20060428 Dave Dodge <dododge@dododge.net>

There's a bug in the macro_twosharps() function, where a pp-number is
not created properly when multiple token pastings are involved.  The
sample code below from jun.lambda@gmail.com demonstrates the problem;
FLAGS(0) should evaluate to 0 but ends up evaluating to 1:

#define SQUISH(n) (!!((n) & 0xF))
#define HEX2BIN(n) (SQUISH(n))
#define FLAGS(f) HEX2BIN(0x##f##U)
int main () { return FLAGS(0); }

What happens internally is that the first pasting of "0x"+"0" creates
the pp-number "0x0".  The buffer containing that result is then used
directly as the current token string.  When the second pasting begins,
the buffer is reset, destroying the current token string before the
pasting operation.  So instead of pasting "0x0"+"U", it ends up with
""+"U".

A solution is to use a different buffer to hold the current token
contents, so that concatenation won't damage it.  The global tokcstr
is normally used alongside tok and tokc when parsing, so I just used
that.

Index: tcc-0.9.23/tcc.c
===================================================================
--- tcc-0.9.23.orig/tcc.c	2006-04-28 03:40:30.000000000 -0400
+++ tcc-0.9.23/tcc.c	2006-04-28 03:43:41.000000000 -0400
@@ -4214,9 +4214,14 @@
                     (t >= TOK_IDENT || t == TOK_PPNUM)) {
                     if (tok == TOK_PPNUM) {
                         /* if number, then create a number token */
-                        /* NOTE: no need to allocate because
-                           tok_str_add2() does it */
-                        tokc.cstr = &cstr;
+                        /* NOTE: we cannot use cstr directly for this
+                           because if there are multiple token pastings
+                           in a sequence the concatenation will reset
+                           cstr before the final token is ready. */
+                        cstr_reset(&tokcstr);
+                        cstr_cat(&tokcstr, cstr.data);
+                        cstr_ccat(&tokcstr, '\0');
+                        tokc.cstr = &tokcstr;
                     } else {
                         /* if identifier, we must do a test to
                            validate we have a correct identifier */