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comparison m4/size_max.m4 @ 272:d5392bb5da3c 2.5

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date Sun, 16 Aug 2009 17:16:49 +0000
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271:3b793ba7a6c6 272:d5392bb5da3c
1 # size_max.m4 serial 7
2 dnl Copyright (C) 2003, 2005-2006, 2008 Free Software Foundation, Inc.
3 dnl This file is free software; the Free Software Foundation
4 dnl gives unlimited permission to copy and/or distribute it,
5 dnl with or without modifications, as long as this notice is preserved.
6
7 dnl From Bruno Haible.
8
9 AC_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
22 Found it
23 #endif
24 ], [gl_cv_size_max=yes])
25 if test -z "$gl_cv_size_max"; then
26 dnl Define it ourselves. Here we assume that the type 'size_t' is not wider
27 dnl than the type 'unsigned long'. Try hard to find a definition that can
28 dnl be used in a preprocessor #if, i.e. doesn't contain a cast.
29 AC_COMPUTE_INT([size_t_bits_minus_1], [sizeof (size_t) * CHAR_BIT - 1],
30 [#include <stddef.h>
31 #include <limits.h>], [size_t_bits_minus_1=])
32 AC_COMPUTE_INT([fits_in_uint], [sizeof (size_t) <= sizeof (unsigned int)],
33 [#include <stddef.h>], [fits_in_uint=])
34 if test -n "$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
64 dnl Autoconf >= 2.61 has AC_COMPUTE_INT built-in.
65 dnl Remove this when we can assume autoconf >= 2.61.
66 m4_ifdef([AC_COMPUTE_INT], [], [
67 AC_DEFUN([AC_COMPUTE_INT], [_AC_COMPUTE_INT([$2],[$1],[$3],[$4])])
68 ])