Re: truth of %nil

[Andy Wingo <wingo@pobox.com>]

On Sun 05 Jul 2009 03:41, Mark H Weaver <mhw@netris.org> writes:

> Below is a proposal for how to make boolean tests and end-of-list
> tests faster and more compact, by renumbering the representations for
> SCM_ELISP_NIL, SCM_EOL, SCM_UNDEFINED, and SCM_EOF_VAL.

That looks like great work, Mark!!

I don't think it's a problem to renumber these constants, no. A couple
of questions though:

> 	loop1(int *p)
> 	{
> 	  while (*p != 0x004)
> 	    p++;
> 	}

Did you mean while (p != 0x004) ?

Also, can you make a third test, equivalent to p == SCM_EOL || p ==
SCM_ELISP_NIL ?

> The size of the resulting loop bodies, in bytes, are as follows:
>
> 	arch   loop1   loop2
> 	--------------------
> 	x86-32   8      13
> 	arm     12      16
> 	sparc   16      20
> 	--------------------
>
> I guess this is not too bad.

I realize this is a bit of a silly benchmark, but can you time these?
Actually, can you time Guile? The changes to Guile should be minimal,
after all.

> What do you think?

Excellence, good sir, excellence!

Andy
-- 
http://wingolog.org/