fix another case

Author: tgross35

src/math/log.rs

@@ -342,8 +342,9 @@ impl DInt64 {
         if (self.sign ^ other.sign) != 0 {
             c = ai - bi;
         } else {
-            c = ai.wrapping_add(bi);
-            if c != 0 {
+            let oflow;
+            (c, oflow) = ai.overflowing_add(bi);
+            if oflow {
                 c += c & 0x1;
                 c = (1u128 << 127) | (c >> 1);
                 m_ex += 1;