2002-05-06 Neil Booth <neil@daikokuya.demon.co.uk>
+doc:
+ * cpp.texi: Update multichar charconst docs.
+
+2002-05-06 Neil Booth <neil@daikokuya.demon.co.uk>
+
* cpplex.c (cpp_interpret_charconst): Sign-extend each
character. Don't ignore excess characters. Treat
multicharacter character constants as signed.
@item The numeric value of character constants in preprocessor expressions.
-The preprocessor and compiler interpret character constants in the same
-way; escape sequences such as @samp{\a} are given the values they would
-have on the target machine.
+The preprocessor and compiler interpret character constants in the
+same way; i.e.@: escape sequences such as @samp{\a} are given the
+values they would have on the target machine.
Multi-character character constants are interpreted a character at a
time, shifting the previous result left by the number of bits per
-character on the host, and adding the new character. For example, 'ab'
-on an 8-bit host would be interpreted as @w{'a' * 256 + 'b'}. If there
-are more characters in the constant than can fit in the widest native
-integer type on the host, usually a @code{long}, the excess characters
-are ignored and a diagnostic is given.
+target character and adding the sign-extended value of the new
+character. They have type @code{int}, and are treated as signed
+regardless of whether single characters are signed or not. If there
+are more characters in the constant than would fit in the target
+@code{int}, a diagnostic is given, and the excess leading characters
+are ignored. This methodology is not fully compatible with versions
+3.1 and earlier of GCC, which used a confusing and inconsistent
+valuation technique.
+
+For example, 'ab' for a target with an 8-bit @code{char} would be
+interpreted as @w{'a' * 256 + 'b'}, and 'a\234' as @w{'a' * 256 +
+'\234'}. GCC 3.1 and earlier would give a different value for the
+latter example, probably @w{'a' * 256 + (unsigned char) '\234'}.
@item Source file inclusion.
--- /dev/null
+/* Copyright (C) 2001 Free Software Foundation, Inc. */
+
+/* { dg-do compile } */
+/* { dg-options -Wno-multichar } */
+
+/* This tests values and signedness of multichar charconsts.
+
+ Neil Booth, 5 May 2002. */
+
+#include <limits.h>
+
+int main ()
+{
+ /* These tests require at least 2-byte ints. 8-) */
+#if INT_MAX > 127
+ int scale = (int) (unsigned char) -1 + 1;
+
+ if ('ab' != ('a' * scale + 'b'))
+ abort ();
+
+ if ('\234b' != ('\234' * scale + 'b'))
+ abort ();
+
+ if ('b\234' != ('b' * scale + '\234'))
+ abort ();
+
+ /* Multichar charconsts have type int and should be signed. */
+#if INT_MAX == 32767
+ if ('\234a' > 0)
+ abort ();
+#elif INT_MAX == 2147483647
+ if ('\234aaa' > 0)
+ abort ();
+#elif INT_MAX == 9223372036854775807
+ if ('\234aaaaaaa' > 0)
+ abort ();
+#endif
+#endif
+ return 0;
+}