
Originally Posted by
Shelwien
1. Take a codec you like (preferably latest paq8px for more precise results, or zstd for speed)
2. Compress the file
3. Calculate bpc as 8*archive_size/original_size
4. If bpc<8 then file is compressible
So actual "tool" can be implemented as a shell script.
There's really no other way to do it - even for paq8px there'd be some files which it can't compress,
but some other tool can.
At most you can optimize some compression algorithm for this task, by cutting off actual output, etc.
But any fast method would be imprecise - it won't do recompression, for example.