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# memmem.m4 serial 29
dnl Copyright (C) 2002-2004, 2007-2024 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_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 $ac_cv_have_decl_memmem = no; then
HAVE_DECL_MEMMEM=0
else
dnl Detect https://sourceware.org/bugzilla/show_bug.cgi?id=12092.
dnl Also check that we handle empty needles correctly.
AC_CACHE_CHECK([whether memmem works],
[gl_cv_func_memmem_works_always],
[AC_RUN_IFELSE([AC_LANG_PROGRAM([[
#include <string.h> /* for memmem */
#define P "_EF_BF_BD"
#define HAYSTACK "F_BD_CE_BD" P P P P "_C3_88_20" P P P "_C3_A7_20" P
#define NEEDLE P P P P P
]], [[
int result = 0;
if (memmem (HAYSTACK, strlen (HAYSTACK), NEEDLE, strlen (NEEDLE)))
result |= 1;
/* Check for empty needle behavior. */
{
const char *haystack = "AAA";
if (memmem (haystack, 3, (const char *) 1, 0) != haystack)
result |= 2;
}
return result;
]])],
[gl_cv_func_memmem_works_always=yes],
[gl_cv_func_memmem_works_always=no],
[dnl glibc 2.9..2.12 and cygwin 1.7.7 have issue #12092 above.
dnl Also empty needles work on glibc >= 2.1 and cygwin >= 1.7.0.
dnl uClibc is not affected, since it uses different source code.
dnl Assume that it works on all other platforms (even if not linear).
AC_EGREP_CPP([Lucky user],
[
#include <string.h> /* for __GNU_LIBRARY__ */
#ifdef __GNU_LIBRARY__
#include <features.h>
#if ((__GLIBC__ == 2 && ((__GLIBC_MINOR > 0 && __GLIBC_MINOR__ < 9) \
|| __GLIBC_MINOR__ > 12)) \
|| (__GLIBC__ > 2)) \
|| defined __UCLIBC__
Lucky user
#endif
#elif defined __CYGWIN__
#include <cygwin/version.h>
#if CYGWIN_VERSION_DLL_COMBINED > CYGWIN_VERSION_DLL_MAKE_COMBINED (1007, 7)
Lucky user
#endif
#else
Lucky user
#endif
],
[gl_cv_func_memmem_works_always="guessing yes"],
[gl_cv_func_memmem_works_always="$gl_cross_guess_normal"])
])
])
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 $REPLACE_MEMMEM = 0; then
AC_CACHE_CHECK([whether memmem works in linear time],
[gl_cv_func_memmem_works_fast],
[AC_RUN_IFELSE([AC_LANG_PROGRAM([[
#include <signal.h> /* for signal */
#include <string.h> /* for memmem */
#include <stdlib.h> /* for malloc */
#include <unistd.h> /* for alarm */
static void quit (int sig) { _exit (sig + 128); }
]], [[
int result = 0;
size_t m = 1000000;
char *haystack = (char *) malloc (2 * m + 1);
char *needle = (char *) malloc (m + 1);
/* Failure to compile this test due to missing alarm is okay,
since all such platforms (mingw) also lack memmem. */
signal (SIGALRM, quit);
alarm (5);
/* Check for quadratic performance. */
if (haystack && needle)
{
memset (haystack, 'A', 2 * m);
haystack[2 * m] = 'B';
memset (needle, 'A', m);
needle[m] = 'B';
if (!memmem (haystack, 2 * m + 1, needle, m + 1))
result |= 1;
}
/* Free allocated memory, in case some sanitizer is watching. */
free (haystack);
free (needle);
return result;
]])],
[gl_cv_func_memmem_works_fast=yes], [gl_cv_func_memmem_works_fast=no],
[dnl Only glibc >= 2.9 and cygwin > 1.7.0 are known to have a
dnl memmem that works in linear time.
AC_EGREP_CPP([Lucky user],
[
#include <features.h>
#ifdef __GNU_LIBRARY__
#if ((__GLIBC__ == 2 && __GLIBC_MINOR__ >= 9) || (__GLIBC__ > 2)) \
&& !defined __UCLIBC__
Lucky user
#endif
#endif
#ifdef __CYGWIN__
#include <cygwin/version.h>
#if CYGWIN_VERSION_DLL_COMBINED > CYGWIN_VERSION_DLL_MAKE_COMBINED (1007, 0)
Lucky user
#endif
#endif
],
[gl_cv_func_memmem_works_fast="guessing yes"],
[gl_cv_func_memmem_works_fast="$gl_cross_guess_normal"])
])
])
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], [:])
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