Implement 1.9 Integer#round

Doesn't follow MRI's goofy NUM2INT RangeError logic.

kernel/common/integer.rb

@@ -29,7 +29,6 @@ def to_i
   end
 
   alias_method :to_int, :to_i
-  alias_method :round, :to_i
   alias_method :truncate, :to_i
   alias_method :ceil, :to_i
   alias_method :floor, :to_i

kernel/common/integer18.rb

@@ -0,0 +1,3 @@
+class Integer
+  alias_method :round, :to_i
+end

kernel/common/integer19.rb

@@ -1,4 +1,33 @@
 class Integer
+  def round(ndigits=undefined)
+    return self if ndigits.equal? undefined
+
+    ndigits = Rubinius::Type.coerce_to(ndigits, Integer, :to_int)
+    if ndigits > 0
+      to_f
+    elsif ndigits == 0
+      self
+    else
+      ndigits = -ndigits
+
+      # We want to return 0 if 10 ** ndigits / 2 > self.abs, or, taking
+      # log_256 of both sides, if log_256(10 ** ndigits / 2) > self.size.
+      # We have log_256(10) > 0.415241 and log_256(2) = 0.125, so:
+      return 0 if 0.415241 * ndigits - 0.125 > size
+
+      f = 10 ** ndigits
+      h = f / 2
+      r = self % f
+      n = self - r
+
+      unless self < 0 ? r <= h : r < h
+        n = n + f
+      end
+
+      n
+    end
+  end
+
   alias_method :magnitude, :abs
 
   #

kernel/common/load_order18.txt

@@ -34,6 +34,7 @@ numeric18.rbc
 ctype.rbc
 precision.rbc
 integer.rbc
+integer18.rbc
 bignum.rbc
 block_environment.rbc
 bytearray.rbc

spec/tags/19/ruby/core/integer/round_tags.txt

@@ -1,6 +1 @@
-fails:Integer#round rounds itself as a float if passed a positive precision
-fails:Integer#round returns itself if passed zero
-fails:Integer#round returns itself rounded if passed a negative value
-fails:Integer#round returns 0 if passed a big negative value
 fails:Integer#round raises a RangeError when its argument can not be converted to a Fixnum
-fails:Integer#round raises a TypeError when its argument can not be converted to an Integer