# memmem.m4 serial 25

dnl Copyright (C) 2002-2004, 2007-2018 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 and functional.

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_CHECK_FUNCS([memmem])

  if test $ac_cv_func_memmem = yes; then

    HAVE_MEMMEM=1

  else

    HAVE_MEMMEM=0

  fi

  AC_CHECK_DECLS_ONCE([memmem])

  if test $ac_cv_have_decl_memmem = no; then

    HAVE_DECL_MEMMEM=0

  else

    dnl Detect https://sourceware.org/bugzilla/show_bug.cgi?id=12092.

    dnl Also check that we handle empty needles correctly.

    AC_CACHE_CHECK([whether memmem works],

      [gl_cv_func_memmem_works_always],

      [AC_RUN_IFELSE([AC_LANG_PROGRAM([[

#include <string.h> /* for memmem */

#define P "_EF_BF_BD"

#define HAYSTACK "F_BD_CE_BD" P P P P "_C3_88_20" P P P "_C3_A7_20" P

#define NEEDLE P P P P P

]], [[

    int result = 0;

    if (memmem (HAYSTACK, strlen (HAYSTACK), NEEDLE, strlen (NEEDLE)))

      result |= 1;

    /* Check for empty needle behavior.  */

    {

      const char *haystack = "AAA";

      if (memmem (haystack, 3, NULL, 0) != haystack)

        result |= 2;

    }

    return result;

    ]])],

        [gl_cv_func_memmem_works_always=yes],

        [gl_cv_func_memmem_works_always=no],

        [dnl glibc 2.9..2.12 and cygwin 1.7.7 have issue #12092 above.

         dnl Also empty needles work on glibc >= 2.1 and cygwin >= 1.7.0.

         dnl uClibc is not affected, since it uses different source code.

         dnl Assume that it works on all other platforms (even if not linear).

         AC_EGREP_CPP([Lucky user],

           [

#ifdef __GNU_LIBRARY__

 #include <features.h>

 #if ((__GLIBC__ == 2 && ((__GLIBC_MINOR > 0 && __GLIBC_MINOR__ < 9) \

                          || __GLIBC_MINOR__ > 12)) \

      || (__GLIBC__ > 2)) \

     || defined __UCLIBC__

  Lucky user

 #endif

#elif defined __CYGWIN__

 #include <cygwin/version.h>

 #if CYGWIN_VERSION_DLL_COMBINED > CYGWIN_VERSION_DLL_MAKE_COMBINED (1007, 7)

  Lucky user

 #endif

#else

  Lucky user

#endif

           ],

           [gl_cv_func_memmem_works_always="guessing yes"],

           [gl_cv_func_memmem_works_always="guessing no"])

        ])

      ])

    case "$gl_cv_func_memmem_works_always" in

      *yes) ;;

      *)

        REPLACE_MEMMEM=1

        ;;

    esac

  fi

  gl_PREREQ_MEMMEM

]) # 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;

      }

    /* Free allocated memory, in case some sanitizer is watching.  */

    free (haystack);

    free (needle);

    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="guessing yes"],

           [gl_cv_func_memmem_works_fast="guessing no"])

        ])

      ])

    case "$gl_cv_func_memmem_works_fast" in

      *yes) ;;

      *)

        REPLACE_MEMMEM=1

        ;;

    esac

  fi

]) # gl_FUNC_MEMMEM

# Prerequisites of lib/memmem.c.

AC_DEFUN([gl_PREREQ_MEMMEM], [:])