Encode with Murmur Hash

MurmurHashEncode.scala

import java.nio.{ByteBuffer, ByteOrder}

// "com.google.guava" % "guava" % "16.0.1"
import com.google.common.hash.Hashing

object MurmurHash {
  private val seed = 0x3c074a61

  def encode(prefix: Int, value: Long): Long = {
    val pb = ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN).putInt(prefix).array()
    val vb = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN).putLong(value).array()
    // TODO: will this be slow ?
    val bs = pb ++ vb
    encodeBytes(bs)
  }

  def encode(prefix1: Int, value1: Long, prefix2: Int, value2: Long): Long = {
    val pb1 = ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN).putInt(prefix1).array()
    val vb1 = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN).putLong(value1).array()
    val pb2 = ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN).putInt(prefix2).array()
    val vb2 = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN).putLong(value2).array()
    // TODO: will this be slow ?
    val bs = pb1 ++ vb1 ++ pb2 ++ vb2
    encodeBytes(bs)
  }

  private def encodeBytes(bytes: Array[Byte]): Long = {
    // the guava version is little-endian variant of the original cpp version
    // so we need to reverse the result byte array
    val hashed = Hashing.murmur3_128(seed).hashBytes(bytes).asBytes().reverse
    // the hash value is 128 bit while we only need 64
    val div = ByteBuffer.wrap(hashed.drop(8)).getLong()
    val mod = 1L << 60
    ((div % mod) + mod) % mod
  }
}