Gas Optimizations

[code423n4]

Variables should not be initialized to defaults (uint256 default is 0):
contracts/AxelarGateway.sol::207 => for (uint256 i = 0; i < symbols.length; i++) {
contracts/auth/AxelarAuthWeighted.sol::68 => uint256 totalWeight = 0;
contracts/auth/AxelarAuthWeighted.sol::69 => for (uint256 i = 0; i < weightsLength; ++i) {
contracts/auth/AxelarAuthWeighted.sol::94 => uint256 operatorIndex = 0;
contracts/auth/AxelarAuthWeighted.sol::95 => uint256 weight = 0;
contracts/auth/AxelarAuthWeighted.sol::98 => for (uint256 i = 0; i < signatures.length; ++i) {

Length of array should be computed outside of for-loop:
contracts/AdminMultisigBase.sol::149 => uint256 adminLength = accounts.length;
contracts/AxelarGateway.sol::49 => if (authModule.code.length == 0) revert InvalidAuthModule();
contracts/AxelarGateway.sol::50 => if (tokenDeployerImplementation.code.length == 0) revert InvalidTokenDeployer();
contracts/AxelarGateway.sol::205 => if (symbols.length != limits.length) revert InvalidSetDailyMintLimitsParams();
contracts/AxelarGateway.sol::207 => for (uint256 i = 0; i < symbols.length; i++) {
contracts/AxelarGateway.sol::228 => if (setupParams.length != 0) {
contracts/AxelarGateway.sol::255 => if (newOperatorsData.length > 0) {
contracts/AxelarGateway.sol::288 => uint256 commandsLength = commandIds.length;
contracts/AxelarGateway.sol::290 => if (commandsLength != commands.length || commandsLength != params.length) revert InvalidCommands();
contracts/AxelarGateway.sol::355 => if (tokenAddress.code.length == uint256(0)) revert TokenContractDoesNotExist(tokenAddress);
contracts/AxelarGateway.sol::388 => if (!success || (returnData.length != uint256(0) && !abi.decode(returnData, (bool)))) revert BurnFailed(symbol);
contracts/AxelarGateway.sol::462 => return success && (returnData.length == uint256(0) || abi.decode(returnData, (bool)));
contracts/AxelarGatewayProxy.sol::19 => if (gatewayImplementation.code.length == 0) revert InvalidImplementation();
contracts/DepositHandler.sol::23 => if (callee.code.length == 0) revert NotContract();
contracts/ECDSA.sol::32 => // Check the signature length
contracts/ECDSA.sol::33 => if (signature.length != 65) revert InvalidSignatureLength();
contracts/ECDSA.sol::75 => // 32 is the length in bytes of hash,
contracts/auth/AxelarAuthWeighted.sol::17 => for (uint256 i; i < recentOperators.length; ++i) {
contracts/auth/AxelarAuthWeighted.sol::60 => uint256 operatorsLength = newOperators.length;
contracts/auth/AxelarAuthWeighted.sol::61 => uint256 weightsLength = newWeights.length;
contracts/auth/AxelarAuthWeighted.sol::93 => uint256 operatorsLength = operators.length;
contracts/auth/AxelarAuthWeighted.sol::98 => for (uint256 i = 0; i < signatures.length; ++i) {
contracts/auth/AxelarAuthWeighted.sol::116 => for (uint256 i; i < accounts.length - 1; ++i) {
contracts/deposit-service/AxelarDepositService.sol::114 => for (uint256 i; i < refundTokens.length; i++) {
contracts/deposit-service/AxelarDepositService.sol::168 => for (uint256 i; i < refundTokens.length; i++) {
contracts/deposit-service/AxelarDepositService.sol::204 => for (uint256 i; i < refundTokens.length; i++) {
contracts/deposit-service/DepositBase.sol::32 => if (symbolBytes.length == 0 || symbolBytes.length > 31) revert InvalidSymbol();
contracts/deposit-service/DepositBase.sol::36 => // Storing string length as the last byte of the data
contracts/deposit-service/DepositBase.sol::37 => symbolNumber |= 0xff & symbolBytes.length;
contracts/deposit-service/DepositBase.sol::49 => // recovering string length as the last byte of the data
contracts/deposit-service/DepositBase.sol::50 => uint256 length = 0xff & uint256(symbolData);
contracts/deposit-service/DepositBase.sol::52 => // restoring the string with the correct length
contracts/deposit-service/DepositBase.sol::58 => // store length in memory
contracts/deposit-service/DepositBase.sol::59 => mstore(symbol, length)
contracts/deposit-service/DepositBase.sol::72 => bool transferred = success && (returnData.length == uint256(0) || abi.decode(returnData, (bool)));
contracts/deposit-service/DepositBase.sol::74 => if (!transferred || tokenAddress.code.length == 0) revert TokenTransferFailed();
contracts/gas-service/AxelarGasService.sol::123 => for (uint256 i; i < tokens.length; i++) {
contracts/gas-service/AxelarGasService.sol::159 => bool transferred = success && (returnData.length == uint256(0) || abi.decode(returnData, (bool)));
contracts/gas-service/AxelarGasService.sol::161 => if (!transferred || tokenAddress.code.length == 0) revert TransferFailed();
contracts/gas-service/AxelarGasService.sol::175 => bool transferred = success && (returnData.length == uint256(0) || abi.decode(returnData, (bool)));
contracts/gas-service/AxelarGasService.sol::177 => if (!transferred || tokenAddress.code.length == 0) revert TransferFailed();
contracts/interfaces/IAxelarForecallable.sol::133 => bool transferred = success && (returnData.length == uint256(0) || abi.decode(returnData, (bool)));
contracts/interfaces/IAxelarForecallable.sol::135 => if (!transferred || tokenAddress.code.length == 0) revert TransferFailed();
contracts/interfaces/IAxelarForecallable.sol::146 => bool transferred = success && (returnData.length == uint256(0) || abi.decode(returnData, (bool)));
contracts/interfaces/IAxelarForecallable.sol::148 => if (!transferred || tokenAddress.code.length == 0) revert TransferFailed();
contracts/util/Upgradable.sol::50 => if (params.length > 0) {

