-# memmem.m4 serial 2
-dnl Copyright (C) 2002, 2003, 2004 Free Software Foundation, Inc.
+# memmem.m4 serial 9
+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_GNU_SOURCE])
+ AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
+ AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
AC_REPLACE_FUNCS(memmem)
AC_CHECK_DECLS_ONCE(memmem)
+ if test $ac_cv_have_decl_memmem = no; then
+ 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], [:])