A file compressor is great for shrinking stored files, but it depresses me whenever I see a file grow instead of shrink. So what I am looking for is a file compression algorithm that never inflates any files, although it is allowed that some files (not all of course!) have the same length after "compression". Ideally it should work on files of all sizes, but I would be satisfied with a compressor that operates only on files larger than 1MB.
Can you provide such an algorithm? No programming knowledge is required for this problem.
(In reply to Impossibility?
The function must be a bijection: if zip(A)=Z, there cannot exist B≠A such that zip(B)=Z.