1 files changed, 53 insertions, 0 deletions
diff --git a/tool/lrama/lib/lrama/digraph.rb b/tool/lrama/lib/lrama/digraph.rb
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+++ b/tool/lrama/lib/lrama/digraph.rb
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+module Lrama
+  # Algorithm Digraph of https://dl.acm.org/doi/pdf/10.1145/69622.357187 (P. 625)
+  class Digraph
+    def initialize(sets, relation, base_function)
+      # X in the paper
+      @sets = sets
+      # R in the paper
+      @relation = relation
+      # F' in the paper
+      @base_function = base_function
+      # S in the paper
+      @stack = []
+      # N in the paper
+      @h = Hash.new(0)
+      # F in the paper
+      @result = {}
+    end
+
+    def compute
+      @sets.each do |x|
+        next if @h[x] != 0
+        traverse(x)
+      end
+
+      return @result
+    end
+
+    private
+
+    def traverse(x)
+      @stack.push(x)
+      d = @stack.count
+      @h[x] = d
+      @result[x] = @base_function[x] # F x = F' x
+
+      @relation[x] && @relation[x].each do |y|
+        traverse(y) if @h[y] == 0
+        @h[x] = [@h[x], @h[y]].min
+        @result[x] |= @result[y] # F x = F x + F y
+      end
+
+      if @h[x] == d
+        while true do
+          z = @stack.pop
+          @h[z] = Float::INFINITY
+          @result[z] = @result[x] # F (Top of S) = F x
+
+          break if z == x
+        end
+      end
+    end
+  end
+end