X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=m4%2Fmemmem.m4;h=383ed4b302fbcfff83762d5f617259750b60bcbe;hb=01dfd1752e938c6fca54e791eb2adc1de29189f5;hp=e6a3da193c7aa17d3a4bc1b3d7922217cc5b81f4;hpb=3740c324b0f14e757b73cc22d88d30c4235d1bcb;p=gnulib.git

diff --git a/m4/memmem.m4 b/m4/memmem.m4
index e6a3da193..383ed4b30 100644
--- a/m4/memmem.m4
+++ b/m4/memmem.m4
@@ -1,10 +1,11 @@
-# memmem.m4 serial 5
-dnl Copyright (C) 2002, 2003, 2004, 2007 Free Software Foundation, Inc.
+# memmem.m4 serial 10
+dnl Copyright (C) 2002, 2003, 2004, 2007, 2008 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
 
-AC_DEFUN([gl_FUNC_MEMMEM],
+dnl Check that memmem is present.
+AC_DEFUN([gl_FUNC_MEMMEM_SIMPLE],
 [
   dnl Persuade glibc <string.h> to declare memmem().
   AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
@@ -16,7 +17,47 @@ AC_DEFUN([gl_FUNC_MEMMEM],
     HAVE_DECL_MEMMEM=0
   fi
   gl_PREREQ_MEMMEM
-])
+]) # gl_FUNC_MEMMEM_SIMPLE
+
+dnl Additionally, check that memmem is efficient and handles empty needles.
+AC_DEFUN([gl_FUNC_MEMMEM],
+[
+  AC_REQUIRE([gl_FUNC_MEMMEM_SIMPLE])
+  if test $ac_cv_have_decl_memmem = yes; then
+    AC_CACHE_CHECK([whether memmem works in linear time],
+      [gl_cv_func_memmem_works],
+      [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <string.h> /* for memmem */
+#include <stdlib.h> /* for malloc */
+#include <unistd.h> /* for alarm */
+]], [[size_t m = 1000000;
+    char *haystack = (char *) malloc (2 * m + 1);
+    char *needle = (char *) malloc (m + 1);
+    void *result = 0;
+    /* Failure to compile this test due to missing alarm is okay,
+       since all such platforms (mingw) also lack memmem.  */
+    alarm (5);
+    /* Check for quadratic performance.  */
+    if (haystack && needle)
+      {
+	memset (haystack, 'A', 2 * m);
+	haystack[2 * m] = 'B';
+	memset (needle, 'A', m);
+	needle[m] = 'B';
+	result = memmem (haystack, 2 * m + 1, needle, m + 1);
+      }
+    /* Check for empty needle behavior.  */
+    return !result || !memmem ("a", 1, 0, 0);]])],
+	[gl_cv_func_memmem_works=yes], [gl_cv_func_memmem_works=no],
+	[dnl pessimistically assume the worst, since even glibc 2.6.1
+	 dnl has quadratic complexity in its memmem
+	 gl_cv_func_memmem_works="guessing no"])])
+    if test "$gl_cv_func_memmem_works" != yes; then
+      REPLACE_MEMMEM=1
+      AC_LIBOBJ([memmem])
+    fi
+  fi
+]) # gl_FUNC_MEMMEM
 
 # Prerequisites of lib/memmem.c.
 AC_DEFUN([gl_PREREQ_MEMMEM], [:])