math overflow fix

contracts/lib/DODOMath.sol

@@ -74,7 +74,8 @@ library DODOMath {
         // V0 = V1*(1+(sqrt-1)/2k)
         // sqrt = √(1+4kidelta/V1)
         // premium = 1+(sqrt-1)/2k
-        uint256 sqrt = (4 * k).mul(i).mul(delta).div(V1).add(DecimalMath.ONE2).sqrt();
+        uint256 sqrt = DecimalMath.multiMulWithDiv((4 * k).mul(i),delta,V1).add(DecimalMath.ONE2).sqrt();
+        // uint256 sqrt = (4 * k).mul(i).mul(delta).div(V1).add(DecimalMath.ONE2).sqrt();
         uint256 premium = DecimalMath.divFloor(sqrt.sub(DecimalMath.ONE), k * 2).add(
             DecimalMath.ONE
         );
@@ -128,7 +129,8 @@ library DODOMath {
             // Q2=Q1/(1+ideltaBQ1/Q0/Q0)
             // temp = ideltaBQ1/Q0/Q0
             // Q1-Q2 = Q1*(temp/(1+temp))
-            uint256 temp = i.mul(delta).mul(V1).div(V0.mul(V0));
+            uint256 temp = DecimalMath.multiMulWithDiv(i.mul(delta),V1,V0).div(V0);
+            // uint256 temp = i.mul(delta).mul(V1).div(V0.mul(V0));
             return V1.mul(temp).div(temp.add(DecimalMath.ONE));
         }
 

contracts/lib/DecimalMath.sol

@@ -45,4 +45,10 @@ library DecimalMath {
     function reciprocalCeil(uint256 target) internal pure returns (uint256) {
         return uint256(10**36).divCeil(target);
     }
+
+    function multiMulWithDiv(uint256 x, uint256 y, uint256 z) internal pure returns (uint256) {
+        uint256 a = x.div(z); uint256 b = x.mod(z); // x = a * z + b
+        uint256 c = y.div(z); uint256 d = y.mod(z); // y = c * z + d
+        return a.mul(b).mul(z).add(a.mul(d)).add(b.mul(c)).add(b.mul(d).div(z));
+    }
 }

contracts/lib/SafeMath.sol

@@ -32,6 +32,11 @@ library SafeMath {
         return a / b;
     }
 
+    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
+        require(b > 0, "MOD_ERROR");
+        return a % b;
+    }
+
     function divCeil(uint256 a, uint256 b) internal pure returns (uint256) {
         uint256 quotient = div(a, b);
         uint256 remainder = a - quotient * b;