Hello!
While profiling a Scheme program, I noticed that ‘string=?’ was
surprisingly high. I ran OProfile on this Scheme program:
--8<---------------cut here---------------start------------->8---
(define s (make-string 123 #\a))
(let loop ()
(string= s s)
(loop))
--8<---------------cut here---------------end--------------->8---
The flat profile was like this:
--8<---------------cut here---------------start------------->8---
samples % symbol name
13683 24.6367 scm_i_string_ref
13447 24.2118 compare_strings
8652 15.5782 scm_i_string_chars
4801 8.6444 vm_debug_engine
4535 8.1654 scm_i_str2symbol
2123 3.8225 scm_ihashq
1338 2.4091 scm_fluid_ref
993 1.7879 scm_i_string_hash
750 1.3504 scm_hash_fn_get_handle
616 1.1091 scm_module_variable
445 0.8012 scm_from_locale_stringn
--8<---------------cut here---------------end--------------->8---
I came up with the following patch, which adds a shortcut for the most
common case:
diff --git a/libguile/srfi-13.c b/libguile/srfi-13.c
index c4e8571..4803830 100644
--- a/libguile/srfi-13.c
+++ b/libguile/srfi-13.c
@@ -1,6 +1,6 @@
/* srfi-13.c --- SRFI-13 procedures for Guile
*
- * Copyright (C) 2001, 2004, 2005, 2006, 2008, 2009 Free Software Foundation, Inc.
+ * Copyright (C) 2001, 2004, 2005, 2006, 2008, 2009, 2010 Free Software Foundation, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
@@ -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);
+ }
+
return compare_strings (FUNC_NAME, 0,
s1, s2, start1, end1, start2, end2,
SCM_BOOL_F, SCM_BOOL_F, SCM_BOOL_F, SCM_BOOL_F, SCM_BOOL_T);
It’s quite inelegant, but it leads to a more balanced profile:
--8<---------------cut here---------------start------------->8---
samples % symbol name
8079 23.3984 scm_string_eq
5649 16.3606 vm_debug_engine
5624 16.2882 scm_i_str2symbol
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
--8<---------------cut here---------------end--------------->8---
... and a 43% execution time improvement on a tight loop that does
‘string=’.
OK to commit? Ideas for a better solution?
Thanks,
Ludo’.
