Update docs

contracts/mocks/SafeMathMemoryCheck.sol

@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/math/SafeMath.sol";
+
+library SafeMathMemoryCheck {
+    function addMemoryCheck() internal pure returns (uint256 mem) {
+        uint256 length = 32;
+        assembly {
+            mem := mload(0x40)
+        }
+        for (uint256 i = 0; i < length; ++i) {
+            SafeMath.add(1, 1);
+        }
+        assembly {
+            mem := sub(mload(0x40), mem)
+        }
+    }
+
+    function subMemoryCheck() internal pure returns (uint256 mem) {
+        uint256 length = 32;
+        assembly {
+            mem := mload(0x40)
+        }
+        for (uint256 i = 0; i < length; ++i) {
+            SafeMath.sub(1, 1);
+        }
+        assembly {
+            mem := sub(mload(0x40), mem)
+        }
+    }
+
+    function mulMemoryCheck() internal pure returns (uint256 mem) {
+        uint256 length = 32;
+        assembly {
+            mem := mload(0x40)
+        }
+        for (uint256 i = 0; i < length; ++i) {
+            SafeMath.mul(1, 1);
+        }
+        assembly {
+            mem := sub(mload(0x40), mem)
+        }
+    }
+
+    function divMemoryCheck() internal pure returns (uint256 mem) {
+        uint256 length = 32;
+        assembly {
+            mem := mload(0x40)
+        }
+        for (uint256 i = 0; i < length; ++i) {
+            SafeMath.div(1, 1);
+        }
+        assembly {
+            mem := sub(mload(0x40), mem)
+        }
+    }
+
+    function modMemoryCheck() internal pure returns (uint256 mem) {
+        uint256 length = 32;
+        assembly {
+            mem := mload(0x40)
+        }
+        for (uint256 i = 0; i < length; ++i) {
+            SafeMath.mod(1, 1);
+        }
+        assembly {
+            mem := sub(mload(0x40), mem)
+        }
+    }
+}