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# 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.
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], [:])
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