Fix a bug that Math.round() returns incorrect results for huge integers.

test/mjsunit/math-round.js

+// Copyright 2010 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
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+//     * Redistributions in binary form must reproduce the above
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+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+assertEquals(0, Math.round(0));
+assertEquals(-0, Math.round(-0));
+assertEquals(Infinity, Math.round(Infinity));
+assertEquals(-Infinity, Math.round(-Infinity));
+assertNaN(Math.round(NaN));
+
+assertEquals(1, Math.round(0.5));
+assertEquals(1, Math.round(0.7));
+assertEquals(1, Math.round(1));
+assertEquals(1, Math.round(1.1));
+assertEquals(1, Math.round(1.49999));
+assertEquals(-Infinity, 1/Math.round(-0.5));
+assertEquals(-1, Math.round(-0.7));
+assertEquals(-1, Math.round(-1));
+assertEquals(-1, Math.round(-1.1));
+assertEquals(-1, Math.round(-1.49999));
+assertEquals(-1, Math.round(-1.5));
+
+assertEquals(9007199254740990, Math.round(9007199254740990));
+assertEquals(9007199254740991, Math.round(9007199254740991));
+assertEquals(-9007199254740990, Math.round(-9007199254740990));
+assertEquals(-9007199254740991, Math.round(-9007199254740991));
+assertEquals(Number.MAX_VALUE, Math.round(Number.MAX_VALUE));
+assertEquals(-Number.MAX_VALUE, Math.round(-Number.MAX_VALUE));