Replace remaining print statements with print function

[bup.git] / cmd / margin-cmd.py

diff --git a/cmd/margin-cmd.py b/cmd/margin-cmd.py
index 85b32890b493ea4df2ea4cd8b0f661d8f2253c4e..b01db3d1864e151fe7e74059b024f3eb08be1ebd 100755 (executable)
--- a/cmd/margin-cmd.py
+++ b/cmd/margin-cmd.py
@@ -1,29 +1,75 @@
-#!/usr/bin/env python
-import sys
-from bup import options, git, _hashsplit
-from bup.helpers import *
+#!/bin/sh
+"""": # -*-python-*-
+bup_python="$(dirname "$0")/bup-python" || exit $?
+exec "$bup_python" "$0" ${1+"$@"}
+"""
+# end of bup preamble
+
+from __future__ import absolute_import, print_function
+import sys, struct, math
+
+from bup import options, git, _helpers
+from bup.helpers import log
 
+POPULATION_OF_EARTH=6.7e9  # as of September, 2010
 
 optspec = """
 bup margin
+--
+predict    Guess object offsets and report the maximum deviation
+ignore-midx  Don't use midx files; use only plain pack idx files.
 """
-o = options.Options('bup margin', optspec)
+o = options.Options(optspec)
 (opt, flags, extra) = o.parse(sys.argv[1:])
 
 if extra:
     o.fatal("no arguments expected")
 
 git.check_repo_or_die()
-#git.ignore_midx = 1
-
-mi = git.MultiPackIndex(git.repo('objects/pack'))
-last = '\0'*20
-longmatch = 0
-for i in mi:
-    if i == last:
-        continue
-    #assert(str(i) >= last)
-    pm = _hashsplit.bitmatch(last, i)
-    longmatch = max(longmatch, pm)
-    last = i
-print longmatch
+git.ignore_midx = opt.ignore_midx
+
+mi = git.PackIdxList(git.repo('objects/pack'))
+
+def do_predict(ix):
+    total = len(ix)
+    maxdiff = 0
+    for count,i in enumerate(ix):
+        prefix = struct.unpack('!Q', i[:8])[0]
+        expected = prefix * total / (1<<64)
+        diff = count - expected
+        maxdiff = max(maxdiff, abs(diff))
+    print('%d of %d (%.3f%%) ' % (maxdiff, len(ix), maxdiff*100.0/len(ix)))
+    sys.stdout.flush()
+    assert(count+1 == len(ix))
+
+if opt.predict:
+    if opt.ignore_midx:
+        for pack in mi.packs:
+            do_predict(pack)
+    else:
+        do_predict(mi)
+else:
+    # default mode: find longest matching prefix
+    last = '\0'*20
+    longmatch = 0
+    for i in mi:
+        if i == last:
+            continue
+        #assert(str(i) >= last)
+        pm = _helpers.bitmatch(last, i)
+        longmatch = max(longmatch, pm)
+        last = i
+    print(longmatch)
+    log('%d matching prefix bits\n' % longmatch)
+    doublings = math.log(len(mi), 2)
+    bpd = longmatch / doublings
+    log('%.2f bits per doubling\n' % bpd)
+    remain = 160 - longmatch
+    rdoublings = remain / bpd
+    log('%d bits (%.2f doublings) remaining\n' % (remain, rdoublings))
+    larger = 2**rdoublings
+    log('%g times larger is possible\n' % larger)
+    perperson = larger/POPULATION_OF_EARTH
+    log('\nEveryone on earth could have %d data sets like yours, all in one\n'
+        'repository, and we would expect 1 object collision.\n'
+        % int(perperson))