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contracts/lib/SafeMath.sol

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+/*
+
+    Copyright 2020 DODO ZOO.
+    SPDX-License-Identifier: Apache-2.0
+
+*/
+
+pragma solidity 0.6.9;
+pragma experimental ABIEncoderV2;
+
+/**
+ * @title SafeMath
+ * @author DODO Breeder
+ *
+ * @notice Math operations with safety checks that revert on error
+ */
+library SafeMath {
+    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
+        if (a == 0) {
+            return 0;
+        }
+
+        uint256 c = a * b;
+        require(c / a == b, "MUL_ERROR");
+
+        return c;
+    }
+
+    function div(uint256 a, uint256 b) internal pure returns (uint256) {
+        require(b > 0, "DIVIDING_ERROR");
+        return a / b;
+    }
+
+    function divCeil(uint256 a, uint256 b) internal pure returns (uint256) {
+        uint256 quotient = div(a, b);
+        uint256 remainder = a - quotient * b;
+        if (remainder > 0) {
+            return quotient + 1;
+        } else {
+            return quotient;
+        }
+    }
+
+    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
+        require(b <= a, "SUB_ERROR");
+        return a - b;
+    }
+
+    function add(uint256 a, uint256 b) internal pure returns (uint256) {
+        uint256 c = a + b;
+        require(c >= a, "ADD_ERROR");
+        return c;
+    }
+
+    function sqrt(uint256 x) internal pure returns (uint256 y) {
+        uint256 z = (x + 1) / 2;
+        y = x;
+        while (z < y) {
+            y = z;
+            z = (x / z + z) / 2;
+        }
+    }
+}