X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=m4%2Fstrstr.m4;h=5a49b07c2c4abcbf220e60386fa94b41c89e9e23;hb=f1fcb8539c9d1c7d9cefb25ce5c07a099ea1f148;hp=97eb0a8bd96287a0525ef4350d34133c59bd2815;hpb=d4d9ba3c78eceac6e5f6755abe28f15cfece96e2;p=gnulib.git

diff --git a/m4/strstr.m4 b/m4/strstr.m4
index 97eb0a8bd..5a49b07c2 100644
--- a/m4/strstr.m4
+++ b/m4/strstr.m4
@@ -1,21 +1,44 @@
-# strstr.m4 serial 6
-dnl Copyright (C) 2002-2003, 2005, 2007 Free Software Foundation, Inc.
+# strstr.m4 serial 2
+dnl Copyright (C) 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.
 
+dnl Check that strstr is efficient.
 AC_DEFUN([gl_FUNC_STRSTR],
 [
   AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
-  dnl No known system has a strstr() function that works correctly in
-  dnl multibyte locales. Therefore we use our version always.
-  AC_LIBOBJ(strstr)
-  REPLACE_STRSTR=1
-  gl_PREREQ_STRSTR
-])
-
-# Prerequisites of lib/strstr.c.
-AC_DEFUN([gl_PREREQ_STRSTR], [
-  AC_REQUIRE([gl_FUNC_MBRTOWC])
-  :
-])
+  AC_CACHE_CHECK([whether strstr works in linear time],
+    [gl_cv_func_strstr_linear],
+    [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 + 2);
+    char *needle = (char *) malloc (m + 2);
+    void *result = 0;
+    /* Failure to compile this test due to missing alarm is okay,
+       since all such platforms (mingw) also have quadratic strstr.  */
+    alarm (5);
+    /* Check for quadratic performance.  */
+    if (haystack && needle)
+      {
+	memset (haystack, 'A', 2 * m);
+	haystack[2 * m] = 'B';
+	haystack[2 * m + 1] = 0;
+	memset (needle, 'A', m);
+	needle[m] = 'B';
+	needle[m + 1] = 0;
+	result = strstr (haystack, needle);
+      }
+    return !result;]])],
+      [gl_cv_func_strstr_linear=yes], [gl_cv_func_strstr_linear=no],
+      [dnl pessimistically assume the worst, since even glibc 2.6.1
+       dnl has quadratic complexity in its strstr
+       gl_cv_func_strstr_linear="guessing no"])])
+  if test "$gl_cv_func_strstr_linear" != yes; then
+    REPLACE_STRSTR=1
+    AC_LIBOBJ([strstr])
+  fi
+]) # gl_FUNC_STRSTR