simple nanosecond timer using mach_absolute_time

Timer.swift

/*
    var t = Timer()
    
    t.start()
    // do something
    t.stop()

    print("took \(t.seconds)")
*/

import Darwin

struct Timer {
    var startTime: UInt64 = 0
    var stopTime: UInt64 = 0
    let numer: UInt64
    let denom: UInt64

    init() {
        var info = mach_timebase_info(numer: 0, denom: 0)
        mach_timebase_info(&info)
        numer = UInt64(info.numer)
        denom = UInt64(info.denom)
    }

    mutating func start() {
        startTime = mach_absolute_time()
    }

    mutating func stop() {
        stopTime = mach_absolute_time()
    }

    var nanoseconds: UInt64 {
        return ((stopTime - startTime) * numer) / denom
    }

    var milliseconds: Double {
        return Double(nanoseconds) / 1_000_000
    }

    var seconds: Double {
        return Double(nanoseconds) / 1_000_000_000
    }
}