Re: Adding assembler code to Lua programs
- From: Mike Pall <mike-1403@xxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Fri, 7 Mar 2014 10:42:27 +0100
Konstantin Olkhovskiy wrote:
> I had a wild idea of implementing attribute extractor with
> DynASM that will craft some specialized piece of code that skips
> unnecessary fields and retrieves the one(s) requested. Is it
> sensible to use DynASM for this purpose? Or Lua version can
> JIT-compile in something comparable in performance?
Dynamically generate Lua source code that scans the data using
the FFI. Something like this, where d is an FFI struct
(untested code, typed into the mail):
local function match_factory(match_list)
-- lookup match function cache here
-- Otherwise generate new match function.
local s = [[
-- Place any immutable upvalues or other dependencies here.
return function(d)
return
]]
local first = true
-- Some loop which accumulates the fields to be checked from match_list
if not first then s = s .. " and "; first = false end
-- Example: equality check for an integer field.
s = s .. string.format("d[i].%s == %d", field_name, field_value)
-- ...
s = s .. [[
end
]]
local match = loadstring(s)()
-- Cache match here.
return match
end
... call it later e.g. to process an array of structs ...
local match = match_factory(match_list)
for i=1,n do
if match(a[i]) then ... end
end
That's pretty easy for the JIT compiler to optimize -- provided
the loop is on the Lua side. Only go the DynASM route if that
approach doesn't perform.
--Mike
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