Fix bug in duplicate detection.
Each node is written to disk as a list of (path, node pointer) pairs. The duplicate detection code was considering the node's children and the node's name. If we only look for the children, we can find much more duplicates. Previous duplicate detection went from 424 nodes to 127. New duplicate detection reduces to 48 nodes. With this better duplicate detection, the prefix compression doesn't appear to be useful anymore. comment it out. Trims an extra 40 bytes off my sample data.
This commit is contained in:
James Bowes
parent
a8a7fd57f6
commit
227e8de979
2 changed files with 71 additions and 106 deletions
2
.gitignore
vendored
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2
.gitignore
vendored
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@ -0,0 +1,2 @@
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unpack
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*.sw?
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169
thing.rb
169
thing.rb
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@ -45,109 +45,47 @@ class BitWriter
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end
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end
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class Children
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attr_accessor :children, :written
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def initialize()
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@children = []
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@written = false
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end
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def each()
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@children.each do |child|
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yield child
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end
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end
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def collect()
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@children.each do |child|
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yield child
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end
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end
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def length()
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@children.length
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end
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def [](i)
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@children[i]
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end
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def []=(i, val)
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@children[i] = val
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end
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def <<(other)
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@children << other
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end
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def join(str)
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@children.join(str)
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end
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def signature
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@children.sort! do |a, b|
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a.path <=> b.path
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end
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"[" + @children.collect { |x| x.path + x.signature }.join("|") + "]"
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end
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end
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class Node
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attr_accessor :path, :children, :de_duped, :offset
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attr_accessor :children, :de_duped, :offset, :written
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def initialize(path)
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@path = path
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@children = Children.new
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@sig = nil
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@children = {}
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@de_duped = false
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@offset = ran_char(2)
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end
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def has_key?(key)
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@children.each do |child|
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if child.path == key
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return true
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end
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end
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return false
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@children.has_key? key
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end
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def get_child(name)
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@children.each do |child|
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if child.path == name
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return child
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end
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end
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return nil
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@children[name]
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end
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def de_duped=(val)
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@de_duped = val
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@children.each do |child|
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@children.each do |key, child|
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child.de_duped = true
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end
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end
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def signature()
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if @sig.nil?
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@sig = @children.signature
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def signature
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sorted = @children.keys.sort do |a, b|
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a <=> b
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end
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@sig
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"[" + sorted.collect { |key| key + @children[key].signature }.join("|") + "]"
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end
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def flatten()
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flat = [self]
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@children.each do |child|
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@children.each do |key, child|
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flat += child.flatten
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end
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flat
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end
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def to_json(*a)
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{
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@path => @children
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}.to_json(*a)
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@children.to_json(*a)
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end
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end
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@ -168,7 +106,7 @@ def mk_hash(sgmts, parent)
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segment = sgmts.shift
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return parent if segment.nil?
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unless parent.has_key?(segment)
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parent.children << mk_hash(sgmts, Node.new(segment))
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parent.children[segment] = mk_hash(sgmts, Node.new(segment))
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else
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mk_hash(sgmts, parent.get_child(segment))
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# else
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@ -178,35 +116,51 @@ def mk_hash(sgmts, parent)
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end
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def compress_prefix(parent)
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parent.children.each do |child|
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parent.children.keys.each do |key|
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child = parent.children[key]
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compress_prefix(child)
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if child.children.length == 1
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puts "compressing #{key} and #{child.children.keys[0]}"
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new_key = key + "/" + child.children.keys[0]
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parent.children[new_key] = child
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child.children = child.children.values[0].children
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parent.children.delete(key)
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end
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if parent.children.length == 1
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puts "compressing #{parent.path} and #{parent.children[0].path}"
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parent.path += "/" + parent.children[0].path
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parent.children = parent.children[0].children
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end
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return parent
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end
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def replace(tree, old, new)
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tree.flatten.uniq.each do |node|
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node.children.keys.each do |key|
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if node.children[key] == old
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node.children[key] = new
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end
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end
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end
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end
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# given a tree of nodes, try and find branches that match the children of node.
