Added RichErrors to SafeMath

contracts/utils/contracts/src/MixinSafeMathRichErrors.sol

@@ -0,0 +1,47 @@
+pragma solidity ^0.5.9;
+
+import "./RichErrors.sol";
+
+
+contract MixinSafeMathRichErrors is
+    RichErrors
+{
+    // bytes4(keccak256("Uint256OverflowError(uint256,uint256)"))
+    bytes4 internal constant UINT256_OVERFLOW_ERROR =
+        0x55101607;
+
+    // bytes4(keccak256("Uint256UnderflowError(uint256,uint256)"))
+    bytes4 internal constant UINT256_UNDERFLOW_ERROR =
+        0x60ee612f;
+
+    // solhint-disable func-name-mixedcase
+    function Uint256OverflowError(
+        uint256 a,
+        uint256 b
+    )
+        internal
+        pure
+        returns (bytes memory)
+    {
+        return abi.encodeWithSelector(
+            UINT256_OVERFLOW_ERROR,
+            a,
+            b
+        );
+    }
+
+    function Uint256UnderflowError(
+        uint256 a,
+        uint256 b
+    )
+        internal
+        pure
+        returns (bytes memory)
+    {
+        return abi.encodeWithSelector(
+            UINT256_UNDERFLOW_ERROR,
+            a,
+            b
+        );
+    }
+}

contracts/utils/contracts/src/SafeMath.sol

@@ -1,7 +1,11 @@
 pragma solidity ^0.5.9;
 
+import "./MixinSafeMathRichErrors.sol";
 
-contract SafeMath {
+
+contract SafeMath is
+    MixinSafeMathRichErrors
+{
 
     function _safeMul(uint256 a, uint256 b)
         internal
@@ -12,10 +16,12 @@ contract SafeMath {
             return 0;
         }
         uint256 c = a * b;
-        require(
+        if (c / a != b) {
-            c / a == b,
+            _rrevert(Uint256OverflowError(
-            "UINT256_OVERFLOW"
+                a,
-        );
+                b
+            ));
+        }
         return c;
     }
 
@@ -33,10 +39,12 @@ contract SafeMath {
         pure
         returns (uint256)
     {
-        require(
+        if (b > a) {
-            b <= a,
+            _rrevert(Uint256UnderflowError(
-            "UINT256_UNDERFLOW"
+                a,
-        );
+                b
+            ));
+        }
         return a - b;
     }
 
@@ -46,10 +54,12 @@ contract SafeMath {
         returns (uint256)
     {
         uint256 c = a + b;
-        require(
+        if (c < a) {
-            c >= a,
+            _rrevert(Uint256OverflowError(
-            "UINT256_OVERFLOW"
+                a,
-        );
+                b
+            ));
+        }
         return c;
     }