问题
I can see various built-in functions (like __builtin_popount, __builtin_clz, etc) in the Xcode auto-completion pop-up. I'm not sure where these are getting picked up from though. Command clicking doesn't lead to a swift definition or any documentation. Are any __builtin_* or equivalent intrinsic functions available in Swift 3 and if so, what modules do I need to include and how can I call them?
来源：https://stackoverflow.com/questions/41353482/are-built-in-intrinsic-functions-available-in-swift-3