Introduce a new type, PtrdiffT.  Replace lots of uses of OffT (all those
that are memory offsets) with PtrdiffT;  OffT should only be used for file
sizes and offsets.

Change Off64T from a ULong to a Long, as it should be.  Replace some uses
of ULong in the address space manager with Off64T to match.

Also add a comment explaining the meanings of the basic types like Addr,
OffT, SizeT, etc.

Also fix the prototype for VG_(pread) -- the last arg is an OffT, not an
Int.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@8959 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/include/pub_tool_oset.h b/include/pub_tool_oset.h
index 1573136..c496523 100644
--- a/include/pub_tool_oset.h
+++ b/include/pub_tool_oset.h
@@ -183,7 +183,7 @@
 //   a deallocation function (such as VG_(free)()) directly will likely
 //   lead to assertions in Valgrind's allocator.
 
-extern OSet* VG_(OSetGen_Create)    ( OffT keyOff, OSetCmp_t cmp,
+extern OSet* VG_(OSetGen_Create)    ( PtrdiffT keyOff, OSetCmp_t cmp,
                                       OSetAlloc_t alloc, HChar* ec,
                                       OSetFree_t free );
 extern void  VG_(OSetGen_Destroy)   ( OSet* os );