708 research outputs found
Scalable Verification of Quantized Neural Networks (Technical Report)
Formal verification of neural networks is an active topic of research, and
recent advances have significantly increased the size of the networks that
verification tools can handle. However, most methods are designed for
verification of an idealized model of the actual network which works over real
arithmetic and ignores rounding imprecisions. This idealization is in stark
contrast to network quantization, which is a technique that trades numerical
precision for computational efficiency and is, therefore, often applied in
practice. Neglecting rounding errors of such low-bit quantized neural networks
has been shown to lead to wrong conclusions about the network's correctness.
Thus, the desired approach for verifying quantized neural networks would be one
that takes these rounding errors into account. In this paper, we show that
verifying the bit-exact implementation of quantized neural networks with
bit-vector specifications is PSPACE-hard, even though verifying idealized
real-valued networks and satisfiability of bit-vector specifications alone are
each in NP. Furthermore, we explore several practical heuristics toward closing
the complexity gap between idealized and bit-exact verification. In particular,
we propose three techniques for making SMT-based verification of quantized
neural networks more scalable. Our experiments demonstrate that our proposed
methods allow a speedup of up to three orders of magnitude over existing
approaches
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Formal Analysis of Arithmetic Circuits using Computer Algebra - Verification, Abstraction and Reverse Engineering
Despite a considerable progress in verification and abstraction of random and control logic, advances in formal verification of arithmetic designs have been lagging. This can be attributed mostly to the difficulty in an efficient modeling of arithmetic circuits and datapaths without resorting to computationally expensive Boolean methods, such as Binary Decision Diagrams (BDDs) and Boolean Satisfiability (SAT), that require “bit blasting”, i.e., flattening the design to a bit-level netlist. Approaches that rely on computer algebra and Satisfiability Modulo Theories (SMT) methods are either too abstract to handle the bit-level nature of arithmetic designs or require solving computationally expensive decision or satisfiability problems. The work proposed in this thesis aims at overcoming the limitations of analyzing arithmetic circuits, specifically at the post-synthesized phase. It addresses the verification, abstraction and reverse engineering problems of arithmetic circuits at an algebraic level, treating an arithmetic circuit and its specification as a properly constructed algebraic system. The proposed technique solves these problems by function extraction, i.e., by deriving arithmetic function computed by the circuit from its low-level circuit implementation using computer algebraic rewriting technique. The proposed techniques work on large integer arithmetic circuits and finite field arithmetic circuits, up to 512-bit wide containing millions of logic gates
Investigations into the feasibility of an on-line test methodology
This thesis aims to understand how information coding and the protocol that it
supports can affect the characteristics of electronic circuits. More specifically, it
investigates an on-line test methodology called IFIS (If it Fails It Stops) and its
impact on the design, implementation and subsequent characteristics of circuits
intended for application specific lC (ASIC) technology.
The first study investigates the influences of information coding and protocol on the
characteristics of IFIS systems. The second study investigates methods of circuit
design applicable to IFIS cells and identifies the· technique possessing the
characteristics most suitable for on-line testing. The third study investigates the
characteristics of a 'real-life' commercial UART re-engineered using the techniques
resulting from the previous two studies. The final study investigates the effects of the
halting properties endowed by the protocol on failure diagnosis within IFIS systems.
The outcome of this work is an identification and characterisation of the factors that
influence behaviour, implementation costs and the ability to test and diagnose IFIS
designs
Digital hologram recording systems: some performance improvements
The work presented in this thesis was performed under the EU's Framework
7 (FP7) project, 'REAL3D'. The aim of this project is to develop methods
based on digital holography for real time capture and display of 3D objects.
This thesis forms a small subset of all the work done in this project. Much of
the research work was aimed towards fullling our part of the requirements
of the REAL3D project. The central theme of the research presented in
this thesis is that of improving the performance of the digital holographic
imaging system for its use in 3D display. This encompasses research into
speed up of reconstruction algorithms, understanding the in
uence of noise
and developing techniques to increase resolution and angular perspective
range in reconstructions.
The main original contributions of this research work presented in this thesis
are:
A computer-interfaced automatic digital holographic imaging
system employing `phase shifting' has been built. This system
is capable of recording high-quality digital holograms of a real world
3D object. The object can be rotated on a rotational stage and a full
360 range of perspectives can be recorded. Speckle reduction using
moving diusers can be performed to improve the image quality of the
reconstructed images. A LabView based user friendly interface has
been developed.
Novel methods based on space-time tradeo and xed point
arithmetic have been developed and implemented for speed-
ing up the reconstruction algorithm used in digital holography.
