Re: Lua/LuaJIT2 performance on Android

[KHMan <keinhong@...>]

On 4/20/2011 1:25 AM, Mike Pall wrote:
> KHMan wrote:
> > On 4/19/2011 11:58 PM, Adam Strzelecki wrote:
> > > > Could the JIT use such optimizations automatically, or maybe at
> > > > least
> > > > remove the intermediate __add and bit.* calls operating on the
> > > > integers
> > > > directly?
> > >
> > > It already there, quoting Mike's earlier response: "The ARM port
> > > uses the dual-number mode of LuaJIT. All Lua numbers
> > > are represented either as integers or doubles internally. This is
> > > transparent to the user of the VM. Except for the performance
> > > effects, of course: e.g. 'for i=1,1e7 do end' runs much faster
> > > than 'for i=1.5,1e7 do end'."
> >
> > IIRC, Michal was talking about inferring and accelerating fixed
> > point arithmetic, which is a legit question that goes further than
> > what you have quoted in the above.
>
> No, the reply was spot on. The LuaJIT dual-number mode is a
> property of the VM. It works even with the pure interpreter. The
> JIT compiler does some extra narrowing to integers. But that's
> rarely needed in dual-number mode (OTOH it's crucial for
> performance in single-number mode, e.g. on x86/x64).

My mistake. Sorry for the noise.

--
Cheers,
Kein-Hong Man (esq.)
Kuala Lumpur, Malaysia