The twitter message you linked to says this: The speedup was caused by replacing setjmp by _setjmp though. I know this may sound mysterious, but for BSD/O

The twitter message you linked to says this: The speedup was caused by replacing setjmp by _setjmp though. I know this may sound mysterious, but for BSD/OSX... "yes". It is "well known" (if you're the sort of person who writes coroutine runtimes [1]) that _setjmp is far faster than setjmp. It's morally equivalent to 'sigsetjmp', but more portable, if less standard. [1] https://github.com/jaroslov/coro/blob/master/coro.hpp https://github.com/jaroslov/coro/blob/master/coro.hpp