Author: Mattias Ulbrich

Proving Line Wrapping in KeY, Why3, Dafny and Frama-C

This is a short comparison report about a verification task solved with KeY, Why3, Dafny and Frama-C.

The original challenge comes from a real-world situation. There is no particular “trick” needed for the specification and verification; it is rather straightforward. Yet, the required annotations to achieve the specification are not too few – making the example a good opportunity to compare different specification languages. Continue reading “Proving Line Wrapping in KeY, Why3, Dafny and Frama-C” →

Proving JDK’s Dual Pivot Quicksort Correct

by Bernhard Beckert, Jonas Schiffl, Peter H. Schmitt and Mattias Ulbrich Sorting is a fundamental functionality in libraries, for which efficiency is crucial. Correctness of the highly optimized implementations is often taken for granted. De Gouw et al. have shown that this certainty is deceptive by revealing a bug in the Java Development Kit (JDK) implementation of TimSort. We have now formally analysed the other implementation of sorting in the JDK standard library: A highly efficient implementation of a dual pivot quicksort algorithm. We were able to deductively prove that the algorithm implementation is correct. However, a loop invariant which is annotated to the source code does not hold. Continue reading “Proving JDK’s Dual Pivot Quicksort Correct” →