3 bup_python="$(dirname "$0")/bup-python" || exit $?
4 exec "$bup_python" "$0" ${1+"$@"}
8 import sys, struct, math
10 from bup import options, git, _helpers
11 from bup.helpers import log
13 POPULATION_OF_EARTH=6.7e9 # as of September, 2010
18 predict Guess object offsets and report the maximum deviation
19 ignore-midx Don't use midx files; use only plain pack idx files.
21 o = options.Options(optspec)
22 (opt, flags, extra) = o.parse(sys.argv[1:])
25 o.fatal("no arguments expected")
27 git.check_repo_or_die()
28 git.ignore_midx = opt.ignore_midx
30 mi = git.PackIdxList(git.repo('objects/pack'))
35 for count,i in enumerate(ix):
36 prefix = struct.unpack('!Q', i[:8])[0]
37 expected = prefix * total / (1<<64)
38 diff = count - expected
39 maxdiff = max(maxdiff, abs(diff))
40 print '%d of %d (%.3f%%) ' % (maxdiff, len(ix), maxdiff*100.0/len(ix))
42 assert(count+1 == len(ix))
51 # default mode: find longest matching prefix
57 #assert(str(i) >= last)
58 pm = _helpers.bitmatch(last, i)
59 longmatch = max(longmatch, pm)
62 log('%d matching prefix bits\n' % longmatch)
63 doublings = math.log(len(mi), 2)
64 bpd = longmatch / doublings
65 log('%.2f bits per doubling\n' % bpd)
66 remain = 160 - longmatch
67 rdoublings = remain / bpd
68 log('%d bits (%.2f doublings) remaining\n' % (remain, rdoublings))
69 larger = 2**rdoublings
70 log('%g times larger is possible\n' % larger)
71 perperson = larger/POPULATION_OF_EARTH
72 log('\nEveryone on earth could have %d data sets like yours, all in one\n'
73 'repository, and we would expect 1 object collision.\n'