hash_combine.swift

public func hash_combine(seed: inout Int, value: Int) {
    if MemoryLayout<Int>.size == 64 {
        // 64 bit hash_combine
        let mul: UInt64 = 0x9ddfea08eb382d69
        let s = UInt64(bitPattern: Int64(seed))
        let v = UInt64(bitPattern: Int64(value))
        var a = (v ^ s) &* mul
        a ^= (a >> 47)
        var b = (s ^ a) &* mul
        b ^= (b >> 47)
        let result = b &* mul
        seed = Int(Int64(bitPattern: result))
    } else if MemoryLayout<Int>.size == 32 {
        // 32 bit hash_combine
        var s = UInt32(bitPattern: Int32(seed))
        let v = UInt32(bitPattern: Int32(value))
        s ^= v &+ 0x9e3779b9 &+ (s << 6) &+ (s >> 2)
        seed = Int(Int32(bitPattern: s))
    } else {
        fatalError()
    }
}