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")/bup-python" || exit $?
13 exec "$bup_python" "$0"
17 from __future__ import absolute_import
18 import sys, struct, math
20 from bup import compat, options, git, _helpers
21 from bup.helpers import log
22 from bup.io import byte_stream
24 POPULATION_OF_EARTH=6.7e9 # as of September, 2010
29 predict Guess object offsets and report the maximum deviation
30 ignore-midx Don't use midx files; use only plain pack idx files.
32 o = options.Options(optspec)
33 opt, flags, extra = o.parse(compat.argv[1:])
36 o.fatal("no arguments expected")
38 git.check_repo_or_die()
40 mi = git.PackIdxList(git.repo(b'objects/pack'), ignore_midx=opt.ignore_midx)
42 def do_predict(ix, out):
45 for count,i in enumerate(ix):
46 prefix = struct.unpack('!Q', i[:8])[0]
47 expected = prefix * total // (1 << 64)
48 diff = count - expected
49 maxdiff = max(maxdiff, abs(diff))
50 out.write(b'%d of %d (%.3f%%) '
51 % (maxdiff, len(ix), maxdiff * 100.0 / len(ix)))
53 assert(count+1 == len(ix))
56 out = byte_stream(sys.stdout)
65 # default mode: find longest matching prefix
71 #assert(str(i) >= last)
72 pm = _helpers.bitmatch(last, i)
73 longmatch = max(longmatch, pm)
75 out.write(b'%d\n' % longmatch)
76 log('%d matching prefix bits\n' % longmatch)
77 doublings = math.log(len(mi), 2)
78 bpd = longmatch / doublings
79 log('%.2f bits per doubling\n' % bpd)
80 remain = 160 - longmatch
81 rdoublings = remain / bpd
82 log('%d bits (%.2f doublings) remaining\n' % (remain, rdoublings))
83 larger = 2**rdoublings
84 log('%g times larger is possible\n' % larger)
85 perperson = larger/POPULATION_OF_EARTH
86 log('\nEveryone on earth could have %d data sets like yours, all in one\n'
87 'repository, and we would expect 1 object collision.\n'