Move MurmurHash to separate file due to license header, see #944
* Also removed unused 'class MurmurHash', we only use 'object MurmurHash'
This commit is contained in:
Patrik Nordwall
parent
ea78e6d805
commit
d74464ba50
2 changed files with 149 additions and 197 deletions
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@ -5,27 +5,6 @@
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package akka.routing
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import scala.collection.immutable.TreeMap
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import java.lang.Integer.{ rotateLeft ⇒ rotl }
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/* __ *\
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** ________ ___ / / ___ Scala API **
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** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
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** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
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** /____/\___/_/ |_/____/_/ | | **
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** |/ **
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\* */
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/**
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* An implementation of Austin Appleby's MurmurHash 3.0 algorithm
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* (32 bit version); reference: http://code.google.com/p/smhasher
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*
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* This is the hash used by collections and case classes (including
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* tuples).
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*
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* @author Rex Kerr
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* @version 2.9
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* @since 2.9
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*/
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// =============================================================================================
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// Adapted from HashRing.scala in Debasish Ghosh's Redis Client, licensed under Apache 2 license
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@ -129,179 +108,3 @@ object ConsistentHash {
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}
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}
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/**
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* A class designed to generate well-distributed non-cryptographic
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* hashes. It is designed to be passed to a collection's foreach method,
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* or can take individual hash values with append. Its own hash code is
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* set equal to the hash code of whatever it is hashing.
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*/
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class MurmurHash[@specialized(Int, Long, Float, Double) T](seed: Int) extends (T ⇒ Unit) {
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import MurmurHash._
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private var h = startHash(seed)
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private var c = hiddenMagicA
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private var k = hiddenMagicB
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private var hashed = false
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private var hashvalue = h
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/** Begin a new hash using the same seed. */
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def reset(): Unit = {
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h = startHash(seed)
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c = hiddenMagicA
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k = hiddenMagicB
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hashed = false
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}
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/** Incorporate the hash value of one item. */
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def apply(t: T): Unit = {
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h = extendHash(h, t.##, c, k)
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c = nextMagicA(c)
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k = nextMagicB(k)
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hashed = false
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}
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/** Incorporate a known hash value. */
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def append(i: Int): Unit = {
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h = extendHash(h, i, c, k)
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c = nextMagicA(c)
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k = nextMagicB(k)
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hashed = false
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}
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/** Retrieve the hash value */
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def hash: Int = {
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if (!hashed) {
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hashvalue = finalizeHash(h)
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hashed = true
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}
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hashvalue
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}
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override def hashCode: Int = hash
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}
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/**
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* An object designed to generate well-distributed non-cryptographic
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* hashes. It is designed to hash a collection of integers; along with
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* the integers to hash, it generates two magic streams of integers to
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* increase the distribution of repetitive input sequences. Thus,
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* three methods need to be called at each step (to start and to
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* incorporate a new integer) to update the values. Only one method
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* needs to be called to finalize the hash.
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*/
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object MurmurHash {
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// Magic values used for MurmurHash's 32 bit hash.
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// Don't change these without consulting a hashing expert!
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final private val visibleMagic: Int = 0x971e137b
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final private val hiddenMagicA: Int = 0x95543787
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final private val hiddenMagicB: Int = 0x2ad7eb25
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final private val visibleMixer: Int = 0x52dce729
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final private val hiddenMixerA: Int = 0x7b7d159c
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final private val hiddenMixerB: Int = 0x6bce6396
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final private val finalMixer1: Int = 0x85ebca6b
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final private val finalMixer2: Int = 0xc2b2ae35
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// Arbitrary values used for hashing certain classes
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final private val seedString: Int = 0xf7ca7fd2
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final private val seedArray: Int = 0x3c074a61
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/** The first 23 magic integers from the first stream are stored here */
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private val storedMagicA: Array[Int] =
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Iterator.iterate(hiddenMagicA)(nextMagicA).take(23).toArray
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/** The first 23 magic integers from the second stream are stored here */
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private val storedMagicB: Array[Int] =
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Iterator.iterate(hiddenMagicB)(nextMagicB).take(23).toArray
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/** Begin a new hash with a seed value. */
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def startHash(seed: Int): Int = seed ^ visibleMagic
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/** The initial magic integers in the first stream. */
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def startMagicA: Int = hiddenMagicA
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/** The initial magic integer in the second stream. */
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def startMagicB: Int = hiddenMagicB
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/**
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* Incorporates a new value into an existing hash.
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*
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* @param hash the prior hash value
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* @param value the new value to incorporate
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* @param magicA a magic integer from the stream
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* @param magicB a magic integer from a different stream
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* @return the updated hash value
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*/
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def extendHash(hash: Int, value: Int, magicA: Int, magicB: Int): Int =
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(hash ^ rotl(value * magicA, 11) * magicB) * 3 + visibleMixer
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/** Given a magic integer from the first stream, compute the next */
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def nextMagicA(magicA: Int): Int = magicA * 5 + hiddenMixerA
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/** Given a magic integer from the second stream, compute the next */
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def nextMagicB(magicB: Int): Int = magicB * 5 + hiddenMixerB
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/** Once all hashes have been incorporated, this performs a final mixing */
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def finalizeHash(hash: Int): Int = {
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var i = (hash ^ (hash >>> 16))
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i *= finalMixer1
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i ^= (i >>> 13)
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i *= finalMixer2
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i ^= (i >>> 16)
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i
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}
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/** Compute a high-quality hash of an array */
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def arrayHash[@specialized T](a: Array[T]): Int = {
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var h = startHash(a.length * seedArray)
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var c = hiddenMagicA
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var k = hiddenMagicB
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var j = 0
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while (j < a.length) {
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h = extendHash(h, a(j).##, c, k)
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c = nextMagicA(c)
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k = nextMagicB(k)
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j += 1
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}
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finalizeHash(h)
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}
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/** Compute a high-quality hash of a string */
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def stringHash(s: String): Int = {
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var h = startHash(s.length * seedString)
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var c = hiddenMagicA
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var k = hiddenMagicB
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var j = 0
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while (j + 1 < s.length) {
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val i = (s.charAt(j) << 16) + s.charAt(j + 1);
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h = extendHash(h, i, c, k)
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c = nextMagicA(c)
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k = nextMagicB(k)
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j += 2
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}
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if (j < s.length) h = extendHash(h, s.charAt(j), c, k)
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finalizeHash(h)
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}
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/**
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* Compute a hash that is symmetric in its arguments--that is,
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* where the order of appearance of elements does not matter.
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* This is useful for hashing sets, for example.
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*/
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def symmetricHash[T](xs: TraversableOnce[T], seed: Int): Int = {
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var a, b, n = 0
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var c = 1
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xs.foreach(i ⇒ {
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val h = i.##
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a += h
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b ^= h
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if (h != 0) c *= h
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n += 1
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})
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var h = startHash(seed * n)
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h = extendHash(h, a, storedMagicA(0), storedMagicB(0))
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h = extendHash(h, b, storedMagicA(1), storedMagicB(1))
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h = extendHash(h, c, storedMagicA(2), storedMagicB(2))
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finalizeHash(h)
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}
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}
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