The smallest grammar problem is the problem of finding the smallest context-free grammar that generates exactly one given sequence. Approximating the problem with a ratio of less than 8569/8568 is known to be NP-hard. Most work on this problem has focused on finding decent solutions fast (mostly in linear time), rather than on good heuristic algorithms. Inspired by a new perspective on the problem presented by Carrascosa et al.\ (2010), we investigate the performance of different heuristics on the problem. The aim is to find a good solution on large instances by allowing more than linear time. We propose a hybrid of a max-min ant system and a genetic algorithm that in combination with a novel local search outperforms the state of the art on all files of the Canterbury corpus, a standard benchmark suite. Furthermore, this hybrid performs well on a standard DNA corpus.

This paper performs an investigation into the security of Xilinx FPGA bitstreams, introducing a tool-chain for reversing bitstreams back to their device-specific netlists. Bitstream reversal is performed by querying a database containing the mapping of bitstream bits to their related configurable FPGA resources and a secondary database describing the FPGA structure. The mapping database is created by applying an algorithm that correlates binary bitstream data with data extracted from a corresponding netlist. The resource database is derived from a textual device description which can be obtained from the Xilinx design flow. The method can successfully reverse certain sections of the bitstream, although complete bitstream reversal remains infeasible for the time being. The presented tool-chain, the Bitfile Interpretation Library (BIL), improves on previous attempts at bitstream reverse engineering. It is made available as open source for further development.

Programs using floating-point arithmetic are prone to accuracy problems caused by rounding and catastrophic cancellation. These phenomena provoke bugs that are notoriously hard to track down: the program does not necessarily crash and the results are not necessarily obviously wrong, but often subtly inaccurate. Further use of these values can lead to catastrophic errors.