> 2007-09-29 Eric Blake <[EMAIL PROTECTED]>
>
> Optimize for Autoconf usage pattern.
> * src/builtin.c (m4_regexp, m4_patsubst): Handle empty regex
> faster.
Less noticeable, but now that Autoconf is doing more single-character
index searches, we might as well cater to that, too. It's appalling how
many platforms still provide O(n*m) strstr implementations, especially
when you consider that Knuth-Morris-Pratt was published in the 70s;
but even on platforms with O(n+m) strstr, strchr tends to be faster
for this special case.
From: Eric Blake <[EMAIL PROTECTED]>
Date: Mon, 1 Oct 2007 14:30:25 -0600
Subject: [PATCH] Another Autoconf usage pattern optimization.
* src/builtin.c (m4_index): Optimize search for one byte.
* doc/m4.texinfo (Index macro, Regexp, Patsubst): Test the new
code paths.
Signed-off-by: Eric Blake <[EMAIL PROTECTED]>
---
ChangeLog | 7 +++++++
doc/m4.texinfo | 21 ++++++++++++++++++---
src/builtin.c | 19 +++++++++++++++----
3 files changed, 40 insertions(+), 7 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index f29b557..396a64f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2007-10-01 Eric Blake <[EMAIL PROTECTED]>
+
+ Another Autoconf usage pattern optimization.
+ * src/builtin.c (m4_index): Optimize search for one byte.
+ * doc/m4.texinfo (Index macro, Regexp, Patsubst): Test the new
+ code paths.
+
2007-09-29 Eric Blake <[EMAIL PROTECTED]>
Optimize for Autoconf usage pattern.
diff --git a/doc/m4.texinfo b/doc/m4.texinfo
index a24d36e..6c76b7b 100644
--- a/doc/m4.texinfo
+++ b/doc/m4.texinfo
@@ -4610,12 +4610,17 @@ index(`gnus, gnats, and armadillos', `dag')
@result{}-1
@end example
-Omitting @var{substring} evokes a warning, but still produces output.
+Omitting @var{substring} evokes a warning, but still produces output;
+contrast this with an empty @var{substring}.
@example
index(`abc')
@error{}m4:stdin:1: Warning: too few arguments to builtin `index'
@result{}0
+index(`abc', `')
[EMAIL PROTECTED]
+index(`abc', `b')
[EMAIL PROTECTED]
@end example
@node Regexp
@@ -4688,12 +4693,17 @@ regexp(`abc', `\(\(d\)?\)\(c\)', `\1\2\3\4\5\6')
@result{}c
@end example
-Omitting @var{regexp} evokes a warning, but still produces output.
+Omitting @var{regexp} evokes a warning, but still produces output;
+contrast this with an empty @var{regexp} argument.
@example
regexp(`abc')
@error{}m4:stdin:1: Warning: too few arguments to builtin `regexp'
@result{}0
+regexp(`abc', `')
[EMAIL PROTECTED]
+regexp(`abc', `', `def')
[EMAIL PROTECTED]
@end example
@node Substr
@@ -4904,12 +4914,17 @@ patreg(`aba abb 121', `\(.\)\(.\)\1', `\2\1\2')
@result{}bab
@end example
-Omitting @var{regexp} evokes a warning, but still produces output.
+Omitting @var{regexp} evokes a warning, but still produces output;
+contrast this with an empty @var{regexp} argument.
@example
patsubst(`abc')
@error{}m4:stdin:1: Warning: too few arguments to builtin `patsubst'
@result{}abc
+patsubst(`abc', `')
[EMAIL PROTECTED]
+patsubst(`abc', `', `-')
[EMAIL PROTECTED]
@end example
@node Format
diff --git a/src/builtin.c b/src/builtin.c
index 65f4585..8974b1a 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -1677,8 +1677,9 @@ static void
m4_index (struct obstack *obs, int argc, token_data **argv)
{
const char *haystack;
- const char *result;
- int retval;
+ const char *needle;
+ const char *result = NULL;
+ int retval = -1;
if (bad_argc (argv[0], argc, 3, 3))
{
@@ -1689,8 +1690,18 @@ m4_index (struct obstack *obs, int argc, token_data
**argv)
}
haystack = ARG (1);
- result = strstr (haystack, ARG (2));
- retval = result ? result - haystack : -1;
+ needle = ARG (2);
+
+ /* Optimize searching for the empty string (always 0) and one byte
+ (strchr tends to be more efficient than strstr). */
+ if (!needle[0])
+ retval = 0;
+ else if (!needle[1])
+ result = strchr (haystack, *needle);
+ else
+ result = strstr (haystack, needle);
+ if (result)
+ retval = result - haystack;
shipout_int (obs, retval);
}
--
1.5.3.2
--
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