Robert Glück

Generative Programming and Active Libraries

We describe generative programming, an approach to generating customized programming components or systems, and active libraries, which are based on this approach. In contrast to conventional libraries, active libraries may contain metaprograms that implement domain-specific code generation, optimizations, debugging, profiling and testing. Several working examples (Blitz++, GMCL, Xroma) are presented to illustrate the potential of active libraries. We discuss relevant implementation technologies

CONJUNCTIVE PARTIAL DEDUCTION: FOUNDATIONS, CONTROL, ALGORITHMS, AND EXPERIMENTS

Abstract Partial deduction in the Lloyd–Shepherdson framework cannot achieve certain optimisations which are possible by unfold/fold transformations. We introduce conjunctive partial deduction , an extension of partial deduction accommodating such optimisations, e.g., tupling and deforestation. We first present a framework for conjunctive partial deduction, extending the Lloyd–Shepherdson framework by considering conjunctions of atoms (instead of individual atoms) for specialisation and renaming. Correctness results are given for the framework with respect to computed answer semantics, least Herbrand model semantics, and finite failure semantics. Maintaining the well-known distinction between local and global control, we describe a basic algorithm for conjunctive partial deduction, and refine it into a concrete algorithm for which we prove termination. The problem of finding suitable renamings which remove redundant arguments turns out to be important, so we give an independent technique for this. A fully automatic implementation has been undertaken, which always terminates. Differences between the abstract semantics and Prologs left-to-right execution motivate deviations from the abstract technique in the actual implementation, which we discuss. The implementation has been tested on an extensive set of benchmarks which demonstrate that conjunctive partial deduction indeed pays off, surpassing conventional partial deduction on a range of small to medium-size programs, while remaining manageable in an automatic and terminating system.

A reversible programming language and its invertible self-interpreter

A reversible programming language supports deterministic forward and backward computation. We formalize the programming language Janus and prove its reversibility. We provide a program inverter for the language and implement a self-interpreter that achieves deterministic forward and backward interpretation of Janus programs without using a computation history. As the self-interpreter is implemented in a reversible language, it is invertible using local program inversion. Many physical phenomena are reversible and we demonstrate the power of Janus by implementing a reversible program for discrete simulation of the Schrödinger wave equation that can be inverted as well as run forward and backward.

Principles of a reversible programming language

The principles of reversible programming languages are explicated and illustrated with reference to the design of a high-level imperative language, Janus. The fundamental properties for such languages include backward as well as forward determinism and reversible updates of data. The unique design features of the language include explicit post-condition assertions, direct access to an inverse semantics and the possibility of clean ({\ie}, garbage-free) computation of injective functions. We suggest the clean simulation of reversible Turing machines as a criterion for computing strength of reversible languages, and demonstrate this for Janus. We show the practicality of the language by implementation of a reversible fast Fourier transform. Our results indicate that the reversible programming paradigm has fundamental properties that are relevant to many different areas of computer science.

Towards Unifying Partial Evaluation, Deforestation, Supercompilation, and GPC

We study four transformation methodologies which are automatic instances of Burstall and Darlingtons fold/unfold framework: partial evaluation, deforestation, supercompilation, and generalized partial computation (GPC). One can classify these and other fold/unfold based transformers by how much information they maintain during transformation.

Reversible arithmetic logic unit for quantum arithmetic

This communication presents the complete design of a reversible arithmetic logic unit (ALU) that can be part of a programmable reversible computing device such as a quantum computer. The presented ALU is garbage free and uses reversible updates to combine the standard reversible arithmetic and logical operations in one unit. Combined with a suitable control unit, the ALU permits the construction of an r-Turing complete computing device. The garbage-free ALU developed in this communication requires only 6n elementary reversible gates for five basic arithmetic–logical operations on two n-bit operands and does not use ancillae. This remarkable low resource consumption was achieved by generalizing the V-shape design first introduced for quantum ripple-carry adders and nesting multiple V-shapes in a novel integrated design. This communication shows that the realization of an efficient reversible ALU for a programmable computing device is possible and that the V-shape design is a very versatile approach to the design of quantum networks.

Partial Deduction and Driving are Equivalent

Partial deduction and driving are two methods used for program specialization in logic and functional languages, respectively. We argue that both techniques achieve essentially the same transformational effect by unification-based information propagation. We show their equivalence by analyzing the definition and construction principles underlying partial deduction and driving, and by giving a translation from a functional language to a definite logic language preserving certain properties. We discuss residual program generation, termination issues, and related other techniques developed for program specialization in logic and functional languages.

An Automatic Program Generator for Multi-Level Specialization

Program specialization can divide a computation into several computation stages. This paper investigates the theoretical limitations and practical problems of standard specialization tools, presents multi-level specialization, and demonstrates that, in combination with the cogen approach, it is far more practical than previously supposed. The program generator which we designed and implemented for a higher-order functional language converts programs into very compact multi-level generating extensions that guarantee fast successive specialization. Experimental results show a remarkable reduction of generation time and generator size compared to previous attempts of multi-level specialization by self-application. Our approach to multi-level specialization seems well-suited for applications where generation time and program size are critical.

A Roadmap to Metacomputation by Supercompilation

This paper gives a gentle introduction to Turchins super-compilation and its applications in metacomputation with an emphasis on recent developments. First, a complete supercompiler, including positive driving and generalization, is defined for a functional language and illustrated with examples. Then a taxonomy of related transformers is given and compared to the supercompiler. Finally, we put supercompilation into the larger perspective of metacomputation and consider three metacomputation tasks: specialization, composition, and inversion.

Optimized reversible binary-coded decimal adders

Babu and Chowdhury [H.M.H. Babu, A.R. Chowdhury, Design of a compact reversible binary coded decimal adder circuit, Journal of Systems Architecture 52 (5) (2006) 272-282] recently proposed, in this journal, a reversible adder for binary-coded decimals. This paper corrects and optimizes their design. The optimized 1-decimal BCD full-adder, a 13x13 reversible logic circuit, is faster, and has lower circuit cost and less garbage bits. It can be used to build a fast reversible m-decimal BCD full-adder that has a delay of only m+17 low-power reversible CMOS gates. For a 32-decimal (128-bit) BCD addition, the circuit delay of 49 gates is significantly lower than is the number of bits used for the BCD representation. A complete set of reversible half- and full-adders for n-bit binary numbers and m-decimal BCD numbers is presented. The results show that special-purpose design pays off in reversible logic design by drastically reducing the number of garbage bits. Specialized designs benefit from support by reversible logic synthesis. All circuit components required for optimizing the original design could also be synthesized successfully by an implementation of an existing synthesis algorithm.