This has resulted in the publication of one peer-reviewed journal pub-
lication and one conference proceeding [1, 2].
The in
uence of additive noise, particularly quantization noise
in digital holography has been studied in detail. A model
has been developed to understand the in
uence of noise on the re-
constructed image quality. Based on this model, a method has been
developed to suppress quantization noise in a memory ecient man-
ner. This work led to the publication of two peer-reviewed journal
publications [3, 4].
A novel method of removing the twin image has been devel-
oped.
Methods to increase the perspectives in holography based on
synthetic aperture have been implemented.
Apart from these primary contributions, the author of this thesis has
also contributed in the form of assisting in experiments, creating gures
for various papers, writing computer programs and discussions during
group meetings. In total, 6 peer-reviewed journal papers (3 being
primary author) have been published and 6 conference proceedings (3
being primary author) have been published. Additionally, 2 talks have
been given at international conferences
Ranking function synthesis for bit-vector relations
Abstract. Ranking function synthesis is a key aspect to the success of modern termination provers for imperative programs. While it is wellknown how to generate linear ranking functions for relations over (mathematical) integers or rationals, efficient synthesis of ranking functions for machine-level integers (bit-vectors) is an open problem. This is particularly relevant for the verification of low-level code. We propose several novel algorithms to generate ranking functions for relations over machine integers: a complete method based on a reduction to Presburger arithmetic, and a template-matching approach for predefined classes of ranking functions based on reduction to SAT-and QBF-solving. The utility of our algorithms is demonstrated on examples drawn from Windows device drivers
Parallel architectures for entropy coding in a dual-standard ultra-HD video encoder
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Includes bibliographical references (p. 97-98).The mismatch between the rapid increase in resolution requirements and the slower increase in energy capacity demand more aggressive low-power circuit design techniques to maintain battery life of hand-held multimedia devices. As the operating voltage is lowered to reduce power consumption, the maximum operating frequency of the system must also decrease while the performance requirements remain constant. To meet these performance constraints imposed by the high resolution and complex functionality of video processing systems, novel techniques for increasing throughput are explored. In particular, the entropy coding functional block faces the most stringent requirements to deliver the necessary throughput due to its highly serial nature, especially to sustain real-time encoding. This thesis proposes parallel architectures for high-performance entropy coding for high-resolution, dual-standard video encoding. To demonstrate the most aggressive techniques for achieving standard reconfigurability, two markedly different video compression standards (H.264/AVC and VC-1) are supported. Specifically, the entropy coder must process data generated from a quad full-HD (4096x2160 pixels per frame, the equivalent of four full-HD frames) video at a frame rate of 30 frames per second and perform lossless compression to generate an output bitstream. This block will be integrated into a dual-standard video encoder chip targeted for operation at 0.6V, which will be fabricated following the completion of this thesis. Parallelism, as well as other techniques applied at the syntax element or bit level, are used to achieve the overall throughput requirements. Three frames of video data are processed in parallel at the system level, and varying degrees of parallelism are employed within the entropy coding block for each standard. The VC-1 entropy encoder block encodes 735M symbols per second with a gate count of 136.6K and power consumption of 304.5 pW, and the H.264 block encodes 4.97G binary symbols per second through three-frame parallelism and a 6-bin cascaded pipelining architecture with a critical path delay of 20.05 ns.by Bonnie K. Y. Lam.S.M
Some new developments in image compression
This study is divided into two parts. The first part involves an investigation of near-lossless compression of digitized images using the entropy-coded DPCM method with a large number of quantization levels. Through the investigation, a new scheme that combines both lossy and lossless DPCM methods into a common framework is developed. This new scheme uses known results on the design of predictors and quantizers that incorporate properties of human visual perception. In order to enhance the compression performance of the scheme, an adaptively generated source model with multiple contexts is employed for the coding of the quantized prediction errors, rather than a memoryless model as in the conventional DPCM method. Experiments show that the scheme can provide compression in the range from 4 to 11 with a peak SNR of about 50 dB for 8-bit medical images. Also, the use of multiple contexts is found to improve compression performance by about 25% to 35%;The second part of the study is devoted to the problem of lossy image compression using tree-structured vector quantization. As a result of the study, a new design method for codebook generation is developed together with four different implementation algorithms. In the new method, an unbalanced tree-structured vector codebook is designed in a greedy fashion under the constraint of rate-distortion trade-off which can then be used to implement a variable-rate compression system. From experiments, it is found that the new method can achieve a very good rate-distortion performance while being computationally efficient. Also, due to the tree-structure of the codebook, the new method is amenable to progressive transmission applications
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