* lib/prime.rb (Prime#prime_division): now decomposes

  negative integer into a decomposition with element [-1, 1].

* test/test_prime.rb: test for it.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@24091 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,10 @@
+Mon Jul 13 22:49:50 2009  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
+
+	* lib/prime.rb (Prime#prime_division): now decomposes
+	  negative integer into a decomposition with element [-1, 1].
+
+	* test/test_prime.rb: test for it.
+
 Mon Jul 13 22:28:03 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* io.c (pipe_open): handles leaked on win32 when an error occurs.

lib/prime.rb

@@ -194,7 +194,12 @@ def int_from_prime_division(pd)
   #
   def prime_division(value, generator= Prime::Generator23.new)
     raise ZeroDivisionError if value == 0
-    pv = []
+    if value < 0
+      value = -value
+      pv = [[-1, 1]]
+    else
+      pv = []
+    end
     for prime in generator
       count = 0
       while (value1, mod = value.divmod(prime)

test/test_prime.rb

@@ -98,10 +98,15 @@ class TestInteger < Test::Unit::TestCase
     def test_prime_division
       pd = PRIMES.inject(&:*).prime_division
       assert_equal PRIMES.map{|p| [p, 1]}, pd
+
+      pd = (-PRIMES.inject(&:*)).prime_division
+      assert_equal [-1, *PRIMES].map{|p| [p, 1]}, pd
     end
 
     def test_from_prime_division
       assert_equal PRIMES.inject(&:*), Integer.from_prime_division(PRIMES.map{|p| [p,1]})
+
+      assert_equal -PRIMES.inject(&:*), Integer.from_prime_division([[-1, 1]] + PRIMES.map{|p| [p,1]})
     end
 
     def test_prime?