Add combine hash

Sources/FirebladeECS/Hashing.swift

@@ -5,6 +5,56 @@
 //  Created by Christian Treffs on 16.10.17.
 //
 
+// MARK: - hash combine
+/// Calculates the combined hash of two values. This implementation is based on boost::hash_combine.
+/// Will always produce the same result for the same combination of seed and value during the single run of a program.
+///
+/// - Parameters:
+///   - seed: seed hash.
+///   - value: value to be combined with seed hash.
+/// - Returns: combined hash value.
+func hash(combine seed: Int, _ value: Int) -> Int {
+	/// http://www.boost.org/doc/libs/1_65_1/doc/html/hash/combine.html
+	/// http://www.boost.org/doc/libs/1_65_1/doc/html/hash/reference.html#boost.hash_combine
+	/// http://www.boost.org/doc/libs/1_65_1/boost/functional/hash/hash.hpp
+	/// http://book.huihoo.com/data-structures-and-algorithms-with-object-oriented-design-patterns-in-c++/html/page214.html
+	/// https://stackoverflow.com/a/35991300
+	/// https://stackoverflow.com/a/4948967
+	/*
+	let phi = (1.0 + sqrt(5.0)) / 2 // golden ratio
+	let a32 = pow(2.0,32.0) / phi
+	let a64 = pow(2.0,64.0) / phi
+	*/
+	#if arch(x86_64) || arch(arm64) // 64 bit
+		let fibA: UInt = 0x9e3779b97f4a7c15 // = 11400714819323198485 aka Fibonacci Hash a value for 2^64; calculate by: 2^64 / (golden ratio)
+	#elseif arch(i386) || arch(arm) // 32 bit
+		let fibA: UInt = 0x9e3779b9 // = 2654435769 aka Fibonacci Hash a value for 2^32; calculate by: 2^32 / (golden ratio)
+	#endif
+	var uSeed = UInt(bitPattern: seed)
+	let uValue = UInt(bitPattern: value)
+	uSeed ^= uValue &+ fibA &+ (uSeed << 6) &+ (uSeed >> 2)
+	return Int(bitPattern: uSeed)
+}
+
+/// Calculates the combined hash value of the elements. This implementation is based on boost::hash_range.
+/// Is sensitive to the order of the elements.
+/// - Parameter hashValues: sequence of hash values to combine.
+/// - Returns: combined hash value.
+func hash<S: Sequence>(combine hashValues: S) -> Int where S.Element == Int {
+	/// http://www.boost.org/doc/libs/1_65_1/doc/html/hash/reference.html#boost.hash_range_idp517643120
+	return hashValues.reduce(0, { hash(combine: $0, $1) })
+}
+
+/// Calculates the combined hash value of the elements. This implementation is based on boost::hash_range.
+/// Is sensitive to the order of the elements.
+/// - Parameter hashValues: sequence of hash values to combine.
+/// - Returns: combined hash value.
+func hash<H: Sequence>(combine hashables: H) -> Int where H.Element == Hashable {
+	/// http://www.boost.org/doc/libs/1_65_1/doc/html/hash/reference.html#boost.hash_range_idp517643120
+	return hashables.reduce(0, { hash(combine: $0, $1.hashValue) })
+}
+
+// MARK: - entity component hash
 extension EntityComponentHash {
 
 	static func compose(entityId: EntityIdentifier, componentTypeHash: ComponentTypeHash) -> EntityComponentHash {

Tests/FirebladeECSTests/HashingTests.swift

@@ -11,7 +11,7 @@ import XCTest
 
 class HashingTests: XCTestCase {
 
-	func test() {
+	func testCollisionsInCritialRange() {
 
 		var hashSet: Set<Int> = Set<Int>()