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# memmem.m4 serial 9

dnl Copyright (C) 2002, 2003, 2004, 2007, 2008, 2009, 2010

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 memmem is present.

AC_DEFUN([gl_FUNC_MEMMEM_SIMPLE],

[

  dnl Persuade glibc <string.h> to declare memmem().

  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], [:])