range.c: fix fixnum loop condition

* range.c (range_step): FIXABLE + FIXABLE never overflow, but may
  not be FIXABLE.  [Feature #12912]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63207 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

range.c

@@ -402,11 +402,10 @@ range_step(int argc, VALUE *argv, VALUE range)
 
     if (FIXNUM_P(b) && NIL_P(e) && FIXNUM_P(step)) {
 	long i = FIX2LONG(b), unit = FIX2LONG(step);
-	while (1) {
+	do {
 	    rb_yield(LONG2FIX(i));
-	    if (i + unit < i) break;
-	    i += unit;
-	}
+	    i += unit;          /* FIXABLE+FIXABLE never overflow */
+	} while (FIXABLE(i));
 	b = LONG2NUM(i);
 
 	for (;; b = rb_funcallv(b, id_succ, 0, 0))

test/ruby/test_range.rb

@@ -3,6 +3,7 @@ require 'test/unit'
 require 'delegate'
 require 'timeout'
 require 'bigdecimal'
+require 'rbconfig/sizeof'
 
 class TestRange < Test::Unit::TestCase
   def test_new
@@ -244,6 +245,11 @@ class TestRange < Test::Unit::TestCase
     (2**32-1 .. ).step(2) {|x| a << x; break if a.size == 2 }
     assert_equal([4294967295, 4294967297], a)
 
+    a = []
+    max = RbConfig::LIMITS["FIXNUM_MAX"]
+    (max..).step {|x| a << x; break if a.size == 2 }
+    assert_equal([max, max+1], a)
+
     o1 = Object.new
     o2 = Object.new
     def o1.<=>(x); -1; end