The twitter message you linked to says this:<p><pre><code>    The speedup was caused by replacing setjmp by _setjmp though.
</code></pre>
I know this may sound mysterious, but for BSD&#x2F;OSX... &quot;yes&quot;. It is &quot;well known&quot; (if you&#x27;re the sort of person who writes coroutine runtimes [1]) that _setjmp is far faster than setjmp. It&#x27;s morally equivalent to &#x27;sigsetjmp&#x27;, but more portable, if less standard.<p>[1] <a href="https:&#x2F;&#x2F;github.com&#x2F;jaroslov&#x2F;coro&#x2F;blob&#x2F;master&#x2F;coro.hpp" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;jaroslov&#x2F;coro&#x2F;blob&#x2F;master&#x2F;coro.hpp</a>