80,283 research outputs found
On the Algorithmic Nature of the World
We propose a test based on the theory of algorithmic complexity and an
experimental evaluation of Levin's universal distribution to identify evidence
in support of or in contravention of the claim that the world is algorithmic in
nature. To this end we have undertaken a statistical comparison of the
frequency distributions of data from physical sources on the one
hand--repositories of information such as images, data stored in a hard drive,
computer programs and DNA sequences--and the frequency distributions generated
by purely algorithmic means on the other--by running abstract computing devices
such as Turing machines, cellular automata and Post Tag systems. Statistical
correlations were found and their significance measured.Comment: Book chapter in Gordana Dodig-Crnkovic and Mark Burgin (eds.)
Information and Computation by World Scientific, 2010.
(http://www.idt.mdh.se/ECAP-2005/INFOCOMPBOOK/). Paper website:
http://www.mathrix.org/experimentalAIT
On partial order semantics for SAT/SMT-based symbolic encodings of weak memory concurrency
Concurrent systems are notoriously difficult to analyze, and technological
advances such as weak memory architectures greatly compound this problem. This
has renewed interest in partial order semantics as a theoretical foundation for
formal verification techniques. Among these, symbolic techniques have been
shown to be particularly effective at finding concurrency-related bugs because
they can leverage highly optimized decision procedures such as SAT/SMT solvers.
This paper gives new fundamental results on partial order semantics for
SAT/SMT-based symbolic encodings of weak memory concurrency. In particular, we
give the theoretical basis for a decision procedure that can handle a fragment
of concurrent programs endowed with least fixed point operators. In addition,
we show that a certain partial order semantics of relaxed sequential
consistency is equivalent to the conjunction of three extensively studied weak
memory axioms by Alglave et al. An important consequence of this equivalence is
an asymptotically smaller symbolic encoding for bounded model checking which
has only a quadratic number of partial order constraints compared to the
state-of-the-art cubic-size encoding.Comment: 15 pages, 3 figure
Transparent code authentication at the processor level
The authors present a lightweight authentication mechanism that verifies the authenticity of code and thereby addresses the virus and malicious code problems at the hardware level eliminating the need for trusted extensions in the operating system. The technique proposed tightly integrates the authentication mechanism into the processor core. The authentication latency is hidden behind the memory access latency, thereby allowing seamless on-the-fly authentication of instructions. In addition, the proposed authentication method supports seamless encryption of code (and static data). Consequently, while providing the software users with assurance for authenticity of programs executing on their hardware, the proposed technique also protects the software manufacturers’ intellectual property through encryption. The performance analysis shows that, under mild assumptions, the presented technique introduces negligible overhead for even moderate cache sizes
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