Make it work when cross-compiling.

[gnulib.git] / m4 / size_max.m4

diff --git a/m4/size_max.m4 b/m4/size_max.m4
index 0336f3a..029e471 100644 (file)
--- a/m4/size_max.m4
+++ b/m4/size_max.m4
@@ -1,5 +1,5 @@
-# size_max.m4 serial 3
-dnl Copyright (C) 2003, 2005 Free Software Foundation, Inc.
+# size_max.m4 serial 4
+dnl Copyright (C) 2003, 2005-2006 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.
@@ -23,28 +23,29 @@ Found it
 ], result=yes)
   if test -z "$result"; then
     dnl Define it ourselves. Here we assume that the type 'size_t' is not wider
-    dnl than the type 'unsigned long'.
-    dnl The _AC_COMPUTE_INT macro works up to LONG_MAX, since it uses 'expr',
-    dnl which is guaranteed to work from LONG_MIN to LONG_MAX.
-    _AC_COMPUTE_INT([(size_t)~(size_t)0 / 10], res_hi,
-      [#include <stddef.h>], result=?)
-    _AC_COMPUTE_INT([(size_t)~(size_t)0 % 10], res_lo,
-      [#include <stddef.h>], result=?)
+    dnl than the type 'unsigned long'. Try hard to find a definition that can
+    dnl be used in a preprocessor #if, i.e. doesn't contain a cast.
+    _AC_COMPUTE_INT([sizeof (size_t) * CHAR_BIT - 1], size_t_bits_minus_1,
+      [#include <stddef.h>
+#include <limits.h>], size_t_bits_minus_1=)
     _AC_COMPUTE_INT([sizeof (size_t) <= sizeof (unsigned int)], fits_in_uint,
-      [#include <stddef.h>], result=?)
-    if test "$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
+      [#include <stddef.h>], fits_in_uint=)
+    if test -n "$size_t_bits_minus_1" && test -n "$fits_in_uint"; then
+      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
+      dnl We cannot use 'expr' to simplify this expression, because 'expr'
+      dnl works only with 'long' integers in the host environment, while we
+      dnl might be cross-compiling from a 32-bit platform to a 64-bit platform.
+      if test $fits_in_uint = 1; then
+        result="(((1U << $size_t_bits_minus_1) - 1) * 2 + 1)"
       else
-        result="$res_hi$res_lo"UL
+        result="(((1UL << $size_t_bits_minus_1) - 1) * 2 + 1)"
       fi
     else
       dnl Shouldn't happen, but who knows...