root/trunk/m4/size_max.m4

# size_max.m4 serial 2
dnl Copyright (C) 2003 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 From Bruno Haible.

AC_DEFUN([gl_SIZE_MAX],
[
  AC_CHECK_HEADERS(stdint.h)
  dnl First test whether the system already has SIZE_MAX.
  AC_MSG_CHECKING([for SIZE_MAX])
  result=
  AC_EGREP_CPP([Found it], [
#include <limits.h>
#if HAVE_STDINT_H
#include <stdint.h>
#endif
#ifdef SIZE_MAX
Found it
#endif
], result=yes)
  if test -z "$result"; then
    dnl Define it ourselves. Here we assume that the type 'size_t' is not wider
    dnl than the type 'unsigned long'.
    dnl The _AC_COMPUTE_INT macro works up to LONG_MAX, since it uses 'expr',
    dnl which is guaranteed to work from LONG_MIN to LONG_MAX.
    _AC_COMPUTE_INT([~(size_t)0 / 10], res_hi,
      [#include <stddef.h>], result=?)
    _AC_COMPUTE_INT([~(size_t)0 % 10], res_lo,
      [#include <stddef.h>], result=?)
    _AC_COMPUTE_INT([sizeof (size_t) <= sizeof (unsigned int)], fits_in_uint,
      [#include <stddef.h>], result=?)
    if test "$fits_in_uint" = 1; then
      dnl Even though SIZE_MAX fits in an unsigned int, it must be of type
      dnl 'unsigned long' if the type 'size_t' is the same as 'unsigned long'.
      AC_TRY_COMPILE([#include <stddef.h>
        extern size_t foo;
        extern unsigned long foo;
        ], [], fits_in_uint=0)
    fi
    if test -z "$result"; then
      if test "$fits_in_uint" = 1; then
        result="$res_hi$res_lo"U
      else
        result="$res_hi$res_lo"UL
      fi
    else
      dnl Shouldn't happen, but who knows...
      result='~(size_t)0'
    fi
  fi
  AC_MSG_RESULT([$result])
  if test "$result" != yes; then
    AC_DEFINE_UNQUOTED([SIZE_MAX], [$result],
      [Define as the maximum value of type 'size_t', if the system doesn't define it.])
  fi
])