Date from UUID in Swift

UUID+Parsing.swift

/* From https://www.famkruithof.net/guid-uuid-make.html
 * and https://www.famkruithof.net/guid-uuid-timebased.html */

extension UUID {
	
	var isTimeUUID: Bool {
		return (uuid.8 & 0xC0) == 0x80 /* Variant is the one we expect */ && (uuid.6 & 0xF0) == 0x10 /* Time-based version of the variant */
	}
	
	var generationDate: Date? {
		guard isTimeUUID else {return nil}
		
		let dateInt: UInt64 = (
			UInt64(uuid.3)        * 0x1 +
			UInt64(uuid.2)        * 0x100 +
			UInt64(uuid.1)        * 0x10000 +
			UInt64(uuid.0)        * 0x1000000 +
			UInt64(uuid.5)        * 0x100000000 +
			UInt64(uuid.4)        * 0x10000000000 +
			UInt64(uuid.7)        * 0x1000000000000 +
			UInt64(uuid.6 & 0x0F) * 0x100000000000000
		)
		
		/* The solution below works too, but on little-endian architectures only. */
//		var dateInt: UInt64 = 0
//		withUnsafeMutableBytes(of: &dateInt) { bytes in
//			bytes[7] = uuid.6 & 0x0F
//			bytes[6] = uuid.7
//			bytes[5] = uuid.4
//			bytes[4] = uuid.5
//			bytes[3] = uuid.0
//			bytes[2] = uuid.1
//			bytes[1] = uuid.2
//			bytes[0] = uuid.3
//		}
		
		return Date(timeInterval: TimeInterval(dateInt)/10000000, since: Date(timeIntervalSince1970: TimeInterval(-12219292800)))
	}
	
}