!= is more efficient than > 0 for uint comparisons:
contracts/AxelarGateway.sol::255 => if (newOperatorsData.length > 0) {
contracts/AxelarGateway.sol::613 => if (limit > 0 && amount > limit) revert ExceedDailyMintLimit(symbol);
contracts/ECDSA.sol::58 => if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) revert InvalidS();
contracts/ERC20Permit.sol::45 => if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) revert InvalidS();
contracts/auth/AxelarAuthWeighted.sol::76 => if (epochForHash[newOperatorsHash] > 0) revert SameOperators();
contracts/deposit-service/AxelarDepositService.sol::165 => if (addressForNativeDeposit(salt, refundAddress, destinationChain, destinationAddress).balance > 0 && msg.sender != refundAddress)
contracts/deposit-service/ReceiverImplementation.sol::23 => if (address(this).balance > 0) refundAddress.transfer(address(this).balance);
contracts/deposit-service/ReceiverImplementation.sol::51 => if (address(this).balance > 0) refundAddress.transfer(address(this).balance);
contracts/deposit-service/ReceiverImplementation.sol::71 => if (address(this).balance > 0) refundAddress.transfer(address(this).balance);
contracts/gas-service/AxelarGasService.sol::128 => if (amount > 0) receiver.transfer(amount);
contracts/gas-service/AxelarGasService.sol::131 => if (amount > 0) _safeTransfer(token, receiver, amount);
contracts/util/Upgradable.sol::50 => if (params.length > 0) {

Switching from division/multiplication to right-shift/left-shift can save gas:
contracts/ECDSA.sol::56 => // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
contracts/ERC20.sol::15 => * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
contracts/interfaces/IERC20.sol::49 => * ethereum/EIPs#20 (comment)
contracts/test/gmp/DestinationChainTokenSwapper.sol::29 => convertedAmount = amount * 2;
contracts/test/gmp/DestinationChainTokenSwapper.sol::33 => convertedAmount = amount / 2;

[re1ro]

Dup #2

Switching from division/multiplication to right-shift/left-shift can save gas:

Ack

[GalloDaSballo]

This is really low quality and I'll penalize.

Less than 100 gas saved

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