CharArray to String benchmark

CharArrayToStringBenchmark.kt

import kotlinx.benchmark.*
import kotlin.math.min

@State(Scope.Benchmark)
@BenchmarkMode(Mode.Throughput)
@Warmup(iterations = 4, time = 5, timeUnit = BenchmarkTimeUnit.SECONDS)
@Measurement(iterations = 4, time = 5, timeUnit = BenchmarkTimeUnit.SECONDS)
public class CharArrayToStringBenchmark {
  private val array = CharArray(1000000) {
    when (it) {
      0 -> 55356.toChar()
      1 -> 57091.toChar()
      2 -> 'c'
      3 -> 'n'
      else -> ('a'..'z').random()
    }
  }

  @Benchmark
  public fun concatenation(blackhole: Blackhole) {
    val str = array.concatToString()
    blackhole.consume(str)
  }

  @Benchmark
  public fun chunking1024(blackhole: Blackhole) {
    val str = array.chunkedConcatToString(1024)
    blackhole.consume(str)
  }

  @Benchmark
  public fun chunking2048(blackhole: Blackhole) {
    val str = array.chunkedConcatToString(2048)
    blackhole.consume(str)
  }

  @Benchmark
  public fun chunking4096(blackhole: Blackhole) {
    val str = array.chunkedConcatToString(4096)
    blackhole.consume(str)
  }

  @Benchmark
  public fun chunking8192(blackhole: Blackhole) {
    val str = array.chunkedConcatToString(8192)
    blackhole.consume(str)
  }

  @Benchmark
  public fun chunking16384(blackhole: Blackhole) {
    val str = array.chunkedConcatToString(16384)
    blackhole.consume(str)
  }

  private fun CharArray.chunkedConcatToString(chunkSize: Int): String {
    if (this.size <= chunkSize) {
      return js("String").fromCharCode.apply(null, this)
    }

    var str = ""
    var start = 0

    while (start < this.size) {
      val end = min(start + chunkSize, this.size)
      val chunk = this.asDynamic().subarray(start, end)
      str += js("String").fromCharCode.apply(null, chunk)
      start = end
    }

    return str
  }
}