[_swa8]

I wrote mine along similar lines, except without using hashing at all. Files of identical size are compared byte-by-byte instead, until first difference or end of file. As many files as possible at a time, of course, to avoid having to read through files multiple times. This avoids any uncertainty about hash collisions.

To find out how many files of each size you have:

find ~ -type f -printf '%s\n' | sort | uniq -c | sort -n

[hvidgaard]

A hash is often use for an online algorithm. If you know the hash you know there is a potential for dedupe, and you can do a byte for byte comparison. I suppose you could use size as a prefilter for dedupe. This is if you do dedupe on a file level. Dedupe on block level doesn't care about the content, only the blocks, and it's not unusual to see for instance mp3 files with the same mp3 stream but different metadata. You cannot do the latter without hashing.