From 0b47b125cfe584f6d6c12a748208ceec3430990e Mon Sep 17 00:00:00 2001
From: Nick Mathewson <nickm@torproject.org>
Date: Sun, 12 Apr 2009 22:02:54 +0000
Subject: [PATCH] Add a new EVUTIL_UPCAST macro so that I do not need to keep
 figuring out the right offsetof magic over and over.

svn:r1160
---
 bufferevent_pair.c | 4 ++--
 util-internal.h    | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/bufferevent_pair.c b/bufferevent_pair.c
index 5e12ae8ae..444b954c1 100644
--- a/bufferevent_pair.c
+++ b/bufferevent_pair.c
@@ -39,6 +39,7 @@
 #include "defer-internal.h"
 #include "bufferevent-internal.h"
 #include "mm-internal.h"
+#include "util-internal.h"
 
 struct bufferevent_pair {
 	struct bufferevent bev;
@@ -56,8 +57,7 @@ upcast(struct bufferevent *bev)
 	struct bufferevent_pair *bev_p;
 	if (bev->be_ops != &bufferevent_ops_pair)
 		return NULL;
-	bev_p = (void*)( ((char*)bev) -
-			 evutil_offsetof(struct bufferevent_pair, bev) );
+	bev_p = EVUTIL_UPCAST(bev, struct bufferevent_pair, bev);
 	assert(bev_p->bev.be_ops == &bufferevent_ops_pair);
 	return bev_p;
 }
diff --git a/util-internal.h b/util-internal.h
index 957e431ab..31f2239f1 100644
--- a/util-internal.h
+++ b/util-internal.h
@@ -101,6 +101,9 @@ extern const char EVUTIL_TOLOWER_TABLE[];
 #define EVUTIL_TOLOWER(c) (EVUTIL_TOLOWER_TABLE[(ev_uint8_t)c])
 #define EVUTIL_TOUPPER(c) (EVUTIL_TOUPPER_TABLE[(ev_uint8_t)c])
 
+#define EVUTIL_UPCAST(ptr, type, field)				\
+	((type *)((char*)ptr) - evutil_offsetof(type, field))
+
 #ifdef __cplusplus
 }
 #endif