64bit "murmur" hash in scala. The builtin murmur hash only outputs 32 bits so if hashing millions of items you will get quite a few conflicts. This method will allow hashing millions of items without any conflicts

murmur64.scala

// Simple function to generate 64 bit hashes using the builtin Murmur hash functionaliy which only outputs 32bits
// we had cases when hashing 15M+ items where we got around 0.08% conflicts
// using this method we were able to hash 15M items with 0 conflicts
object ExtendedMurmurHash {
  val seed = 0xf7ca7fd2

  def hash(u: String): Long = {
    val a = scala.util.hashing.MurmurHash3.stringHash(u, seed)
    val b = scala.util.hashing.MurmurHash3.stringHash(u.reverse.toString, seed)
    // shift a 32 bits to the left, leaving 32 lower bits zeroed
    // mask b with "1111...1" (32 bits)
    // bitwise "OR" between both leaving a 64 bit hash of the string using Murmur32 on each portion
    val c: Long = a.toLong << 32 | (b & 0xffffffffL)
    c
  }
}