refactor DODOMath

contracts/lib/DecimalMath.sol

@@ -10,7 +10,6 @@ pragma experimental ABIEncoderV2;
 
 import {SafeMath} from "./SafeMath.sol";
 
-
 /**
  * @title DecimalMath
  * @author DODO Breeder
@@ -21,24 +20,33 @@ library DecimalMath {
     using SafeMath for uint256;
 
     uint256 constant ONE = 10**18;
+    uint256 constant ONE2 = 10**36;
 
     function mul(uint256 target, uint256 d) internal pure returns (uint256) {
-        return target.mul(d) / ONE;
+        return target.mul(d) / (10**18);
     }
 
     function mulFloor(uint256 target, uint256 d) internal pure returns (uint256) {
-        return target.mul(d) / ONE;
+        return target.mul(d) / (10**18);
     }
 
     function mulCeil(uint256 target, uint256 d) internal pure returns (uint256) {
-        return target.mul(d).divCeil(ONE);
+        return target.mul(d).divCeil(10**18);
     }
 
     function divFloor(uint256 target, uint256 d) internal pure returns (uint256) {
-        return target.mul(ONE).div(d);
+        return target.mul(10**18).div(d);
     }
 
     function divCeil(uint256 target, uint256 d) internal pure returns (uint256) {
-        return target.mul(ONE).divCeil(d);
+        return target.mul(10**18).divCeil(d);
+    }
+
+    function reciprocalFloor(uint256 target) internal pure returns (uint256) {
+        return uint256(10**36).div(target);
+    }
+
+    function reciprocalCeil(uint256 target) internal pure returns (uint256) {
+        return uint256(10**36).divCeil(target);
     }
 }