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1 # size_max.m4 serial 9
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2 dnl Copyright (C) 2003, 2005-2006, 2008-2010 Free Software Foundation, Inc.
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3 dnl This file is free software; the Free Software Foundation
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4 dnl gives unlimited permission to copy and/or distribute it,
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5 dnl with or without modifications, as long as this notice is preserved.
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6
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7 dnl From Bruno Haible.
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8
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9 AC_DEFUN([gl_SIZE_MAX],
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10 [
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11 AC_CHECK_HEADERS([stdint.h])
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12 dnl First test whether the system already has SIZE_MAX.
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13 AC_CACHE_CHECK([for SIZE_MAX], [gl_cv_size_max], [
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14 gl_cv_size_max=
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15 AC_EGREP_CPP([Found it], [
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16 #include <limits.h>
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17 #if HAVE_STDINT_H
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18 #include <stdint.h>
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19 #endif
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20 #ifdef SIZE_MAX
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21 Found it
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22 #endif
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23 ], [gl_cv_size_max=yes])
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24 if test -z "$gl_cv_size_max"; then
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25 dnl Define it ourselves. Here we assume that the type 'size_t' is not wider
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26 dnl than the type 'unsigned long'. Try hard to find a definition that can
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27 dnl be used in a preprocessor #if, i.e. doesn't contain a cast.
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28 AC_COMPUTE_INT([size_t_bits_minus_1], [sizeof (size_t) * CHAR_BIT - 1],
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29 [#include <stddef.h>
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30 #include <limits.h>], [size_t_bits_minus_1=])
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31 AC_COMPUTE_INT([fits_in_uint], [sizeof (size_t) <= sizeof (unsigned int)],
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32 [#include <stddef.h>], [fits_in_uint=])
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33 if test -n "$size_t_bits_minus_1" && test -n "$fits_in_uint"; then
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34 if test $fits_in_uint = 1; then
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35 dnl Even though SIZE_MAX fits in an unsigned int, it must be of type
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36 dnl 'unsigned long' if the type 'size_t' is the same as 'unsigned long'.
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37 AC_TRY_COMPILE([#include <stddef.h>
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38 extern size_t foo;
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39 extern unsigned long foo;
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40 ], [], [fits_in_uint=0])
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41 fi
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42 dnl We cannot use 'expr' to simplify this expression, because 'expr'
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43 dnl works only with 'long' integers in the host environment, while we
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44 dnl might be cross-compiling from a 32-bit platform to a 64-bit platform.
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45 if test $fits_in_uint = 1; then
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46 gl_cv_size_max="(((1U << $size_t_bits_minus_1) - 1) * 2 + 1)"
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47 else
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48 gl_cv_size_max="(((1UL << $size_t_bits_minus_1) - 1) * 2 + 1)"
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49 fi
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50 else
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51 dnl Shouldn't happen, but who knows...
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52 gl_cv_size_max='((size_t)~(size_t)0)'
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53 fi
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54 fi
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55 ])
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56 if test "$gl_cv_size_max" != yes; then
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57 AC_DEFINE_UNQUOTED([SIZE_MAX], [$gl_cv_size_max],
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58 [Define as the maximum value of type 'size_t', if the system doesn't define it.])
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59 fi
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60 dnl Don't redefine SIZE_MAX in config.h if config.h is re-included after
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61 dnl <stdint.h>. Remember that the #undef in AH_VERBATIM gets replaced with
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62 dnl #define by AC_DEFINE_UNQUOTED.
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63 AH_VERBATIM([SIZE_MAX],
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64 [/* Define as the maximum value of type 'size_t', if the system doesn't define
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65 it. */
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66 #ifndef SIZE_MAX
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67 # undef SIZE_MAX
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68 #endif])
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69 ])
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70
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71 dnl Autoconf >= 2.61 has AC_COMPUTE_INT built-in.
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72 dnl Remove this when we can assume autoconf >= 2.61.
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73 m4_ifdef([AC_COMPUTE_INT], [], [
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74 AC_DEFUN([AC_COMPUTE_INT], [_AC_COMPUTE_INT([$2],[$1],[$3],[$4])])
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75 ])
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