Maelstrom: Fixed 64-bit compile issue on Mac OS X

From 780d816b6b69924f816272c31cab2c3da542f020 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Wed, 24 Aug 2011 20:29:57 -0400
Subject: [PATCH] Fixed 64-bit compile issue on Mac OS X

---
 screenlib/SDL_FrameBuf.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/screenlib/SDL_FrameBuf.cpp b/screenlib/SDL_FrameBuf.cpp
index d1e087fd..2e6ac7fb 100644
--- a/screenlib/SDL_FrameBuf.cpp
+++ b/screenlib/SDL_FrameBuf.cpp
@@ -848,8 +848,8 @@ FrameBuf:: AddDirtyRect(SDL_Rect *rect)
 			for ( i=0; i<dirtymaplen; ++i ) {
 				if ( dirtymap[i] != NULL ) {
 					dirtymap[i] = (SDL_Rect *)(
-					((int)dirtymap[i]-(int)updatelist) +
-								(int)newlist
+					((ptrdiff_t)dirtymap[i]-(ptrdiff_t)updatelist) +
+								(ptrdiff_t)newlist
 					);
 				}
 			}