fill array fast.scala

      val arr = new Array[Byte](size)
      @tailrec
      def loopFill(numChild: Int, idx0: Int): Array[Byte] =
        if (idx0 == size) arr
        else {
          node(numChild) match {
            case EmptyChild => loopFill(numChild + 1, idx0)

            case Leaf(prefix, value, varLength) =>
              arr(idx0) = numChild.toByte
              val idxSecondByte   = idx0 + 1
              val idxPrefixStart  = idxSecondByte + 1
              val prefixSize: Int = prefix.size.toInt
              if (varLength) {
                //01000000b | (size & 00011111b)
                arr(idxSecondByte) = (0x40 | (prefixSize & 0x1F)).toByte //second byte - type and size of prefix
                for (i <- 0 until prefixSize) arr(idxPrefixStart + i) = prefix(i.toLong)
                val idxValueSize = idxPrefixStart + prefixSize
                val valueSize    = value.size.toInt
                arr(idxValueSize) = valueSize.toByte
                val idxValueStart = idxValueSize + 1
                for (i <- 0 until valueSize) arr(idxValueStart + i) = value(i.toLong)
                loopFill(numChild + 1, idxValueStart + valueSize)
              } else {
                //size & 00011111b
                arr(idxSecondByte) = (prefixSize & 0x1F).toByte //second byte - type and size of prefix
                for (i <- 0 until prefixSize) arr(idxPrefixStart + i) = prefix(i.toLong)
                val idxValueStart = idxPrefixStart + prefixSize
                for (i <- 0 until 32) arr(idxValueStart + i) = value(i.toLong)
                loopFill(numChild + 1, idxValueStart + 32)
              }
            case NodePtr(prefix, ptr) =>
              arr(idx0) = numChild.toByte
              val idxSecondByte   = idx0 + 1
              val prefixSize: Int = prefix.size.toInt
              //10000000b | (size & 00011111b)
              arr(idxSecondByte) = (0x80 | (prefixSize & 0x1F)).toByte //second byte - type and size of prefix
              val idxPrefixStart = idxSecondByte + 1
              for (i <- 0 until prefixSize) arr(idxPrefixStart + i) = prefix(i.toLong)
              val idxPtrStart = idxPrefixStart + prefixSize
              for (i <- 0 until 32) arr(idxPtrStart + i) = ptr(i.toLong)
              loopFill(numChild + 1, idxPtrStart + 32)
          }
        }
      loopFill(0, 0)