Upgrade solidity version

contracts/common/Decimal.sol

@@ -1,4 +1,5 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
 
 library Decimal {
     // unit is used for decimals, e.g. 0.123456

contracts/common/Initializable.sol

@@ -1,5 +1,5 @@
-pragma solidity >=0.4.24 <0.7.0;
-
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
 
 /**
  * @title Initializable
@@ -29,7 +29,7 @@ contract Initializable {
    * @dev Modifier to use in the initializer function of a contract.
    */
   modifier initializer() {
-    require(initializing || isConstructor() || !initialized, "Contract instance has already been initialized");
+    require(initializing || !initialized, "Contract instance has already been initialized");
 
     bool isTopLevelCall = !initializing;
     if (isTopLevelCall) {
@@ -44,19 +44,6 @@ contract Initializable {
     }
   }
 
-  /// @dev Returns true if and only if the function is running in the constructor
-  function isConstructor() private view returns (bool) {
-    // extcodesize checks the size of the code stored in an address, and
-    // address returns the current address. Since the code is still not
-    // deployed when running a constructor, any checks on its code size will
-    // yield zero, making it an effective way to detect if a contract is
-    // under construction or not.
-    address self = address(this);
-    uint256 cs;
-    assembly { cs := extcodesize(self) }
-    return cs == 0;
-  }
-
   // Reserved storage space to allow for layout changes in the future.
   uint256[50] private ______gap;
 }

contracts/common/ReentrancyGuard.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
+
 import "./Initializable.sol";
 
 /**

contracts/erc20/base/ERC20.sol

@@ -1,6 +1,6 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
 
-import "../../common/SafeMath.sol";
 import "./IERC20.sol";
 import "../../common/Initializable.sol";
 
@@ -29,8 +29,6 @@ import "../../common/Initializable.sol";
  * allowances. See {IERC20-approve}.
  */
 contract ERC20 is Initializable, IERC20 {
-    using SafeMath for uint256;
-
     mapping(address => uint256) private _balances;
 
     mapping(address => mapping(address => uint256)) private _allowances;
@@ -97,7 +95,8 @@ contract ERC20 is Initializable, IERC20 {
      */
     function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
         _transfer(sender, recipient, amount);
-        _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(amount, "ERC20: transfer amount exceeds allowance"));
+        require(amount <= _allowances[sender][msg.sender], "ERC20: transfer amount exceeds allowance");
+        _approve(sender, msg.sender, _allowances[sender][msg.sender] - amount);
         return true;
     }
 
@@ -114,7 +113,7 @@ contract ERC20 is Initializable, IERC20 {
      * - `spender` cannot be the zero address.
      */
     function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
-        _approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue));
+        _approve(msg.sender, spender, _allowances[msg.sender][spender] + addedValue);
         return true;
     }
 
@@ -133,7 +132,8 @@ contract ERC20 is Initializable, IERC20 {
      * `subtractedValue`.
      */
     function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
-        _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
+        require(subtractedValue <= _allowances[msg.sender][spender], "ERC20: decreased allowance below zero");
+        _approve(msg.sender, spender, _allowances[msg.sender][spender] - subtractedValue);
         return true;
     }
 
@@ -155,8 +155,9 @@ contract ERC20 is Initializable, IERC20 {
         require(sender != address(0), "ERC20: transfer from the zero address");
         require(recipient != address(0), "ERC20: transfer to the zero address");
 
-        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
-        _balances[recipient] = _balances[recipient].add(amount);
+        require(_balances[sender] >= amount, "ERC20: transfer amount exceeds balance");
+        _balances[sender] = _balances[sender] - amount;
+        _balances[recipient] = _balances[recipient] + amount;
         emit Transfer(sender, recipient, amount);
     }
 
@@ -172,8 +173,8 @@ contract ERC20 is Initializable, IERC20 {
     function _mint(address account, uint256 amount) internal {
         require(account != address(0), "ERC20: mint to the zero address");
 
