Recompressing Compressed Files Using SSW Algorithm

We defined a compression algorithm called Skip Second Word (SSW) and a hierarchical partitioning schema for obtaining 256-Kbyte segments from a compressed file by 7-Zip File Manager. SSW has two main procedures. The first one is finding and skipping words, and the second one is efficiently encoding their locations (i.e., EAI) for decompression. The initial step is to find two identical 16-bit words within a 64-byte page. If there is such a page having an encoding advantage, then we can save the first word in the output file and compress the other one by skipping. We developed Recursive, Incremental, and Iterative programs based on the SSW algorithm. We also implemented two non-SSW programs, Heuristic and Sequence, obtaining sub-files for further recompressions using 7-Zip. We tested all programs and chose the best versions of them to build a compression suite [1]. In this work, to obtain an original compression application with similar time performance, non-SSW programs are not included. Recursive and Iterative have better rate advantages than Incremental, but they are too slow. Incremental program, which iterates each segment as possible, is as fast as non-SSW ones but has no such rates. We improved it by adding an iteration parameter more and by shuffling and shifting segment contents, resulting in eight versions that are evaluated at the same run. As a result, we achieved better Space Saving rates than three SSW programs, obtaining more than 0.01% related files given in the Table.