1# size_max.m4 serial 4
2dnl Copyright (C) 2003, 2005-2006 Free Software Foundation, Inc.
3dnl This file is free software; the Free Software Foundation
4dnl gives unlimited permission to copy and/or distribute it,
5dnl with or without modifications, as long as this notice is preserved.
6
7dnl From Bruno Haible.
8
9AC_DEFUN([gl_SIZE_MAX],
10[
11  AC_CHECK_HEADERS(stdint.h)
12  dnl First test whether the system already has SIZE_MAX.
13  AC_MSG_CHECKING([for SIZE_MAX])
14  result=
15  AC_EGREP_CPP([Found it], [
16#include <limits.h>
17#if HAVE_STDINT_H
18#include <stdint.h>
19#endif
20#ifdef SIZE_MAX
21Found it
22#endif
23], result=yes)
24  if test -z "$result"; then
25    dnl Define it ourselves. Here we assume that the type 'size_t' is not wider
26    dnl than the type 'unsigned long'. Try hard to find a definition that can
27    dnl be used in a preprocessor #if, i.e. doesn't contain a cast.
28    _AC_COMPUTE_INT([sizeof (size_t) * CHAR_BIT - 1], size_t_bits_minus_1,
29      [#include <stddef.h>
30#include <limits.h>], size_t_bits_minus_1=)
31    _AC_COMPUTE_INT([sizeof (size_t) <= sizeof (unsigned int)], fits_in_uint,
32      [#include <stddef.h>], fits_in_uint=)
33    if test -n "$size_t_bits_minus_1" && test -n "$fits_in_uint"; then
34      if test $fits_in_uint = 1; then
35        dnl Even though SIZE_MAX fits in an unsigned int, it must be of type
36        dnl 'unsigned long' if the type 'size_t' is the same as 'unsigned long'.
37        AC_TRY_COMPILE([#include <stddef.h>
38          extern size_t foo;
39          extern unsigned long foo;
40          ], [], fits_in_uint=0)
41      fi
42      dnl We cannot use 'expr' to simplify this expression, because 'expr'
43      dnl works only with 'long' integers in the host environment, while we
44      dnl might be cross-compiling from a 32-bit platform to a 64-bit platform.
45      if test $fits_in_uint = 1; then
46        result="(((1U << $size_t_bits_minus_1) - 1) * 2 + 1)"
47      else
48        result="(((1UL << $size_t_bits_minus_1) - 1) * 2 + 1)"
49      fi
50    else
51      dnl Shouldn't happen, but who knows...
52      result='((size_t)~(size_t)0)'
53    fi
54  fi
55  AC_MSG_RESULT([$result])
56  if test "$result" != yes; then
57    AC_DEFINE_UNQUOTED([SIZE_MAX], [$result],
58      [Define as the maximum value of type 'size_t', if the system doesn't define it.])
59  fi
60])
61