nobu	2017-04-16 00:29:09 +0900 (Sun, 16 Apr 2017)

  New Revision: 58366

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=58366

  Log:
    bignum.c: fix inexact estimation
    
    * bignum.c (estimate_initial_sqrt): estimated square root is
      inexact if it is not equal to its ceil, needs Newton's method.
      [ruby-core:80696] [Bug #13440]

  Modified files:
    trunk/bignum.c
    trunk/test/ruby/test_integer.rb
Index: bignum.c
===================================================================
--- bignum.c	(revision 58365)
+++ bignum.c	(revision 58366)
@@ -6824,6 +6824,9 @@ estimate_initial_sqrt(VALUE *xp, const s https://github.com/ruby/ruby/blob/trunk/bignum.c#L6824
 	if (lowbits || (lowbits = !bary_zero_p(nds, len-dbl_per_bdig)))
 	    ++d;
     }
+    else {
+	lowbits = 1;
+    }
     rshift /= 2;
     rshift += (2-(len&1))*BITSPERDIG/2;
     if (rshift >= 0) {
Index: test/ruby/test_integer.rb
===================================================================
--- test/ruby/test_integer.rb	(revision 58365)
+++ test/ruby/test_integer.rb	(revision 58366)
@@ -488,5 +488,17 @@ class TestInteger < Test::Unit::TestCase https://github.com/ruby/ruby/blob/trunk/test/ruby/test_integer.rb#L488
       assert_equal(exact, Integer.sqrt(x+1), "10**#{i}+1")
       assert_equal(exact-1, Integer.sqrt(x-1), "10**#{i}-1")
     end
+
+    bug13440 = '[ruby-core:80696] [Bug #13440]'
+    too_big = []
+    too_small = []
+    0.step(to: 50, by: 0.001) do |i|
+      n = (10**i).to_i
+      int_root = Integer.sqrt(n)
+      too_big   << n  if int_root*int_root > n
+      too_small << n  if (int_root+1)*(int_root+1) <= n
+    end
+    assert_empty(too_big, bug13440)
+    assert_empty(too_small, bug13440)
   end
 end

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