[Unicon-ldif] Structure of dword in DESC

[Bruce & B. R. <br...@dc...>]

Good evening to all,

I have a question relating to the flags within the dword of a
descriptor. In the file rmacros.h, there are a number of macros defined
that set up the type flags for the various available types within the
runtime system.

There is also a macro called D_Var which has no type code flag set and
is used in various places within the runtime system.

My question relates to the inconsistency of trapped variables of various
kinds having a type code value and the use of the D_Var macro to create
descriptors that have no type code but are pointers to variables. is
this an inconsistency or is there a specific reason for the way this is
used? Since if the code uses the TypeMask macro, the type code value
obtained for such a variable is the same as for the Null descriptor.

Of all the places in the code base, there is one location where the type
code value that would be returned from the used of the TypeMask would
not be 0. This is to be found in the file imisc.r at around line 280
where the code is

   Arg0.dword = D_Var + ((word *)dp - (word *)rp);


Clarification would be greatly appreciated.

regards

Bruce Rennie