PPMexe: PPM for Code Compression

With the emergence of software delivery platforms such as Microsoft’s .NET, code compression has become one of the core enabling technologies strongly affecting system performance. In this paper, we present compression mechanisms for executables that explore their syntax and semantics to achieve superior compression rates. The fundament of our compression codec is the generic paradigm of prediction by partial matching (PPM). We combine PPM with two pre-processing steps: (i) instruction rescheduling to improve prediction rates and (ii) partitioning of a program binary. We improve the traditional PPM algorithm by (iii) using an additional alphabet of frequent variable-length super-symbols extracted from the input stream of fixed-length symbols. (iv) a low-overhead mechanism that enables decompression starting from an arbitrary instruction of the executable, a feature pivotal for run-time software delivery. The compression algorithm is implemented for x86 binaries and tested on several large Microsoft applications. Binaries compressed using the PPM algorithm enhanced with (i -iv), are 16-23% smaller than files created using off-the-shelf PPMD, the best available compressor.