Constraint rounding 360

func main() {
    let (scale, n) = findMagic()


    let device = UIDevice.current
    let env = ProcessInfo.processInfo.environment
    let model = env["SIMULATOR_MODEL_IDENTIFIER"] ?? {
        var systemInfo = utsname()
        uname(&systemInfo)
        return withUnsafePointer(to: &systemInfo.machine) {
            String(cString: UnsafeRawPointer($0).assumingMemoryBound(to: CChar.self))
        }
    }()
    print(model, device.systemName, device.systemVersion, scale, "->", n)
}


func findMagic() -> (CGFloat, Int) {
    let view = UIView()
    view.translatesAutoresizingMaskIntoConstraints = false

    let w = view.widthAnchor.constraint(equalToConstant: 0)
    w.isActive = true

    let scale = UIScreen.main.scale
    var lo: CGFloat = 6.4 / scale
    var hi: CGFloat = 6.6 / scale
    while true {
        let mid = (lo + hi) / 2
        if mid == lo || mid == hi {
            let n = findScale(lo, hi)
            return (scale, n)
        }
        w.constant = mid

        let size = view.systemLayoutSizeFitting(
            UIView.layoutFittingCompressedSize,
            withHorizontalFittingPriority: .fittingSizeLevel,
            verticalFittingPriority: .fittingSizeLevel
        )

        if size.width < 6.5 / scale {
            lo = mid
        } else {
            hi = mid
        }
    }
}

func findScale(_ lo: CGFloat, _ hi: CGFloat) -> Int {
    var n = 1
    while round(lo * CGFloat(n)) == round(hi * CGFloat(n)) {
        n += 1
    }
    return n
}