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@ctreffs
Created October 18, 2017 06:48
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[Swift] hash combine and hash range
/// 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) })
}
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ghost commented Apr 9, 2025

Is this MurMurHash? I have a friend who has code which uses "0x9E3779B97F4A7C15" and it's known.

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