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