Solving Bit-Vector Equations of Fixed and Non-Fixed Size

This report is concerned with solving equations on fixed andnon-fixed size bit-vector terms. We define an equational transformationsystem for solving equations on terms where all sizes ofbit-vectors and extraction positions are known. This transformationsystem suggests a generalization for dealing with bit-vectorsof unknown size and unknown extraction positions. Both solversadhere to the principle of splitting bit-vectors only on demand,thereby making them quite effective in practice

Safety Performance of Neural Networks in the Presence of Covariate Shift

Covariate shift may impact the operational safety performance of neural networks. A re-evaluation of the safety performance, however, requires collecting new operational data and creating corresponding ground truth labels, which often is not possible during operation. We are therefore proposing to reshape the initial test set, as used for the safety performance evaluation prior to deployment, based on an approximation of the operational data. This approximation is obtained by observing and learning the distribution of activation patterns of neurons in the network during operation. The reshaped test set reflects the distribution of neuron activation values as observed during operation, and may therefore be used for re-evaluating safety performance in the presence of covariate shift. First, we derive conservative bounds on the values of neurons by applying finite binning and static dataflow analysis. Second, we formulate a mixed integer linear programming (MILP) constraint for constructing the minimum set of data points to be removed in the test set, such that the difference between the discretized test and operational distributions is bounded. We discuss potential benefits and limitations of this constraint-based approach based on our initial experience with an implemented research prototype