Max size necessary for output buffer when compressing

[nemequ]

I'm thinking about adding a Squash plugin for squish, but I don't see a way to determine the destination buffer size necessary to store a specified number of bytes of source material under the worst-case scenario (like random data).

It would be good to have at least a description of how to calculate that (e.g., from the bzip2 documentaion: "To guarantee that the compressed data will fit in its buffer, allocate an output buffer of size 1% larger than the uncompressed data, plus six hundred extra bytes."), or even better a macro or function to calculate it (like compressBound in zlib or LZ4_COMPRESSBOUND/LZ4_compressBound in LZ4).