diff --git a/ChangeLog b/ChangeLog index 3f63ebba08..ef1f3c90bc 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,10 @@ +Mon Jul 13 22:49:50 2009 Yuki Sonoda (Yugui) + + * 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 * io.c (pipe_open): handles leaked on win32 when an error occurs. diff --git a/lib/prime.rb b/lib/prime.rb index 50b78d9b0e..68253897ca 100644 --- a/lib/prime.rb +++ b/lib/prime.rb @@ -194,7 +194,12 @@ class Prime # 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) diff --git a/test/test_prime.rb b/test/test_prime.rb index e7c025a55a..307d53afb3 100644 --- a/test/test_prime.rb +++ b/test/test_prime.rb @@ -98,10 +98,15 @@ class TestPrime < 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?