Anand R. Tripathi

Packet switching in banyan networks

This paper presents a formal scheme for addressing base and apex nodes in SW-banyan networks. This scheme is used for routing packets in the network. Packet-switching, in conjunction with the the circuit-switch mode of operation, offers a very flexible and powerful mechanism for interprocess communication in the multiprocessor architectures based on the banyan networks. Finally, a fault-tolerent scheme for re-routing the packets in the network is presented, in case the packet encounters a faulty node in its path.

A preliminary evaluation of verifiability in Ada

In this paper we examine Ada with regard to program verification and make certain suggestions towards writing potentially provable Ada programs. We attempt to isolate and discuss those features of Ada which are not susceptible to current verification techniques. From verifiability considerations, the most critical features in Ada appear to be those which deal with data sharing under concurrent processing, direct referencing of non-local variables, access variables, “approximate” data-types, and generic program units. The independence of program units along with well defined interfaces for interactions is presented as desirable not only from software engineering aspects but also from the formal proof considerations. However, the possibility of having a large number of variables, potentially sharable among concurrent processes, is likely to make the proofs of Ada programs unmanageable. It is asserted, however, that with a certain discipline on the programmer verifiable programs can be written in Ada.

Design of a Verifiable Subset for HAL/S

An attempt to evaluate the applicability of program verification techniques to the existing programming language, HAL/S is discussed. HAL/S is a general purpose high level language designed to accommodate the software needs of the NASA Space Shuttle project. A diversity of features for scientific computing, concurrent and real-time programming, and error handling are discussed. The criteria by which features were evaluated for inclusion into the verifiable subset are described. Individual features of HAL/S with respect to these criteria are examined and justification for the omission of various features from the subset is provided. Conclusions drawn from the research are presented along with recommendations made for the use of HAL/S with respect to the area of program verification.

HAL/S/V: a verifiable subset for HAL/S

The research described in this paper was an attempt to evaluate the applicability of program verification techniques to an existing programming language, HAL/S [2,3]. HAL/S is a general purpose high level language designed to accomodate the software needs of the NASA Space Shuttle project. The breadth of this goal mandated a diversity of features for scientific computing, concurrent and real-time programming, error handling, etc. Many of the features, however, are not susceptible to existing techniques of program proving. Our concern was to examine the various features of HAL/S, evaluate them for verifiability, and isolate a subset, HAL/S/V, containing only those constructs which lend themselves to program ver if icat ion.