LNUM 2008 patch is ready :)

[Asko Kauppi <askok@...>]

Hi, everyone.

I'd like to initiate discussion about number modes in Lua. It's  
sometimes seen on the list that people find it hard to change the  
default number types (they can be changed in Lua, but not all  
implications are in the luaconf.h file). I'd like to ask, which  
_needs_ people have to change the type, and which would be the best  
set of number modes to answer such needs.

My experience below, but first a short summary to those not familiar  
with LNUM patch.

LNUM patch enables integer mode number optimizations, without changing  
the existing Lua scripting or C API interfaces. It allows moderate to  
huge speed increases, depending on the system. It also makes it easy  
to change number modes between any combination of: float / double /  
long double, 32/64-bit integers, optional complex arithmetics.

The LNUM patch is now ready and tested for Lua 5.1.3, and I'd like to  
get feedback on how people actually use it, as well as to bring out  
some complexities found in making it.


To start the discussion, here's my feelings about usefulness of  
various number modes:

LNUM_DOUBLE + LNUM_INT32:	Useful as a default, absolutely ANSI C. No  
portability issues.

LNUM_INT64	Useful, and rather portable though 'long long' is not ANSI  
C. The added integer precision should be valuable (double only has 50+  
bits).

LNUM_FLOAT	Problematic. Math functions not ANSI C. Limited or no  
support on Windows.
				The only benefit I see is less memory consumption on embedded  
devices (speedwise, not much difference with LNUM_DOUBLE+LNUM_INT32).
				Is anyone actually using 'float' currently, and what is the main  
reason you do?

LNUM_LDOUBLE	Problematic. Not ANSI C, limited or no support on Windows.
				I've hit a few weird behaviours on Lua 5.1.3 when lua_Number is  
defined as 'long double'. OS X Intel crashes; Linux x86 gives stack  
warnings.
				The reason for these is unsolved; is someone actually using  
(unpatched) Lua 5.1.3 with 'long double' on such systems?
				On other systems (OS X PowerPC, Windows XP) long double seems to  
work fine.

LNUM_COMPLEX	It's neat, and it works (with any number mode).  
Surprisingly little portability issues, but it does require C99.

-asko


News I placed to LuaForge:	http://luaforge.net/forum/forum.php?forum_id=1582
Download the patch / performance sheet:	http://luaforge.net/frs/?group_id=214