/usr/lib/ruby/vendor_ruby/diff/lcs/internals.rb is in ruby-diff-lcs 1.2.5-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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class << Diff::LCS
def diff_traversal(method, seq1, seq2, callbacks, &block)
callbacks = callbacks_for(callbacks)
case method
when :diff
traverse_sequences(seq1, seq2, callbacks)
when :sdiff
traverse_balanced(seq1, seq2, callbacks)
end
callbacks.finish if callbacks.respond_to? :finish
if block
callbacks.diffs.map do |hunk|
if hunk.kind_of? Array
hunk.map { |hunk_block| block[hunk_block] }
else
block[hunk]
end
end
else
callbacks.diffs
end
end
private :diff_traversal
end
module Diff::LCS::Internals # :nodoc:
end
class << Diff::LCS::Internals
# Compute the longest common subsequence between the sequenced
# Enumerables +a+ and +b+. The result is an array whose contents is such
# that
#
# result = Diff::LCS::Internals.lcs(a, b)
# result.each_with_index do |e, i|
# assert_equal(a[i], b[e]) unless e.nil?
# end
def lcs(a, b)
a_start = b_start = 0
a_finish = a.size - 1
b_finish = b.size - 1
vector = []
# Prune off any common elements at the beginning...
while ((a_start <= a_finish) and (b_start <= b_finish) and
(a[a_start] == b[b_start]))
vector[a_start] = b_start
a_start += 1
b_start += 1
end
b_start = a_start
# Now the end...
while ((a_start <= a_finish) and (b_start <= b_finish) and
(a[a_finish] == b[b_finish]))
vector[a_finish] = b_finish
a_finish -= 1
b_finish -= 1
end
# Now, compute the equivalence classes of positions of elements.
b_matches = position_hash(b, b_start..b_finish)
thresh = []
links = []
string = a.kind_of?(String)
(a_start .. a_finish).each do |i|
ai = string ? a[i, 1] : a[i]
bm = b_matches[ai]
k = nil
bm.reverse_each do |j|
if k and (thresh[k] > j) and (thresh[k - 1] < j)
thresh[k] = j
else
k = replace_next_larger(thresh, j, k)
end
links[k] = [ (k > 0) ? links[k - 1] : nil, i, j ] unless k.nil?
end
end
unless thresh.empty?
link = links[thresh.size - 1]
while not link.nil?
vector[link[1]] = link[2]
link = link[0]
end
end
vector
end
# This method will analyze the provided patchset to provide a
# single-pass normalization (conversion of the array form of
# Diff::LCS::Change objects to the object form of same) and detection of
# whether the patchset represents changes to be made.
def analyze_patchset(patchset, depth = 0)
raise "Patchset too complex" if depth > 1
has_changes = false
# Format:
# [ # patchset
# # hunk (change)
# [ # hunk
# # change
# ]
# ]
patchset = patchset.map do |hunk|
case hunk
when Diff::LCS::Change
has_changes ||= !hunk.unchanged?
hunk
when Array
# Detect if the 'hunk' is actually an array-format
# Change object.
if Diff::LCS::Change.valid_action? hunk[0]
hunk = Diff::LCS::Change.from_a(hunk)
has_changes ||= !hunk.unchanged?
hunk
else
with_changes, hunk = analyze_patchset(hunk, depth + 1)
has_changes ||= with_changes
hunk.flatten
end
else
raise ArgumentError, "Cannot normalise a hunk of class #{hunk.class}."
end
end
[ has_changes, patchset.flatten(1) ]
end
# Examine the patchset and the source to see in which direction the
# patch should be applied.
#
# WARNING: By default, this examines the whole patch, so this could take
# some time. This also works better with Diff::LCS::ContextChange or
# Diff::LCS::Change as its source, as an array will cause the creation
# of one of the above.
#
# Note: This will be deprecated as a public function in a future release.
def intuit_diff_direction(src, patchset, limit = nil)
string = src.kind_of?(String)
count = left_match = left_miss = right_match = right_miss = 0
patchset.each do |change|
count += 1
case change
when Diff::LCS::ContextChange
le = string ? src[change.old_position, 1] : src[change.old_position]
re = string ? src[change.new_position, 1] : src[change.new_position]
case change.action
when '-' # Remove details from the old string
if le == change.old_element
left_match += 1
else
left_miss += 1
end
when '+'
if re == change.new_element
right_match += 1
else
right_miss += 1
end
when '='
left_miss += 1 if le != change.old_element
right_miss += 1 if re != change.new_element
when '!'
if le == change.old_element
left_match += 1
else
if re == change.new_element
right_match += 1
else
left_miss += 1
right_miss += 1
end
end
end
when Diff::LCS::Change
# With a simplistic change, we can't tell the difference between
# the left and right on '!' actions, so we ignore those. On '='
# actions, if there's a miss, we miss both left and right.
element = string ? src[change.position, 1] : src[change.position]
case change.action
when '-'
if element == change.element
left_match += 1
else
left_miss += 1
end
when '+'
if element == change.element
right_match += 1
else
right_miss += 1
end
when '='
if element != change.element
left_miss += 1
right_miss += 1
end
end
end
break if (not limit.nil?) && (count > limit)
end
no_left = (left_match == 0) && (left_miss > 0)
no_right = (right_match == 0) && (right_miss > 0)
case [no_left, no_right]
when [false, true]
:patch
when [true, false]
:unpatch
else
case left_match <=> right_match
when 1
:patch
when -1
:unpatch
else
raise "The provided patchset does not appear to apply to the provided value as either source or destination value."
end
end
end
# Find the place at which +value+ would normally be inserted into the
# Enumerable. If that place is already occupied by +value+, do nothing
# and return +nil+. If the place does not exist (i.e., it is off the end
# of the Enumerable), add it to the end. Otherwise, replace the element
# at that point with +value+. It is assumed that the Enumerable's values
# are numeric.
#
# This operation preserves the sort order.
def replace_next_larger(enum, value, last_index = nil)
# Off the end?
if enum.empty? or (value > enum[-1])
enum << value
return enum.size - 1
end
# Binary search for the insertion point
last_index ||= enum.size
first_index = 0
while (first_index <= last_index)
i = (first_index + last_index) >> 1
found = enum[i]
if value == found
return nil
elsif value > found
first_index = i + 1
else
last_index = i - 1
end
end
# The insertion point is in first_index; overwrite the next larger
# value.
enum[first_index] = value
return first_index
end
private :replace_next_larger
# If +vector+ maps the matching elements of another collection onto this
# Enumerable, compute the inverse of +vector+ that maps this Enumerable
# onto the collection. (Currently unused.)
def inverse_vector(a, vector)
inverse = a.dup
(0...vector.size).each do |i|
inverse[vector[i]] = i unless vector[i].nil?
end
inverse
end
private :inverse_vector
# Returns a hash mapping each element of an Enumerable to the set of
# positions it occupies in the Enumerable, optionally restricted to the
# elements specified in the range of indexes specified by +interval+.
def position_hash(enum, interval)
string = enum.kind_of?(String)
hash = Hash.new { |h, k| h[k] = [] }
interval.each do |i|
k = string ? enum[i, 1] : enum[i]
hash[k] << i
end
hash
end
private :position_hash
end
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