r <TT>double</TT>
because the library uses a varargs
interface and ANSI C restricts the type of the parameter before an
ellipsis to be a promoted type.  <TT>toff_t</TT> is defined as
<TT>int32</TT> because
TIFF file offsets are (unsigned) 32-bit quantities.  A signed
value is used because some interfaces return -1 on error (sigh).
Finally, note that <TT>tidata_t</TT> is used internally to the library to
manipulate internal data.  User-specified data references are
passed as opaque handles and only cast at t