Fix floor when ndigits is large

[Bug #20654]

This commit fixes Integer#floor and Float#floor when the number is
negative and ndigits is large such that 10**ndigits is a bignum.

Previously, it would return 0 in such cases. However, this would cause
unexpected behaviour such as:

    puts -1.floor(-5) # => -100000
    puts -1.floor(-10) # => -10000000000
    puts -1.floor(-20) # => 0

This commit changes the last result so that it will return
-100000000000000000000.

2 files changed, 8 insertions, 0 deletions

diff --git a/test/ruby/test_float.rb b/test/ruby/test_float.rb
index b91b904d1e..78c37cd3ee 100644
--- a/test/ruby/test_float.rb
+++ b/test/ruby/test_float.rb
@@ -530,6 +530,10 @@ class TestFloat < Test::Unit::TestCase
     assert_raise(TypeError) {1.0.floor(nil)}
     def (prec = Object.new).to_int; 2; end
     assert_equal(0.99, 0.998.floor(prec))
+
+    assert_equal(-10000000000, -1.0.floor(-10), "[Bug #20654]")
+    assert_equal(-100000000000000000000, -1.0.floor(-20), "[Bug #20654]")
+    assert_equal(-100000000000000000000000000000000000000000000000000, -1.0.floor(-50), "[Bug #20654]")
   end
 
   def test_ceil_with_precision
diff --git a/test/ruby/test_integer.rb b/test/ruby/test_integer.rb
index 0f33fde78a..3dfd0e2d7b 100644
--- a/test/ruby/test_integer.rb
+++ b/test/ruby/test_integer.rb
@@ -465,6 +465,10 @@ class TestInteger < Test::Unit::TestCase
 
     assert_int_equal(1111_1111_1111_1111_1111_1111_1111_1111, 1111_1111_1111_1111_1111_1111_1111_1111.floor(1))
     assert_int_equal(10**400, (10**400).floor(1))
+
+    assert_int_equal(-10000000000, -1.floor(-10), "[Bug #20654]")
+    assert_int_equal(-100000000000000000000, -1.floor(-20), "[Bug #20654]")
+    assert_int_equal(-100000000000000000000000000000000000000000000000000, -1.floor(-50), "[Bug #20654]")
   end
 
   def test_ceil