test-revlog-raw: fix "genbits" implementation

The "genbits" implementation is actually incorrect. This patch fixes it. A
good "genbits" implementation should pass the below assertion:

    n = 3 # or other number
    l = list(genbits(n))
    assert 2**(n*2) == len(set((l[i]<<n)+l[i+1] for i in range(len(l)-1)))

An assertion is added to make sure "genbits" won't work unexpectedly.

tests/test-revlog-raw.py

@@ -1,290 +1,293 b''
 # test revlog interaction about raw data (flagprocessor)
 
 from __future__ import absolute_import, print_function
 
 import sys
 
 from mercurial import (
     encoding,
     node,
     revlog,
     transaction,
     vfs,
 )
 
 # TESTTMP is optional. This makes it convenient to run without run-tests.py
 tvfs = vfs.vfs(encoding.environ.get('TESTTMP', b'/tmp'))
 
 # Enable generaldelta otherwise revlog won't use delta as expected by the test
 tvfs.options = {'generaldelta': True, 'revlogv1': True, 'revlogv1': True}
 
 # The test wants to control whether to use delta explicitly, based on
 # "storedeltachains".
 revlog.revlog._isgooddelta = lambda self, d, textlen: self.storedeltachains
 
 def abort(msg):
     print('abort: %s' % msg)
     # Return 0 so run-tests.py could compare the output.
     sys.exit()
 
 # Register a revlog processor for flag EXTSTORED.
 #
 # It simply prepends a fixed header, and replaces '1' to 'i'. So it has
 # insertion and replacement, and may be interesting to test revlog's line-based
 # deltas.
 _extheader = b'E\n'
 
 def readprocessor(self, rawtext):
     # True: the returned text could be used to verify hash
     text = rawtext[len(_extheader):].replace(b'i', b'1')
     return text, True
 
 def writeprocessor(self, text):
     # False: the returned rawtext shouldn't be used to verify hash
     rawtext = _extheader + text.replace(b'1', b'i')
     return rawtext, False
 
 def rawprocessor(self, rawtext):
     # False: do not verify hash. Only the content returned by "readprocessor"
     # can be used to verify hash.
     return False
 
 revlog.addflagprocessor(revlog.REVIDX_EXTSTORED,
                         (readprocessor, writeprocessor, rawprocessor))
 
 # Utilities about reading and appending revlog
 
 def newtransaction():
     # A transaction is required to write revlogs
     report = lambda msg: None
     return transaction.transaction(report, tvfs, {'plain': tvfs}, b'journal')
 
 def newrevlog(name=b'_testrevlog.i', recreate=False):
     if recreate:
         tvfs.tryunlink(name)
     rlog = revlog.revlog(tvfs, name)
     return rlog
 
 def appendrev(rlog, text, tr, isext=False, isdelta=True):
     '''Append a revision. If isext is True, set the EXTSTORED flag so flag
     processor will be used (and rawtext is different from text). If isdelta is
     True, force the revision to be a delta, otherwise it's full text.
     '''
     nextrev = len(rlog)
     p1 = rlog.node(nextrev - 1)
     p2 = node.nullid
     if isext:
         flags = revlog.REVIDX_EXTSTORED
     else:
         flags = revlog.REVIDX_DEFAULT_FLAGS
     # Change storedeltachains temporarily, to override revlog's delta decision
     rlog.storedeltachains = isdelta
     try:
         rlog.addrevision(text, tr, nextrev, p1, p2, flags=flags)
         return nextrev
     except Exception as ex:
         abort('rev %d: failed to append: %s' % (nextrev, ex))
     finally:
         # Restore storedeltachains. It is always True, see revlog.__init__
         rlog.storedeltachains = True
 
 def addgroupcopy(rlog, tr, destname=b'_destrevlog.i', optimaldelta=True):
     '''Copy revlog to destname using revlog.addgroup. Return the copied revlog.
 
     This emulates push or pull. They use changegroup. Changegroup requires
     repo to work. We don't have a repo, so a dummy changegroup is used.
 
     If optimaldelta is True, use optimized delta parent, so the destination
     revlog could probably reuse it. Otherwise it builds sub-optimal delta, and
     the destination revlog needs more work to use it.
 
     This exercises some revlog.addgroup (and revlog._addrevision(text=None))
     code path, which is not covered by "appendrev" alone.
     '''
     class dummychangegroup(object):
         @staticmethod
         def deltachunk(pnode):
             pnode = pnode or node.nullid
             parentrev = rlog.rev(pnode)
             r = parentrev + 1
             if r >= len(rlog):
                 return {}
             if optimaldelta:
                 deltaparent = parentrev
             else:
                 # suboptimal deltaparent
                 deltaparent = min(0, parentrev)
             return {'node': rlog.node(r), 'p1': pnode, 'p2': node.nullid,
                     'cs': rlog.node(rlog.linkrev(r)), 'flags': rlog.flags(r),
                     'deltabase': rlog.node(deltaparent),
                     'delta': rlog.revdiff(deltaparent, r)}
 
     def linkmap(lnode):
         return rlog.rev(lnode)
 
     dlog = newrevlog(destname, recreate=True)
     dlog.addgroup(dummychangegroup(), linkmap, tr)
     return dlog
 
 def lowlevelcopy(rlog, tr, destname=b'_destrevlog.i'):
     '''Like addgroupcopy, but use the low level revlog._addrevision directly.
 