-        _totalSupply = _totalSupply.add(amount);
-        _balances[account] = _balances[account].add(amount);
+        _totalSupply = _totalSupply + amount;
+        _balances[account] = _balances[account] + amount;
         emit Transfer(address(0), account, amount);
     }
 
@@ -191,8 +192,9 @@ contract ERC20 is Initializable, IERC20 {
     function _burn(address account, uint256 amount) internal {
         require(account != address(0), "ERC20: burn from the zero address");
 
-        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
-        _totalSupply = _totalSupply.sub(amount);
+        require(_balances[account] >= amount, "ERC20: burn amount exceeds balance");
+        _balances[account] = _balances[account] - amount;
+        _totalSupply = _totalSupply - amount;
         emit Transfer(account, address(0), amount);
     }
 
@@ -225,7 +227,8 @@ contract ERC20 is Initializable, IERC20 {
      */
     function _burnFrom(address account, uint256 amount) internal {
         _burn(account, amount);
-        _approve(account, msg.sender, _allowances[account][msg.sender].sub(amount, "ERC20: burn amount exceeds allowance"));
+        require(amount <= _allowances[account][msg.sender], "ERC20: burn amount exceeds allowance");
+        _approve(account, msg.sender, _allowances[account][msg.sender] - amount);
     }
 
     uint256[50] private ______gap;

contracts/erc20/base/ERC20Burnable.sol

@@ -1,4 +1,5 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
 
 import "./ERC20.sol";
 
@@ -25,12 +26,4 @@ contract ERC20Burnable is ERC20 {
     function burnFrom(address from, uint256 value) public {
         _burnFrom(from, value);
     }
-
-    /**
-     * @dev Overrides ERC20._burn in order for burn and burnFrom to emit
-     * an additional Burn event.
-     */
-    function _burn(address who, uint256 value) internal {
-        super._burn(who, value);
-    }
 }

contracts/erc20/base/ERC20Detailed.sol

@@ -1,12 +1,13 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
 
-import "./IERC20.sol";
 import "../../common/Initializable.sol";
+import {ERC20} from "./ERC20.sol";
 
 /**
  * @dev Optional functions from the ERC20 standard.
  */
-contract ERC20Detailed is Initializable, IERC20 {
+contract ERC20Detailed is ERC20 {
     string private _name;
     string private _symbol;
     uint8 private _decimals;
@@ -16,10 +17,10 @@ contract ERC20Detailed is Initializable, IERC20 {
      * these values are immutable: they can only be set once during
      * construction.
      */
-    function initialize(string memory name, string memory symbol, uint8 decimals) internal initializer {
-        _name = name;
-        _symbol = symbol;
-        _decimals = decimals;
+    function initialize(string memory tokenName, string memory tokenSymbol, uint8 tokenDecimals) internal initializer {
+        _name = tokenName;
+        _symbol = tokenSymbol;
+        _decimals = tokenDecimals;
     }
 
     /**

contracts/erc20/base/ERC20Mintable.sol

@@ -1,4 +1,5 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
 
 import "./ERC20.sol";
 import "./MinterRole.sol";

contracts/erc20/base/IERC20.sol

@@ -1,6 +1,6 @@
-// SPDX-License-Identifier: MIT
+// SPDX-License-Identifier: UNLICENSED
 
-pragma solidity ^0.5.0;
+pragma solidity ^0.8.19;
 
 /**
  * @dev Interface of the ERC20 standard as defined in the EIP.

contracts/erc20/base/MinterRole.sol

@@ -1,4 +1,5 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
 
 import "./Roles.sol";
 

contracts/erc20/base/Roles.sol

@@ -1,4 +1,5 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
 
 
 /**

contracts/ownership/Ownable.sol

@@ -1,4 +1,5 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
 
 import "../common/Initializable.sol";