probabilities.rb in games_dice-0.3.8

- old
+ new

@@ -181,22 +181,12 @@
       raise TypeError, "parameter to add_distributions is not a GamesDice::Probabilities"
     end
 
     combined_min = pd_a.min + pd_b.min
     combined_max = pd_a.max + pd_b.max
-    new_probs = Array.new( 1 + combined_max - combined_min, 0.0 )
-    probs_a, offset_a = pd_a.to_ao
-    probs_b, offset_b = pd_b.to_ao
 
-    probs_a.each_with_index do |pa,i|
-      probs_b.each_with_index do |pb,j|
-        k = i + j
-        pc = pa * pb
-        new_probs[ k ] += pc
-      end
-    end
-    GamesDice::Probabilities.new( new_probs, combined_min )
+    add_distributions_internal combined_min, combined_max, 1, pd_a, 1, pd_b
   end
 
   # Combines two distributions with multipliers to create a third, that represents the distribution
   # created when adding weighted results together.
   # @param [Integer] m_a Weighting for first distribution
@@ -215,22 +205,11 @@
     combined_min, combined_max = [
       m_a * pd_a.min + m_b * pd_b.min, m_a * pd_a.max + m_b * pd_b.min,
       m_a * pd_a.min + m_b * pd_b.max, m_a * pd_a.max + m_b * pd_b.max,
       ].minmax
 
-    new_probs = Array.new( 1 + combined_max - combined_min, 0.0 )
-    probs_a, offset_a = pd_a.to_ao
-    probs_b, offset_b = pd_b.to_ao
-
-    probs_a.each_with_index do |pa,i|
-      probs_b.each_with_index do |pb,j|
-        k = m_a * (i + offset_a) + m_b * (j + offset_b) - combined_min
-        pc = pa * pb
-        new_probs[ k ] += pc
-      end
-    end
-    GamesDice::Probabilities.new( new_probs, combined_min )
+    add_distributions_internal combined_min, combined_max, m_a, pd_a, m_b, pd_b
   end
 
   # Returns a symbol for the language name that this class is implemented in. The C version of the
   # code is noticeably faster when dealing with larger numbers of possible results.
   # @return [Symbol] Either :c or :ruby
@@ -244,24 +223,25 @@
   # @return [GamesDice::Probabilities] new distribution
   def repeat_sum n
     n = Integer( n )
     raise "Cannot combine probabilities less than once" if n < 1
     raise "Probability distribution too large" if ( n * @probs.count ) > 1000000
-    revbin = n.to_s(2).reverse.each_char.to_a.map { |c| c == '1' }
     pd_power = self
     pd_result = nil
-    max_power = revbin.count - 1
 
-    revbin.each_with_index do |use_power, i|
-      if use_power
+    use_power = 1
+    loop do
+      if ( use_power & n ) > 0
         if pd_result
           pd_result = GamesDice::Probabilities.add_distributions( pd_result, pd_power )
         else
           pd_result = pd_power
         end
       end
-      pd_power = GamesDice::Probabilities.add_distributions( pd_power, pd_power ) unless i == max_power
+      use_power = use_power << 1
+      break if use_power > n
+      pd_power = GamesDice::Probabilities.add_distributions( pd_power, pd_power )
     end
     pd_result
   end
 
   # Calculates distribution generated by summing best k results of n iterations
@@ -273,10 +253,12 @@
     n = Integer( n )
     k = Integer( k )
     raise "Cannot combine probabilities less than once" if n < 1
     # Technically this is a limitation of C code, but Ruby version is most likely slow and inaccurate beyond 170
     raise "Too many dice to calculate numbers of arrangements" if n > 170
+    check_keep_mode( kmode )
+
     if k >= n
       return repeat_sum( n )
     end
     new_probs = Array.new( @probs.count * k, 0.0 )
     new_offset = @offset * k
@@ -307,10 +289,25 @@
     GamesDice::Probabilities.new( new_probs, new_offset )
   end
 
