instead of unions use double cast for data pointer <-> function pointer

[p5sagit/p5-mst-13.2.git] / perl.h

diff --git a/perl.h b/perl.h
index aedc918..3df67eb 100644 (file)
--- a/perl.h
+++ b/perl.h
@@ -208,7 +208,7 @@
  
 /* gcc -Wall:
  * for silencing unused variables that are actually used most of the time,
- * but we cannot quite get rid of, such `ax' in PPCODE+noargs xsubs
+ * but we cannot quite get rid of, such as "ax" in PPCODE+noargs xsubs
  */
 #define PERL_UNUSED_VAR(var) ((void)var)
 
@@ -320,7 +320,7 @@ register struct op *Perl_op asm(stringify(OP_IN_REGISTER));
  */
 #if !(defined(STMT_START) && defined(STMT_END))
 # if defined(__GNUC__) && !defined(PERL_GCC_BRACE_GROUPS_FORBIDDEN) && !defined(__cplusplus)
-#   define STMT_START  (void)( /* gcc supports ``({ STATEMENTS; })'' */
+#   define STMT_START  (void)( /* gcc supports "({ STATEMENTS; })" */
 #   define STMT_END    )
 # else
    /* Now which other defined()s do we need here ??? */
@@ -1495,6 +1495,19 @@ typedef UVTYPE UV;
 #  define PTR2ul(p)    INT2PTR(unsigned long,p)        
 #endif
 
+/* According to strict ANSI C89 one cannot freely cast between
+ * data pointers and function (code) pointers.  There are at least
+ * two ways around this.  One (used below) is to do two casts,
+ * first the other pointer to an (unsigned) integer, and then
+ * the integer to the other pointer.  The other way would be
+ * to use unions to "overlay" the pointers.  For an example of
+ * the latter technique, see union dirpu in struct xpvio in sv.h.
+ * The only feasible use is probably temporarily storing
+ * function pointers in a data pointer (such as a void pointer). */
+
+#define DPTR2FPTR(t,p) ((t)PTR2UV(p)) /* data pointer to function pointer */
+#define FPTR2DPTR(t,p) ((t)PTR2UV(p)) /* function pointer to data pointer */
+
 #ifdef USE_LONG_DOUBLE
 #  if defined(HAS_LONG_DOUBLE) && LONG_DOUBLESIZE == DOUBLESIZE
 #      define LONG_DOUBLE_EQUALS_DOUBLE