+]) # gl_FUNC_MEMMEM_SIMPLE
+
+dnl Additionally, check that memmem has linear performance characteristics
+AC_DEFUN([gl_FUNC_MEMMEM],
+[
+ AC_REQUIRE([gl_FUNC_MEMMEM_SIMPLE])
+ if test $HAVE_DECL_MEMMEM = 1 && test $REPLACE_MEMMEM = 0; then
+ AC_CACHE_CHECK([whether memmem works in linear time],
+ [gl_cv_func_memmem_works_fast],
+ [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <signal.h> /* for signal */
+#include <string.h> /* for memmem */
+#include <stdlib.h> /* for malloc */
+#include <unistd.h> /* for alarm */
+static void quit (int sig) { exit (sig + 128); }
+]], [[
+ int result = 0;
+ size_t m = 1000000;
+ char *haystack = (char *) malloc (2 * m + 1);
+ char *needle = (char *) malloc (m + 1);
+ /* Failure to compile this test due to missing alarm is okay,
+ since all such platforms (mingw) also lack memmem. */
+ signal (SIGALRM, quit);
+ alarm (5);
+ /* Check for quadratic performance. */
+ if (haystack && needle)
+ {
+ memset (haystack, 'A', 2 * m);
+ haystack[2 * m] = 'B';
+ memset (needle, 'A', m);
+ needle[m] = 'B';
+ if (!memmem (haystack, 2 * m + 1, needle, m + 1))
+ result |= 1;
+ }
+ return result;
+ ]])],
+ [gl_cv_func_memmem_works_fast=yes], [gl_cv_func_memmem_works_fast=no],
+ [dnl Only glibc >= 2.9 and cygwin > 1.7.0 are known to have a
+ dnl memmem that works in linear time.
+ AC_EGREP_CPP([Lucky user],
+ [
+#include <features.h>
+#ifdef __GNU_LIBRARY__
+ #if ((__GLIBC__ == 2 && __GLIBC_MINOR__ >= 9) || (__GLIBC__ > 2)) \
+ && !defined __UCLIBC__
+ Lucky user
+ #endif
+#endif
+#ifdef __CYGWIN__
+ #include <cygwin/version.h>
+ #if CYGWIN_VERSION_DLL_COMBINED > CYGWIN_VERSION_DLL_MAKE_COMBINED (1007, 0)
+ Lucky user
+ #endif
+#endif
+ ],
+ [gl_cv_func_memmem_works_fast=yes],
+ [gl_cv_func_memmem_works_fast="guessing no"])
+ ])
+ ])
+ if test "$gl_cv_func_memmem_works_fast" != yes; then
+ REPLACE_MEMMEM=1
+ AC_LIBOBJ([memmem])
+ fi
+ fi
+]) # gl_FUNC_MEMMEM