git-annex hashing functions

# See docs in http://git-annex.branchable.com/internals/hashing/ and implementation in http://sources.debian.net/src/git-annex/5.20140227/Locations.hs/?hl=408#L408

import hashlib
import struct

def hashdirlower(key):
    hasher = hashlib.md5()
    hasher.update(key)
    digest = hasher.hexdigest()
    return "%s/%s/" % (digest[:3], digest[3:6])

def hashdirmixed(key):
    hasher = hashlib.md5()
    hasher.update(key)
    digest = hasher.digest()
    first_word = struct.unpack('<I', digest[:4])[0]
    nums = [first_word >> (6 * x) & 31 for x in xrange(4)]
    letters = ["0123456789zqjxkmvwgpfZQJXKMVWGPF"[i] for i in nums]
    return "%s%s/%s%s/" % (letters[1], letters[0], letters[3], letters[2])

what is hashdirmixed? i am unclear as to why the struct is necessary?

It mimics the corresponding function in git-annex, see https://sources.debian.net/src/git-annex/5.20150731-1/Annex/DirHashes.hs/?hl=63#L63.

I realize these functions are relatively trivial, but I also appreciated not having to write them myself :).

I'm using them in https://github.com/DanielDent/git-annex-remote-rclone/blob/master/migrations/frankencase-to-mixed/frankencase-to-mixed-helper.py and would like to provide my users with a clear license for the code. Would you be able to clarify the terms under which this code is provided?