Re: LuaJit FFI with iOS
- From: Mike Pall <mike-1306@xxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Mon, 24 Jun 2013 22:26:19 +0200
Joe Riedel wrote:
> Does this mean that on targets that don't support JIT that the
> C API is faster than the FFI?
Yes, in many cases. Depends on the number and types of arguments
and results.
E.g. lua_tonumber() (Classic Lua/C API) is rather cheap. Whereas
lj_cconv_ct_tv() (interpreted FFI) is costly and nested within
another costly function that handles the calling conventions.
[The equivalent for JIT-compiled FFI would be zero-cost, because
the compiler arranges for the number to be in the right argument
register.]
OTOH userdata type checks with lookups in the registry etc. are
probably more expensive than FFI type checks.
[Those are more or less zero-cost when compiled, too.]
--Mike
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