# ptrdiff_max.m4 serial 1
dnl Copyright (C) 2003 Free Software Foundation, Inc.
dnl This file is free software, distributed under the terms of the GNU
dnl General Public License.  As a special exception to the GNU General
dnl Public License, this file may be distributed as part of a program
dnl that contains a configuration script generated by Autoconf, under
dnl the same distribution terms as the rest of that program.

dnl From Bruno Haible.

AC_DEFUN([gl_PTRDIFF_MAX],
[
  AC_CHECK_TYPE([ptrdiff_t], ,
    [AC_DEFINE([ptrdiff_t], [long],
       [Define as the type of the result of subtracting two pointers, if the system doesn't define it.])
    ])
  AC_CHECK_HEADERS_ONCE(stdint.h)
  dnl First test whether the system already has PTRDIFF_MAX.
  AC_MSG_CHECKING([for PTRDIFF_MAX])
  result=
  AC_EGREP_CPP([Found it], [
#include <limits.h>
#if HAVE_STDINT_H
#include <stdint.h>
#endif
#ifdef PTRDIFF_MAX
Found it
#endif
], result=yes)
  if test -z "$result"; then
    dnl Define it ourselves. Here we assume that the type 'ptrdiff_t' is not
    dnl wider than the type 'long'.
    dnl The _AC_COMPUTE_INT macro works up to LONG_MAX, since it uses 'expr',
    dnl which is guaranteed to work from LONG_MIN to LONG_MAX.
    _AC_COMPUTE_INT([STYPE_MAXIMUM (ptrdiff_t)], res, [
#include <stddef.h>
#include <limits.h>
#define STYPE_MINIMUM(t) (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))
#define STYPE_MAXIMUM(t) ((t) (~ (t) 0 - STYPE_MINIMUM (t)))
], result=?)
    _AC_COMPUTE_INT([sizeof (ptrdiff_t) <= sizeof (int)], fits_in_int,
      [#include <stddef.h>], result=?)
    if test "$fits_in_int" = 1; then
      dnl Even though PTRDIFF_MAX fits in an int, it must be of type
      dnl 'long' if the type 'ptrdiff_t' is the same as 'long'.
      AC_TRY_COMPILE([#include <stddef.h>
        extern ptrdiff_t foo;
        extern long foo;
        ], [], fits_in_int=0)
    fi
    if test -z "$result"; then
      if test "$fits_in_int" = 1; then
        result="$res"
      else
        result="$res"L
      fi
    else
      dnl Shouldn't happen, but who knows...
      result='((ptrdiff_t)(~(ptrdiff_t)0-(~(ptrdiff_t)0<<(sizeof(ptrdiff_t)*CHAR_BIT-1))))'
    fi
  fi
  AC_MSG_RESULT([$result])
  if test "$result" != yes; then
    AC_DEFINE_UNQUOTED([PTRDIFF_MAX], [$result],
      [Define as the maximum value of type 'ptrdiff_t', if the system doesn't define it.])
  fi
])