3 # https://sourceware.org/bugzilla/show_bug.cgi?id=26034
4 export "BUP_ARGV_0"="$0"
7 export "BUP_ARGV_${arg_i}"="$arg"
11 # Here to end of preamble replaced during install
12 bup_python="$(dirname "$0")/../../config/bin/python" || exit $?
13 exec "$bup_python" "$0"
17 from __future__ import absolute_import
19 # Intentionally replace the dirname "$0" that python prepends
21 sys.path[0] = os.path.dirname(os.path.realpath(__file__)) + '/..'
25 from bup import compat, options, git, _helpers
26 from bup.helpers import log
27 from bup.io import byte_stream
29 POPULATION_OF_EARTH=6.7e9 # as of September, 2010
34 predict Guess object offsets and report the maximum deviation
35 ignore-midx Don't use midx files; use only plain pack idx files.
37 o = options.Options(optspec)
38 opt, flags, extra = o.parse(compat.argv[1:])
41 o.fatal("no arguments expected")
43 git.check_repo_or_die()
45 mi = git.PackIdxList(git.repo(b'objects/pack'), ignore_midx=opt.ignore_midx)
47 def do_predict(ix, out):
50 for count,i in enumerate(ix):
51 prefix = struct.unpack('!Q', i[:8])[0]
52 expected = prefix * total // (1 << 64)
53 diff = count - expected
54 maxdiff = max(maxdiff, abs(diff))
55 out.write(b'%d of %d (%.3f%%) '
56 % (maxdiff, len(ix), maxdiff * 100.0 / len(ix)))
58 assert(count+1 == len(ix))
61 out = byte_stream(sys.stdout)
70 # default mode: find longest matching prefix
76 #assert(str(i) >= last)
77 pm = _helpers.bitmatch(last, i)
78 longmatch = max(longmatch, pm)
80 out.write(b'%d\n' % longmatch)
81 log('%d matching prefix bits\n' % longmatch)
82 doublings = math.log(len(mi), 2)
83 bpd = longmatch / doublings
84 log('%.2f bits per doubling\n' % bpd)
85 remain = 160 - longmatch
86 rdoublings = remain / bpd
87 log('%d bits (%.2f doublings) remaining\n' % (remain, rdoublings))
88 larger = 2**rdoublings
89 log('%g times larger is possible\n' % larger)
90 perperson = larger/POPULATION_OF_EARTH
91 log('\nEveryone on earth could have %d data sets like yours, all in one\n'
92 'repository, and we would expect 1 object collision.\n'