Fix `Integer.sqrt` to never exceed actual value

`Integer.sqrt` uses `sqrt(3)` from libm for small values.
This method must return a value less than or equal to the actual integer
square root, but libm's sqrt does not always guarantee that.

This change corrects that by decrementing the result if necessary.

Fixes [Bug #21217]

1 files changed, 4 insertions, 0 deletions

diff --git a/test/ruby/test_integer.rb b/test/ruby/test_integer.rb
index 1dbb3fbb45..fb7aabba35 100644
--- a/test/ruby/test_integer.rb
+++ b/test/ruby/test_integer.rb
@@ -708,6 +708,10 @@ class TestInteger < Test::Unit::TestCase
     assert_equal(x, Integer.sqrt(x ** 2), "[ruby-core:95453]")
   end
 
+  def test_bug_21217
+    assert_equal(0x10000 * 2**10, Integer.sqrt(0x100000008 * 2**20))
+  end
+
   def test_fdiv
     assert_equal(1.0, 1.fdiv(1))
     assert_equal(0.5, 1.fdiv(2))