fix magnification in round3

Author: bsteinb

src/util/mod.rs

@@ -159,7 +159,7 @@ where
     debug_assert!(s0 == s0 + s1);
     debug_assert!(s1 == s1 + s2);
     if s1.has_half_ulp_form() && s1.sign() == s2.sign() {
-        s0 + s1.next()
+        s0 + if s1.is_sign_positive() { s1.next() } else { s1.prev() }
     } else {
         s0
     }