@kenshirriff US Patent 6883087 (now expired so I can talk about it) describes a method to compress x86 instructions by splitting the bytes depending on their meaning in the instruction, i.e. a stream of opcodes, a stream of ModR/M, a stream of immediates, etc..., and decompressing by following a very similar decoding logic. Compression was around 5x in practice, compared to 2x with zlib.