   private
 
+  def self.add_distributions_internal combined_min, combined_max, m_a, pd_a, m_b, pd_b
+    new_probs = Array.new( 1 + combined_max - combined_min, 0.0 )
+    probs_a, offset_a = pd_a.to_ao
+    probs_b, offset_b = pd_b.to_ao
+
+    probs_a.each_with_index do |pa,i|
+      probs_b.each_with_index do |pb,j|
+        k = m_a * (i + offset_a) + m_b * (j + offset_b) - combined_min
+        pc = pa * pb
+        new_probs[ k ] += pc
+      end
+    end
+    GamesDice::Probabilities.new( new_probs, combined_min )
+  end
+
   def check_probs_array probs_array
     raise TypeError unless probs_array.is_a?( Array )
     probs_array.map!{ |n| Float(n) }
     total = probs_array.inject(0.0) do |t,x|
       if x < 0.0 || x > 1.0
@@ -323,45 +320,45 @@
     end
     probs_array
   end
 
   def calc_keep_distributions k, q, kmode
-    if kmode == :keep_best
-      keep_distributions = [ GamesDice::Probabilities.new( [1.0], q * k ) ]
-      if p_gt(q) > 0.0 && k > 1
-        kd_probabilities = given_ge( q + 1 )
-        (1...k).each do |n|
-          extra_o = GamesDice::Probabilities.new( [1.0], q * ( k - n ) )
-          n_probs = kd_probabilities.repeat_sum( n )
-          keep_distributions[n] = GamesDice::Probabilities.add_distributions( extra_o, n_probs )
-        end
+    kd_probabilities = calc_keep_definite_distributions q, kmode
+
+    keep_distributions = [ GamesDice::Probabilities.new( [1.0], q * k ) ]
+    if kd_probabilities && k > 1
+      (1...k).each do |n|
+        extra_o = GamesDice::Probabilities.new( [1.0], q * ( k - n ) )
+        n_probs = kd_probabilities.repeat_sum( n )
+        keep_distributions[n] = GamesDice::Probabilities.add_distributions( extra_o, n_probs )
       end
-    elsif kmode == :keep_worst
-      keep_distributions = [ GamesDice::Probabilities.new( [1.0], q * k ) ]
-      if p_lt(q) > 0.0 && k > 1
-        kd_probabilities = given_le( q - 1 )
-        (1...k).each do |n|
-          extra_o = GamesDice::Probabilities.new( [1.0], q * ( k - n ) )
-          n_probs = kd_probabilities.repeat_sum( n )
-          keep_distributions[n] = GamesDice::Probabilities.add_distributions( extra_o, n_probs )
-        end
-      end
-    else
-      raise "Keep mode #{kmode.inspect} not recognised"
     end
+
     keep_distributions
   end
 
+  def calc_keep_definite_distributions q, kmode
+    kd_probabilities = nil
+    case kmode
+    when :keep_best
+      p_definites = p_gt(q)
+      kd_probabilities = given_ge( q + 1 ) if p_definites > 0.0
+    when :keep_worst
+      p_definites = p_lt(q)
+      kd_probabilities = given_le( q - 1 ) if p_definites > 0.0
+    end
+    kd_probabilities
+  end
+
   def calc_p_table q, p_maybe, kmode
-    if kmode == :keep_best
+    case kmode
+    when :keep_best
       p_kept = p_gt(q)
       p_rejected = p_lt(q)
-    elsif kmode == :keep_worst
+    when :keep_worst
       p_kept = p_lt(q)
       p_rejected = p_gt(q)
-    else
-      raise "Keep mode #{kmode.inspect} not recognised"
     end
     [ p_rejected, p_maybe, p_kept ]
   end
 
   # Convert hash to array,offset notation
@@ -384,9 +381,13 @@
 
   def calc_expected
     total = 0.0
     @probs.each_with_index { |v,i| total += (i+@offset)*v }
     total
+  end
+
+  def check_keep_mode kmode
+    raise "Keep mode #{kmode.inspect} not recognised" unless [:keep_best,:keep_worst].member?( kmode )
   end
 
 end # class GamesDice::Probabilities
 
 # @!visibility private