Re: Optimizing ‘string=’

[Andy Wingo <wingo@pobox.com>]

Hi,

Nice profile-driven debugging :)

On Tue 22 Jun 2010 21:40, ludo@gnu.org (Ludovic Courtès) writes:

> @@ -1168,6 +1168,21 @@ SCM_DEFINE (scm_string_eq, "string=", 2, 4, 0,
>  	    "value otherwise.")
>  #define FUNC_NAME s_scm_string_eq
>  {
> +  if (SCM_LIKELY (scm_i_is_narrow_string (s1) == scm_i_is_narrow_string (s2)
> +		  && SCM_UNBNDP (start1) && SCM_UNBNDP (end1)
> +		  && SCM_UNBNDP (start2) && SCM_UNBNDP (end2)))
> +    {
> +      size_t len1, len2;
> +
> +      len1 = scm_i_string_length (s1);
> +      len2 = scm_i_string_length (s2);
> +
> +      if (SCM_LIKELY (len1 == len2))
> +	return scm_from_bool (memcmp (scm_i_string_chars (s1),
> +				      scm_i_string_chars (s2),
> +				      len1) == 0);
> +    }
> +

Nasty, but OK I guess if you need it. Why not also add a fast path for
scm_is_eq (s1, s2), or for comparing stringbufs, or something ?

> It’s quite inelegant, but it leads to a more balanced profile:
>
> samples  %        symbol name
> 8079     23.3984  scm_string_eq
> 5649     16.3606  vm_debug_engine
> 5624     16.2882  scm_i_str2symbol
                    ^ What is this doing here?

And for the matter, what are the rest about? Did you just do a really
short profile?

> 2840      8.2252  scm_ihashq
> 1755      5.0828  scm_i_string_hash
> 1637      4.7411  scm_fluid_ref
> 1027      2.9744  scm_i_string_ref
> 1011      2.9281  scm_hash_fn_get_handle
> 877       2.5400  scm_i_string_chars
> 793       2.2967  scm_module_variable
> 553       1.6016  scm_from_locale_stringn
> 471       1.3641  scm_from_stringn
> 426       1.2338  scm_sym2var
> 384       1.1121  scm_i_make_string
> 317       0.9181  scm_module_lookup

Andy
-- 
http://wingolog.org/