1# size_max.m4 serial 5
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  AC_CACHE_VAL([gl_cv_size_max], [
15    gl_cv_size_max=
16    AC_EGREP_CPP([Found it], [
17#include <limits.h>
18#if HAVE_STDINT_H
19#include <stdint.h>
20#endif
21#ifdef SIZE_MAX
22Found it
23#endif
24], gl_cv_size_max=yes)
25    if test -z "$gl_cv_size_max"; then
26      dnl Define it ourselves. Here we assume that the type 'size_t' is not wider
27      dnl than the type 'unsigned long'. Try hard to find a definition that can
28      dnl be used in a preprocessor #if, i.e. doesn't contain a cast.
29      _AC_COMPUTE_INT([sizeof (size_t) * CHAR_BIT - 1], size_t_bits_minus_1,
30        [#include <stddef.h>
31#include <limits.h>], size_t_bits_minus_1=)
32      _AC_COMPUTE_INT([sizeof (size_t) <= sizeof (unsigned int)], fits_in_uint,
33        [#include <stddef.h>], fits_in_uint=)
34      if test -n "$size_t_bits_minus_1" && test -n "$fits_in_uint"; then
35        if test $fits_in_uint = 1; then
36          dnl Even though SIZE_MAX fits in an unsigned int, it must be of type
37          dnl 'unsigned long' if the type 'size_t' is the same as 'unsigned long'.
38          AC_TRY_COMPILE([#include <stddef.h>
39            extern size_t foo;
40            extern unsigned long foo;
41            ], [], fits_in_uint=0)
42        fi
43        dnl We cannot use 'expr' to simplify this expression, because 'expr'
44        dnl works only with 'long' integers in the host environment, while we
45        dnl might be cross-compiling from a 32-bit platform to a 64-bit platform.
46        if test $fits_in_uint = 1; then
47          gl_cv_size_max="(((1U << $size_t_bits_minus_1) - 1) * 2 + 1)"
48        else
49          gl_cv_size_max="(((1UL << $size_t_bits_minus_1) - 1) * 2 + 1)"
50        fi
51      else
52        dnl Shouldn't happen, but who knows...
53        gl_cv_size_max='((size_t)~(size_t)0)'
54      fi
55    fi
56  ])
57  AC_MSG_RESULT([$gl_cv_size_max])
58  if test "$gl_cv_size_max" != yes; then
59    AC_DEFINE_UNQUOTED([SIZE_MAX], [$gl_cv_size_max],
60      [Define as the maximum value of type 'size_t', if the system doesn't define it.])
61  fi
62])
63