     It exercises some code paths that are hard to reach easily otherwise.
     '''
     dlog = newrevlog(destname, recreate=True)
     for r in rlog:
         p1 = rlog.node(r - 1)
         p2 = node.nullid
         if r == 0:
             text = rlog.revision(r, raw=True)
             cachedelta = None
         else:
             # deltaparent is more interesting if it has the EXTSTORED flag.
             deltaparent = max([0] + [p for p in range(r - 2) if rlog.flags(p)])
             text = None
             cachedelta = (deltaparent, rlog.revdiff(deltaparent, r))
         flags = rlog.flags(r)
         ifh = dlog.opener(dlog.indexfile, 'a+')
         dfh = None
         if not dlog._inline:
             dfh = dlog.opener(dlog.datafile, 'a+')
         dlog._addrevision(rlog.node(r), text, tr, r, p1, p2, flags, cachedelta,
                           ifh, dfh)
     return dlog
 
 # Utilities to generate revisions for testing
 
 def genbits(n):
     '''Given a number n, generate (2 ** (n * 2) + 1) numbers in range(2 ** n).
     i.e. the generated numbers have a width of n bits.
 
     The combination of two adjacent numbers will cover all possible cases.
     That is to say, given any x, y where both x, and y are in range(2 ** n),
     there is an x followed immediately by y in the generated sequence.
     '''
     m = 2 ** n
 
     # Gray Code. See https://en.wikipedia.org/wiki/Gray_code
     gray = lambda x: x ^ (x >> 1)
+    reversegray = dict((gray(i), i) for i in range(m))
 
     # Generate (n * 2) bit gray code, yield lower n bits as X, and look for
     # the next unused gray code where higher n bits equal to X.
 
     # For gray codes whose higher bits are X, a[X] of them have been used.
     a = [0] * m
 
     # Iterate from 0.
     x = 0
     yield x
     for i in range(m * m):
+        x = reversegray[x]
         y = gray(a[x] + x * m) & (m - 1)
+        assert a[x] < m
         a[x] += 1
         x = y
         yield x
 
 def gentext(rev):
     '''Given a revision number, generate dummy text'''
     return b''.join(b'%d\n' % j for j in range(-1, rev % 5))
 
 def writecases(rlog, tr):
     '''Write some revisions interested to the test.
 
     The test is interested in 3 properties of a revision:
 
         - Is it a delta or a full text? (isdelta)
           This is to catch some delta application issues.
         - Does it have a flag of EXTSTORED? (isext)
           This is to catch some flag processor issues. Especially when
           interacted with revlog deltas.
         - Is its text empty? (isempty)
           This is less important. It is intended to try to catch some careless
           checks like "if text" instead of "if text is None". Note: if flag
           processor is involved, raw text may be not empty.
 
     Write 65 revisions. So that all combinations of the above flags for
     adjacent revisions are covered. That is to say,
 
         len(set(
             (r.delta, r.ext, r.empty, (r+1).delta, (r+1).ext, (r+1).empty)
             for r in range(len(rlog) - 1)
            )) is 64.
 
     Where "r.delta", "r.ext", and "r.empty" are booleans matching properties
     mentioned above.
 
     Return expected [(text, rawtext)].
     '''
     result = []
     for i, x in enumerate(genbits(3)):
         isdelta, isext, isempty = bool(x & 1), bool(x & 2), bool(x & 4)
         if isempty:
             text = b''
         else:
             text = gentext(i)
         rev = appendrev(rlog, text, tr, isext=isext, isdelta=isdelta)
 
         # Verify text, rawtext, and rawsize
         if isext:
             rawtext = writeprocessor(None, text)[0]
         else:
             rawtext = text
         if rlog.rawsize(rev) != len(rawtext):
             abort('rev %d: wrong rawsize' % rev)
         if rlog.revision(rev, raw=False) != text:
             abort('rev %d: wrong text' % rev)
         if rlog.revision(rev, raw=True) != rawtext:
             abort('rev %d: wrong rawtext' % rev)
         result.append((text, rawtext))
 
         # Verify flags like isdelta, isext work as expected
         if bool(rlog.deltaparent(rev) > -1) != isdelta:
             abort('rev %d: isdelta is ineffective' % rev)
         if bool(rlog.flags(rev)) != isext:
             abort('rev %d: isext is ineffective' % rev)
     return result
 
 # Main test and checking
 
 def checkrevlog(rlog, expected):
     '''Check if revlog has expected contents. expected is [(text, rawtext)]'''
     # Test using different access orders. This could expose some issues
     # depending on revlog caching (see revlog._cache).
     for r0 in range(len(rlog) - 1):
         r1 = r0 + 1
         for revorder in [[r0, r1], [r1, r0]]:
             for raworder in [[True], [False], [True, False], [False, True]]:
                 nlog = newrevlog()
                 for rev in revorder:
                     for raw in raworder:
                         t = nlog.revision(rev, raw=raw)
                         if t != expected[rev][int(raw)]:
                             abort('rev %d: corrupted %stext'
                                   % (rev, raw and 'raw' or ''))
 
 def maintest():
     expected = rl = None
     with newtransaction() as tr:
         rl = newrevlog(recreate=True)
         expected = writecases(rl, tr)
         checkrevlog(rl, expected)
         print('local test passed')
         # Copy via revlog.addgroup
         rl1 = addgroupcopy(rl, tr)
         checkrevlog(rl1, expected)
         rl2 = addgroupcopy(rl, tr, optimaldelta=False)
         checkrevlog(rl2, expected)
         print('addgroupcopy test passed')
         # Copy via revlog.clone
         rl3 = newrevlog(name='_destrevlog3.i', recreate=True)
         rl.clone(tr, rl3)
         checkrevlog(rl3, expected)
         print('clone test passed')
         # Copy via low-level revlog._addrevision
         rl4 = lowlevelcopy(rl, tr)
         checkrevlog(rl4, expected)
         print('lowlevelcopy test passed')
 
 try:
     maintest()
 except Exception as ex:
     abort('crashed: %s' % ex)