[SCM] GNU M4 source repository branch, master, updated. 8b55caca720db14c67afcbc78294d56a02a0e6a0

[Eric Blake]

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- Log -----------------------------------------------------------------
commit 8b55caca720db14c67afcbc78294d56a02a0e6a0
Author: Eric Blake <address@hidden>
Date:   Mon Oct 1 16:40:12 2007 -0600

    Another Autoconf usage pattern optimization.
    
    * modules/m4.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 <address@hidden>

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog      |    7 +++++++
 doc/m4.texinfo |   21 ++++++++++++++++++---
 modules/m4.c   |   16 ++++++++++++++--
 3 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 2c31728..307a697 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2007-10-01  Eric Blake  <address@hidden>
+
+       Another Autoconf usage pattern optimization.
+       * modules/m4.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  <address@hidden>
 
        Optimize for Autoconf usage pattern.
diff --git a/doc/m4.texinfo b/doc/m4.texinfo
index 844d48a..b5dc467 100644
--- a/doc/m4.texinfo
+++ b/doc/m4.texinfo
@@ -5749,12 +5749,17 @@ 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: index: too few arguments: 1 < 2
 @result{}0
+index(`abc', `')
address@hidden
+index(`abc', `b')
address@hidden
 @end example
 
 @node Regexp
@@ -5822,12 +5827,17 @@ 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: regexp: too few arguments: 1 < 2
 @result{}0
+regexp(`abc', `')
address@hidden
+regexp(`abc', `', `def')
address@hidden
 @end example
 
 If @var{resyntax} is given, @var{regexp} must be given according to
@@ -6078,12 +6088,17 @@ 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: patsubst: too few arguments: 1 < 2
 @result{}abc
+patsubst(`abc', `')
address@hidden
+patsubst(`abc', `', `-')
address@hidden
 @end example
 
 @node Format
diff --git a/modules/m4.c b/modules/m4.c
index eef3a61..b39c5f2 100644
--- a/modules/m4.c
+++ b/modules/m4.c
@@ -913,8 +913,20 @@ M4BUILTIN_HANDLER (len)
 M4BUILTIN_HANDLER (index)
 {
   const char *haystack = M4ARG (1);
-  const char *result = strstr (haystack, M4ARG (2));
-  int retval = result ? result - haystack : -1;
+  const char *needle = M4ARG (2);
+  const char *result = NULL;
+  int retval = -1;
+
+  /* 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;
 
   m4_shipout_int (obs, retval);
 }


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