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Percolation scheduling with resource constraints
This paper presents a new approach to resource-constrained compiler extraction of fine-grain parallelism, targeted towards VLIW supercomputers, and in particular, the IBM VLIW (Very Large Instruction Word) processor. The algorithms described integrate resource limitations into Percolation Scheduling—a global parallelization technique—to deal with resource constraints, without sacrificing the generality and completeness of Percolation Scheduling in the process. This is in sharp contrast with previous approaches which either applied only to conditional-free code, or drastically limited the parallelization process by imposing relatively local heuristic resource constraints early in the scheduling process
Optimal Scheduling Using Branch and Bound with SPIN 4.0
The use of model checkers to solve discrete optimisation problems is appealing. A model checker can first be used to verify that the model of the problem is correct. Subsequently, the same model can be used to find an optimal solution for the problem. This paper describes how to apply the new PROMELA primitives of SPIN 4.0 to search effectively for the optimal solution. We show how Branch-and-Bound techniques can be added to the LTL property that is used to find the solution. The LTL property is dynamically changed during the verification. We also show how the syntactical reordering of statements and/or processes in the PROMELA model can improve the search even further. The techniques are illustrated using two running examples: the Travelling Salesman Problem and a job-shop scheduling problem
Implications of Structured Programming for Machine Architecture
Based on an empirical study of more than 10,000 lines of program text written in a GOTO-less language, a machine architecture specifically designed for structured programs is proposed. Since assignment, CALL, RETURN, and IF statements together account for 93 percent of all executable statements, special care is given to ensure that these statements can be implemented efficiently. A highly compact instruction encoding scheme is presented, which can reduce program size by a factor of 3. Unlike a Huffman code, which utilizes variable length fields, this method uses only fixed length (1-byte) opcode and address fields. The most frequent instructions consist of a single 1-byte field. As a consequence, instruction decoding time is minimized, and the machine is efficient with respect to both space and time. © 1978, ACM. All rights reserved
From MinX to MinC: Semantics-Driven Decompilation of Recursive Datatypes
Reconstructing the meaning of a program from its binary executable is known as
reverse engineering; it has a wide range of applications in software security, exposing piracy, legacy systems, etc. Since reversing is ultimately a search for meaning, there is much interest in inferring a type (a meaning) for the elements of a binary in a consistent way. Unfortunately existing approaches do not guarantee any semantic relevance for their reconstructed types. This paper presents a new and semantically-founded approach that provides strong guarantees for the reconstructed types. Key to our approach is the derivation of a witness program in a high-level language alongside the reconstructed types. This witness has the same semantics as the binary, is type correct by construction, and it induces a (justifiable) type assignment on the binary. Moreover, the approach effectively yields a type-directed decompiler. We formalise and implement the approach for reversing Minx, an abstraction of x86, to MinC, a type-safe dialect of C with recursive datatypes. Our evaluation compiles a range of textbook C algorithms to MinX and then recovers the original structures
Description and Optimization of Abstract Machines in a Dialect of Prolog
In order to achieve competitive performance, abstract machines for Prolog and
related languages end up being large and intricate, and incorporate
sophisticated optimizations, both at the design and at the implementation
levels. At the same time, efficiency considerations make it necessary to use
low-level languages in their implementation. This makes them laborious to code,
optimize, and, especially, maintain and extend. Writing the abstract machine
(and ancillary code) in a higher-level language can help tame this inherent
complexity. We show how the semantics of most basic components of an efficient
virtual machine for Prolog can be described using (a variant of) Prolog. These
descriptions are then compiled to C and assembled to build a complete bytecode
emulator. Thanks to the high level of the language used and its closeness to
Prolog, the abstract machine description can be manipulated using standard
Prolog compilation and optimization techniques with relative ease. We also show
how, by applying program transformations selectively, we obtain abstract
machine implementations whose performance can match and even exceed that of
state-of-the-art, highly-tuned, hand-crafted emulators.Comment: 56 pages, 46 figures, 5 tables, To appear in Theory and Practice of
Logic Programming (TPLP
The Reach-Avoid Problem for Constant-Rate Multi-Mode Systems
A constant-rate multi-mode system is a hybrid system that can switch freely
among a finite set of modes, and whose dynamics is specified by a finite number
of real-valued variables with mode-dependent constant rates. Alur, Wojtczak,
and Trivedi have shown that reachability problems for constant-rate multi-mode
systems for open and convex safety sets can be solved in polynomial time. In
this paper, we study the reachability problem for non-convex state spaces and
show that this problem is in general undecidable. We recover decidability by
making certain assumptions about the safety set. We present a new algorithm to
solve this problem and compare its performance with the popular sampling based
algorithm rapidly-exploring random tree (RRT) as implemented in the Open Motion
Planning Library (OMPL).Comment: 26 page
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