feat: add computeCreateAddress helper function in Script (#109)

src/Script.sol

@@ -11,4 +11,29 @@ abstract contract Script {
         address(bytes20(uint160(uint256(keccak256('hevm cheat code')))));
 
     Vm public constant vm = Vm(VM_ADDRESS);
+
+    /// @dev Compute the address a contract will be deployed at for a given deployer address and nonce
+    /// @notice adapated from Solmate implementation (https://github.com/Rari-Capital/solmate/blob/main/src/utils/LibRLP.sol)
+    function computeCreateAddress(address deployer, uint256 nonce) internal pure returns (address) {
+        // The integer zero is treated as an empty byte string, and as a result it only has a length prefix, 0x80, computed via 0x80 + 0.
+        // A one byte integer uses its own value as its length prefix, there is no additional "0x80 + length" prefix that comes before it.
+        if (nonce == 0x00)             return addressFromLast20Bytes(keccak256(abi.encodePacked(bytes1(0xd6), bytes1(0x94), deployer, bytes1(0x80))));
+        if (nonce <= 0x7f)             return addressFromLast20Bytes(keccak256(abi.encodePacked(bytes1(0xd6), bytes1(0x94), deployer, uint8(nonce))));
+
+        // Nonces greater than 1 byte all follow a consistent encoding scheme, where each value is preceded by a prefix of 0x80 + length.
+        if (nonce <= type(uint8).max)  return addressFromLast20Bytes(keccak256(abi.encodePacked(bytes1(0xd7), bytes1(0x94), deployer, bytes1(0x81), uint8(nonce))));
+        if (nonce <= type(uint16).max) return addressFromLast20Bytes(keccak256(abi.encodePacked(bytes1(0xd8), bytes1(0x94), deployer, bytes1(0x82), uint16(nonce))));
+        if (nonce <= type(uint24).max) return addressFromLast20Bytes(keccak256(abi.encodePacked(bytes1(0xd9), bytes1(0x94), deployer, bytes1(0x83), uint24(nonce))));
+
+        // More details about RLP encoding can be found here: https://eth.wiki/fundamentals/rlp
+        // 0xda = 0xc0 (short RLP prefix) + 0x16 (length of: 0x94 ++ proxy ++ 0x84 ++ nonce)
+        // 0x94 = 0x80 + 0x14 (0x14 = the length of an address, 20 bytes, in hex)
+        // 0x84 = 0x80 + 0x04 (0x04 = the bytes length of the nonce, 4 bytes, in hex)
+        // We assume nobody can have a nonce large enough to require more than 32 bytes.
+        return addressFromLast20Bytes(keccak256(abi.encodePacked(bytes1(0xda), bytes1(0x94), deployer, bytes1(0x84), uint32(nonce))));
+    }
+
+    function addressFromLast20Bytes(bytes32 bytesValue) internal pure returns (address) {
+        return address(uint160(uint256(bytesValue)));
+    }
 }

src/test/Script.t.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: Unlicense
+pragma solidity >=0.7.0 <0.9.0;
+
+import "../Test.sol";
+
+contract ScriptTest is Test
+{
+     function testGenerateCorrectAddress() external {
+        address creation = computeCreateAddress(0x6C9FC64A53c1b71FB3f9Af64d1ae3A4931A5f4E9, 14);
+        assertEq(creation, 0x68b3465833fb72A70ecDF485E0e4C7bD8665Fc45);
+    }
+}