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hashtree: a couple of tiny improvements

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* calculate depth-first with math instead of traversing the actual tree
 * don't mark a node with a red dot if you instead compare it with an extant hash value (tiny optimization)
 * edit a comment about checking the root node
This commit is contained in:
Zooko O'Whielacronx 2009-04-03 16:30:37 -07:00
parent b12a7f9ee8
commit d381bdc905
1 changed files with 15 additions and 17 deletions
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32
src/allmydata/hashtree.py
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@ -1,5 +1,7 @@
# -*- test-case-name: allmydata.test.test_hashtree -*-
from allmydata.util import mathutil # from the pyutil library
"""
Read and write chunks from files.
@ -162,14 +164,10 @@ class CompleteBinaryTreeMixin:
def get_leaf(self, leafnum):
return self[self.first_leaf_num + leafnum]
def depth_of(self, i):
"""Return the depth or level of the given node. Level 0 contains node
Level 1 contains nodes 1 and 2. Level 2 contains nodes 3,4,5,6."""
depth = 0
while i != 0:
depth += 1
i = self.parent(i)
return depth
def depth_of(i):
"""Return the depth or level of the given node. Level 0 contains node 0
Level 1 contains nodes 1 and 2. Level 2 contains nodes 3,4,5,6."""
return mathutil.log_floor(i+1, 2)
def empty_leaf_hash(i):
return tagged_hash('Merkle tree empty leaf', "%d" % i)
@ -411,7 +409,7 @@ class IncompleteHashTree(CompleteBinaryTreeMixin, list):
# to the root, discard every hash we've added.
try:
num_levels = self.depth_of(len(self)-1)
num_levels = depth_of(len(self)-1)
# hashes_to_check[level] is set(index). This holds the "red dots"
# described above
hashes_to_check = [set() for level in range(num_levels+1)]
@ -419,8 +417,7 @@ class IncompleteHashTree(CompleteBinaryTreeMixin, list):
# first we provisionally add all hashes to the tree, comparing
# any duplicates
for i,h in new_hashes.iteritems():
level = self.depth_of(i)
hashes_to_check[level].add(i)
level = depth_of(i)
if self[i]:
if self[i] != h:
@ -430,6 +427,7 @@ class IncompleteHashTree(CompleteBinaryTreeMixin, list):
base32.b2a(self[i]),
self._name_hash(i)))
else:
hashes_to_check[level].add(i)
self[i] = h
remove_upon_failure.add(i)
@ -438,11 +436,11 @@ class IncompleteHashTree(CompleteBinaryTreeMixin, list):
while this_level:
i = this_level.pop()
if i == 0:
# The root has no sibling. How lonely. TODO: consider
# setting the root in our constructor, then throw
# NotEnoughHashesError here, because if we've
# generated the root from below, we don't have
# anything to validate it against.
# The root has no sibling. How lonely. You can't
# really *check* the root; you either accept it
# because the caller told you what it is by including
# it in hashes, or you accept it because you
# calculated it from its two children.
continue
siblingnum = self.sibling(i)
if self[siblingnum] is None:
@ -460,7 +458,7 @@ class IncompleteHashTree(CompleteBinaryTreeMixin, list):
else:
self[parentnum] = new_parent_hash
remove_upon_failure.add(parentnum)
parent_level = self.depth_of(parentnum)
parent_level = depth_of(parentnum)
assert parent_level == level-1
hashes_to_check[parent_level].add(parentnum)