std C/C++ patch #4

[David Scott Page]

Hi,

This patch makes two changes. The first assumes the "pad" comment
implies 8-byte alignment (strictest host alignment?) is desired for
the data area (_x[]), and attempts to achieve this via the usual union
with an appropriate type. I believe double will force _x to an 8-byte
alignment anywhere it matters (until long double comes into vogue).

The second change is from _x[0], which I believe is forbidden in any
std C/C++ prior to C99 (and should be expressed _x[] in C99), to
_x[1], and replacing the sizeof with the appropriate offsetof.

--
Scott Page

--------------------------------- 8< ---------------------------------
diff -Naur click-stdC++.3a/include/click/bighashmap_arena.hh click-stdC++.4/include/click/bighashmap_arena.hh
--- click-stdC++.3a/include/click/bighashmap_arena.hh	Thu Apr 25 20:59:13 2002
+++ click-stdC++.4/include/click/bighashmap_arena.hh	Thu Apr 25 20:57:17 2002
@@ -3,14 +3,16 @@
 
 struct BigHashMap_Arena {
   
-  enum { SIZE = 128 };
-  int _first;
-  int _padding;		// pad to 8-byte boundary
-  unsigned char _x[0];
+  enum { SIZE = 128 } ;
+  union {
+    int _first;
+    double _padding;		// align _x to 8-byte boundary
+  } _un ;
+  unsigned char _x[1];
 
   static BigHashMap_Arena *new_arena(unsigned esize);
   static void delete_arena(BigHashMap_Arena *);
-  void clear()				{ _first = 0; }
+  void clear()				{ _un._first = 0; }
   void *alloc(unsigned esize);
   void *elt(unsigned esize, int i)	{ return (_x + esize*i); }
   
@@ -19,8 +21,8 @@
 inline void *
 BigHashMap_Arena::alloc(unsigned esize)
 {
-  if (_first < SIZE)
-    return elt(esize, _first++);
+  if (_un._first < SIZE)
+    return elt(esize, _un._first++);
   else
     return 0;
 }
diff -Naur click-stdC++.3a/lib/bighashmap_arena.cc click-stdC++.4/lib/bighashmap_arena.cc
--- click-stdC++.3a/lib/bighashmap_arena.cc	Fri May 25 00:04:04 2001
+++ click-stdC++.4/lib/bighashmap_arena.cc	Thu Apr 25 20:57:17 2002
@@ -23,9 +23,9 @@
 BigHashMap_Arena::new_arena(unsigned esize)
 {
   BigHashMap_Arena *arena =
-    reinterpret_cast<BigHashMap_Arena *>(new unsigned char[sizeof(BigHashMap_Arena) + esize*SIZE]);
+    reinterpret_cast<BigHashMap_Arena *>(new unsigned char[offsetof(BigHashMap_Arena,_x) + esize*SIZE]);
   if (arena)
-    arena->_first = 0;
+    arena->_un._first = 0;
   return arena;
 }