split("split-3")
+ * stopwatch.stop(TAG)
+ * ```
+ */
+class Stopwatch @JvmOverloads constructor(private val title: String, private val decimalPlaces: Int = 0) {
+  private val startTimeNanos: Long = System.nanoTime()
+  private val splits: MutableList<Split> = mutableListOf()
+
+  /**
+   * Create a new split between now and the last event.
+   */
+  fun split(label: String) {
+    val now = System.nanoTime()
+
+    val previousTime = if (splits.isEmpty()) {
+      startTimeNanos
+    } else {
+      splits.last().nanoTime
+    }
+
+    splits += Split(
+      nanoTime = now,
+      durationNanos = now - previousTime,
+      label = label
+    )
+  }
+
+  /**
+   * Stops the stopwatch and logs the results with the provided tag.
+   */
+  fun stop(tag: String) {
+    Log.d(tag, stopAndGetLogString())
+  }
+
+  /**
+   * Similar to [stop], but instead of logging directly, this will return the log string.
+   */
+  fun stopAndGetLogString(): String {
+    val now = System.nanoTime()
+
+    splits += Split(
+      nanoTime = now,
+      durationNanos = now - startTimeNanos,
+      label = "total"
+    )
+
+    val splitString = splits
+      .joinToString(separator = ", ", transform = { it.displayString(decimalPlaces) })
+
+    return "[$title] $splitString"
+  }
+
+  private data class Split(val nanoTime: Long, val durationNanos: Long, val label: String) {
+    fun displayString(decimalPlaces: Int): String {
+      val timeMs: String = durationNanos.nanoseconds.toDouble(DurationUnit.MILLISECONDS).roundedString(decimalPlaces)
+      return "$label: $timeMs"
+    }
+  }
+}