package hashing

Type Members

final class ByteswapHashing[T] extends Hashing[T]

A fast multiplicative hash by Phil Bagwell.

trait Hashing[T] extends Serializable

Hashing is a trait whose instances each represent a strategy for hashing instances of a type.

Hashing ‘s companion object defines a default hashing strategy for all objects - it calls their ## method.

Note: when using a custom Hashing , make sure to use it with the Equiv such that if any two objects are equal, then their hash codes must be equal.

Value Members

object ByteswapHashing extends Serializable

object Hashing extends Serializable

object MurmurHash3 extends MurmurHash3

An implementation of Austin Appleby’s MurmurHash 3 algorithm (MurmurHash3_x86_32). This object contains methods that hash values of various types as well as means to construct Hashing objects.

This algorithm is designed to generate well-distributed non-cryptographic hashes. It is designed to hash data in 32 bit chunks (ints).

The mix method needs to be called at each step to update the intermediate hash value. For the last chunk to incorporate into the hash mixLast may be used instead, which is slightly faster. Finally finalizeHash needs to be called to compute the final hash value.

This is based on the earlier MurmurHash3 code by Rex Kerr, but the MurmurHash3 algorithm was since changed by its creator Austin Appleby to remedy some weaknesses and improve performance. This represents the latest and supposedly final version of the algorithm (revision 136).

Value Members From scala.util.hashing

def byteswap32(v: Int): Int

Fast multiplicative hash with a nice distribution.

(defined at scala.util.hashing)

def byteswap64(v: Long): Long

Fast multiplicative hash with a nice distribution for 64-bit values. (defined at scala.util.hashing)

Full Source:

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2006-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |           **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package util

package object hashing {

  /** Fast multiplicative hash with a nice distribution.
  def byteswap32(v: Int): Int = {
    var hc = v * 0x9e3775cd
    hc = java.lang.Integer.reverseBytes(hc)
    hc * 0x9e3775cd

  /** Fast multiplicative hash with a nice distribution
   *  for 64-bit values.
  def byteswap64(v: Long): Long = {
    var hc = v * 0x9e3775cd9e3775cdL
    hc = java.lang.Long.reverseBytes(hc)
    hc * 0x9e3775cd9e3775cdL