Is dynamic compilation possible for embedded systems ?

International audienceJIT compilation and dynamic compilation are powerful techniques allowing to delay the final code generation to the run-time. There is many benefits : improved portability, virtual machine security, etc. Unforturnately the tools used for JIT compilation and dynamic compilation does not met the classical requirement for embedded platforms: memory size is huge and code generation has big overheads. In this paper we show how dynamic code specialization (JIT) can be used and be beneficial in terms of execution speed and energy consumption with memory footprint kept under control. We based our approaches on our tool de-Goal and on LLVM, that we extended to be able to produce lightweight runtime specializers from annotated LLVM programs. Benchmarks are manipulated and transformed into templates and a specialization routine is build to instantiate the routines. Such approach allows to produce efficient special-izations routines, with a minimal energy consumption and memory footprint compare to a generic JIT application. Through some benchmarks, we present its efficiency in terms of speed, energy and memory footprint. We show that over static compilation we can achieve a speed-up of 21 % in terms of execution speed but also a 10 % energy reduction with a moderate memory footprint

ALPGEN, a generator for hard multiparton processes in hadronic collisions

This paper presents a new event generator, ALPGEN, dedicated to the study of multiparton hard processes in hadronic collisions. The code performs, at the leading order in QCD and EW interactions, the calculation of the exact matrix elements for a large set of parton-level processes of interest in the study of the Tevatron and LHC data. The current version of the code describes the following final states: (W -> ffbar') QQbar+ N jets (Q being a heavy quark, and f=l,q), with N f fbar)+QQbar+Njets (f=l,nu), with N ffbar') + charm + N jets (f=l,q), N f fbar') + N jets (f=l,q) and (Z/gamma* -> f fbar)+ N jets (f=l,nu), with N<=6; nW+mZ+lH+N jets, with n+m+l+N<=8 and N<=3 including all 2-fermion decay modes of W and Z bosons, with spin correlations; Q Qbar+N jets (N b f fbar' decays and relative spin correlations included if Q=t; Q Qbar Q' Qbar'+N jets, with Q and Q' heavy quarks (possibly equal) and N b f fbar' decays and relative spin correlations included if Q=t; N jets, with N<=6. Parton-level events are generated, providing full information on their colour and flavour structure, enabling the evolution of the partons into fully hadronised final states.Comment: 1+38 pages, uses JHEP.cls. Documents code version 1.2: extended list of processes, updated documentation and bibliograph

Automatic code generation for ATLAS communications drivers

ATLAS is a software development platform created in our Department. Among other benefits, it provides support to easily distribute applications over a network. In these applications, communications issues among the different processes should be faced. Pursuing to isolate application developers from the intricacies of these issues, communication drivers are automatically generated from an interface declaration of each process. This automatic code generation --not unlike the generation of stubs in CORBA from the IDL specification-- is the main topic of this report.Postprint (published version

New version of PLNoise: a package for exact numerical simulation of power-law noises

In a recent paper I have introduced a package for the exact simulation of power-law noises and other colored noises (E. Milotti, Comput. Phys. Commun. {\bf 175} (2006) 212): in particular the algorithm generates $1/f^\alpha$ noises with $0 < \alpha \leq 2$. Here I extend the algorithm to generate $1/f^\alpha$ noises with $2 < \alpha \leq 4$ (black noises). The method is exact in the sense that it produces a sampled process with a theoretically guaranteed range-limited power-law spectrum for any arbitrary sequence of sampling intervals, i.e., the sampling times may be unevenly spaced.Comment: 3 figures, submitted to Computer Physics Communication

GPERF : a perfect hash function generator

gperf is a widely available perfect hash function generator written in C++. It automates a common system software operation: keyword recognition. gperf translates an n element user-specified keyword list keyfile into source code containing a k element lookup table and a pair of functions, phash and in_word_set. phash uniquely maps keywords in keyfile onto the range 0 .. k - 1, where k &gt;/= n. If k = n, then phash is considered a minimal perfect hash function. in_word_set uses phash to determine whether a particular string of characters str occurs in the keyfile, using at most one string comparison.This paper describes the user-interface, options, features, algorithm design and implementation strategies incorporated in gperf. It also presents the results from an empirical comparison between gperf-generated recognizers and other popular techniques for reserved word lookup

SKIRT: the design of a suite of input models for Monte Carlo radiative transfer simulations

The Monte Carlo method is the most popular technique to perform radiative transfer simulations in a general 3D geometry. The algorithms behind and acceleration techniques for Monte Carlo radiative transfer are discussed extensively in the literature, and many different Monte Carlo codes are publicly available. On the contrary, the design of a suite of components that can be used for the distribution of sources and sinks in radiative transfer codes has received very little attention. The availability of such models, with different degrees of complexity, has many benefits. For example, they can serve as toy models to test new physical ingredients, or as parameterised models for inverse radiative transfer fitting. For 3D Monte Carlo codes, this requires algorithms to efficiently generate random positions from 3D density distributions. We describe the design of a flexible suite of components for the Monte Carlo radiative transfer code SKIRT. The design is based on a combination of basic building blocks (which can be either analytical toy models or numerical models defined on grids or a set of particles) and the extensive use of decorators that combine and alter these building blocks to more complex structures. For a number of decorators, e.g. those that add spiral structure or clumpiness, we provide a detailed description of the algorithms that can be used to generate random positions. Advantages of this decorator-based design include code transparency, the avoidance of code duplication, and an increase in code maintainability. Moreover, since decorators can be chained without problems, very complex models can easily be constructed out of simple building blocks. Finally, based on a number of test simulations, we demonstrate that our design using customised random position generators is superior to a simpler design based on a generic black-box random position generator.Comment: 15 pages, 4 figures, accepted for publication in Astronomy and Computin

Fitting of dust spectra with genetic algorithms - I. Perspectives & Limitations

Aims: We present an automatised fitting procedure for the IR range of AGB star spectra. Furthermore we explore the possibilities and boundaries of this method. Methods: We combine the radiative transfer code DUSTY with the genetic algorithm PIKAIA in order to improve an existing spectral fit significantly. Results: In order to test the routine we carried out a performance test by feeding an artificially generated input spectrum into the program. Indeed the routine performed as expected, so, as a more realistic test set-up, we tried to create model fits for ISO spectra of selected AGB stars. Here we were not only able to improve existing fits, but also to show that a slightly altered dust composition may give a better fit for some objects. Conclusion: The use of a genetic algorithm in order to automatise the process of fitting stellar spectra seems to be very promising. We were able to improve existing fits and further offer a quantitative method to compare different models with each other. Nevertheless this method still needs to be studied and tested in more detail.Comment: 9 pages, 5 figures, accepted for publication in Astronomy and Astrophysic

HERBVI - a program for simulation of baryon- and lepton- number violating processes

We describe a Monte Carlo event generator for the simulation of baryon- and lepton-number violating processes at supercolliders. The package, {\HERBVI}, is designed as a hard-process generator interfacing to the general hadronic event simulation program {\HW}. In view of the very high multiplicity of gauge bosons expected in such processes, particular attention is paid to the efficient generation of multiparticle phase space. The program also takes account of the expected colour structure of baryon-number violating vertices, which has important implications for the hadronization of the final state.Comment: 19 pages, standard LaTeX, no figure