I was actually surprised to see nearly a factor ten between C99 and LuaJIT. In previous measurements (on x86, see e.g. https://github.com/rochus-keller/Are-we-fast-yet/blob/main/L...) there was rather a factor five. So either GCC 12.2 produces much faster code than GCC 4.8, or LuaJIT 2.1 got much slower, or the C99 version of Are-we-fast-yet is much better supported by the CPU cache of the T480 than my previous EliteBook 2530. I don't think that the x86 vs x86_64 makes such a difference (at least I didn't observe this in many other experiments).