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# if found, replace those branches with node's children
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def de_dupe(tree, node)
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tree.flatten.each do |sub_tree|
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if sub_tree.children == node.children
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tree.flatten.uniq.each do |sub_tree|
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if sub_tree == node
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# nothing
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elsif node.signature == sub_tree.signature
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sub_tree.de_duped = true
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sub_tree.children = node.children
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replace(tree, sub_tree, node)
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puts "Found dupe! " + node.signature unless node.signature == "[]"
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end
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end
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end
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def de_dupe_driver(tree)
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before = tree.flatten.length
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tree.flatten.each do |node|
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de_dupe(tree, node) unless node.de_duped
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end
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puts "Total nodes Before: #{before} After: #{tree.flatten.uniq.length}"
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end
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# simulate random file offsets
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@ -221,22 +175,16 @@ def binary_write(file, parent, string_huff, node_huff)
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#offset to child node indicies
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# not needed, can just go write to children indicies
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#file.write(ran_char)
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if parent.children.written
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puts "not writing children of #{parent.path}"
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if parent.written
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return
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end
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# number of paths
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length = parent.children.length.to_s
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# path_count = (3 - length.length).times.collect { |i| "0" }.join + length
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# file.write(path_count)
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# puts "CHILD COUNT: " + parent.children.length.to_s
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parent.children.each do |child|
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parent.children.each do |path, child|
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# puts "PATH: " + child.path
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# file.write(child.path)
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# file.write("\0")
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# index of path string
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file.write_bits(string_huff.encode(child.path))
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file.write_bits(string_huff.encode(path))
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# offset to node
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# index of node, that is.
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file.write_bits(node_huff.encode(child))
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@ -244,16 +192,15 @@ def binary_write(file, parent, string_huff, node_huff)
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# reserve null byte for end of node info
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# 3 0s are reserved in our name huffman table to denote end of node
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file.write_bits("000")
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parent.children.each do |child|
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parent.children.each do |path, child|
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binary_write(file, child, string_huff, node_huff)
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child.children.written = true
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child.written = true
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end
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end
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def write_strings(file, strings)
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string_io = StringIO.new()
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strings.each_key do |string|
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puts "STRING: " + string
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string_io.write(string)
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string_io.write("\0")
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end
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@ -263,22 +210,38 @@ end
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def collect_strings(parent)
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strings = {}
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parent.flatten.each do |node|
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strings[node.path] = [0, ran_char(1)] unless strings.has_key? node.path
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strings[node.path][0] += 1
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parent.flatten.uniq.each do |node|
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node.children.each_key do |key|
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strings[key] ||= 0
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strings[key] += 1
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end
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end
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strings
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end
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def build_huffman_for_strings(parent)
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nodes = parent.flatten.uniq
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paths = nodes.collect {|node| node.path}
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table = HuffmanEncoding.new paths
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paths = []
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parent.flatten.uniq.each do |node|
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node.children.each_key {|key| paths << key}
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end
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HuffmanEncoding.new paths
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end
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def build_huffman_for_nodes(parent)
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nodes = parent.flatten
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table = HuffmanEncoding.new nodes
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nodes = parent.flatten.uniq
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refs = {}
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nodes.each do |node|
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node.children.each do |key, node|
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refs[node] ||= 0
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refs[node] += 1
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end
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end
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refs[parent] = 1
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expanded = []
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refs.each do |node, freq|
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freq.times {expanded << node}
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end
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table = HuffmanEncoding.new expanded
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end
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if $0 == __FILE__
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@ -322,7 +285,7 @@ if $0 == __FILE__
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# prime the signatures
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parent.signature
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de_dupe_driver(parent)
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parent = compress_prefix(parent)
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# parent = compress_prefix(parent)
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string_huff = build_huffman_for_strings(parent)
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node_huff = build_huffman_for_nodes(parent)
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