Re: m4sugar speedups [was: Multi-Line Definitions]

On Sep 30, 2007, at 5:48 AM, Eric Blake wrote:

> From b2dda0adc778b0d3004950048211289958da2abc Mon Sep 17 00:00:00 2001
> From: Eric Blake <[email protected]>
> Date: Sat, 29 Sep 2007 21:44:10 -0600
> Subject: [PATCH] Speed optimization: avoid m4 regex when other  
> algorithms work.
>
> * lib/m4sugar/m4sh.m4 (AS_LITERAL_IF): Rewrite without regex.
> (_AS_QUOTE_IFELSE): Likewise.
> * lib/m4sugar/m4sugar.m4 (m4_strip): Reduce from 3 to 2 regex.
> (m4_bpatsubsts): Split...
> (_m4_bpatsubsts): ...so that recursion can avoid patsubst on empty
> regex.
> (_m4_divert()): Define, to avoid m4 warning on `m4_divert'.
> (m4_qlen): Optimize on short strings, to avoid regex.
> (m4_sign): Avoid regex, and fix bug with `01' and `-0'.
> * lib/autoconf/general.m4 (AC_CACHE_VAL): Rewrite without regex.
> (AC_DEFINE_TRACE): Likewise.
>
> Signed-off-by: Eric Blake <[email protected]>
[...]
> @@ -1449,16 +1458,20 @@ m4_define([m4_flatten],
>  #
>  # Because we want to preserve active symbols, STRING must be  
> double-quoted.

Hmm if you changed [[$1]] to [$1 ], STRING no longer needs to be  
double quoted, right?

>  #
> -# Then notice the 2 last patterns: they are in charge of removing the
> +# First, notice that we guarantee trailing space.  Why?  Because  
> regex
> +# are greedy, and `.* ?' always groups the space into the .* portion.
> +# The algorithm is simpler by avoiding `?' at the end.  The algorithm
> +# correctly strips everything if STRING is just ` '.
> +#
> +# Then notice the second pattern: it is in charge of removing the
>  # leading/trailing spaces.  Why not just `[^ ]'?  Because they are
> -# applied to doubly quoted strings, i.e. more or less [[STRING]].  So
> -# if there is a leading space in STRING, then it is the *third*
> -# character, since there are two leading `['; equally for the last  
> pattern.
> +# applied to over-quoted strings, i.e. more or less [STRING], due
> +# to the limitations of m4_bpatsubsts.  So the leading space in  
> STRING
> +# is the *second* character; equally for the trailing space.
>  m4_define([m4_strip],
> -[m4_bpatsubsts([[$1]],
> +[m4_bpatsubsts([$1 ],
>  	       [[	 ]+], [ ],
> -	       [^\(..\) ],    [\1],
> -	       [ \(..\)$],    [\1])])
> +	       [^. ?\(.*\) .$], [[[\1]]])])
>
>


Nice work!

-- 
Benoit Sigoure aka Tsuna
EPITA Research and Development Laboratory