09/10/87  Virtual Pointers

The cv_ptr_ function converts virtual pointers that contain one or two
components -- a segment identifier and an optional offset into the
segment.  Altogether, seventeen forms are accepted.  They are shown in
the list below.

In the list that follows, W is an octal word offset from the beginning
of the segment.  It may have a value from 0 to 777777 inclusive.  B is
a decimal bit offset within the word.  It may have a value from 0 to 35
inclusive.


List of virtual pointers:
path|W(B)
   points to octal word W, decimal bit B of segment or MSF identified
   by absolute or relative pathname path.  If the path given identifies
   a multisegment file, the offset given is in component 0 of the MSF.
path|W
   same as path|W(0).
path|
   same as path|0(0).
path
   same as path|0(0).
path|entry_pt
   points to word identified by entry point entry_pt in the object file
   (segment or MSF) identified by path.


dir>entry$entry_pt
   points to word identified by entry point entry_pt in the object file
   identified by pathname dir>entry.
<dir>entry$entry_pt
   points to word identified by entry point entry_pt in the object file
   identified by pathname <dir>entry.
<entry$entry_pt
   points to word identified by entry point entry_pt in the object file
   identified by pathname <entry.


ref_name$entry_pt
   points to word identified by entry point entry_pt in the file whose
   reference name is ref_name.
ref_name$W(B)
   points to octal word W, decimal bit B of segment or MSF whose
   reference name is ref_name.  If ref_name is a reference name on a
   multisegment file (ie. on component 0 of the MSF), the word and bit
   offsets are applied within component 0.
ref_name$W
   same as ref_name$W(0).
ref_name$
   same as ref_name$0(0).


segno|W(B)
   points to octal word W, decimal bit B of segment whose octal
   segment number is segno.
segno|W
   same as segno|W(0).
segno|
   same as segno|0(0).
segno
   same as segno|0(0).
segno|entry_pt
   points to word identified by entry point entry_pt in segment whose
   octal segment number is segno.  If segno identifies component 0 of
   an object MSF, the pointer returned may not point within the segment
   identified, since the target of a definition in component 0 of an
   object MSF will be in another component of the object MSF.


Notes:  A null pointer is represented by the virtual pointer 77777|1,
by -1|1, or by -1.


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Historical Background

This edition of the Multics software materials and documentation is provided and donated
to Massachusetts Institute of Technology by Group BULL including BULL HN Information Systems Inc. 
as a contribution to computer science knowledge.  
This donation is made also to give evidence of the common contributions of Massachusetts Institute of Technology,
Bell Laboratories, General Electric, Honeywell Information Systems Inc., Honeywell BULL Inc., Groupe BULL
and BULL HN Information Systems Inc. to the development of this operating system. 
Multics development was initiated by Massachusetts Institute of Technology Project MAC (1963-1970),
renamed the MIT Laboratory for Computer Science and Artificial Intelligence in the mid 1970s, under the leadership
of Professor Fernando Jose Corbato. Users consider that Multics provided the best software architecture 
for managing computer hardware properly and for executing programs. Many subsequent operating systems 
incorporated Multics principles.
Multics was distributed in 1975 to 2000 by Group Bull in Europe , and in the U.S. by Bull HN Information Systems Inc., 
as successor in interest by change in name only to Honeywell Bull Inc. and Honeywell Information Systems Inc. .

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Permission to use, copy, modify, and distribute these programs and their documentation for any purpose and without
fee is hereby granted,provided that the below copyright notice and historical background appear in all copies
and that both the copyright notice and historical background and this permission notice appear in supporting
documentation, and that the names of MIT, HIS, BULL or BULL HN not be used in advertising or publicity pertaining
to distribution of the programs without specific prior written permission.
    Copyright 1972 by Massachusetts Institute of Technology and Honeywell Information Systems Inc.
    Copyright 2006 by BULL HN Information Systems Inc.
    Copyright 2006 by Bull SAS
    All Rights Reserved