Hacker News Reader

Lua does

I thought one of Lua’s selling points is that it’s written in highly standard-compliant C code. I wouldn’t expect it to do anything non-portable like bitwise manipulation of pointers?

It's fine to use techniques like this in standard C provided you guard them with the preprocessor and provide a fallback option on unsupported hardware.

PUC Lua doesn't use these tricks; every value in the VM is represented with a POD struct with explicit tag and value members. The OP may have been thinking of LuaJIT, which uses NaN boxing, but not pointer tagging.

PUC Lua does rely on two's complement integer representation, though, as well as long long, while nominally adhering to C90, so not quite strictly conforming.

Reply on news.ycombinator.com