lib/eratostene_sieve.rb in eratostene_sieve-0.0.2.alpha vs lib/eratostene_sieve.rb in eratostene_sieve-0.0.3.alpha

@@ -1,40 +1,55 @@
 require 'eratostene_sieve/version'
 require 'eratostene_sieve/railtie' if defined? Rails
 
 # Utility to get:
 # - nth_prime(n): the nth prime number.
-# - prime_serie: an enumerator on prime number serie.
+# - enumerator: an enumerator on prime number serie.
 module EratosteneSieve
   Inf = 1.0 / 0.0
 
   def self.nth_prime(index)
-    return first_primes[index] if index < first_primes.size
-    counter = first_primes.size - 1
+    return first_primes[index - 1] if index <= first_primes.size
+    counter = first_primes.size
     ((first_primes.last + 2)..Inf).step(2) do |candidate|
       (2..((candidate**0.5).to_i)).each do |m|
         break if candidate % m == 0
         counter += 1 if m == (candidate**0.5).to_i
       end
       return candidate.to_i if counter == index
     end
   end
 
-  def self.prime_serie
+  def self.enumerator
     Enumerator.new do |y|
-      a = 1
-      b = 2
-      index = 2
+      a = 2
+      b = 3
+      index = 3
       loop do
         y << a
         a, b = b, nth_prime(index)
         index += 1
       end
     end
   end
 
+  def self.serie(options = {})
+    from = options[:from] || 1
+    up_to = options[:up_to] || 10
+    fail "from option must be an integer, given #{from}." unless from.is_a?(Integer)
+    fail "up_to option must be an integer, given #{up_to}." unless up_to.is_a?(Integer)
+    fail "from option must be > 0, given #{from}." if from < 1
+    serie = []
+    enumerator = EratosteneSieve.enumerator
+    lowest_index = from < up_to ? from : up_to
+    (lowest_index - 1).times { enumerator.next }
+    ((from - up_to).abs + 1).times { serie << enumerator.next }
+    serie.reverse! if from > up_to
+    serie
+  end
+
   private
 
   def self.first_primes
-    @first_primes ||= [1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
+    @first_primes ||= [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31]
   end
 end