Added jmh benchmark for FLoatArrayBuffer

elastiknn-api4s/src/main/java/com/klibisz/elastiknn/api/FloatArrayBuffer.java

@@ -36,7 +36,9 @@ public void append(float f) {
     }
 
     public float[] toArray() {
-        nextInitialCapacity = Math.min(maxInitialCapacity, Math.max(minInitialCapacity, index));
+        if (nextInitialCapacity != index) {
+            nextInitialCapacity = Math.min(maxInitialCapacity, Math.max(minInitialCapacity, index));
+        }
         if (this.array.length == index) {
             return this.array;
         } else {

elastiknn-jmh-benchmarks/src/main/scala/com/klibisz/elastiknn/jmhbenchmarks/FloatArrayBufferBenchmarks.scala

@@ -0,0 +1,49 @@
+package com.klibisz.elastiknn.jmhbenchmarks
+
+import com.klibisz.elastiknn.api.FloatArrayBuffer
+import org.openjdk.jmh.annotations._
+
+import scala.collection.mutable.ArrayBuffer
+import scala.util.Random
+
+@State(Scope.Benchmark)
+class FloatArrayBufferBenchmarksState {
+  implicit private val rng: Random = new Random(0)
+  val lst768 = (0 until 768).map(_ => rng.nextFloat()).toList
+}
+
+class FloatArrayBufferBenchmarks {
+
+  @Benchmark
+  @BenchmarkMode(Array(Mode.Throughput))
+  @Fork(value = 1)
+  @Warmup(time = 5, iterations = 1)
+  @Measurement(time = 5, iterations = 1)
+  def scalaAppendFixedInitialSize(state: FloatArrayBufferBenchmarksState): Int = {
+    val buf = new ArrayBuffer[Float]()
+    state.lst768.foreach(buf.append)
+    buf.toArray.length
+  }
+
+  @Benchmark
+  @BenchmarkMode(Array(Mode.Throughput))
+  @Fork(value = 1)
+  @Warmup(time = 5, iterations = 1)
+  @Measurement(time = 5, iterations = 1)
+  def scalaAppendKnownInitialSize(state: FloatArrayBufferBenchmarksState): Int = {
+    val buf = new ArrayBuffer[Float](768)
+    state.lst768.foreach(buf.append)
+    buf.toArray.length
+  }
+
+  @Benchmark
+  @BenchmarkMode(Array(Mode.Throughput))
+  @Fork(value = 1)
+  @Warmup(time = 5, iterations = 1)
+  @Measurement(time = 5, iterations = 1)
+  def customAppend(state: FloatArrayBufferBenchmarksState): Int = {
+    val buf = new FloatArrayBuffer()
+    state.lst768.foreach(buf.append)
+    buf.toArray.length
+  }
+}