[SCM] GNU M4 source repository branch, branch-1.6, updated. v1.5.89a-88-gb9c165b

[Eric Blake]

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- Log -----------------------------------------------------------------
commit b9c165b394c06d2da657caae33efd5843689ff3b
Author: Eric Blake <address@hidden>
Date:   Mon Feb 9 06:16:28 2009 -0700

    Enhance index to support starting offset.
    
    * src/builtin.c (m4_index): Add optional third argument.
    * NEWS: Document this.
    * doc/m4.texinfo (Index macro): Likewise.
    (Macro Arguments): Adjust tests.
    
    Signed-off-by: Eric Blake <address@hidden>

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

Summary of changes:
 ChangeLog      |    8 ++++++++
 NEWS           |    4 ++++
 doc/m4.texinfo |   29 ++++++++++++++++++++++++-----
 src/builtin.c  |   30 ++++++++++++++++++++++++------
 4 files changed, 60 insertions(+), 11 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 5763258..b96dccc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2009-02-09  Eric Blake  <address@hidden>
+
+       Enhance index to support starting offset.
+       * src/builtin.c (m4_index): Add optional third argument.
+       * NEWS: Document this.
+       * doc/m4.texinfo (Index macro): Likewise.
+       (Macro Arguments): Adjust tests.
+
 2009-01-24  Eric Blake  <address@hidden>
 
        Add URLs to --help output.
diff --git a/NEWS b/NEWS
index cbea814..bfcb684 100644
--- a/NEWS
+++ b/NEWS
@@ -59,6 +59,10 @@ Software Foundation, Inc.
    example of how to recover M4 1.4.x behavior, as well as an example of
    simulating the new negative argument semantics with older M4.
 
+** The `index' builtin now takes an optional third argument as the index
+   to begin searching from, with a negative argument relative to the end of
+   the string.
+
 ** The `-d'/`--debug' command-line option now understands `-' and `+'
    modifiers, the way the builtin `debugmode' has always done; this allows
    `-d-V' to disable prior debug settings from the command line, similar to
diff --git a/doc/m4.texinfo b/doc/m4.texinfo
index 37600c4..8341cc9 100644
--- a/doc/m4.texinfo
+++ b/doc/m4.texinfo
@@ -1648,8 +1648,8 @@ index(`abc')
 @result{}0
 index(`abc',)
 @result{}0
-index(`abc', `b', `ignored')
address@hidden:stdin:3: Warning: index: extra arguments ignored: 3 > 2
+index(`abc', `b', `0', `ignored')
address@hidden:stdin:3: Warning: index: extra arguments ignored: 4 > 3
 @result{}1
 @end example
 
@@ -1660,7 +1660,7 @@ index(`abc')
 @result{}0
 index(`abc',)
 @result{}0
-index(`abc', `b', `ignored')
+index(`abc', `b', `', `ignored')
 @result{}1
 @end example
 
@@ -6113,11 +6113,13 @@ len(`abcdef')
 @cindex substrings, locating
 Searching for substrings is done with @code{index}:
 
address@hidden Builtin index (@var{string}, @var{substring})
address@hidden Builtin index (@var{string}, @var{substring}, @ovar{offset})
 Expands to the index of the first occurrence of @var{substring} in
 @var{string}.  The first character in @var{string} has index 0.  If
 @var{substring} does not occur in @var{string}, @code{index} expands to
address@hidden
address@hidden  If @var{offset} is provided, it determines the index at
+which the search starts; a negative @var{offset} specifies the offset
+relative to the end of @var{string}.
 
 The macro @code{index} is recognized only with parameters.
 @end deffn
@@ -6142,6 +6144,23 @@ index(`abc', `b')
 @result{}1
 @end example
 
address@hidden @acronym{GNU} extensions
+As an extension, an @var{offset} can be provided to limit the search to
+the tail of the @var{string}.  A negative offset is interpreted relative
+to the end of @var{string}, and it is not an error if @var{offset}
+exceeds the bounds of @var{string}.
+
address@hidden
+index(`aba', `a', `1')
address@hidden
+index(`ababa', `ba', `-3')
address@hidden
+index(`abc', `a', `4')
address@hidden
+index(`abc', `bc', `-4')
address@hidden
address@hidden example
+
 @node Regexp
 @section Searching for regular expressions
 
diff --git a/src/builtin.c b/src/builtin.c
index 6594cb9..a398fdb 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -1828,20 +1828,23 @@ m4_len (struct obstack *obs, int argc, macro_arguments 
*argv)
   shipout_int (obs, ARG_LEN (1));
 }
 
-/*-------------------------------------------------------------------------.
-| The macro expands to the first index of the second argument in the first |
-| argument.                                                               |
-`-------------------------------------------------------------------------*/
+/*-------------------------------------------------------------------.
+| The macro expands to the first index of the second argument in the |
+| first argument.  As an extension, start the search at the index    |
+| indicated by the third argument.                                  |
+`-------------------------------------------------------------------*/
 
 static void
 m4_index (struct obstack *obs, int argc, macro_arguments *argv)
 {
   const char *haystack;
+  size_t haystack_len;
   const char *needle;
   const char *result = NULL;
+  int offset = 0;
   int retval = -1;
 
-  if (bad_argc (arg_info (argv), argc, 2, 2))
+  if (bad_argc (arg_info (argv), argc, 2, 3))
     {
       /* builtin(`index') is blank, but index(`abc') is 0.  */
       if (argc == 2)
@@ -1850,11 +1853,26 @@ m4_index (struct obstack *obs, int argc, 
macro_arguments *argv)
     }
 
   haystack = ARG (1);
+  haystack_len = ARG_LEN (1);
   needle = ARG (2);
+  if (!arg_empty (argv, 3) && !numeric_arg (arg_info (argv), ARG (3), &offset))
+    return;
+  if (offset < 0)
+    {
+      offset += haystack_len;
+      if (offset < 0)
+       offset = 0;
+    }
+  else if (haystack_len < offset)
+    {
+      shipout_int (obs, -1);
+      return;
+    }
 
   /* Rely on the optimizations guaranteed by gnulib's memmem
      module.  */
-  result = (char *) memmem (haystack, ARG_LEN (1), needle, ARG_LEN (2));
+  result = (char *) memmem (haystack + offset, haystack_len - offset, needle,
+                           ARG_LEN (2));
   if (result)
     retval = result - haystack;
 


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